Newbie needs tuning help....

[Agent4573]

Hey guys, I just wanted to take the time to say hi. I just bought a 91 GS500E. It used to be a race bike and was converted back to a commuter for me. I'm having some trouble getting it dialed in correctly on the street. I just had the carbs apart for a thorough cleaning and everything looked good. I've adjusted it so that at idle I can blip the throttle and the revs respond nicely and fall back down without lag. My problem is that when I'm actually riding it, I can't get going unless the revs are over 3000 RPM (it misses and sputters and has ZERO power under load below this) and then it maxes out about 7500 and won't rev any higher. In nuetral if you gas it, it will rev nicely to 7500 and delay for a bit, then jump up to about 9 grand or so, at which time i stopped revving it.  I'm hoping you guys can lead me in the right direction on where to go with tuning it.

Current setup:
Race exhaust (basically open)
Aftermarket filter (not sure which kind)
It just had new pisonts and rings installed, and the valves adjusted.
Float height checked is very close to where it should be.
Main Jets: 150
Primary Jets: 30
Needle Shims: none
Mixture screw: 2.5 turns out

Thanks in advance! 

[mach1]

I can only chime in on one of your problems and thats the GS doesnt like taking off under 3k you got to take off above 3k and you'll be fine. As far as not going over 7.5k check your throttle cable make shure its not getting stuck on anything restricting it from opening the butterflys all the way. just my .02

[ohgood]

Back when mine used to actually run... Sigh... taking off from idle + a twist was not a big deal. It would pull nice and smoothly right up to around 5500, stumble a little, then clean up at 6500 and pull strong to 10k. You should be able to slip the clutch from idle to 2200 and roll the throttle smoothly all the way up. Having to REV to 3,000 just to leave means something is off.

but anyway, iirc you'll want 40 primary jets, 150 mains, one or two #4's on the needle, and 2.5 - 3.5 turns out.

[Agent4573]

I did some tuning so far and heres what the results were. With 147.5 mains and 40 pilots and 2 #4 washers, it spews black smoke at low RPM and won't hold an idle. The mixture screw does nothing to affect RPM at all, nor does the idle screw, only way to hold it at 2k RPM is to twist the throttle about a 1/4 turn. If you can get it off idle, it will rev to 9000 RPM now before it tops out. I forgot to mention in the original post that I'm at 2300 feet also. I'm gonna go change the pilots to 35's and see if I can get an idle, and if not I'll go back to 30's and deal with no power below 3000 rpm i guess. After that I'll try to deal with the topend. Thanks for the help, I'll try to keep you informed on what the effects are after every change.

[Agent4573]

Ok, so I stepped down a size on the pilot jet to a 35 and I could get it to idle, but its rough. The IDLE screw is maxed out to get it to sit at like 1200 rpm. Adjusting the right carb mixture screw doesn't do anything, adjust the left carb mixture screw I got the revs to come up to about 6 grand, then the bike died and now it won't start. I'm gonna let it sit and see if I flooded it. Still a slightly black exhaust smoke when its at idle.


Still has no power under like 3-4 grand and misses, sputters and dies. Pulls great from 4-9 grand and starts sputtering again at 9 grand. I did one full throttle run and had it maxed at 9 grand for about 15 seconds, as soon as I let off, it died and wouldn't start again for 30 seconds or so.

It seems very random in everything it does. Sometimes it will barely idle at all, other times I'll let off the gas and it will sit at 4-5 grand for 30 seconds before coming to a rough idle. Most of the time, it just stalls when I pull in the clutch. I'm at a loss for what to do next.

[spc]

Rip the carbs off.  Remove everything.  Soak all metal parts in carb cleaner for a day.  Inspect all the non-metal parts.   Clean every port you can find with a wire.  Re-assemble. 

[Agent4573]

Aight, got the bike to finally hit redline..... an accomplishment. I appearantly messed up setting the float height in one of the carbs. Floats are now at 14.6 +-.1mm. Main jet is a 47.5, pilot is a 35. Mixture screws are 1/2 turn out. It runs about the same with the mixture screw totally in or completely removed. I might gain about 200 RPM if i turn both screws completely in. Its still rough below 3-4 and requires about a 5 grand takeoff to do it without spitting, popping and dieing. I'm going to go back to a 30 pilot and see if I can get some adjustment out of the mixture screws. It pulls really nice from 5 grand all the way up to 11 grand now and it finally (barely) catches itself and stays running if I pull in the clutch when I come to stop. I still only get about 500-750 rpm change from no idle screw to maxing out the idle screw.

[Agent4573]

Final adjustment for the night.... I tried to go back to the 30 pilot jet to get some adjustability out of the mixture screw and it ran worse. It stumbled at 6-7k and only revved to 9k. No matter what pilot i put in there, 30,35 or 40, the mixture screw doesn't do anything to the RPMS on either carb. The RPMs go up about 50-100 when the screw is totally in, as in zero turns out. I can only get about 500 rpms range with the idle screw. If i max the idle screw out, it will run about 1800 rpm, and i can adjust it down to around 1100 before the bike just dies. I'm gonna go back to the 35 pilot tomorrow to get back to the setup that actually hit redline. Don't know why a pilot jet would effect 8000+ WOT running, but it does.

On a side note, what nipples on the carbs go to what? There are 3 nipples on each carb, one coming out of the black top cover, one coming out of the right side right by the little brass tube thats part of the choke circuit, and one nipple coming out of the bottom right in front of the bowls. I have the top nipple on each carb connected together with a vaccuum tube, and the same for the bottom nipple. The middle nipples are just capped off. Will this work or should I cap them all separately?

[spc]

they should all be capped seperately.