Please! only jetting expert respond...i don't want any high school kids with a 85 moto4 giving me advice on jetting...THX-------Problem...my 87 zilla runs very rich at 1/8 throttle. Has been doing this since I bought it 4 yrs ago. Have recently bought 3 next size up needles (larger in diameter) only to find out that this would lean out at 1/4 throttle and still rich at 1/8. Am waiting for leaner pilot jets (ordered). Could these be my problem? Did a leak down test all OK, green lights across the board. But still rich at 1/8. I have a keihin 38 PJ...running a 185 main...CGL needle (original since other ones are too lean) and 58 pilot. Can any one tell me what they are running for a pilot with the same carb? It's just to give me a ball park pilot #.

THX

 

hahaha i tried everything went back to my mechanic seems my new car had 2 bigga pilot jet for between 0-1/4 throttle. shes screaming now. i dont have any idea the needle or jet numbers on ur carb but zukzilla can pry help ya out with ball park good luck btw i bought every damn main 5 sizes each way for no reason and 2 needles.

 

I had the same problem with my 89 (39mm pwk keihin). I went from a #55 pilot down to a #50, that seemed to do the trick, the bike starts much easier. I am at about 2500ft. above sea level, just to give an idea for how lean you may or may not want to go. Also make sure your float height is properly adjusted. Hope this helps.

 

I am basing this info off of the carb being an older model. When you lean out the midrange with a needle change and the bike is still rich at an idle, then only 2 things can be happening. Either the pilot is too big, or the needle jet (where the needle rides up and down) is worn out. The later of the 2 is the most common. We run a 50 pilot in our 87 Zilla (neighbor's). If the pilot does not fix it then the needle jet is worn.

 

I know that on some carbs, you can change the needle jet but I'm not sure on a Keihin? Anyone?

 

Looking at the breakdowns on the Keihin's, there doesnt appear to be a replaceable needle jet there. Yesterday we changed a 34PJ off of my neigbor's 250R Honda because it was running rich at part throttle. I had already went from a 48 to a 38 pilot and it helped some but did not clear it up completely. Another better carb fixed the problem. If the needle jet isnt worn out too bad a pilot might be a good cure. Also you might be able to get a different needle with a little larger taper on the top, but you might have to end up trying several different ones and that could get costly. On the mikuni carbs, there is only about .008 difference between the smallest and largest needle jet orifices. So it is easy to see where some wear would cause problems. After owning 3 LT's and having to change needle jets on all, it is a fairly common problem. Most people I think get it close or just plain live with it, because honestly more people dont know how to tune a carb in comparison. Hope this helps,Bubba

 

My LT had a similar problem with the stock carb until I replaced the needle jet.

 

Since you have a 38mm carb, I would first try the stock jet sizes of the stock Mikuni. I don't have my mechanics manual in front of me, but I do remember that the 87's were jetted much larger from the factory than the later years.

Also, I'm surprised that the larger needles lean you out at any throttle. I would only think they would richen you up at more throttle. One thing you might try is a hotter spark plug. My brother's 89 Zilla was fouling plugs and he kept jetting down until he was back to stock which didn't make sense with a PT pipe and holes in his airbox lid. Then he tried a hotter spark plug and it fixed the problem and he was able to jet it back up.

Hope this helps.