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TECHNICAL CARB QUERY

  • Thread starter Thread starter Anonymous
  • Start date Start date
A

Anonymous

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:twisted: :?: IVE RECENTLY PURCHASED A 1979 GS 750E IT HAS A STRAIGHT THRU S/S EXHAUST BIKE SEEMS NOT TO REV OUT FULLY ANY IDEAS?ALSO WHAT SIZE JETS IN CARB?UPJETTING MAYBE?ANY HELP/ADVICE MUCH APPRECIATED THANX!!
 
"WHY IS EVERYONE YELLING AT ME!?"

j/k.

welcome to the forum, congrats on your bike purchase. you said it has S&S mufflers on it? that's pretty amusing, considering they're for Harley's originally...i worked at S&S last summer, they just came out with the mufflers while i was there.

before you go worrying about the carbs excessivly, i would first make sure everything else is in order. check the points on the bike, make sure the gap is set properly (.014 in) and that they aren't worn bad. also grab the little black rotor in the middle of the timing wheel and rotate it. this will move the mechanical advancer. make sure it moves a bit. spray some WD40 in behind the timing wheel if you must.

second, set the timing on the bike. you'll need a timing light or someone with one to help. run the bike above 2500 RPM (using the throttle stop) and make sure the advance mark lines up with the F mark. adjust it with the 3 screws that hold the plate down. after this...you can see how it runs. you should see no sparks flying at the points.

jetting info for a good exhaust is not 'written in stone' it will require work to get it right. the jetting guide i have suggests: GS750 2Valve - Increase main jet to a 115. Pilot jet should be increased to a 17.5. The needle will have to be raised a notch (lower clip). you probably can remove your stock airbox lid as well.

hope this helps, as i said though, first verify your timing and points and condensors are in good shape. my bike used to cut out at 6000 RPM due to bad condensor/points.

~Adam
 
either way, carbs are going to need some work with an open exhaust.
 
A free-flow header alone does not require much jetting change. The jetting changes recommended with my GS1000's Yoshimura header was to raise the mains 1 step (95 to 97.5) and raise the needle 1 notch. This worked wonderfully and I drove it this way for, oh, 40,000 miles. Then I put K&N individual filters on and had to raise the mains to 115 and play with the mixture screws. Changing the pilot size is unnecessary.
 
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