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#1 cylinder dead, stumped

  • Thread starter Thread starter stain
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stain

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Ok so I have a 1981 GS850G that I purchased out of a long storage. 23k miles
New plugs
New air filter
New cylinder head carb boots
New coils
Carbs rebuilt by one of our GS members
Valves adjusted
Compression 145-150 across the board.
I cannot get the #1 cylinder to fire. I have switched plugs, coils and wires and #1 stays dead. RPM's do not change when removing plug wire at idle or at @2500 rpm . Idle does not change when adjusting the air screw, heck I took it right out with no effect. Rpms do not change when giving the intake boot a squirt of carb clean with air filter door removed. The boots inside the air box have been chewed but I cant get it to pick up #1 even with the airbox off.
I am stumped and frustrated at this point and just had to walk away for a bit.
Any ideas would be welcome at this point.
 
have you taken plug 1 out and held it against the engine and cranked it to see if theres a spark..and if so is it pretty bright or weak and dim???
 
I have. The spark seems pretty decent. I went so far as to take the wires from #4 and swap it with #1 and the problem stays at #1.
The only other thing I haven't done is remove the header pipe and look for a restriction, although my experience with exhaust restriction makes plugs foul quickly. Maybe tonight.
 
Remove the drain screw on carb and make sure you are getting fuel, may have a stuck only valve. Or just tap the carb with a screw driver handle. Seen it happen before
 
The bowls have fuel. Pilot jet looks good. Pulling the choke seems to have no effect. I might replace the pilots anyway as i have a set from my old 850.
Thanks
 
Put your hand over that carb and crank it to see how much suction it feels like as compared to another one thats getting hot. But you stated so real good compression numbers though...HMMM.
 
Ok, I put the carbs back on, double checked my coil wiring and removed the #1 exhaust pipe---no change.
I then disconnected the choke on the #1 carb so I could operate it separate from the other 3. At idle, when I pull the choke on #1 ONLY, cylinder starts to fire, the idle rises @1k rpms, cylinder exhaust and head temps rise to match the other 3. I would assume this means the cylinder is LEAN. BUT I would assume by placing my hand over the carb throat at idle I could get the same effect---but I don't, it floods.
Not sure what this means, I will have to study my carb diagram again after dinner...............
 
It will flood easily with your hand over the carb...use a shop rag or a few layers of Tshirt for restriction. Im thinking maybe the #1 butterfly isnt as open as #2 as they are on the same adjuster screw. May have to fiddle with the sync screw a little bit each way to see if it opens the butterfly and she catches. Ive seen it happen even with a real close bench sync..little more tweeking and magic.
 
The thing is that cylinder never comes in even after idle unless that choke is pulled. I did a vacuum synch and it seemed all was well. ???
I am not gong to get much more done on it tonight, or tomorrow for that matter. Daughter hit a deer with the wife's car and I got to fix that also. It never ends......
 
Possibly, but all 4 were dipped 24 hrs and all 4 got the same rinse, carb spray, and air in very copious amounts...I know because I did them. I Pmed Rich saying if he wanted to send that body back I would gladly dip it again and assume all his shipping costs and I myself am at a loss as to why too.

So, Rich, if you want to send that body back I stand behind the work 100%. Its quite possible that body had way more than the others but the spray and air flowed nicely. In any case Just PM me for the address again if you dont still have it and I will redo it. let me kn ow.
 
I am wondering if the float/float level could be the culprit? I know the pilot jets are clean, needs to double check the passage.
Thanks Chuck, you are a man of your word for sure. I will try to get to this late tonight if possible.
 
Last edited:
Float level won't cause a cylinder not to fire at all. It's something else.
 
But low float level would cause a no fuel situation, correct? Or is the main jet/ pilot jet so far in the bowl it would be impossible to starve it for fuel? It seems The choke circuit pulls fuel from the bottom of the bowl.
Thanks for any insight.
 
The choke has a brass pick up tube that often plugs. The tube sticks into a passage inside the float bowl that often plugs up too.

And yes, the main jet picks up fuel deep down into the bowl.
 
They are all the same and I believe they were at 21.something which was within the specs so I never touched the floats hts. 3 fire and 1 doesnt with all 4 being the same? Nope it isnt floats.
 
Well, problem found. My #1 carb throat is cracked on the engine side. Any one got a carb body for sale.?
 
No kidding??? I didnt see that when i had them. Those are hard to crack. I would just use a dremel and a small wheel and grind a ditch along the crack and fill it with JB Weld and smooth it off with a file once it hardens. Probably never be a problem again. Take pics of that as I would like to see it.
 
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