2 Strokes Down Under

Hello fellow 2 strokers

Unfortunately my yz 125 has been having a problem upon cold starts, but it does not affect the bike in any way other than when it's cold.

What happens is when the bike is first started of a day the engine will rev uncomfortably high until it has warmed up after about 5 minutes or so.

There isn't a starting problem or anything like that, but I will usually turn the bike off for fear of damage. Turning the bike on and off a few times normally reduces the revs enough for me to feel comfortable to leave it idle like that till it warms up.

Once the bike is warm / hot the bike will idle fine after, even after sitting to cool down over 2 - 3 hours.

I've done a little bit of research and I think it's possible it could be an air leak or perhaps the carb is worn?

It's a 2002 model with a .25 over sized bore, to my knowledge.

Anyway, I'm not the greatest with mechanical things so any help on what to do or what it could do would be greatly appreciated

I would guess an air leak on the intake side. Around the carby would be a good place to start. It's gunna be small. Spray with some very soapy water to see if you can see bubbles any where.

But maybe the main seals as well.

It could be curd in the carbs.

1/ I would start with the soapy water, 2/No fix? then clean the carb 3/ No fix? then the main seals.

My 2cents

Ciao.

Definitely sounds like a seal that softens and seals when the bike warms up.

As above you have a air leak that is closing when things heat up, you could try spraying WD40 around areas and listening for the revs shooting up, that will be where the leak is.