stalling when warm, black smoke on startup

[Lodogg2221]

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...

[Pacman]

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

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

[azr]

Hey about the Petcock. Is it better to rebuild or to buy a new one? the new ones are a bit of $$$. Opinions?

[Lodogg2221]

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...

[azr]

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.

[psyguy]

so, all good now?

[azr]

I'm waiting for 2 new mixture screws from Z1 and then I'll let you know. I can't really afford the carb synchronizer so I'm trying the old make your own. I know it will work fine for a 2 carb system..but I have 4...so I'm hoping it will do for now.

[Steve]

I'm waiting for 2 new mixture screws from Z1 and then I'll let you know. I can't really afford the carb synchronizer so I'm trying the old make your own. I know it will work fine for a 2 carb system..but I have 4...so I'm hoping it will do for now.

Save yourself some money and a LOT of aggravation. Read this thread to see what I mean:
Trying to synch GS650 carbs, too much vacuum?

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...

For the VM carbs on the '79 and older bikes, #3 is the vacuum source.
For the BS carbs (also known as CV carbs) on the '80 and newer bikes, #2 is the vacuum source.
AZR (the original poster) has a '79.
Mike81gs850 (hijacker) has an '81.

Yes, the cylinders are numbered left-to-right. Clutch hand to throttle hand.

.

[azr]

I took everyones advice and ordered my Carbtune, should be here in 2 weeks at most. I got the bike together but it won't start. I rechecked the timing, the plug wires, all good. I reset the air and fuel mixtures to factory settings and I'll try again tomorrow. It turns over but won't catch, just pops and then eventually backfires with black smoke...arrrrr. Not sure what I've done wrong.

[psyguy]

Check things
Battery
compression
Valve clearance
wire connections

what's the status of the items above?

i assume you are using the choke

[azr]

I tried staring it today, no luck. Still just pops and backfires, and I am using the choke. It's as if I have the timing way off, or the plug wires are mixed but I've checked all of them and they are all correct according to my manual. The plug wires actually have cylinder makers on them for a no brainer, and I've reset the timing twice by the book. this isn't making any sense. And I did check to make sure there is fuel in the float bowl and there is.

[psyguy]

double check that you do get a spark on all 4

the airbox+filter has to be on

[azr]

Thanks PS, I checked my wiring and I had crossed the Coil wires (White...Black...what's the difference...BIG DIFFERENCE!). So she lives once again. She running pretty rough though. I don't think I did the bench sync right. My Carbtune is 2 wks away though. My #2 carb had the fuel mixture hole expanded so I set the needle in farther that OEM. Any ideas on how I will be able to tell if it is too far or not far enough?

[psyguy]

once you have the carbs ballanced you can dial that screw in completely and then work your way out until you get the highest idle / smooth sound

or you can use "colortune"

or replace that one carb body

get the valve clearances sorted BEFORE syncing the carb

[azr]

I wasn't going to set the valve clearances simple due to the fact that it was supposed to be done last year by a shop the PO had it sent to. And I'm running out of money for valve shims. I am just hoping this will do the trick for now and I can get a bit of ridding time on it. I was going to try setting the air mixture and fuel mixture screws by the best idle method tomorrow. Is this a bad thing to do before I have my carbs synched?