Running lean...really lean stock '80 GS650G after carb rebuild

[mhobryan]

Typical symptoms of lean running engine...won't hold an idle no matter where I set the idle screw, slow response to throttle, hanging rpm's when letting off the throttle.

I rebuilt the carbs; let them soak in Berrymans completely disassembled, replaced all the O rings, including the ones behind the intake boots. First try i discovered the intake boots were leaking (confirmed by spraying with starter fluid and observing idle speed increase significantly), so ordered new and replaced. Now there isn't any leaks around the boots, so am scratching my head a bit. Airbox is on, so is the air filter...as well as the stock exhaust and stock jets (bike is completely stock). It's running so poorly, haven't even attempted to ride it, heck... can't even get it to idle decently enough to idle and balance the carbs (btw main jets are set at 2 1/2 turns out IIRC....turning out more doesn't seem to help).

Oh yeah, valves are adjusted, and I'm getting spark. I'm probably going to tear the carbs a part and attempt another rebuild, however, thought I'd post in case there is something obvious I may be over looking, or haven't thought of that would cause this severe of a lean running condition. My other question is it possible that I am chasing the wrong cause of the above symptoms? Is there a different root cause that I should be considering?

Thanks,
Mike

 

[Guest]

Hi Mike,

I'm a fellow 650 owner and I battle through the same problem as you. Just won't to make sure of one thing before I continue. You said you have the MAIN jets 2.5 turns out. I'm assuming you mean the pilot screw not the Main jet in the carb bowl which screws into the emulsion tube. Probably just typo just wanted to make sure because the jets in the carbs should be screwed in tight.

If the lean issue is mostly at low rpm's (<4000rpm) then that suggest that pilot jets are plugged or the circuit is dirty. I like to blow about 100 psi of air through the pilot jet to ensure that its clear of debris. Another possibility is that the orings under the pilot screw are shot/non existant and air is being sucked in. Check those orings.
Further more the rubber caps that block off the vacuum sync ports can sometimes make a poor seal allowing air in. Check those aswell.

Only other thing I could think of would be tight valves but you said they weren't all in spec so I'm ruling that out.

 

[portdave]

Float level? Have you checked the bowls while on the bike? You can get something like this?

http://www.ebay.com/itm/Mikuni-Carb...ash=item3f59189704:g:5WsAAOxyf1dTKD80&vxp=mtr

 

[mhobryan]

Thanks for the suggestions. Yes, meant pilot screw and not main jets. I did replace the o rings below them. The little rubber stoppers are there, but fit lose, will order some new ones.

As for float level, I checked with a ruler, but they may not have been accurate enough. Will double check all of these when I pull the carbs again - appreciate all of the thoughts.

 

[Guest]

Yeah if those rubber nipples aren't right that could be it. It's best to check the float levels with a digit caliper if you have one.

 

[Zagg]

I read your thread because I am wrapping up the carb cleaning and hope to hear my bike run soon and because it was the most recent..... Anyway, after reading it I began reading the sticky "Help! My bike don't run right"

I am not the old-timer who's been here forever answering the same question and is sick of it so please understand ---- I saw symptoms and possible solutions immediately and thought they could help. I would suggest reading it just to see if anything jumps out at you... Keep us posted.

 

[tom203]

SpecialK is on the right track here. But if you pull carbs again (ouch!) make sure you inspect the choke plungers as another source of potential leaking. They need to retract fully and block/seal air off in closed position.

 

[60ratrod]

Have you done a vacuum sync on those carbs yet? I ask because i chased my tail on both my gs and kz thinking it was a vacuum leak, and once i sync'd the carbs, all my issues went away. Figured I'd ask since you didn't mention syncing the carbs

 

[tkent02]

Float level? Have you checked the bowls while on the bike? You can get something like this?

http://www.ebay.com/itm/Mikuni-Carb...ash=item3f59189704:g:5WsAAOxyf1dTKD80&vxp=mtr

What he said, I have checked fuel levels on quite a few GSes, it is rare to have all four at the perfect level no matter how careful you are at setting the floats. This and a little bit off on the synchronization could be the problem.