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correct carburation

  • Thread starter Thread starter Chooka
  • Start date Start date
C

Chooka

Guest
Hello, I have a 1985 GS1100G that has just been fitted with a JE Piston big bore kit, due to an oil ring failure.
Stock engine size was 1074cc but is now 1134cc and 10.25:1 compression. Air box is stock as is exhausts.
Carbies are stock BS34SS Mikunis that did have a standard rebuild kit fitted about 12 months ago.
Do I need to change the jetting of the carbies, (if so what size do you recommend), or do I need to adjust the needle height.
Any information would be much appreciated.
Thanks
Chooka
 
You bumped the compression and displacement, did you use different camshafts too? The increase in compression works best with different cam timing , specifically longer durations, and if you degree the cam differently you might eek out a small improvement.
The larger engine will flow slightly more air at a given RPM but without aggressive cam changes you won't see much of a difference.

If your cylinder head is stock it won't require much change, again it's the total package that must be considered.

Do so plug chops and see what you get.
 
Your carbs probably won't need changing but, bearing in mind the standard setting would have been on the lean side, it's worth doing plug chops as duaneage suggests.
 
I would, at the LEAST, remove the mixture screw plugs & adjust the mixture screws using the "fastest idle" method. After that, try doing a few plug chops. You won't know till you start running it. You may or may not need to go up a size or 2 on the main jets. You might also need to shim the needles .040 or so. Welcome to the site! Ray.
 
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