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KLR 650 pilot mixture adjustment


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Hello, I've been trying to troubleshoot my KLR 650 and do a basic 'tune up'. it's a 2003. My problem is that over time I've had to continuously increase my 'idle stop screw' and turn it in to keep the bike idleing and not dying out. The screw is now pretty much at it's max and the spring is fully compressed. In addition, I do get backfires when using engine braking to slow down. Reading the manual I thought the combination of the two lead to the pilot mixture screw being too lean. After tearing down the carb, cleaning out, and rebuilding I have the same problem. All components of the carburator looked in good shape. The pilot mixture adjustment is hard to make once the carb is back on there. I keep opening up the pilot screw to richen the low end mixture but I haven't gotten to a place where the backfires stop and the idle is happy. I replaced air filter, fuel lines are good, new gas and all the carb checks from the Clymer's manual were good. Any feedback is much appreciated....!👍

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Are you sure that the idle jets have been cleaned properly? Sometimes it takes a soaking in real carb cleaner. If you're sure then it could be several things... start with the fuel supply. Sometimes the vacuum operated shutoff on the fuel selector leaks & that shuts down fuel supply. Same can be caused by a bad hose that feeds the valve... partly closes valve and leaks air into the manifold. Pull the fuel line & see that fuel flows freely when cranking the engine, Look the hoses over real good.

The backfiring might be due to the coasting enrichment (the little diaphragm) leaking.

A small washer under the needle will fatten up the mix.

There is an idle mix screw available that you can hand adjust.

Lots of cv40 stuff on the web...

http://www.gadgetjq.com/keihin_carb.htm

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Hello, I've been trying to troubleshoot my KLR 650 and do a basic 'tune up'. it's a 2003. My problem is that over time I've had to continuously increase my 'idle stop screw' and turn it in to keep the bike idleing and not dying out. The screw is now pretty much at it's max and the spring is fully compressed. In addition, I do get backfires when using engine braking to slow down. Reading the manual I thought the combination of the two lead to the pilot mixture screw being too lean. After tearing down the carb, cleaning out, and rebuilding I have the same problem. All components of the carburator looked in good shape. The pilot mixture adjustment is hard to make once the carb is back on there. I keep opening up the pilot screw to richen the low end mixture but I haven't gotten to a place where the backfires stop and the idle is happy. I replaced air filter, fuel lines are good, new gas and all the carb checks from the Clymer's manual were good. Any feedback is much appreciated....!👍

I own an 09 KLR and have not been in the carb yet; hence my ignorance on the facts. My thought is that you are running in the low speed circuit i.e. the slide valve is not fully returning to idle position or perhaps the float level is running high. I hope you get it fixed and post your solution. Good luck.

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  • 2 months later...

the other cause of decel pops is a leak on the exhaust pipe. The motor is a pump and on decel it gets fresh air sucked in if there is a minor leak and it pops the unburned fuel. VERY common on bikes. Most people try and MASK the problem by richening the idle circuit with the carb and then if it gets better they think its fixed, but then you lose off idle snap and it doesnt run cleanly. Just an FYI if the carb doesnt fix it.

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+ 1 on checking the header-to-head connection for leaks . . .

Also, backfiring could result from a deficient AIR CUT VALVE, or COASTING ENRICHER.

Clean carb, fuel ("pilot air") screw out 1.75 turns, needle shimmed with one # 4 washer, stock bike oughta run o.k.!

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