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I usually stick to riding around in the woods and trails and stuff but I noticed that the bike bogs out a lot. I have done a lot of reading around and from what I understand, the stock carb is 38mm. Reducing the size of the carb may help with my low end power right? It struggles quite a bit in first gear and second gear putting around and going up steep hills but when the bike is on the pipe it absolutely hammers, the throttle response is ridiculous. If anyone can inform me a bit better or recommend a smaller carb then please do so.
Thanks.

Have you fooled with the air screw?

Have you tried a smaller pilot jet?

KDXGarage wrote: 05:45 pm Aug 30 2020 Have you fooled with the air screw?

Have you tried a smaller pilot jet?

Have messed with the screw plenty, the jets are standard for my elevation. Bike just bogs out all the time and carb constantly fills with gas at low RPM

Don't be afraid to try a smaller pilot jet. "Standard" is what makes it run perfectly.

Any chance the float valve is not fully sealing?

Most 125's are not going to run crisply at low RPM's. I have a 2005 KX125. It has taught me not to hope for such things. :-)

KDXGarage wrote: 11:08 pm Aug 30 2020 Don't be afraid to try a smaller pilot jet. "Standard" is what makes it run perfectly.

Any chance the float valve is not fully sealing?

Most 125's are not going to run crisply at low RPM's. I have a 2005 KX125. It has taught me not to hope for such things. :-)

I just want it to even idle man. If it runs for just 15 minutes it will no longer idle. I would like to get a wide transmission kit as well, I just wanna make it more like an enduro bike since I'm not much of a racing guy.

Clean, clean and re-clean the carb. Check the little rubber stopper on the float valve as well as the carb body seat. It may be slightly leaking past the rubber tip. If it is worn or the body is s=worn, that will throw it off.

If it won't idle ever, then there's a clog in there somewhere.

KDXGarage wrote: 10:03 pm Sep 01 2020 Clean, clean and re-clean the carb. Check the little rubber stopper on the float valve as well as the carb body seat. It may be slightly leaking past the rubber tip. If it is worn or the body is s=worn, that will throw it off.

If it won't idle ever, then there's a clog in there somewhere.

Ive taken the carb apart 4 or 5 different times for cleaning.
No matter what I’ve done I can’t get it to idle right after it’s warmed up. It will die if it doesn’t have gas, and if you’re at lower gears and you’re not on the pipe it will flood. I’m assuming the carb is old and is in need of a rebuild, but also I heard from quite a few people the 38mm that’s stock is way too big of a carb for a 125 and is only to squeeze out as much HP as possible for MX. I’m hoping to kill 2 birds with one stone and get a new 36mm PWK

Does it have a PWK Keihin now??

KDXGarage wrote: 02:46 am Sep 02 2020 Does it have a PWK Keihin now??

I believe it’s a 38mm PWK airstriker

Uh oh. Search on here for "jet block gasket".

KDXGarage wrote: 03:24 am Sep 02 2020 Uh oh. Search on here for "jet block gasket".

I can tell you for a fact without checking that I just straight up don’t have one lmao

In a PWK, there is supposed to be a jet block gasket. It won't idle properly if it is not in there and sealing properly. I thought it was a Mikuni or I would have mentioned it earlier.

A 38mm carb for a 125 is really on the large side. They do that for motorcross where you are riding WOT most of the time. For woods work and trail riding you'd be better off going down to a PWK33 or 35 and jetting it. With that big carb on there at idle your engine is likely not generating enough vacuum to properly fuel the bike.

very true