Undressing the Sterling Nikki...

When compared to a stock Nikki that's been stripped down of all it's emissions controls and extraneous components, the most noticeable difference is the reduction in linkage. The cable bracket is reduced in size, and roughly 2/3rds of the linkage is removed. The remaining linkage is modified according to the new bracket design, and the throttle return spring setup is simplified and fail-proof. The result is a much simpler and more compact linkage, none of which needs to be removed when removing the air horn for accessing air and fuel jets save the one hair-pin clip that holds the fast idle linkage pivot in place.

New allen key button head cap screws replace the original screws, completing the easy - access modifications designed for quick track side or street tuning.
All vacuum ports are either capped or blocked, and the choke shaft holes in the air horn are plugged. The Fuel Bowl Ventilation Solenoid (FBVS) is removed, and the bung it threads into is either removed, or turned 90 degrees (depending on what year carb), blocking off the internal air vent port. The remaining hole is then blocked with epoxy. This leaves nothing but the fuel lines attached to the air horn.

From the outside, the exterior of the Sterling Nikki looks like little more than a prettied-up stripped down stock Nikki carburetor. Even the vacuum secondary box is left attached. But the external modifications made to the Sterling Nikki for ease of tuning and servicing pale in comparison to the modifications made internally for performance...

The reduced linkage of the Sterling Nikki makes for a more compact carburetor that's easier to work on, easier to tune, and more aesthetically pleasing. Button head metric cap screws can tolerate a higher number of removals for jet changing than the soft stock slot head screws, and add to the visual appeal.

Flipping the top off the Sterling Nikki is now simpler than ever, allowing for easy access to jets and float assemblies for tuning and maintenance. With just the removal of the fast idle link, the center stud, and the allen-key button head air horn skirt screws, the air horn can be lifted off in less than 2 minutes with practice. Repetitive test runs at the track can be done with only the center stud in place and one allen screw to keep the air horn straight. This makes jet changes in between runs even faster, allowing the most efficient use of rented track time.

Note that the choke valve assembly has been removed for better air flow. The Sterling Nikki comes with a fast idle, and no choke. I have many North American customers in the cold climate of Canada and the Great Lakes region who have no trouble starting their Sterling Nikki carburetors during the winter months with just the fast idle linkage to help them. I strongly discourage customers from ordering a choke on any SMW performance Nikki, unless race sanctioning rules insist, because I rarely hear of anyone with a Sterling actually needing to use it, and the choke valve and shaft assembly presents a flow impediment within the air horn, particularly on the 84-85 Nikkis. The presence of the choke valve and shaft would basically render many of the modifications done to improve air flow useless.

Flow bench tests have demonstrated that no further streamlining need be done to the stock air horn to make it flow adequately for 12a application. It's these same flow bench test results that demonstrate that even the smaller opening of the primary half of the later model Nikki tops allow for more than adequate flow, busting the myth that the earlier, wider air horns increase performance on 12a applications. The earlier air horns, 79-83, have a larger opening for the primary side of the carburetor, although flow tests surprisingly showed no advantage in flow for the Sterling Nikki when compared to the later, small-mouth style. However, even though the later small-mouth style air horn flows adequately for the rest of the Sterling Nikki, the installation of the choke assembly is almost certainly a flow impediment, whereas it's most likely not such an impediment if installed in an earlier, large-mouth style air horn.

Further flow bench testing by Carl Perez will demonstrate concrete information, with which I will certainly update my site. Often he and I are surprised at flow results that seem counterintuitive. We shall see...

I do not install baffles in my race carburetors. A complete explanation of why, as well as my alternative measures that actually work are detailed on the Race Nikki page of my website. The substitution of the larger early Nikki floats and Grose jet valve assemblies are options that can be added for an additional, relatively nominal fee. Details are on the SMW Services Details & Price chart.

The complete re-designing of the Nikki linkage using only stock linkage parts is what makes the removal of the air horn so easy. The photo at the left shows the Sterling Nikki throttle return linkage in it's simplest form, with the addition of a refinished stock throttle return spring mounted on the back of the bracket. This customer had asked for additional throttle return tension.

Different throttle shaft and throttle body configurations, must be used in order to add components like the deceleration dashpot or AC idle compensation valve. This is why it is so important that I know what you need before I begin work on your Sterling Nikki. Surprising me with the need of additional components later is not much trouble, but it can add to the completion time.

