For street use, keep the injector system. If you are concerned about oil, get the injector-use castor-based oil by Blendzall (available here in the US). Great stuff, and has that wonderful smell.
Use all the add-ons listed by Tyga (power-up kits), and the Tyga pipes are seriously tough to beat. And do the front head conversion. This will net you a very fast, but very reliable bike in the 60hp range. To make the bike even quicker, you can lighten the flywheel and remove the kickstart system.
Bumping up the compression higher than stock will make the bike want to run high-octane gas. Especially with the ignition derestriction. Not advisable on a street-going bike.
Modifiying the airbox will change the jetting requirements alot, depending on how far you go. I originally cut the top and installed a Daytona filter. This helped a bit, requiring leaner pilots and richer mains. I later found out that the Daytona filters have a restrictive plastic layer between the two layers of foam. I peeled mine apart, removed the plastic, and used sewing thread around the edges to keep the two foam layers together. Once again, I had to go a tad higher on the mains. I also custom-made some inserts that tapered and enlarged the rubber intake boots (between carbs and airbox) by a large margin. This gave the same power as having the box entirely removed, but keeps the filter in place. It made my jetting requirements jump ALOT on the mains. Power was up at peak, but midrange is a tad softer.
As for the jet kits, they are all pretty much the same. The JHA units are actually just relabled HRC kits. I used an HRC kit once, and had nightmares trying to get it right. Getting the jetting correct for high-rpms would make the lower rpms run too ruch and get a ton of spooge out the pipe. Overall drivability and low-mid power suffered. Am I the only one who has experienced this?? I currently run the stock setup, but have a set of Bakudan adjustable needles I just happened to stumble upon. This seems to work fine, even with my overbore. At least it did before I left Japan. I still dont have the bike registered here, so have had no chance to change the jetting for local conditions. Still looking for ways to get it licensed...
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Paul Herr
'88 FZR4/GSXR/YZF Frankenbike
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