This one, the one I just put a Supertrapp aluminum racing series 2" ID x 13" L x 4" OD on.

Had quite the weekend with this bike's carburetors in below freezing outdoor temperatures in a garage with doors cracked to allow ventilation for gasoline fumes. This bike came to me as a third owner bike that looked wonderful on the outside but was basically a butchered mess on the inside. I doubt the second owner did any of that, he didn't seem like the mechanical DIY type. The original owner had dumped some money into it, from obvious inspection, that the bike was a trackbike with lights. One of the major issues I'd been having with it was the carburetors or perhaps exhaust flow. With all of those component settings and options exhausted, the last ditch item must have been the old exhaust muffler. Thus the Supertrapp, which I thought would be my last possible option in restoring the bike's power from idle to about 3/4 throttle. When that didn't do the trick, I knew it had to be an issue with how the carburetors were modified and I was right, finally!

Fortunately for me I had a spare set of decade old unused carburetors that fit my bike. I had purchased a rebuild kit from Parts Unlimited that was an OEM match, so I simply needed to drop in the stock parts from the modified carbs that were on the bike and use those settings as a starting point. In the process I finally saw what had been done to the working set that came with the bike. They'd been modified with a race kit from Factory Pro for the 49-state version of my bike, not my version, which is made for California. The CRB-K88-1.7-RK, 'race kit' wasn't a fit for the bike, even though there's a case study by a shop in Oregon on FP's Web site of doing exactly this modification to exactly this bike model using the 49-state race kit.

They start by saying Peak HP was 131.6 on the dynojet dynomometer and end up saying YEEE HAAA! What do you know.... 144.7 HP! 13.1 HP gained on top and significant gains throughout the RPM range above 5K RPM. I think this was what the original owner tried to emulate. He modified the carburetors exactly as that shop did, less the pilot jet increase. He replaced the stock exhaust with a full Muzzy exhaust, pulled out the main air jet and put in the RK air jet from FP, all basically the same as the shop did, but wow, did it fall short of expectations!!! The bike falls on its face off the line, like I said all the way up until about 3/4 throttle and 7,500 RPMs, when it finally comes alive. I bagged that set of carbs and returned them to the settings I found them at. I'd experimented with all of the possible combinations of components and while I'd see some hope in making one area better, another would go to crap. ENOUGH! As a race set of carburetors, they'd probably be okay. But I don't ride track, so it is of little use to me.

The other tidbits I'll add about the Factory Pro case study was that their 2000 ZX-9R was shop tuned in Hillsboro, OR, which has a base elevation of basically sea-level, 194' AMSL. The motorcycle's owner, Jim Gilbert of Ashland, Oregon, lived at a base elevation of 2,000' AMSL. It's a carbureted bike! You don't jet a carbureted bike rich for sea-level and send the owner up into the mountains with it! JHC! You have to detune it approximately one step for every 2,000' in elevation. Kawasaki recommends a reduction of 4% for 2,000' AMSL and 8% for 4,000.'

The shop tuner noted ďcustomer complained about terrible "lean surge" at cruising and low speeds when he brought it in.Ē Which, as any ZX-9R owner who knows anything about their bike or has asked other owners online about it will tell you, is a simple combination $1.00 fix with a throttle body synchronization and pilot fuel screw reset. You add a 0.5 mm shim (washer) under the stock jet needle to effectively raise it, synchronized the carburetor throttle bodies, and set all of the pilot air screws to OEM turns out. PROBLEM SOLVED!

The stock settings on a 2000 ZX-9R are: Pilot Fuel Screw 1 5/8 turns out, #38 x 4 pilot jet, 4 mm +/- 2 mm float heights, N9BB jet needles on a standard 0.6 mm OEM wear washer, and a #160 out/#165 inside - Keihin main round jet stagger. The owner had already modified the main jet stagger however prior to dropping it off at the shop, putting in #165 out/#170 inside, an increase of 3% equally on all jet sizes.

The shop apparently missed that fact, one of many. They bumped his #165/#170 main stagger, calling it ďstock,Ē with Factory Pro reverse staggered #178/#175 mains, a bump in fuel delivery of 8% on the outside cylinders and 3% on the inside over the previous jetting and 11% on the outside and 6% on the inside, over stock. They don't explain why they did it this way, but may have concluded incorrectly that Jim's ZX-9R was a 2002, which does use reverse stagger main jets, with staggered jet needles, as well. Factory Pro doesnít mention reversing the stagger either as the way to install their RK race kit. But they didnít point out the oddity either on their Web site. On top of all the other richer settings, the shop also bumped Jim's ZX-9R pilot jets 5% richer, from #38 to #40. Lastly, they installed an Akrapovic full exhaust system.

Neither the shop nor Factory Pro caught any of the problematic tuning errors: not the glaring elevation error, raising fuel delivery on a bike whose base elevation is 2,000' above where it is being tuned nor the compounding of larger than stock main jets nor the reverse stagger errors. But that's all beside the point. The shop showed a 10% gain in HP from their near sea-level elevation dyno. Which is either a false flubbing of some corrected dyno result numbers or a brilliant discovery. Jim was sent home with his tuned-for-sea-level carburetted sportbike with the oddest jetting configuration I've ever heard of, outside of some DIY horror stories.

I would love to speak to Jim Gilbert to see if he loved the bike and still owns it. However, there is no record or follow-up to the story that I can find. Which is kind of odd in this day of Internet and social media chit-chat. Yeah the shop work was from 2000, but this is the pinnacle case study used as the benchmark of all benchmarks! Other than a final dyno run, we have nothing further to confirm the veracity of this monster tune that somehow turned compounded errors into massive results.

Moving back to my project though. I installed the used spare set with the same best-of settings as were on the FP set of carbs and the results were immediate. Better throttle response and power. Easier to get the bike off the line. Not perfect obviously. And this is where the UEGO comes into play again. There's no guesswork in what needs improving. I cannot diffuser my way out of this with my Supertrapp alone. The UEGO showed me where my initial jetting is deficient, so I know what I need to try next. I might even need to adjust in or out some of the Supertrapp diffusers too.