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Late starting cylinder.

  • Thread starter Thread starter GS750GUY
  • Start date Start date
G

GS750GUY

Guest
Dear GS family.
I have noticed the last few times I have ridden my 78 GS750EC that the the bike starts with the first bump of the starter button but when standing behind the bike I noticed the sound and pressure coming from the right exhaust pipe did not sound right. It was quieter and the pressures felt weaker than the left pipe. Upon further investigation I found that the header pipe for the #4 cylinder was still cold or just slightly warm when the remaining three were hot.
Each time this has happened I would go ahead and let the engine warm up a bit and then hop on the bike and just ride it around the block once. By the time I get back to my driveway the #4 header pipe is now just as hot as the other three and the bike from there on runs and performs beautifully. It only does this at cold start and always corrects itself. After warmed up it will not do this again.
Am I correct in guessing that this is probably a float needle sticking closed on the #4 carb? I'm guessing my short trip around the block is enough to jar it loose and then all is fine.
I appreciate your input!!
GS750GUY
 
No one out there wants to venture a cause regarding this symptom??:-k
 
Sounds like maybe the pilot has some crap stuck in it. Same thing Ive found on my cafe, but only from sitting for weeks at a time between me touching it unfortunately. Just not enough hours in the day:oops:
 
Maybe the passageway leading to/from the choke is blocked?
Maybe that cylinder can't fire until the engine gets hot enough to run without any choke?
Could also be the screw or the lever attaching the choke rod to that individual choke plunger is loose or missing, or maybe the nylon piece around the top of the plunger shaft is missing.

You didn't mention if the choke is being used when it happened or not.

Don't think it would be a float needle sticking, as there should be some fuel in the bowl from the last time it was run, unless it was a week or so since.
 
tkent02 said:
Maybe the passageway leading to/from the choke is blocked?
Maybe that cylinder can't fire until the engine gets hot enough to run without any choke?
Could also be the screw or the lever attaching the choke rod to that individual choke plunger is loose or missing, or maybe the nylon piece around the top of the plunger shaft is missing.

You didn't mention if the choke is being used when it happened or not.

Don't think it would be a float needle sticking, as there should be some fuel in the bowl from the last time it was run, unless it was a week or so since.
Click to expand...

Aaaaaa great points. Yes..... I for got to mention this is taking place when choked from a stone cold start. I discovered it is not the float because prior to starting the engine the last time I removed the bowl drain plug and a full bowl of fuel drained out. The choke theory makes plenty of sense because after the engine reaches operating temperature it performs beautifully and when I pull the plug wire cap after warm up the engine immediately slows and stumbles and then returns to normal when the plug wire is returned to the plug. Also when warmed up the bike restarts with just a bump of the starter button.
I will check out the chock mechanism.
Thanks for your wisdom!!
Gs750guy:)
 
TheCafeKid said:
Sounds like maybe the pilot has some crap stuck in it. Same thing Ive found on my cafe, but only from sitting for weeks at a time between me touching it unfortunately. Just not enough hours in the day:oops:
Click to expand...

Thanks CafeKid. Good points but I'm tending to think it may be choke mechanism problems somewhere rather than crap in the pilot. The tank, carbs, and fuel system is operating room clean with just 1000 miles on it. I've also got and in line fuel filter which I just replaced and probably didn't need to. I will check out choke linkage first and then start looking for crud in the system.
Thanks again!!
GS750guy
 
If you've got a timing light, i would check the #4 plug just to make sure you've got spark when you have that condition present. Then you can rule out electrical.
 
My 850G did the same thing, o'rings on the intake were leaking when cold and ran fine hot. Spray some water at the o'rings esp. #4. Maybe???
 
tkent02 said:
Maybe the passageway leading to/from the choke is blocked?
Maybe that cylinder can't fire until the engine gets hot enough to run without any choke?
Could also be the screw or the lever attaching the choke rod to that individual choke plunger is loose or missing, or maybe the nylon piece around the top of the plunger shaft is missing.

You didn't mention if the choke is being used when it happened or not.

Don't think it would be a float needle sticking, as there should be some fuel in the bowl from the last time it was run, unless it was a week or so since.
Click to expand...

TKENT02 WOULD HAVE WON THE BET ON THIS ONE. I found the choke linkage to be all present and in good shape so I disconnected the linkage and removed the choke plunger and side air screw and gave both a few blasts of compressed air and a shot of carb cleaner. I reassembled it......fired it up ......and now all four chokes operate flawlessly.
Just goes to show the guys that preach absolute cleanliness in carb cleaning know their stuff. Even when I though I had a thoroughly clean system and even an in-line filter some crap still got through. And maybe it would not take much to mess up a choke.
Thanks again!!
GS750GUY
 
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