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1981 CB650 Pilot Screws Adjustments

Posted: Fri Aug 28, 2015 8:26 pm
by CBDCL
Carbs on this model can be a headache. You already have pressed recessed slow jets making cleaning hell. So perhaps anything helps us unfortunate carb owners.

Most of my trouble was in finding answers online, so I thought it would be nice to contribute pilot adjustments to help perfect your mixtures. If you have different direction, please share.

The factory / initial setting is 2 1/8 out from lightly seated. Rollin in this setting has you running lean. If your ride has a delayed acceleration or surges / stutters, you're probably running lean and need to rich your mix by going out. But this is the factory setting, where you start. Get a pilot screw tool to do this, unless you want to burn the shit out of your hands. Not fun. Been there. You also need a detailed tach. I didn't have this luxury but it's absolutely necessary.

1. Heat bike, ride 10 minutes, stopping and going.
2. Set to factory setting; 2 1/8 turns out
3. Adjust the idle screw getting to the ideal idle speed; 1,050 RPMs +/- -100
4. Turn each pilot screw OUT 1/2 turn. If speed increases 50+ RPMs, continue to turn each a 1/2 turn OUT until speed decreases by 50 RPMs.
5. Repeat step 3.
6. Turn IN pilot on carb #1 until speed drops by 50 RPMs, then turn it OUT one full turn. Then repeat step 3.
7. Do step 6. For carbs 2, 3, and 4.

Test ride and response from idle should be rapid without hesitation.

Hope this helps someone.

Re: 1981 CB650 Pilot Screws Adjustments

Posted: Thu Jun 22, 2017 2:09 am
by Rakestraw
CBDeCL wrote:Carbs on this model can be a headache. You already have pressed recessed slow jets making cleaning hell. So perhaps anything helps us unfortunate carb owners.

Most of my trouble was in finding answers online, so I thought it would be nice to contribute pilot adjustments to help perfect your mixtures. If you have different direction, please share.


Thanks for the super helpful guide CBDCL!

Re: 1981 CB650 Pilot Screws Adjustments

Posted: Sun Jul 15, 2018 10:50 pm
by KennethChambliss
CBDCL wrote:1. Heat bike, ride 10 minutes, stopping and going.
2. Set to factory setting; 2 1/8 turns out
3. Adjust the idle screw getting to the ideal idle speed; 1,050 RPMs +/- -100
4. Turn each pilot screw OUT 1/2 turn. If speed increases 50+ RPMs, continue to turn a fan of phenq each a 1/2 turn OUT until speed decreases by 50 RPMs.
5. Repeat step 3.
6. Turn IN pilot on carb #1 until speed drops by 50 RPMs, then turn it OUT one full turn. Then repeat step 3.
7. Do step 6. For carbs 2, 3, and 4.


This is the best practical and concise guide for adjusting CB650 Pilot Screws. Helped me a lot. Thanks for writing this guide.

Re: 1981 CB650 Pilot Screws Adjustments

Posted: Mon Apr 08, 2019 2:48 pm
by HughMitzel
CBDCLO wrote:

1. Heat bike, ride 10 minutes, stopping and going.
2. Set to factory setting; 2 1/8 turns out
3. Adjust the idle screw getting to the ideal idle speed; 1,050 RPMs +/- -100
4. Turn each pilot screw OUT 1/2 turn. If speed increases 50+ RPMs, continue to turn each a 1/2 turn OUT until speed decreases by 50 RPMs.
5. Repeat step 3.
6. Turn IN pilot on carb #1 until speed drops by 50 RPMs, then turn it OUT one full turn. Then repeat step 3.
7. Do step 6. For carbs 2, 3, and 4.

Test i hope you have phentermine otc ride and response from idle should be rapid without hesitation.

Hope this helps someone.


i took the carbs apart and with compressed air it doesnt seem to pass through the pilot jets?