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No Power Off Idle -- '79 GS 550L

  • Thread starter Thread starter fr8_pilot
  • Start date Start date
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fr8_pilot

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The bike had a 2500-3000 rpm idle after riding for a while and coming to a stop. I had been advised this was a likely intake leak. So I dipped the carbs, sprayed carb cleaner into the passages and indiviually cleaned the jets and needles, blowed each clean with compressed air. I replaced intake boots and o-rings, carb o-rings with Mr. Barr's kit, set float level to 26mm per Clymers.

The bike idles at 1100 now. Problem is if I crack the throttle it will bog down and die. The only way I can increase rpm is to add choke, but I don't keep it on very long as to not foul the plugs.

It doesn't seem to be idling on all 4cyl, when I pull the wire from #1 it makes no difference in idle and the pipe is not nearly as hot as #4 pipe. I have spark on all 4 cyl.

I have vacuum synched the carbs yet, but did bench synch them. I am going to replace all 4 sparkplugs.

The bike is stock except for K&N filter, not pods, I have cleaned and lightly re-oiled filter per instructions. I even tried no oil on filter, it made no real difference

I have rigged up a temp "fuel tank" I have 2' of 5/16" fuel line attached to the fuel tee. At the other end I shoved the fuel line through a small funnel tied to the left hand grip. The fuel line is not kinked or restricted on either end. I pour new fuel from a clean gas can until the funnel is no lower than 1/4 filled at all times. Could I possibly need a bigger fuel line? Or does the fuel screw on the bottom of the carbs need adjusted? I have plugged the carb vaccum line for these tests also.

Thanks for your advice!
 
Last edited:
Clue Found! Duh!

Clue Found! Duh!

I installed new sparkplugs B8-ES, didn't help much. While checking for air leaks I put my hand in front of the air intake and the rpm's shot up! This is understandable as an increase in choke also increased rpm's. As I mentioned the bike is stock so I shouldn't have to fiddle around with jets and needles etc... So should I adjust the air screws first to lean the mixture or enrichen the mixture with the fuel screws, or a combination of the two? Is there another way to enrichen the mixture that I should try? Sorry for all the questions. Thanks!
 
You did have an intake leak and your cleaning/carb rebuild/manifold o-ring replacement fixed that.
Now you have what sounds like fuel starvation when you crack the throttle. I assume it didn't bog and die before?
The bike idles fine but it apparently can't get the fuel it needs as you open the throttle.
If you did the above work correctly, that wouldn't cause this new problem.
Only other thing you've done is adjust the floats. I think 26mm is way too high and your fuel level in the bowls is too low now. Something closer to 24mm -MAX- is correct?
Any '79 550 owners have a factory manual? The "other" manuals are infamous for wrong info.
 
Also, the side air screws are adjusted using the highest rpm method.
They generally end up 1 1/2 to 2 turns out.
The pilot fuel screws (underneath) on a stock bike, are generally 1 turn out. Their factory setting can vary some. About 3/4 to 1 1/4 turns out is typical. Seat them LIGHTLY if adjusting because the sharp tips can break off in the carb body and your pilot circuit will be lean.
Adjust the pilot fuel screws and THEN adjust the side air screws for best idle using 1,100 rpm's as a base idle. Fine tuning the pilot fuel screws is usually necessary.
Go ahead and try these adjustments first if you like and see if it helps.
When I first read your repair attempts I somehow assumed you made these adjustments but now see you didn't.
I'm still thinking the floats are set too high though.
 
You said you put your hand in front of the air intake and the idle shot up? Are you doing this without the airbox on? If so it will starve if you do not have your air box on and sealed properly.My bike runs perfect but if i take the top off the air box it will bog down when I try to throttle up.you must have the airbox on or it wont begin to run right.
 
Keith:

"Now you have what sounds like fuel starvation when you crack the throttle. I assume it didn't bog and die before?"

The bike did not bog down and die at the crack of the throttle before the air leak was fixed. It did have that trouble under load before it was warmed up though.

"I think 26mm is way too high and your fuel level in the bowls is too low now."

The Clymer manual calls for 26mm. Can I re-adjust the float level with the VM carbs on the bike?

"The pilot fuel screws (underneath) on a stock bike, are generally 1 turn out. Their factory setting can vary some. About 3/4 to 1 1/4 turns out is typical."

Some of the pilot fuel screws were set at 1/2 to over 1. Not sure of the PO's reasons for those settings. Should I just set the air screws to 2 turns and the pilot fuel screws to 1 turn as a base to start adjustments instead of maintaining the previous settings (they were all over the map). I had been afraid of changing those settings due to the warnings in the manual about disturbing factory settings, however, I think the previous owner already made changes.

"Adjust the pilot fuel screws and THEN adjust the side air screws for best idle using 1,100 rpm's as a base idle."

Glad you mentioned this. As I was unsure of the correct order to make these changes.


tconroy:

"Are you doing this without the airbox on?"

The airbox, filter and lid are in place. I placed my hand in the opening on the airbox lid and the rpm's rose dramatically. By manipulating how much of my hand was obstructing the intake I could get a very enthusiastic throttle response.

Thank you both for your comments and advice.

I will put more sweat equity into it tomorrow.
 
Covering the intake works for a moment because you're assisting/forcing the jets to draw fuel.
Your VM carbs will run fine without the airbox, though lean of course. The CV carbs will not run well without the airbox attached.
You can't correctly adjust the floats with the carbs on the bike. I'd make a new specific float level topic to try to get someone who has a factory manual to respond. I really don't think 26 mm is correct, though I could be wrong. A low fuel level certainly fits your symptoms.
Adjusting the pilot fuel screws will take some tinkering because they're sensitive. No way to know where they were so I'd just start at 1 turn out and go from there. They should end up somewhere around 3/4 to 1 1/4 out.
The side air screws must be adjusted using the highest rpm method. You can start them at about 1 3/4 turns out and then set them.
I'll be at work today and try to check in tonight if you need help.
 
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