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stalling when warm, black smoke on startup

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Guest

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Hey all. I have a 79' GS850G that I just bought. When I start the bike up black smoke is coming out of one of the pipes, just for a bit then clears up. The bike starts up fine enough with the choke. I ride it for awhile and everything is good. It idles pretty good, not perfect, but no stalling. Once it warms up it won't maintain an idle at a stop for more than a few seconds and then stalls. It restarts fine but will continue to stall at a stop and when I'm riding it once it's warm I can tell she's just not running smooth. I'm sure she needs a carb rebuild and a few other things. Would appreciate some direction as this is my first bike project. Thanks muchly.
 
I am having these same problems and I am very interested in this as well.
 
Is the smoke at startup oil or fuel?
There is a VM carb cleaning series somewhere on this site.
 
Sounds like valve oil stem seals. Pull the head after season is over and replace.
Find a good day to clean out the carbs.
Check things
Battery
compression
Valve clearance
wire connections
 
wouldn't an oil problem cause a blue smoke though? this smoke almost seems like a bad mixture thing.
 
if it smokes on startup only and only at idle, the smoke (if oil) would be due to the bad valve stem seals
if it smokes more as you push it harder that would be your oil rings going bad (or stuck)

the shutting-off when warm may be due to an air leak at the carbs-to-engine rubber boots (or due to a very dirty carbs)
 
Black smoke is usually due to overly rich mixture. Bluish smoke is oil.

Pull the carbs clean and replace all Orings from the vendor on here. While you have them off replace the intake Orings from the same vendor. Check valve clearance and adjust as necessary. Since this is a '79 check timing and point gap. Also, check for even compression on all cylinders.

This will give you a good starting point to tune from there. Once you've gotten these things done get back on here for final tuning of the carbs. There are a ton of threads on how to set the air screws and mixture screws on the '79 with the VM carbs.

Chris

ETA, the heavy black smoke at start up may point to a bad petcock leaking extra fuel into the carbs which then leak into the cylinder causing an excessively rich mixture for a short time at start up. Pull the tank and check to see that fuel doesn't leak from the fuel outlet on the petcock in the reserve and run positions but does in the prime position.
 
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thanks for all the suggestions. This site is proving to be invaluable. I'll let you know how it all goes.
 
According to the manual, the idle needs to be adjusted when warm. It's seen like your bike's idle is too low and that the reason it stall at intersection. Adjust the idle a little higher to see if it helps.
 
Hi, I am having a smoke issue on my 81 gs 850 L. It smells like unburnt fuel. I have cleaned the carbs and set all the adjustments to the specs in the factory service manual. At idle the number 2 cylinder wet fouls the plug, on take off it smokes horribly then at around 4,000rpm it smooths out. I wonder if my problem is incorrect spark timing. Does this engine have mechanically advanced timing? Like the distributor on a car? My bike doesn't have points to be gapped, or condenser to change. It makes sense to me though that if the timing is advanced at higher rpm and the engine smooths out, perhaps I have the timing wrong. Give me some ideas please
 
mike81gs850 said:
Hi, I am having a smoke issue on my 81 gs 850 L. It smells like unburnt fuel. I have cleaned the carbs and set all the adjustments to the specs in the factory service manual. At idle the number 2 cylinder wet fouls the plug, on take off it smokes horribly then at around 4,000rpm it smooths out. I wonder if my problem is incorrect spark timing. Does this engine have mechanically advanced timing? Like the distributor on a car? My bike doesn't have points to be gapped, or condenser to change. It makes sense to me though that if the timing is advanced at higher rpm and the engine smooths out, perhaps I have the timing wrong. Give me some ideas please
Click to expand...
Check the vacuum line from the petcock to cylinder #2 for gas. Sounds like a bad petcock.
 
Mike,

Try starting a new thread...

You might get more responses related to your issue...
 
Mike,
BTW, isnt it the #3? Left to right? I thought the two on the left, #1 and #2 looked good when we pulled them, and that #3 was fouled and wet, and #4 was pretty dark, but firing...
 
mike81gs850 said:
Hi, I am having a smoke issue on my 81 gs 850 L. It smells like unburnt fuel. I have cleaned the carbs and set all the adjustments to the specs in the factory service manual. At idle the number 2 cylinder wet fouls the plug, on take off it smokes horribly then at around 4,000rpm it smooths out. I wonder if my problem is incorrect spark timing. Does this engine have mechanically advanced timing? Like the distributor on a car? My bike doesn't have points to be gapped, or condenser to change. It makes sense to me though that if the timing is advanced at higher rpm and the engine smooths out, perhaps I have the timing wrong. Give me some ideas please
Click to expand...

If you are fouling on only one cylinder then it isn't likely the timing as that would affect all cylinders equally. I think you need to check the float needle valves because I believe they are stuck open on a couple of your carbs causing fuel to fill up and overflow the float bowls then the motor sucks the fuel in and then that cylinder is overly rich.

Pull the carbs, pull the float bowls and turn the carbs upside down. The floats should be held up/open by their springs and you can blow into the fuel inlet tube that was connected to the petcock. You should be able to blow and the air comes out of all the float needle valves. Then push each of the floats to their top most position gently. This should cut off air going to that float bowl. If it doesn't cut off the air to one or more by moveing the float to it's upmost position then that carb is overfilling it's float bowl and leaking gas into the engine and also likely into the airbox.

Chris
 
Hey about the Petcock. Is it better to rebuild or to buy a new one? the new ones are a bit of $$$. Opinions?
 
Ive read a ton on here about the petcock, and most recommend a new one over rebuilding.
I also found the Suzuki part, not a universal, or aftermarket, at bikebandit for $59. Ordered that and the seals too and a couple other things while I was there...
I figure the aftermarket one was about $48-$50, and Ill pay extra for an OEM part...
 
An update about my original posting (black smoke and stalling). I pulled the carbs apart and the #2 and #4 carb both had their idle mixture screw broken off. #2 carb was a nightmare the tip was lodged in the output hole. It was crazy in the end I had to punch it out with a tapered bit, crazy! So there is my reason for a VERY lean mixture and stalling at idle.
 
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