Carb tor removal screw setting

Blastermit

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Mar 13, 2019
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have a 1989 yamaha blaster thats bored .2 over with a weisco piston, boyeson power reeds, stock expansion chamber, aftermarket pipe dont know the brand sticker was burnt, oil injection, aftermarket airfilter no airboxlid, currently running a 250 mainjet, needle clip is set on third in the middle of the needle the carb is clean fresh plug. i recently removed the tors and and installed the screw in the carb im wondering how many turns out it should be or wheres a good place to start messing with it and also i was wondering if the clip on the needle would need to be moved and if id have to change jet sizes since the tors removal. i can get it to full speed eventually but the torque and power isnt there
Any help would be appreciated thank you
 
The screw you installed is the idle screw, it only sets the RPM's you want it to idle at

your comment about turns out refers to the airscrew, which is right behind where you installed the new idle screw
turns out should be between 1/2 and 2 turns out, 1/4 turns until you find where it idles the highest, let 20-30 seconds between turns for the engine to catch up with the new fuel/air ratio
then readjust idle screw to get your desired RPM's

airscrew tuning: https://www.blasterforum.com/threads/adjusting-your-airscrew-pilot-jet.51060/

middle slot on the needle has worked for every blaster I've worked on

I would do some plug chops to confirm that 250 main jetting....
https://www.blasterforum.com/threads/how-to-plug-chop.53237/
 
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The screw you installed is the idle screw, it only sets the RPM's you want it to idle at

your comment about turns out refers to the airscrew, which is right behind where you installed the new idle screw
turns out should be between 1/2 and 2 turns out, 1/4 turns until you find where it idles the highest, let 20-30 seconds between turns for the engine to catch up with the new fuel/air ratio
then readjust idle screw to get your desired RPM's

airscrew tuning: https://www.blasterforum.com/threads/adjusting-your-airscrew-pilot-jet.51060/

middle slot on the needle has worked for every blaster I've worked on

I would do some plug chops to confirm that 250 main jetting....
https://www.blasterforum.com/threads/how-to-plug-chop.53237/
Thank you also where should the nut be set on the new throttle cable on top of the carb and where should the thumb throttle be set twist in my case or is it all just a rough estimate
 
Last edited:
No set adjustment, you take almost all the slack out of the cable.
My bike was running good and hard for while then it started back firing and stalled and wouldn’t start for a minute and it did it again and hasnt started since ive changed the plug thinking maybe it was that carb was cleaned the other day
 
The screw you installed is the idle screw, it only sets the RPM's you want it to idle at

your comment about turns out refers to the airscrew, which is right behind where you installed the new idle screw
turns out should be between 1/2 and 2 turns out, 1/4 turns until you find where it idles the highest, let 20-30 seconds between turns for the engine to catch up with the new fuel/air ratio
then readjust idle screw to get your desired RPM's

airscrew tuning: https://www.blasterforum.com/threads/adjusting-your-airscrew-pilot-jet.51060/

middle slot on the needle has worked for every blaster I've worked on

I would do some plug chops to confirm that 250 main jetting....
https://www.blasterforum.com/threads/how-to-plug-chop.53237/
My bike was running good and hard for while then it started back firing and stalled and wouldn’t start for a minute and it did it again and hasnt started since ive changed the plug thinking maybe it was that carb was cleaned the other day
 
Backfires are usually bad reeds or sheared woodruff key on the flywheel, allowing the flywheel to rotate out of timing