One cylinder not firing when cold???

[00.]

Hi I have 1978 gs850 with the old mikuni carbs.

The problem I'm having is that when I start the bike the number 3cylinder is not working, the reason I know this is that when I touch the exhaust on that cylinder it is not hot while the other exhaust pipes are burning melting hot. I don't know if this is a carb problem or an electric problem but here is what I did to try to fix it.

I took the carbs completely appart and cleaned every passage and replaced all orings and needless, basically they are in brand new condition. I also replaced sparkplugs.

My question is does anyone know what my problem could be?? Also when I have the chocke on and I try to give the bike any gas it will die, all my other bikes liked to have more gas when cold but this one will die anytime I twist the throttle, don't know if that could be related. Help please.....

 

[Guest]

Make sure the copper choke tube that goes in the float bowl is clear.

 

[Guest]

Is number 3 getting good spark? how was the bike running before? what do you have your air and fuel mixture screws set to?

 

[Steve]

What corner of the world do you call "home" that you have a '78 850? :-k

They were introduced to the US market as a '79, but rumor has it they were available elsewhere a bit earlier.

.

 

[tkent02]

Does the pipe eventually get hot when you go for a ride?
How does it run after a long ride?
Did you ensure the fuel passages in the bowls themselves (fuel feed to the enrichment circuit) were clear?

 

[BassCliff]

Hi,

Is the airbox installed with a clean, very lightly oiled air filter?


Thank you for your indulgence,

BassCliff

 

[00.]

Hi, the bike has a stock air box, stock pipes, everything on the bike is stock and original. The number 3 cylinder does get hot after a while and runs fine, but sometime it tends to smoke a lot out of that exhaust, but I guess that could just be valve seals. But not sure on what I can do to make this bike run right. I have had problems on other suzuki gs bikes with the one cylinder not heating up and I can't ever solve this problem. any help would be great on this

 

[Steve]

Two questions:

1. Which one are you calling "#3"? The cylinders are numbered from left to right as you sit on the bike.
That means that #1 is under your clutch hand and #4 is under your throttle hand.

2. Have you cleaned the carbs? A clogged enrichener tube ("choke") would prevent proper operation while cold.
If not the enrichener tube, the pilot circuit could be clogged.
Both scenarios are cured by proper cleaning of the carbs and installation of new o-rings.

.

 

[00.]

the cylinder is #3 from the left. I have cleaned the carbs two times now. I had the bodies completely apart every part was taken apart and cleaned, I blew compressed air through all of the passages.

WHere are the enrichement tubes located. and where is the pilot circuit located? I will try to check that.

 

[tom203]

the cylinder is #3 from the left. I have cleaned the carbs two times now. I had the bodies completely apart every part was taken apart and cleaned, I blew compressed air through all of the passages.

WHere are the enrichement tubes located. and where is the pilot circuit located? I will try to check that.

Is the petcock vacuum hose connected to this #3 carb? If so, petcock might be leaking down this hose causing the # 3 plug to foul until bike runs for a while.

 

[Guest]

Had a similar problem on my '79 GS1000E. When I choked it No. 1 cylinder's header wouldn't heat up, at least not like the others, until I backed off the choke then it would warm right up. Bike ran good afterwards and otherwise.
I just recently changed my old stock exhaust to a newer set of stock exhaust and the problem seems to have diminished or dissapeared altogether. Very puzzling. Think my old exhaust had too much carbon
build up in it, restricting air flow, noticed that when I removed them.

 

[Big T]

Is the petcock vacuum hose connected to this #3 carb? If so, petcock might be leaking down this hose causing the # 3 plug to foul until bike runs for a while.

Yes, the vacuum port is on the #3 carb on the VMs

Test your petcock, see if there's any gas in the vacuum line

 

[00.]

Ok I will check the petcock, this is something I have not done yet. The exhaust being carboned up is strange but I gues could have some effect. I supprised not more people have the problem with one pipe not heating up. I have had this happen on a few gs bikes now and can't ever solve the damn problem.

 

[70ronzdart]

i have a 81 gs with the same problem only on number 1 cylinder when cold when i was cleaning the carbs i accidently broke a torch tip cleaner that i was using 2 clean out the enrichment tubes off in the bottom of the tube had no way of getting it out just left it for now no problems running after bike warms up for a bit

 

[BassCliff]

i have a 81 gs with the same problem only on number 1 cylinder when cold when i was cleaning the carbs i accidently broke a torch tip cleaner that i was using 2 clean out the enrichment tubes off in the bottom of the tube had no way of getting it out just left it for now no problems running after bike warms up for a bit

Hi,

How To Clean The Carbs Properly <<Click.

Feel free to post an introductory thread in the "GS Owners" section. You'll receive a TON of good information in your welcome package.

Then start a new thread of your own in one of the tech sections instead of hijacking someone else's thread. That way you can receive specialized information regarding your particular issue and there will be no confusion as to which advice is meant for which poster.

Thank you for your indulgence,

BassCliff

 

[GS750]

DO a compression test first!!!!

My friend had a similar problem on his 650G Katana which he could not trace the problem.... He eventually bought the bike to me and after doing a compression test that showed lack of compression, I discovered that the inlet and exhaust valves were not sealing at all (2PSI).

Stripped it down and the valves ALLwere shot, one had a small chip in it and I suspect that it went into the piston as it had a very small hole in it about 1mm round, almost like someone had drilled into it.

The thing is that the bike was doing exactly what you said but there was only a minor oil leak (.5 litre a week), the exhaust pipe was stone cold until it had been running for 15-20 minutes, and then it would eventually come up to temperature.

We traced the likely cause of the problem back to a long run he did with a group through the mountains on a very hot summer day on and off the throttle, then when they had stopped for some midday refreshments, almost as soon as he turned the bike off there was a massive storm which I think shock cooled the bike and released the chips from the valves.

A strip and then rebuild and all was fine again! 4 years later and it is still going perfectly!



I also had a similar problem on one of my old CowaSaki 4's and it was actually an ignition coil lead that was broken, and I guess that after the engine heated up enough, the coil lead would make a connection.
If it was a coil or ignition problem then it would do it on 2 cyls because the coil actually fires both plugs at the same time.


As I said, I would check compression first though and go from there!

 

[BassCliff]

DO a compression test first!!!!

My friend had a similar problem on his 650G Katana which he could not trace the problem.... He eventually bought the bike to me and after doing a compression test that showed lack of compression, I discovered that the inlet and exhaust valves were not sealing at all (2PSI).

Stripped it down and the valves ALLwere shot, one had a small chip in it and I suspect that it went into the piston as it had a very small hole in it about 1mm round, almost like someone had drilled into it.

This sounds more like lousy maintenance. No valve adjustments and a leaky air intake system causing a lean running condition. It eventually burned the valves and holed a piston.

Valve adjustments and tightly sealed air intake systems (intake boots, O-rings, airbox, etc) are critical the the good health of a GS.


Thank you for your indulgence,

BassCliff