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Weak idle until hot

DimitriT

DimitriT

Forum Sage
Past Site Supporter
Hi folks, got a 82 GS550L with 60k on her. Daily ride. This season seems to have developed a problem where the idle gets weak when the bike is partially warmed up. Bike starts great when cold and idles on choke and off choke (after about a mile on a mild temp day). It also idles strong when fully warmed up (by that I mean a 20 min ride on the highway or something like that). But when the bike is half warmed up (like a slow 2 or 3 mile ride) the idle is really weak and needs a blip of throttle to keep running. I noticed this more after an oil change (Pennzoil 10w40). Also when the bike idles weak it will do a little better in neutral as opposed to being in gear with the clutch pulled in. Could the clutch be dragging? The oil change also seemed to bring on some gear change roughness but that cleared up after a couple of hundred miles. I posted this in carb section but this could go in the engine section.

Do folks run 5w40 oil?

Carbs feel well balanced and clean (rides smooth and strong off throttle). Ignition system looks fine. Yanking the ignition wires indicates that all cylinders are contributing but #3 seems a little weaker but not bad. I've had this bike for 20+ years and this is literally the only problem I have with it.
 
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What can I do about it? Only thing I know about clutch is the little adjustment wheel on the clutch lever. Also why would it idle ok in gear when cold but not when partially warmed up? Does the clutch tolerance change as it heats up?
 
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This seems normal to me, old air cooled bikes need to be fully warmed up before idling well, they're analog. It takes progressively longer as the weather gets colder.
PS: In the manual for the same vintage Honda CB750F the use of a thinner oil in winter is recommended.

PPS: As for clutch drag, test that by pulling the bike up on it's center stand and see if the wheel spins while idling in neutral.
 
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DimitriT said:
Hi folks, got a 82 GS550L with 60k on her. Daily ride. This season seems to have developed a problem where the idle gets weak when the bike is partially warmed up. Bike starts great when cold and idles on choke and off choke (after about a mile on a mild temp day). It also idles strong when fully warmed up (by that I mean a 20 min ride on the highway or something like that). But when the bike is half warmed up (like a slow 2 or 3 mile ride) the idle is really weak and needs a blip of throttle to keep running. I noticed this more after an oil change (Pennzoil 10w40). Also when the bike idles weak it will do a little better in neutral as opposed to being in gear with the clutch pulled in. Could the clutch be dragging? The oil change also seemed to bring on some gear change roughness but that cleared up after a couple of hundred miles. I posted this in carb section but this could go in the engine section.

Do folks run 5w40 oil?

Carbs feel well balanced and clean (rides smooth and strong off throttle). Ignition system looks fine. Yanking the ignition wires indicates that all cylinders are contributing but #3 seems a little weaker but not bad. I've had this bike for 20+ years and this is literally the only problem I have with it.
Click to expand...

Sucking air till heat expands parts and seals.
unless your clutch has adjusted itself by means of cable stretch.
or the oils viscosity rating across Temps is some odd variable. Check Pennzoil site for specs. Iirc only two Temps are test points so........

clutch us easy to check use the fine manual if adjustment needed..
 
Today I followed the same route as usual and got a steady idle at the stops where it would stall before. Air temps were about the same but the bike just ran better. Now I'm thinking maybe its an intermittent ignition thing.
 
This is pretty common with older air-cooled bikes. They need to be fully warmed up for a smooth idle. Weak idle when partly warm could be oil viscosity or a dragging clutch.

Try 5w40 oil for smoother shifts and less drag. Check carb sync and fuel screws too,small tweaks can help. If #3 cylinder feels weak, swap plugs or wires. Also, check clutch free play at lever and case.

Old bikes can be tricky but with patience you’ll fix it.
​
 
Use Shell Rotella T4 or T6 15W-40. Your clutch and valve train will thank you.

As for the idle, it's an odd pattern if it idles ok when cold, then goes through a temp range where it idles poorly, then gets hotter and idles better. With the clutch pulled in agrravating the issue, it points more to a dragging clutch.

As was mentioned, put the bike on the centerstand, put it in frist gear, and see if the rear wheel turns. If it does and your cable is out of adjustment range, get a new cable, OEM if you can find one.
 
Griffin said:
As was mentioned, put the bike on the centerstand, put it in frist gear, and see if the rear wheel turns. If it does and your cable is out of adjustment range, get a new cable, OEM if you can find one.
Click to expand...

Isn't it supposed to do that?
 
Griffin said:
Use Shell Rotella T4 or T6 15W-40. Your clutch and valve train will thank you.

As for the idle, it's an odd pattern if it idles ok when cold, then goes through a temp range where it idles poorly, then gets hotter and idles better. With the clutch pulled in agrravating the issue, it points more to a dragging clutch.

As was mentioned, put the bike on the centerstand, put it in frist gear, and see if the rear wheel turns. If it does and your cable is out of adjustment range, get a new cable, OEM if you can find one.
Click to expand...

Is there some adjustment I can make either at the clutch lever or at the left engine cover which will have the clutch pull a little further to account for a stretched cable?
 
Griffin said:
Use Shell Rotella T4 or T6 15W-40. Your clutch and valve train will thank you.

As for the idle, it's an odd pattern if it idles ok when cold, then goes through a temp range where it idles poorly, then gets hotter and idles better. With the clutch pulled in agrravating the issue, it points more to a dragging clutch.

As was mentioned, put the bike on the centerstand, put it in frist gear, and see if the rear wheel turns. If it does and your cable is out of adjustment range, get a new cable, OEM if you can find one.
Click to expand...

T6 is $30 OTD at the major stores and there's a $15 rebate right now on a gallon. Just picked up some. Their website says which stores are valid for the rebate.
 
DimitriT said:
Is there some adjustment I can make either at the clutch lever or at the left engine cover which will have the clutch pull a little further to account for a stretched cable?
Click to expand...

There is adjustment at both those places. On mine ('82 11E) it's on the right side of the engine, right on top of...wait for it...the clutch. :tickled_pink:
 
clutch actuators on the GS550's are totally different than the 1000's and 1100's, and not near as simple. Metal rod goes all the way thru eng to release clutch...
 
Happened again this morning and she cut out twice in traffic. Ran fine a few minutes later when warmed up. I'm wondering if it's a float level problem. Could a needle valve get stuck closed and starve a carb for fuel until it warms up enough to get unstuck? It really feels like it's firing on three until it warms up full.

The odd thing is it's idling fine off choke when it's cold. It's a weak idle only after running for 5 min
 
Stop fishing. Time to go back to square one and verify everything. Start with cam timing. Valve clearances. Ting advance working right and not stuck and no freeplay in the counterweight springs. Then dynamic timing. Carb sync with guages. Mixture screws set right. Are plugs sooty or ash grey... .. everything matters. To me it sounds that when its hot it leans out for some reason. Are the pilot and main jets the right size according to the manual.....
 
chuck hahn said:
Stop fishing. Time to go back to square one and verify everything. Start with cam timing. Valve clearances. Ting advance working right and not stuck and no freeplay in the counterweight springs. Then dynamic timing. Carb sync with guages. Mixture screws set right. Are plugs sooty or ash grey... .. everything matters. To me it sounds that when its hot it leans out for some reason. Are the pilot and main jets the right size according to the manual.....
Click to expand...

Appreciate the advice. The leaning out is what I'm thinking as well. Maybe it's a case where some cylinders are rich on idle and some are lean.
 
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