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Throttle slide needle

  • Thread starter Thread starter knotzilla
  • Start date Start date
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knotzilla

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Hi, I suspect that my gs850 is running a bit lean. When I pulled the plugs they were on the whitish side and when decelerating there is a popping noise from the exhaust. I am planning to raise the slide needle to richen the mixture. At present the circlip is in the middle position. Would raising the needle 2 notches to the max be too much or should I play it safe and go only one notch. Thanks for your input, Ted
 
If your running ok but just a little lean I'd start with one notch. You can also go half notch with a washer set at Radio shack. One washer is a half notch.
 
I agree that 2 notches is way too much to start. If your bike is stock though, make sure your airbox is sealed perfectly, and intake boots are in good shape and not leaking before you start adjusting your carbs.
 
You have all the textbook signs of an intake leak and deteriorated seals on the airbox sides. There's also a foam seal on top of the air filter cage that rots out.

Replace all the foam seals with weatherstripping. Don't start screwing around with rejetting.
 
Thanks for your advice. I know that I do not have any intake leaks. I forgot to mention that the previous owner installed a 4 in 1 exhaust system, so there is a chance that it needs rejetting. I will be dismantling the carbs next week to verify all the jet sizes. I'II be on the safe side and raise the needle only one notch. By the way, what is the part number for the washers at Radio Shack. Thanks Ted
 
Exhaust popping can also come from poor synchronization or leaks at the header.

Brad bt
 
I just bought a bag of small assorted washers. You can tell which one is the right one. They match the one that is already installed on your needle.
 
For just a pipe, stock airbox (lid still on?), one position richer will be enough and possibly too much. A half position may be better. Depends on what the plugs say after a 1/3 throttle chop test.
Don't blame the jet needles for lean plugs unless you tested at 1/3 throttle. If the reads were after riding around town/slower city speeds, approx' 1/5 throttle and less, you may be better off focusing on the pilot circuit.
Decel' popping can also be leaking exhaust gaskets.
Where are the mixture screws set right now?
 
The mixture screws are between 1 1/2 and 2 turns. I syncronized the carbs in August. I had an idea that might make adjusting the mixture screws easier. Would using a handheld tachometer on the end of the crankshaft where the ignition plate is and adjusting the screws for the highest rpm take the guess work out of it. What do you think?
 
I've always just listened for highest rpm. Even if the bike has a good tach, I just set by ear and never look at the tach. Never had a problem that way.
I suppose using a very accurate tach as you say could make it better, but I think it's overkill.
The mixture screws should be adjusted correctly, and then the vacuum synch. Some guys even re-check the screw adjustments after the vacuum synch just to be sure they're set as good as possible.
 
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