I have just bought a Gs500 from a friend , it is a 1994 S model.
With the bike i was given a spare set of carbs as the mixture screw was seized on one of the original carbs.
I think the spare carbs were from an earlier model and had 120 main jets, 1.3mm air jet and from my haynes manual should have a pilot screw setting of 2 1/4 turns out which is what they were set to.
The carbs on the bike have a 125 left main jet, 122.5 right main jet and the pilot screw was set to 1 7/8 turns as in the book.
I have put the original main jets in the spare carbs but the pilot jet looks like i cant swap them as the older type are a screw type and the new look fixed.
The bike will idle fine but if i touch the throttle it goes to 3k and stays there for a while and drops really slowly.
I have ridden the bike and its smooth through the rev range but just wont drop to tickover when under 3k unless i use the clutch/gears to do it
I have tried adjusting the pilot screw both ways but without any luck
If i backoff the tickover screw it will drop the revs quicker but obviously wont tick over.
I have tried disconnecting the throttle and choke cable and it still does it
The air filter is clean
The jets are all clean
SO HELP PLEASE :)
sounds like a vacuum problem... is the vacuum line from the petcock to left carb connected properly? or else maybe there is a leak where the carbs attach to the boots... when its idling, spray wd40 around there to see if the revs go up. if so, you've got a leak....
hope this helps.
After checking every petrol/vaccum pipe, stripping the carbs several times, altering mixture screws, raising needles, swearing alot :( , checking plugs, balancing the carbs, doing a compression check, swearing more :x , i finally found the problem. :)
It turned out to be tight exhaust valve clearances. I had to go .15mm down on both shims to get a .05mm feeler gauge in.
So it must have been holding the exhaust valves open very slightly.
It now ticksover like a dream and runs much better.
I would never have thought that such and erratic problem would be due to something like this but trust me it was.
Rob
Thanks for the feedback!
Maybe we should recommend valve clearance checks even more than we do around here...?
Quote from: vcrabroThe carbs on the bike have a 125 left main jet, 122.5 right main jet and the pilot screw was set to 1 7/8 turns as in the book.
What I want to know about is why there were two different sized main jets?
Is it the cure to the fuel starvation problem? To compensate for the vacuum loss to the petcock?
I have a theory that if I bias the vacuum to be greater on the left carburetor that it would be less suseptable to the fuel starvation problem.
I had an interesting thing happen to me on the way back from shopping yesterday, in that my bike began to hesitate at 5900rpms. I slowed down to 5000rpms, and switched to PRI, and while that helped, it did not cure the problem. I thought it might be the crosswind that I was getting off of the bay, across open marshes; so it was a high-speed and powerful crosswind. I thought to "close up" the area behind the airbox where the end of the floatbowl vent tube resides, by scooting my feet back on the pegs, and volia, no more hesitation!
Quote from: scratchQuote from: vcrabroThe carbs on the bike have a 125 left main jet, 122.5 right main jet and the pilot screw was set to 1 7/8 turns as in the book.
What I want to know about is why there were two different sized main jets?
On the GS500 th only reason for two different size main jets would be that somebody screwed up when they re-jetted.