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carb problem? idle no good, high speed fine

  • Thread starter Thread starter mits6dr5
  • Start date Start date
M

mits6dr5

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i have what i hope is a carb issue. there is a stage 1 kit in it. if you didn't know better, you would think the engine is running just fine... but i know better haha. #1 cylinder is cold at idle (header temp). it starts firing well between 2500 and 3000 rpm and seems to stay that way. when i let it idle again, it stays firing for about 10 seconds or just under. i have check the spark plug, wire etc. took the float bowl off and checked for dust etc without finding any. took the idle jet out and cleaned it just to be safe. no change. took the hex plug off the corresponding intake tube and it had very good suction (hoping its not engine damage). tried adjusting the idle mixture at idle and just above (around 2000rpm) with no luck, makes no difference to engine sound or the way it runs. the bike is a 1980 gs750e with factory mikuni carbs. there is a 4 into 1 exhaust (vance and hines) with stock airbox and filter. spark plugs are ngk's with approx 8000kms on them. factory original coils and wires. factory original charging system as well.:confused:
 
Sounds to me like your pilot circuit is plugged on the #1 carb. When was the last time the carbs were completely taken apart and cleaned? One thing I would check first is that there is fuel in the #1 carb. Remove the bowl and lift up the float, gas should pour out. If the flow is restricted the float needle may be damaged. If there is plenty of fuel than I would suspect you have a blockage.
 
Yeah the bowl fills quickly when reassembled but when i push the float up... nothing comes through. I also thought about the idle circuit being plugged. To my knowledge, the carbs haven't ever been completely tore down.
 
mits6dr5 said:
Yeah the bowl fills quickly when reassembled but when i push the float up... nothing comes through. I also thought about the idle circuit being plugged. To my knowledge, the carbs haven't ever been completely tore down.
Click to expand...

Then it is time to do a carb rebuild. New orings from cycleorings.com, some new bowl gaskets, new fuel line, probably new needle and seats (use OEMs) and change out the phillips screws with SS allen heads and install new rubber carb boots on both sides. Since you have a V&H 4-1 I would install a K&N air-filter. While the carbs are off, up the main jets ( may not have to do this with a stage 1 kit) with the new air filter by 2 steps or so. Not sure what your altitude is there so take that into consideration upping the main jets. Last but not least, adjust the valves, bench sync the carbs, install, set the idle mixture screws and vacuum sync the carbs. Oh, don't forget to inspect, clean and test the petcock as well.
 
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