A comprehensive chart for such options is found on the SMW Services page of my website.

The reduction in linkage makes for a cleaner looking carburetor and a less cluttered engine bay. All carburetors can misbehave at some point, and working on and diagnosing the Sterling Nikki is far easier than a stock Nikki.

The SMW Bare Nikki enjoys the same stripped down, reduced linkage as the Sterling Nikki.

When we remove the air horn of the Sterling Nikki, three major differences from the stock Nikki are immediately noticeable; the venturis, venturi boosters, and the emulsion tubes have all been modified.

On the stock carburetor each booster venturi has an additional arm on it. This may appear to be an unnecessary over building of these components, and for performance purposes, it is. However, they are cast that way for easy alignment within the carburetor body during assembly. These are cut off on the Sterling Nikki, and the remaining arm that suspends the booster is reshaped by hand to give it an airfoil shape; round and smooth on top, tapering to a sharp point on the bottom. The lines present from casting are also filed smooth, and then each one is slightly polished.

Also removed from the path of flowing air are the brass oil metering pump tubes. These have been cut to a shorter length in the Sterling Nikki so as not to impede air flow.

With increased signal to the main circuit at higher air flow , the carburetor can now make even better use of the emulsion system to aerate the fuel mixture, which will improve atomization. But it's also necessary to be able to bleed of excess vacuum signal to the main circuits so as not to run too rich. The ability to tune the signal to each venturi is invaluable to race drivers who are competing in classes that allow such modifications. For street application, most people will experiment with changing air and fuel jets and find a combination that suits their driving style, and will not find a need to re-jet often after that, if at all.

The tops of the emulsion tubes in the Sterling Nikki are chucked in a watchmaker's lathe, drilled, countersunk, and threaded to accept standard 1/4" crown, 10-32 thread Holley air bleeds. Holley air jets are readily available, come in a large range, and also fit the Nikki fuel jet threads as their thread pitches are extremely close, even though the Nikki fuel jet threading is metric.

The heads of the emulsion tubes are brass, and are delicate, particularly on the primary tubes, due to thinning from machining. Please exercise caution and be sure to use an appropriate size screw driver when changing jets. Do not over tighten.

Useable jet sizes and jetting guidelines for performance and economy tuning are available on the Nikki Tuning section of my website.

Additional linkage modifications include the conversion of the secondary main circuit from vacuum operation to mechanical operation. This is not done by the usual semi-permanent means of wiring or welding linkage together. Instead, it's done by customizing one single piece of linkage. When this part is installed during initial assembly, it's adjusted to the rest of the linkage so that the primary and secondary throttle shafts are perfectly calibrated, and are both fully open at wide open throttle.

This piece of linkage has been specially designed so that when it is removed and reinstalled backwards, it allows for the conversion back to vacuum secondary operation. All the user has to do is flip the part around, unplug the vacuum port and reinstall the stock vacuum box, all of which can easily be accessed with the carburetor on the vehicle, and completed in less than 10 minutes.

If the customer chooses, the vacuum secondary prompting box can be kept on the Sterling Nikki, with it's link to the secondary throttle shaft hooked up. Even when the modified link is in place, all set fro mechanical secondary throttle shaft operation, the vacuum box will not hamper performance.

In this manor, the secondary throttle operation can be changed from vacuum to mechanical operation, and vice versa, in about a minute and a half with some practice.

My good friend Jon Walker, a.k.a. "Vipernicus", has dubbed this little piece of modified linkage "The Sterling Flip-O-Matic"!

Research and development in 2009 will include modifications made to the Sterling Nikki designed to increase fuel mileage when you need such efficiency, while retaining the gas guzzling performance jetting. I hope to make use of some of the solenoids that I usually discard along with some of the circuits normally sealed on the Sterling and SMW Bare Nikkis to design an auxiliary circuit specifically for highway driving. This would be a bit like a carburetor controlled manual overdrive, complete with a dash-mounted toggle switch.

If tests demonstrate this to be a substantial enough gain in fuel efficiency, I hope to make it available as a kit by 2010.

Difficult to notice without disassembly are the many modifications made to the accelerator pump. In the Sterling Nikki accelerator pump, the volume of the fuel Is increased by over 1 cc, roughly 50%, and the linkage is extended so that the pump does not finish it's full stroke until the carburetor is at wide open throttle. The accelerator pump modifications allow for smooth transitioning from the primary to secondary operation.

