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To the carb gods. HELP!

  • Thread starter Thread starter NEO
  • Start date Start date
N

NEO

Guest
After 4 days of searching, pulling,adjusting,replacing parts,and cursing, im asking you carb kings for your help. I have a 1979 gs550 with pods and straight pipes.
Upon adjusting the carbs i noticed carb #2 adjustment screw makes no difference in idle quality. All others were set to highest idle then idle was re adjusted per the carb pages. Pulling the spark plug wire off the #2 spark plug makes no difference either. The plug is dry when i pull it out. The plug wire will zap me when i pull it and the cylinder has compression.I cannot for the life of me figure out what is. Any thoughts or suggestion?
 
NEO said:
After 4 days of searching, pulling,adjusting,replacing parts,and cursing, im asking you carb kings for your help. I have a 1979 gs550 with pods and straight pipes.
Upon adjusting the carbs i noticed carb #2 adjustment screw makes no difference in idle quality. All others were set to highest idle then idle was re adjusted per the carb pages. Pulling the spark plug wire off the #2 spark plug makes no difference either. The plug is dry when i pull it out. The plug wire will zap me when i pull it and the cylinder has compression.I cannot for the life of me figure out what is. Any thoughts or suggestion?
Click to expand...

Sounds like you're not getting fuel to the #2 cylinder. Have you cleaned the carbs? Can you confirm that there is fuel in the #2 bowl by pulling the drain plug? If not, the next thing to check is the float to see if it's hanging up. If not, then there is a good chance that the float screen is plugged.

Do all other cylinders fire and the pipes get hot? How about #2...
 
#2 cylinder carb bowl is filling with fuel. I turned on the fuel with the bowl off and it poured.Ive cleaned them 3 times and the float isnt hanging. all other pipes are just hot enough to not touch for too long,i can hold the #2 all day. Header wrapped of course.
 
Is it running on three if you go ride it, or just if it sits there idling?
If it runs on all four except when idling, maybe the throttle is completely closed, have you synched the carbs?
 
The adjustment screws are about 1.5 turns out each. This bike has some chatter sound under light throttle and decel but i doubt this has anything to do with it. Putting my hand over the exhaust for the #2 cylinder shows it has the most air coming out,but makes no noise difference if i cover it.All others do and have less air pressure coming out.
 
I'm just a lowly visitor in the house of the carb gods, but maybe a little bit has rubbed off, so I'll offer my two cents from my own personal experience on a somewhat similar model. If you've got fuel in the float bowl, I would guess you have a plug somewhere in the pilot circuit. Either the pilot jet or one of the passages. Could also be a vacuum leak. Have the O-rings and carburetor boots ever been changed? If not and 79 550, they are likely leaking like a sieve.
Now I'll let someone who really knows what they are talking about chime in.
 
Thanks for the replies guys. Keep it coming as i will be checking the boots and orings. Bench syncing is a bit beyond me,but im up for trying.
 
Bench sync but more importantly, vacuum sync after the engine is back together.

One thought on the problem at hand; the tips of the pilot fuel screws tend to break off, pluging the hole in the carb body in the process. Remove the screw and look to see if it has a nice sharp point - if the tip is rounded off, a chunk of the screw may be lodged in the carb body orifice.

Good luck.
 
Nessism, are you talking about the pilot airscrew on the side of the carb or the fuel meter screw underneath? I've found carbs with the latter bust off (real flimsy things) but never seen a pilot airscrew bust.

My guess it is a blockage on the pilot circuit, one of the two in-line jets - that second one is a bugger, or the fuel meter screw wound in too much or bust, or just a bit of crap somewhere in there. Or as Tomm suggests, a airleak in the boot (wrap it electrical tape as a test, not a fix).

Wally
 
hampshirehog said:
Nessism, are you talking about the pilot airscrew on the side of the carb or the fuel meter screw underneath? I've found carbs with the latter bust off (real flimsy things) but never seen a pilot airscrew bust.

My guess it is a blockage on the pilot circuit, one of the two in-line jets - that second one is a bugger, or the fuel meter screw wound in too much or bust, or just a bit of crap somewhere in there. Or as Tomm suggests, a airleak in the boot (wrap it electrical tape as a test, not a fix).

Wally
Click to expand...
I have pulled all of the jets out and metering screws and cleaned them out many times. There clean. The only thing i havent done is use compressed air in all of the passages. Only carb cleaner. Ill try that again. Funny thing is when adjusting the top/side screw, upon very first turn clockwise, it raises idle for a half second them goes back down. It will not make it idle up constantly though. Would adjusting the lower screw more help?
 
also spraying starting fluid or carb cleaner makes little to no difference in idle as well.
 
It's the fuel screws that have the fragile tips, not the air screws.

Regarding a possible air leak, it's mandatory to replace the boot O-rings if you have not done so already. I have a stack of them (for VM equipped 550's) so PM me and I'll send you a set for the cost of postage.
 
Nessism said:
It's the fuel screws that have the fragile tips, not the air screws.

Regarding a possible air leak, it's mandatory to replace the boot O-rings if you have not done so already. I have a stack of them (for VM equipped 550's) so PM me and I'll send you a set for the cost of postage.
Click to expand...

I think i have vm's. pm sent.
 
If you have spark at #2, fuel in the bowl, clean jets, but a dry plug preventing combustion...
you have either a large intake leak not allowing sufficient fuel to enter the cylinder, an intake valve/flat cam not allowing sufficient mixture in, or very low compression at that cylinder.
 
KEITH KRAUSE said:
If you have spark at #2, fuel in the bowl, clean jets, but a dry plug preventing combustion...
you have either a large intake leak not allowing sufficient fuel to enter the cylinder, an intake valve/flat cam not allowing sufficient mixture in, or very low compression at that cylinder.
Click to expand...


I thought so too,but putting my hand over the carb gives me the same suction as the rest of the cylinders. I will pull the carbs off again and hit them with some compressed air.Thanks for the input though. Any other thoughts?
 
NEO said:
I thought so too,but putting my hand over the carb gives me the same suction as the rest of the cylinders. I will pull the carbs off again and hit them with some compressed air.Thanks for the input though. Any other thoughts?
Click to expand...
I did forget another thought. Not as likely and I'd think it more obvious to see while inspecting and comparing visually to the other "good" carbs...but there could be something wrong with the throttle valve adjuster screw or holder nut assembly that is effecting vacuum. Loosening the holder nut and adjusting the screw should show correct slide movement.
And I do know what you mean by covering the carbs and comparing suction but that's not an accurate test to prove things are right.
Low compression will not allow good combustion.
Intake leak still a possibility. This will obviously effect vacuum and the jets can't draw near enough fuel. An intake leak will effect all 3 jetting circuits, pilot/needle/main, so regardless of throttle position, the jets will not draw enough fuel, if any, to allow combustion. Quick and easy to check the manifolds and inner o-ring.
Valve clearances, as part of basic tuning, should be checked.
 
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