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Low power below half-throttle

  • Thread starter Thread starter teedubya56
  • Start date Start date
T

teedubya56

Guest
1982 GS1100GK
Stock Airbox
Stock Exhaust

I am the original owner. It has sat in the corner of my basement since 1995.

What's been done so far:
Valves clearances adjusted
Tank cleaned
Carbs stripped and dipped in Berryman's Chem Dip
New carb o-rings
Float level set to 22.4
New intake boots
New intake boot o-rings
New airbox boots
New Uni air filter
Airbox sealed with weatherstripping
Attempted highest-idle mixture setting, but to my untrained ear, turning mixture screws doesn't seem to have much effect
Vacuum synced carbs
Petcock seems to work properly
(Other maintenance not related to the problem at hand)

Bike starts easily, idles smoothly. When I blip the throttle, it revs quickly, then promptly returns to idle.

Below half-throttle, it struggles - makes a sputtering noise and has low power. At half-throttle, it takes off and runs great.
Also pops some through the exhaust on closing throttle.

I removed the carbs and disassembled them again. The only thing I found out of place - When I removed the mixture screw from #2,
the o-ring, washer, and spring, were not attached to the screw. Could this be the cause of my problem?

Can someone give me a direction to look while I have the carbs disassembled?

Thanks to all for a great source of information and for your willingness to help.
 
Last edited:
It's probably just mad that you ignored it so long! Anyways, that's an impressive done maintenance list. And going back into carbs for second look, you set a good example.
I would think turning in mixture screws would have some effect-unless blocked/damaged-did the screws look ok? Does this bike have the ignition advance built into ignitor- no spinning weights? Have you check timing from idle up to 4k to makes sure it appears to smoothly increase?
 
You may be right. I'll have speak softly and try to soothe its hurt feelings :).

The mixture screws look ok - not worn or broken. Just the one that came out and left the spring, washer and o-ring behind. When I removed those parts, they looked ok too. In trying to adjust for highest idle, I couldn't detect a change in engine speed/sound until the screws were almost completely closed - probably just my inexperience.

I hadn't considered ignition or timing because it runs so well above half-throttle. It has electronic ignition - does that mean the advance is in the ignitor? I'll have to do a search for ignition timing procedure. Guess I'll need a timing light?

Thanks for the suggestions.
 
The parts on the mixture screw do sometimes get separated as you remove the screw. This is not a problem, but the only thing to watch is to reassemble in the correct order.

I am not a fundi on CV carbs, but it sounds to me as if you could be lean on the needle setting. Your pilot circuit and main circuit seem to be OK, as your bike idles properly and pulls well at wider open throttle.

The needle can be raised to a richer setting by using small washers or moving the circlip to another position if you have a number of grooves at the top of the needle.

There are many descriptions of the correct procedure to be found with "search" function. Someone who knows these carbs well will also chime in soon to help you out.

Well done in bringing her back to life!
 
Thanks 2B. I did a search and found the info on raising the needles. I'll give it a try.
 
highest idle setting... start at 2 turns out, then turn 1/4 turn at a time and pause for a couple seconds , listen, repeat. .. on my bike, it took almost two seconds for the idle to change. So each time you turn the screw 1/4, you have to pause and listen. once you hear a change, turn back 1/8th and listen. If it changes, 1/8th out again, if it does not, leave it. That Carb is done.

Be sure the bike is fully warmed up, no choke, and you have a fan blowing on the bike to keep it from getting too hot.

That whole pause and listen part is often missed!
 
I'm thinking lean since it pops throught the exhaust. I should have checked the plugs. I'll do that when I get home.
 
Thanks Keman. Maybe I wasn't waiting long enough for a response before. I'll try again and wait longer once I get it back together.
 
When tightening the clamps, did they bottom out or do you still have a little room to tighten more? If they bottomed out so that both sides are touching, you may need new clamps.
 
The clamps are new. I'll check when I put the carbs back on to see if they are bottoming out.
 
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