  The stock Nikki is set up so that adequate fuel is pumped by the accelerator pump to help in acceleration through the opening of the primary throttle, but the pump terminates it's stroke when the secondary throttle begins to open, about midway for the primaries. The reason for this is that the original stock vacuum secondary operation is load dependant, so introducing more fuel while the secondary circuit is open could cause the carburetor to have a noticeable flutter under certain driving circumstances. It is for this reason that the accelerator pump should be readjusted when converting back to vacuum secondary operation.

At the left is a photo of the finished prototype showing off the AP modifications. This picture eventually came to be the poster-shot for the Sterling Nikki. Today, however, the modifications of the Sterling Nikki AP are done internally and remain hidden from view, with the exception of the trademark AP lever extension. The development of the Sterling AP modification was a key inspiration for me to embark on the journey of modifying the Nikki carburetor for production. It was the first thing I ever did to actually make my own modified Nikki better and more unique than those of other successful Nikki carburetor modifiers.

Information regarding tuning the Nikki accelerator pump can be found in the Nikki Tuning section of my website. The AP tuning applies to all 4 bbl Nikki carburetors.

The heart of the carburetor is the venturi, and in the case of the Nikki, it has four. The venturis dictate the maximum flow potential of the carburetor, as well as the maximum vacuum signal to the main circuit. If the venturis are not cut correctly, performance will suffer terribly.

The venturis for the Sterling Nikki are precisely cut to a specific shape on a lathe. The process is long and arduous, as very little material can be removed at once. More than a handful of venturis have gone whizzing across the shop from trying to cut them too fast. The result is always a mangled mess that's too time consuming to try to fix.

Venturis are all done in batches of a few dozen at a time to ensure consistency. The set up time for the lathes would drain me if I were to do the carburetors individually, so I've tried to "batch" every process that I can. Still consuming the most time are the booster venturis, which I have to do by hand with files and a polisher.

The story of why I must go through all of this to obtain the magical flow of 465 cfm is outlined in a rant on my Air Delivery page, hyper-linked below and on the main menu. Basically, when Carl Perez first started testing different venturi cuts I sent him, we knew then that all the Sterling Nikki needed was a minor venturi reshaping and to have the smaller flow impediments reduced or eliminated. The flow of 415 cfm that we had originally achieved was in keeping with the very best of the modified Nikkis ever offered to the general public, but reality set in to our back yard mechanic's joint venture, and we knew we would not be able to turn an eye to examine the Sterling Nikki if the flow wasn't comparable to the very popular Racing Beat Holley 465. It was this conundrum that set the both of us out on a mission to cut the most efficient venturi configuration possible from the stock Nikki parts.

After much trial and error and testing, we ultimately ended up with a venturi cut that flowed enough to yield the "magic" 465 cfm, but that did not cause the rotary to fall flat on it's face at low RPM; something that most oversized carburetors suffer from.

The irony is that when I go against some critics and lay out my theories regarding the unfortunately popular over-sized carburetor installation of the rotary engine, I'm sometimes met with a cynical tone written into the question, "...well then why is your carburetor so big?" So I have to explain that in order to make enough sales to keep my interest in all of this, I too, had to fall victim to the machine that markets to ignorance. I didn't like it, but I had to do it. My saving grace is that I worked extremely hard to successfully produce a product that overcomes the very problem I criticize in other oversized carburetor choices. But I still remain championed at spreading the thought provoking ideas, theories and facts that will help stamp out some of the more prevalent common ignorance regarding carburetors.

Another irony is that the result of all of this extra "for naught" effort is a modified Nikki carburetor that flows much more than is required for most 12a applications, but that's now appropriate for many 13b applications as well, including street ported 13b engines. It was only halfway into the testing that this dawned on me, and I realized the tremendous benefit of versatility of such a carburetor. This inspired me to continue making progressive changes to make the Sterling Nikki as versatile as possible, with things like easily changeable secondary throttle operation from mechanical to vacuum, and vice versa. This quest for penultimate versatility in a performance carburetor is what feeds my desire for projects in the future, such as an electronically controlled fuel saving "granny circuit".

The primary venturis are bored 10% larger from the stock 20 mm to 22 mm, and the secondary venturis are bored 3.5% larger from the stock 28 mm to 29 mm. Though this resizing only yields an increase of combined inside venturi area of 11.9%, that measurement does not directly reflect the increase in overall air flow from a stock Nikki to a Sterling Nikki. Rather, it is testament to the fact that it is the reshaping of the venturis that actually yields more flow potential, and the special reshaping done for the Sterling Nikki plays the most important part in the fact that the finished product can flow 465 cfm, as compared to the stock 313 cfm, a nearly 50% increase.

