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Carb Re-Jetting

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

Anonymous

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Ok, so here is what I did. I have an '83 GS750E that is stock except for a set of pod filters and a Katana exhaust system. The stock jet sizes are 37.5 for the pilots, and 117.5 for the main jets. I have replaced those with 40 for the pilots, and 120 for the main. I was wondering if that was enough jetting, and if anyone has any ideas for tuning those other than what I have already done. I know that my number one cylinder was a little rich, but I think that was due to some holes in the old exhaust system. 8)
 
It's tough to get jetting right without a jet kit once you start changes pipes and filters. The main reason is the needles are non-adjustable. That's the most valuable part that comes in jet kits. You can get the idle and wide open throttle jetting right without a kit, but everything in between is going to be tough. You can try shimming the needles to raise them a bit.
 
mixture screws

mixture screws

Thanks for the idea, Bill, that will give me something to do when it gets slow at work tomorrow. By the way, does the jetting I chose sound about right for my setup? The Katana pipes still have the baffles in. :twisted:
 
Are the pods K&N? They flow better than most other pods. The stock Kat exhaust will help keep things from getting too lean. You'll have to do some plug readings to see where you stand on the jetting. The only way to do it right is get out on a deserted road somewhere and open it up.

Run the bike up to about 6,000 rpm or so and hold it there for as long as you can. Then hit the kill switch and pull the plugs to check the color. This will tell you alot about the needle heighth. You don't have to do these runs in 5th. Pick a gear that keeps speed down to a level that's not going to get you pulled over.

Then you'll have to open it up to about 9,000 or so to do another reading to check the mains. The trouble with checking the mains is the throttle has to be held wide open. A lower gear probably will redline without the throttle held wide open.

Let it sit and idle for awhile and check the plugs again. This will let you know if the mixture screws need adjusting. Usually I just set each screw for the highest, smoothest idle.
 
I see, I think I will have to adjust the needles up a little bit to help with the low, and mid-range. I could probaly find a road around here, and ride in second gear at 9000 to check the main-jets. I appreiciate your help, and will post to let you know how things go. By the way, I am using Emgo filters, I couldnt afford the K&N's. Hmm, well, I have no idea on where to set the mixture screws for a baseline. All I know is that the damn thing wont idle below 1500-1700RPM. I will do some messing with it tomorrow and see how things go. :twisted:
 
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