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How do I adjust fuel mixture once I'm at 2.5 turns out?

  • Thread starter Thread starter Anonymous
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Anonymous

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I have cleaned and sync'd my carbs, and set the fuel mixture/air jets to 2.5 turns out. Then three, as my bike seems to be very lean.

But aren't they supposed to be individually tuned somehow?

Here is my impression of how it's done, please correct me and elaborate where necessary.

1. Start with cleaned & sync'd carbs
2. Set air jets/fuel mixture to 2.5 turns out
3. one carb at a time, turn the jets out 1/2 turn out at a time until the bike starts to run worse, then turn it in just past that point. (1 turn?)

Any help is appreciated, as I'm sure I'm not the only one to have this problem. (if we get good responses, maybe we can make it a sticky thread or archive it somewhere?)

Thanks!

Jeremy
 
I've heard many times to "adjust the idle screws for the highest idle", but I sure can't hear any difference when adjusting one at a time. All the way in to 4 turns out = no difference in idle. At all.

I know that a large variation in idle speed when hot vs. cold is a sign of a lean idle mixture, so I ended up adjusting the screws several times after test rides based on the stability of idle speed. I ended up at 2 turns out on #1 and #4 and 2.5 turns out on #2 and #3.

My bike runs and idles great and all, but I sure would like to be able to do this "the right way". Whatever that is.
 
Do the 850s have CV carbs with a pilot fuel mixture screw set on top the neck of the carb where they seat in the intake boots? One of the issues I commonly run into is that aftermarket (rebuild kit type) mixture screws are not made carefully enough and do NOT seat down THROUGH the hole in the neck opening. Some have to be carefully reshaped a tad. Second, the pilot fuel mixture screws ONLY affect idle and their position has a very small effect. Set the mixture screws to 2.5 turns out. With the bike idling, turn the #1 screw back and forth a bit (no more than 1 turn either way) and try to get max idle. If you can't make a difference, put it back to 2.5 turns out and do the same for #2, #3 and #4 in turn. Set your idle back between each carburetor adjustment. If you are running pods, your pilot jet may be too small and your 2.5 turns out will still be too lean and that is another reason adjusting the pilot screws has little effect. Once you have installed larger pilot jets, the process needs to be repeated and you will probably find that there is MORE affect when you turn then screws at 2.5 turns out.
 
wiredgeorge said:
Do the 850s have CV carbs with a pilot fuel mixture screw set on top the neck of the carb where they seat in the intake boots?
Click to expand...

Yes. They are the CV carbs with the rubber diaphrams inside.


wiredgeorge said:
One of the issues I commonly run into is that aftermarket (rebuild kit type) mixture screws are not made carefully enough and do NOT seat down THROUGH the hole in the neck opening.
Click to expand...

Mine are stock. I will try the rest of the stuff you mention.

I'm also going to read the plugs, and I expect to see signs of leanness. If that is the case, I'm going to have to rejet. I have aftermarket exhaust of dubious descent (J.C. Whitney?) and that may be causing the problem.

If the adjusting of the mixture screws doesn't do anything, I'm going to throw in the towel and take it to a shop. I've wasted so much potential riding time on the thing so far...

I bet it just needs rejetting.

How do I find out the stock jet size? Where can I get new jets?

Thanks for your help.

Jeremy
 
you'll actually see the jet size on the jet itself(118, 122.5, etc.)you can pick them up through k&n, etc. but i would go up only a jet or two, any higher and the problems will only get worse(118--->120)
 
The standard pilot jet size for a '82 GS850GZ is 40. Mine was running lean around town with a lot of popping from the exhaust. Turning out the mixture screws helped some, but didn't come close to eliminating the problem. I gave up after six turns out.

I got four Mikuni #45 jets from a local dealer ($4.00 each). I'm now at 3 turns with these, and the popping is gone. The plugs are a nice light tan instead of a nearly white tanish gray.

Suzuki sure made these carbs run lean! There is a #42.5 if you don't want to go up too much.

I find that I'm using perhaps 1/8 to 1/4 throttle most of the time, so changing the pilot jets seemed to be the way to go. Based on my results, I'd say I'm on the right track.
 
Thanks a ton George! That is precisely the information I was looking for. I think my bike may have other problems too, but I have always had the popping and absolutely NO power from 3-5k. I'm going to try that I guess, before I give in and throw money at a local mechanic.

Is your bike running stock exhaust?

I may wind up throwing some money towards a MAC exhaust system, since they're about the only ones who give good tuning specs. Then again, if those !@#$% fasteners are rusted all up, I may not even bother with that...
 
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