Simply reshaping and opening up the venturis alone will not allow the Nikki to flow this high. Other flow impediments, such as the boosters and the throttle shafts must be re-profiled. However, flow bench testing done by my associate Carl Perez has shown the stock Nikki venturi shape to be so inefficient and far from optimal that flow gains comparable to boring the venturis several mm can be achieved solely by optimizing shape. The ultimate difference is that an optimized venturi shape allows air flow to produce a stronger signal to the main fuel circuit, whereas simply boring out the venturis to attain the equivalent air flow will weaken the signal at low to mid throttle so much that the carburetor will have little power below 3500 RPM.

More of the science behind the venturi, as well as other basic air flow dynamics information can be found here, on the Air Delivery page of the Carburetor Basics section.

Here we can see the differences in the throttle shafts. The throttle shafts of the Sterling Nikki are milled to remove more than half of their flow impeding area at wide open throttle.

The primary throttle shafts are more fragile as a result of this modification, and they could be subject to twisting if the throttle cable is installed incorrectly. Make certain there is adequate slack in the throttle cable during installation. Use caution while handling the carburetor so as not to put undue stress on the primary shaft linkage, and make certain the primary throttle can not be operated past vertical (the WOT position) when installing the cable.

 

The throttle shafts of the Sterling Nikki are shaved as thin as possible and the valves are installed using smooth "button head" allen cap screws. The threaded ends are crimped to ensure they never back out. Even the stock screws used to mount the valves on the Nikki carburetor have demonstrated to be significant impediments to air flow.
Milling the throttle shafts for the Sterling Nikki often takes more patience than turning the venturis. One slip and all that's left is a "parts" carb.
The throttle shafts are milled as this as possible while still retaining the necessary strength to endure years of racing use. However, they are much more delicate than stock shafts, and must be treated with care when installing the Sterling Nikki. Enough undue force or trauma on the throttle shaft can bend the shaft slightly, causing binding and idle problems that can only be corrected by removing and straightening the shaft.

The Sterling Nikki is finished  ultimately with silver engine paint. But the entire finishing process is far more involved than simply painting old parts.

First, old Nikkis are stripped into piles of individual parts. Everything gets tossed in degreaser and then rinsed clean. Main bodies, throttle bodies and air horns get bead blasted or acid dipped. Linkage is sorted, modified, bead blasted and prepared for the zinc plating process. All of the jetting is separated and modified or re-drilled. The venturis, booster, accelerator pump covers, and throttle shafts are sent to the lathe area for turning & milling modifications.

The linkage is made of steel, and definitely needs to be protected. I zinc plate all the linkage, but even zinc plating needs to be covered in paint or clear coat, or else it will begin to turn white and pasty. The main housing is made of "pot metal" that contains zinc and other metals, but the plating process doesn't work too well on them. They won't rust, but they will corrode, so I paint the main bodies silver. The air horns are cast aluminum and will not receive plating at all. These will darken, so I paint them, as well. The throttle bodies are cast steel and rust easily, so it's extremely important to coat them, though I don't zinc plate them because the plating would coat the inside of the idle circuits, causing problems. Instead, they get painted with a special oil and baked in a kiln, and then painted.

It's very important to remember that the finish on these carburetors is simply paint, with only the linkage having any protection underneath. Avoid going nuts with carb cleaner and ether because they will dissolve the paint and make the finish run.

The paint I use is high temperature engine paint, and upon request, I can offer different color schemes for a nominal cost. Pictures of one such color scheme (as yet) can be found on the SMW Gallery page of my website.

The stock Nikkis were plated in cadmium for a time, but the cadmium plating process is dangerous to humans. Cadmium is a "heavy metal", and neurotoxic. So zinc plating, along with a special chromating process, eventually phased out cadmium plating. It's extremely difficult for me to get the same rainbow sheen on these carburetor parts as the stock cadmium plating gave. There are special chemicals that I use, but they don't tolerate the clear coating very well, and the rainbow sheen effect seems to fade. This is a process I've been working on, as I've gotten a surprising number of customers interested in stock looking Nikki rebuilds for complete restoration projects, which is always a great thing to know people are still doing.

