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81 Gs750 1/4 throttle cut out.

  • Thread starter Thread starter nickbarnstom
  • Start date Start date
N

nickbarnstom

Guest
Got an 81 GS750 that had not run in 8 years or so. Threw some fresh fuel in it and tried to fire it up. wouldnt fire so i gave it a quick once over to check it out. good spark bad fuel. drained the tank, removed the carbs. Cleaned the carbs and rebuilt with new jets, orings, gaskets, etc. This bike is 100% stock, replaced everything with stock componets. Bike will fire up and idle nice and smooth. it comes off of idle alright, but somewhere between 1/8 and 1/4 throttle it starts to hesitage and gets a serious bog (to the point it will die if i thorttle to hard). i can play with the throttle and make my way through the bog. it starts to clear up around half throttle and 3500rpm then runs beautiful after that. needles are all clean and in great shape. all with stock shims. diaphrams are in great shape. Im kind of at a loss at this point.
 
nickbarnstom said:
Got an 81 GS750 that had not run in 8 years or so. Threw some fresh fuel in it and tried to fire it up. wouldnt fire so i gave it a quick once over to check it out. good spark bad fuel. drained the tank, removed the carbs. Cleaned the carbs and rebuilt with new jets, orings, gaskets, etc. This bike is 100% stock, replaced everything with stock componets. Bike will fire up and idle nice and smooth. it comes off of idle alright, but somewhere between 1/8 and 1/4 throttle it starts to hesitage and gets a serious bog (to the point it will die if i thorttle to hard). i can play with the throttle and make my way through the bog. it starts to clear up around half throttle and 3500rpm then runs beautiful after that. needles are all clean and in great shape. all with stock shims. diaphrams are in great shape. Im kind of at a loss at this point.
Click to expand...

Is the air cleaner installed?
 
Sounds like you shot yourself in the foot by rebuilding those carbs with "new jets". Nobody uses rebuild kits; you simply replace prongs from Robert bar.
 
posplayr said:
Sounds like you shot yourself in the foot by rebuilding those carbs with "new jets". Nobody uses rebuild kits; you simply replace prongs from Robert bar.
Click to expand...

what is the issue with using new jets? All were the same size as stock.
 
nickbarnstom said:
what is the issue with using new jets? All were the same size as stock.
Click to expand...
Sure as long as they genuine mikuni- aftermarket stuff is poorer quality. Jets and needles just get dirty, so no need to replace - provided they have not been butchered.
did you put the rubber plug back over the pilot jet tunnel ?
how did you clean these carbs? A long soak or ultrasonic ?
It's hard to clean the pilot circuit passages quickly and clogged ones will give you problems as engine transitions from low to midrange.
 
Yes new rubber plugs were installed on the pilot jet tunnel. carbs were removed, heavy stuff brushed off then soaked in an ultrasonic cleaner. i will remove the new jets and reintall the old ones all cleaned up to see if that makes a change.
 
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