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carb jetting for gs650

  • Thread starter Thread starter Badbandit
  • Start date Start date
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Badbandit

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newbie just got my gs650g running complete restoration does anyone know the correct main jet size for a stock engine with pods and a mac 4 into 1 header ? I'm sure some one out there has already figured this out thanks in advance
 
The only option is the Dynojet kit. Comes with two different size mains to try. I recently rebuilt my carbs with pods and a 4-into-1, but I can't get the damn thing running on all cylinders.
 
10 to 12 sizes bigger for pipe and pods. I think I would go with 10. example, if stock was #100main go to a #110main
 
how is that only 2 sizes bigger if they step up in 2-1/2 increments, that would be 4 or 5 steps by that way of thinking.
 
Read about how the sizes go. A 2.5 increment in Mikuni main jets is a half size. .5 is one size.

And it's not enough anyway, for instance I have gone from an 80 to a 105 on my 550, it runs perfectly at 6,000 ft. elevation where I live. At sea level it would probably take a 110.
Different engine, different carbs, but the theory is mostly the same.

The DJ kit is a far better option, because it comes with appropriate jet needles.
 
tkent02 said:
Read about how the sizes go. A 2.5 increment in Mikuni main jets is a half size. .5 is one size.

And it's not enough anyway, for instance I have gone from an 80 to a 105 on my 550, it runs perfectly at 6,000 ft. elevation where I live. At sea level it would probably take a 110.
Different engine, different carbs, but the theory is mostly the same. Ok, I do appricate you clearing that up for me about jet sizing. but back to this guys question. I just looked on a carb spec chart and it said that an81 thru 83 gs650e had 97.5 mains. wouldnt you say 112.5s would be a good place to star
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Last edited:
helmutholderbenz said:
Ok, I do appricate you clearing that up for me about jet sizing. but back to this guys question. I just looked on a carb spec chart and it said that an81 thru 83 gs850e had 97.5 mains. wouldnt you say 112.5s would be a good place to star
Click to expand...

No, I'd start bigger and work my way down. CV carbs should be tuned from the top down, that is run it wide open and get the main jet right before doing any of the low power tuning. Running an engine wide open while it is too lean can burn holes in pistons or valves. I'd start with the largest jet and go smaller one half size at a time until I got it right. It does take a lot of time and effort, which is why a DJ kit is good, they have done some of the thinking already.
 
Yes, your right man, I was just trying to give this guy a little jump start cos I just got through doing what you said on my bike, added pipe and pods. stock jet was117.5s and I started with 140s and have worked my way down through every size to 130s and I still feel like I could go down one more half size to 127.5s and it will be perfect
 
One more thing I'd like to mention is fuel level! fuel level is so important in getting your bike to run right!
 
Well if you go with the Dynojet kit in order to get the adjustable needles, toss the jet size comparisons with stock out the window. They come with 155 and 160 jets, because the needle profile is entirely different and they have you change up the idle air circuit (at least that's why I think they get away with such large jets).
 
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