Applications for the Sterling Nikki carburetor include stock 12a, stock 13b, Street Ported 12a, Street Ported 13b, and to a lesser extent, the Bridge Ported 12a and Mild bridge Ported 13b. I have yet to see it perform on a Bridge Ported 13b, though it is my opinion that the carburetor will flow enough for this application. I believe the Sterling Nikki to be one of very few carburetors that may be able to alleviate some of the problems with idling on a bridge port application, due to it's tunability. However, street port and bridge port applications will definitely require a ported manifold, something that I am currently working on.

The Sterling Nikki lends itself well to street performance, track racing, and auto cross. I even have someone who will be testing the Sterling in drag race application on a 12a.

I do not make a habit of dissuading potential customers by suggesting that the Sterling Nikki could not perform well in a boosted application. I believe it would perform very well, and I will be working closely with someone who will be using this carburetor in a draw through turbo application. Carl and I will eventually be using the Sterling Nikki in supercharged applications, again in a draw through configuration on 12a engines.

However, currently I have no jetting data what so ever with regards to boost applications for this carburetor, and we have not made a successful attempt at a blow through application. as a result, I do not currently offer boost prepping for the Sterling Nikki, as the boost applications we will be working with in the near future are all draw through, which requires no further modification to the carburetor.

The Sterling Nikki will perform fantastically on the track, and optional larger Nikki floats along with Grose jets can virtually eliminate the bog normally associated with left hand curve exits.

I have also started to get quite an auto-cross following, as the Sterling Nikki provides the low end grunt necessary for these complex driving needs.

The requirements of the Sterling Nikki are no different from any other rotary applied performance carburetor; it requires more fuel than the stock fuel pump can deliver at wide open throttle and requires a free flowing header exhaust. For fuel delivery, I recommend the Carter 7 lb pump. It's an inexpensive robust fuel pump that delivers plenty of fuel. If the fuel pump is bigger than 7 lbs, you will probably have problems with inconsistencies in the fuel delivery system in the form of fuel pressure surges. A Holley 4 pound regulator and a decent pressure gage is also a must. Don't make the mistake of skimping on the regulator, and you'll have to do some research on your own about which choice you go with. I always thought the Holley 4 psi regulator was great, and it always worked well for me, but I've read a number of times where it has disappointed. -Then again, I've read that about nearly every other brand, as well.

You will also need a good pressure gauge. A FPG is an essential tool that you should never feel bad about spending good money on. Paul Yaw had a write-up on his website years ago about testing he had done on fuel gauges. The variances were astounding, and disappointing. Gauges  marked and distributed by well known and trusted brands were off by as much as 1/2 a psi, and when your operating in the window of 2-3 psi, that's not very helpful!

I recommend one of Racing Beat's header exhaust systems. It's the best we can currently get for cheap that's engineered for maximum flow, and is built to last. Robert of Rotaryshack (a link is on my Links & Resources page) has just announced (as of this update) a custom made header that is pricey, but looks really good. I have a buddy, Kentetsu, who's trying to rally interest and support enough to get the old Mindtrain exhaust remanufactured. Unfortunately, there are very few options available. The rotary needs a free flowing exhaust if it's expected to be used as a performance engine.

When you receive your Sterling Nikki, the idle speed will be set high, and you can find both idle and performance tuning instructions right on this site. Part of the sale of any SMW carburetor is my personal commitment to help you get up and running. Don't ever hesitate to ask me about something. I even have a forum with sections specifically for the Nikki and the modified Nikki, and I encourage anyone that owns an SMW Nikki or anyone having any Nikki troubles to join and participate in the discussions.

The carburetor with arrive with a refurbished vacuum secondary box installed, even though the secondaries are mechanized. The vacuum box does not interfere with the mechanical secondary operation, but you can choose to remove the box and linkage, and plug the port if you wish. Development goals in 2009 include making use of the secondary vacuum box and circuit in an effort to add an adjustable secondary timing system. It is advised that the box not be discarded and the port not permanently plugged, as I will be offering retrofitting kits in the future.

Fine tuning the performance will require you to purchase more Holley jets, but your Sterling Nikki will be sent to you with baseline performance jetting. This means that you're fuel mileage will be far less than your old stock Nikki. it will be up to you to find a compromise between performance and fuel conservation that you can be satisfied with. However, the Sterling Nikki is every bit as capable of getting high fuel mileage as the stock Nikki, if jetted accordingly, and you will have the reassurance, even when you are jetted for performance, that you can always re-jet for conservation.

