Jetting

Hello all. I got a set of carbs from craigslist an got them installed but I am still having some carb issues. First off, I have rebuilt all of the carbs and have installed 122 mains, 17.5 pilots and have the needle clip at number 4 groove. I have pods and a 4-into-1 exhaust. Prior to putting in the pilots I would have to turn the fuel screws (on the bottom) out around 3-4 turns to get it to idle. With the 17.5 it idles with the screws turned out only 1 turn. I am not sure how well I am doing at synching the things because at idle I never get a reading (around 0) I have to rev the motor in order to get a reading above 10cm Hg. So the low end does not pick up as much as it should. The mid range acceleration is pretty good, but at WOT the bike makes a low pitch gurgling wound. I am pretty sure this is indicative of a too large main jet flooding the cylinder and I should get smaller mains. I also bought a jet kit from Z1 (rip off as it cost $100 and you can get a couple of sets of mains for about $45 other places) and the main jets had smaller heads than did the jets I took off of my carbs (vm22s) I do not know if this can affect the performance. Any thoughts?

Look at your pluga at different settings. They will tell you rich or lean.
Steve

I am not sure how well I am doing at synching the things because at idle I never get a reading (around 0) I have to rev the motor in order to get a reading above 10cm Hg.

something doesn't sound right there, no vacuum at all = no fuel/air mix in at idle.

Are all your diaphragm rubbers ok?

Tweaking the needle position upp and down will give you a better or worse feel for your main jet selection.
Sometimes making it worse is good news as it helps you narrow down the problem if you can feel it react to the change.

something doesn't sound right there, no vacuum = no fuel/air mix in at idle.

It idles really well, I am not sure as to why there is no reading obviously there is vacuum of some sort. I just dont get a reading.

Are you using vacum or murcury gauges? You should have 20 CM.





If you don't have that, you need to find out why.
Steve

Im using vacuum gauges but vacuum is measured in cm (or inches) Hg. Although, I agree, I should have some vacuum at idle, it is just not showing up. I have done a leak test. With carb cleaner there is no change to the idle.

Do a compression test. It's wonder it runs at all.
Steve

Compression is not the best but they are all around 100. One cylinder was around 80 but went up after I adjusted the valve clearances. I replaced the jets I got with the jet kit with 102s I got in my rebuild kit and now the top end situation is taken care of. The only problems I still have are midrange bogdown, which I believe I can take care of with a needle adjustment, and the slow to return to idle. Also the lack of vacuum showing up on the gauges. I have to admit the gauges are pieced together with vacuum gauges from harbor freight, "limiters" I got from a pet supply store and for tube clamps I am using zip ties. The whole setup is terrible. Might be a problem.