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Carb tuning

Posted: Sun Aug 02, 2015 11:10 pm
by Bspurge
Recently got out my uncles old 1979 Yamaha DT 125, the bike is very clean but has a carburetor issue (I think :roll: ). I removed the carburetor and cleaned it, I sprayed carb cleaner through all the different holes and used compressed air too. Here is the problem I am having: I'll start the bike with full choke, RPMs climb to 5000 and then scream to 8000 without giving any throttle. If I turn the choke off (push in) the bike will not idle and die. If I continue to rev the bike, it stays alive but bogs down before RPMs climb. Also if I am reving the bike and it gets around/below 3500 RPMs, it's going to die. I have messed with the idle set screw but i'm guessing it's something internal.
Thanks for any info!

Re: Carb tuning

Posted: Mon Aug 03, 2015 1:03 am
by drvirago777
Sounds like the Pilot Jet may be clogged or the
fuel level is incorrect from a failing needle valve seat and needle valve.
Ultrasonic Cleaning in hot water and then blowing out all the passages with 100 lbs air pressure
when they first come out of the Cleaner, is the best way to make sure everythings cleared.
I like to then blast all the passages with carb cleaner and then air pressure again.
I may go a little overkill.

Re: Carb tuning

Posted: Mon Aug 03, 2015 8:00 pm
by Bspurge
drvirago777 wrote:Sounds like the Pilot Jet may be clogged or the
fuel level is incorrect from a failing needle valve seat and needle valve.
Ultrasonic Cleaning in hot water and then blowing out all the passages with 100 lbs air pressure
when they first come out of the Cleaner, is the best way to make sure everythings cleared.
I like to then blast all the passages with carb cleaner and then air pressure again.
I may go a little overkill.
Awesome, thanks for your reply! I'll stick it out and let you know how it goes.

Re: Carb tuning

Posted: Tue Aug 04, 2015 10:14 am
by Johnj
Sounds like a intake leak to me.