Extensive jetting information can be found in the Nikki Tuning section of my website, and I will be adding more to those important pages over time as I dyno-test more configurations. I welcome anyone with dymeter test results with careful collaboration of the jetting configurations tested to submit them to me for publishing.

The purchase of a Sterling Nikki comes with a 30 day, limited money back warranty. This is my best attempt to stand behind my product. If you are unsatisfied, or completely all out frustrated despite all of my efforts to help, you can send it back to me for a full refund; shipping cost is on you, though. The "limitations" to that warranty are laid out very specifically on the "SMW Warranty" page. Please read it! I feel I am going a measurable distance for my customers, and I expect a reciprocation in only that you read my warranty, my disclaimer, my core return policy, and my shipping & packing page. These all contain very important details that can help avoid a unsatisfactory transaction.

The Racing Nikki

 Obviously the racing Nikki has to meet high performance demands on the track, but the modifications allowed to be made to them are set forth by the sanctioned racing class rules and regulations. The least restrictive racing rules apply to auto cross and SCCA E- production. The most restrictive for the Rx-7 is the SCCA Spec 7 class, where the carburetor must remain almost completely stock. SCCA IT7 & Pro 7 classes fall somewhere in between with specific modifications allowed, or depending upon interpretation, "tolerated". Differences in the usual SCCA class racing Nikkis can be found on this chart .

The Legendary 'Left Hand Stumble'

When I discuss racing applications with regards to Nikki modifications, I usually use auto cross as my primary example. This is not just because I have several customers who auto cross with Sterling Nikkis, but also because the demands of auto cross racing are the highest. There is a great need for good mid range acceleration in auto cross, as well as for the carburetor to decelerate quickly and corner without stumbling. As I've stated many times, in any case, running at WOT can be optimized just the same no matter what the performance application. So the auto cross racing Nikki must meet the demands of all types of racing, with the exception of drag racing.

The Sterling Nikki is as optimised for the street as it is for auto cross. The only difference between a Sterling Street Nikki and a Sterling Racing Nikki built for competition with few modification regulations is the float set that I use. In auto cross and track racing there is a problem with the Holley, and to a lesser extent the Nikki, where upon exiting a left hand turn, there is a stumble. This is a known annoyance that most SCCA racers learn to "drive around". But any time that can be shaved off the track, and any distraction that can be eliminated is going to be good for the racer.

People are usually surprised when I explain to them what is actually happening inside the carburetor in these instances. The series of events that follows a hard left corner is rather simple but the problem caused by them is compounded and unique. Understanding what's really going on inside the carburetor will help those racers that are forced to drive around the issue because their class rules do not allow for one very simple modification...

Because of the orientation of the carburetor, the fuel is forced to the back of the float bowls with great force during left hand turns. As the fuel collects at the back of the float bowls, the primary emulsion tubes, and in severe cases even the primary fuel jets, are uncovered and starved of fuel for an undetermined, but minute amount of time. Two things happen while the carburetor is in this state; The main circuit delivers a lean condition, though the driver may never notice a decrease in power associated with it if he's feathering the pedal through the turn, and the floats drop, letting in more fuel.

When the car exits the turn and the G-forces acting on the fuel let up, the fuel returns to a fairly level position, but there's far too much of it. The emulsion tubes are completely submerged, and the carburetor is flooded. Because there is usually a down shift in the turn and a "power out" attempt upon exiting the turn, the driver is pressing on the throttle, trying to accelerate. At this point, the flooded carb would normally drop down to the appropriate fuel level fairly quickly on it's own. But the accelerator pump is adding even more fuel to the incoming air for a duration, and the engine bog that drivers experience is actually due to a rich condition from the combination of the siphoning of fuel from the over-loaded emulsion system and the action of the accelerator pump.

I've had many racers tell me ( in some cases, insist ) that they want baffles installed in the air horn of their race Nikki. I try once to explain why that won't work, and if they insist I do it anyway, I charge extra and I make it clear that I take no responsibility for the fact that it will make no difference. This is because the air horn gasket already traps the fuel and keeps it from climbing back up into the void at the top of the airhorn as much as any baffle ever could. No baffle installation is going to keep the fuel from going where artificial sideways gravity dictates. This baffle installation modification is a carry-over from the 70s when the gaskets used on the Nikki did actually allow for terrible fuel slosh. The current replacement gaskets are the same design for both the earlier Nikkis and the later ones, so there is no reason not to use an early Nikki.

