baby yamaha troubleshoot

[andyoutandabout]

Peeps, decided to tap into the vast engineering knowledge to help me fix my buddy's, daughter's Yamaha ttr125 dirt bike.
The problem - overflows at the carb bowls; but runs well, idles wellish, but takes ages to return to idle once revved in neutral.

Things I've tried and or discovered:
I can already hear the chorus of float heights. However, i did clean the gunk out the carb, which was easy having only one simple unit to deal with. Jets are clean, etc and I set the float height from a utube vid on the bench using the tube/fluid level method.
But it still overflowed. So I stripped the needle valve assembly and dremel polished the needle valve itself and the brass seating to mirror level using a Qtip and metal polish.
The cone on the needle looked good - no grooves - so I became confident that the needle valve was working and the floats were set at the right height.
With great flourish, it was put back on the bike - I expected it all to run perfect.

Alas - same thing on testing  - drips from the bowl overflow, poor return to idle.

SO - the bike rides ok, but I don't like that vague throttle shutdown since my buddy's daughter is a learner.
Andy

[flips]

Hi Andy.

I am not familiar with a ttr125 but if I had To guess....Could it be that O'ring 32 is perished and leaking around the float valve assembly?

I have had this problem on ny FJ.



Cheers,

Jeff P

[flips]

Here's an article about a carb upgrade...
http://motocrosshideout.com/ttr125-mikuni-vm24-carb-swap-best-bang-for-your-buck/
Cheers,

Jeff P

[Pat Conlon]

Good call Jeff. My thoughts exactly...knackered float needle seat o ring, same as our FJ's.

[scarylarry]

just fixed the same problem on my bike thanks to pat and George and company.
that stinkin' needle seat o-ring

[andyoutandabout]

Thanks for the link Jeff - looks like an easy upgrade and a tried and tested one as well.
Come on Yamaha, don't muddy the waters by cheaping your customers on important parts.
Andy

[andyoutandabout]

And thanks fintip for my first and cheapest option. Much as the replacement unit sounds like a winner, i like the simple o ring idea.
Andy