A very simple and much more effective solution to this problem is to install the floats designed for early Nikki carburetors. These floats are only found in pre '79 and some '79 - '80 Nikki carbs, as far as I know, and they are full sized, as opposed to the later design that look like they are diagonally cut in half. I have not measured the volume of each float yet, but it's inconsequential. What actually matters is that they displace as much fuel as possible inside the bowl. The larger floats work by taking up room that would otherwise become a void that would fill with fuel when the float drops from the sideways G-force that throws the fuel to the back of the carburetor, when the float no longer has anything supporting it to keep it closing the needle valve. The carburetor will still go through the first stage of the cornering issue where the primary main emulsion tubes and fuel jets are uncovered, though it might be less likely that the fuel jet would be uncovered, depending upon your fuel pressure. But the second stage of the corning issue, where the float normally drops down allowing fuel to enter in will be much less dramatic, if it even happens at all. I have yet to test side by side comparisons of this issue. Testing such things is always difficult for me as I don't have easy access to a track, and racing around on roads is just never a good idea to check these types of things.

Fuel Pressure

The race Nikki should have fuel pressure that is only as high as the highest fuel demands. This way, the emulsion system is kept from being overwhelmed as much as possible. Fine tuning for performance is a must to be competitive on the track, and tuning the emulsion system is the key to fine tuning the modified Nikki. If the emulsion system is drowned in fuel at any time during a race, you can bet the law of averages that it's going to be when you rely on it the most! So keep that fuel pressure down to where is just meets the demands of your engine at the highest RPM.

Ideally, the fuel level should be kept right at the halfway point of the site glass no matter what the demand is at any given time. This would enable the emulsion system to work to it's fullest potential, consistently. About the best we can do to maintain a consistent fuel level is to lower the fuel pressure so it does not exceed the maximum fuel demands of the carburetor, and to install Grose jets. Grose jets are a special needle & seat assembly that eliminate the need for the complex, rather less precise OEM needle & seat assemblies. Their advantages include the fact that they already have a consistent matched drop, the valve is actually a glass ball that can't bind, and the fuel inlet is .099 inches, whereas the fuel inlet on OEM seats measures .075 inches. This trouble free operation, and an increase in fuel flow to the bowls, which translates into a more consistent bowl level.

The Grose jets are an added expense, also, and they seem to be a bit difficult for me to locate thus far.

All SMW class specific racing Nikkis are modified only within the parameters defined by the sanctioning body. It is the customer's responsibility, if not obligation to be completely familiar with the rules and the "accepted interpretations" of them. Customers will need to be responsible for any regional-specific rules, amendments, clauses, etc that may further limit the modifications allowed on the Nikki carburetor for their class. I stand behind my work, but I only know as much as I'm told. I am aware of the basic SCCA rules for most classes, but I make it my policy to discuss them with my customers so that we are "on the same page". I can't afford the energy trying to defend myself combating a possible bad reputation if someone gets caught racing with illegal modifications on a carb I built for him.

Racers are among my most serious tuners and are more often inclined to hit the dynamometer with their car than most. I offer racing teams breaks on prices when I can by working out deals for dyno data. I don't have easy access to a dynamometer so any data I receive is always welcome, provided all the jetting and engine configuration details are also provided, along with permission to accredit the team with the dyno data. I will also work out situations with non-racing customers with the same conditions, but usually only after the sale is complete, and I am confident they do know what they are doing. In such cases I would offer future carb work at a reduced price, or perhaps a reduced price on a ported manifold or some other new product. I'm always open to service exchange ideas, but I'm not always in the best financial position to make such deals, so they are "hit or mss" opportunities all the way around. Never be shy about asking.

Track side assistance while jet tuning is pretty rare for me. That's why I hardly ever give out my cell phone number. If it's an emergency situation, I still need to know in advance, and then I'm usually willing to set up a call time. But basically, I'm making a huge effort to include everything I would ever suggest for performance tuning on the section of this site dedicated to that.

I also highly encourage racers to join and participate in the Back yard Mechanic's Club . There is a separate section devoted to racing, and all input from racers is always a healthy addition to any sports car enthusiast's forum.

If you have any questions at all, please feel free to post them on my forum: The Back Yard Mechanics' Club , or simply email me, and I'll be glad to help.