Help with lack of low end


I'm working on my first 2-stroke, and I have a lot of learning to do. First off bike specs

95 kx250

Pilot: 45

Main: 158

Needle: 4th position(as in 4th from top, Cylmer guide recomendation)

Air Screw: 1.5 turns out

Head Pipe: FMF Fatty

Silencer: FMF Power core 2

Reeds: I don't know, but they are carbon fiber and they look new

Compression: about 120psi

I got this bike from a friend who knew nothing about it. I put on the pipes, cleaned up the carb, new handlebars, fuel tank, and some plastic. It runs, but it feels like it has no low rev power. The power band feels like it hits in full force at 3/4 throttle, and trys to spit me off of the back of the bike. Also my float bowl likes to leak a little if I leave the fuel on.

I think I'm close to having a fun toy to play with, but I need some sugestions for dialing in this carb.

Thanks in advance


120 psi is a bit low I think,should be in the upper 100's closer to the 200's.

Forgot to mention that my ridding type is Woods, and I live in Indiana where it is about 90 deg F and humid right now.

Thanks again

I know that 120 is low, but I didn't want to rebuild the top end untill next season. I don't have a lot of time to ride this summer.

im not too sure if this is relevant, but your clip position on your needle seems awfully low. My 2001 with the exact same pipe combo is at the 2nd position, per fmf's reccomendations. Seems like that would make the bike run awfully rich.

First, there's no point trying to jet a worn-out engine, you'll never get it right.

To me, your pilot sounds lean and your needle setting sounds rich

Your description also sounds like a power valve stuck in the open position.

I say check the powervalve too, if stuck open you have lower compresion cuz the exhaust port is higher and you have no low end power.


I would say rebuild first. You can ride it for now, but it seriously takes a whole umm about maybe 2 hours depending on how good you are with topends. (not that hard, anyone can do it). If you order your stuff from rockymountain, cheap and you get it quick!. You can do it over the period of two days or three days.

As already stated.... determine if the PV is stuck first. If operational and you're only getting 120psi then yes... rebuild.

As far as jetting a worn engine... you can make it better, but it's unlikely going to be perfect.

Also..... as previously stated, the PJ seem a bit on the lean side.

New total top end rebuild kit is in the mail. I guess I'm going to do this right.

I pulled the cylinder, and my exhaust valve was nasty. It was by far the dirtiest mechanical job I've ever done. After I pulled the exhaust covers from the cylinder it took three cans of carb cleaner to even start identifing what stuff was. The cylinder is clean with the ID coated with premix, and patiently waiting on my workbench. I cleaned most of the parts, but I can't get all of the carbon off of the steel valve parts. They are curntly soaking in carb cleaner overnight.

If anyone has a neat tip for cleaning these that would be great. Also how do you clean the 20mm ish holes that the drum/ sproket/ rotary girters mount into? I don't know how 2 stroke valves work, but this one could not have.

Thanks for the help so far.

I used an abrasive buff for my dremel to do all the little parts on my KDX powervalve conglomeration. It got em nice and clean and did a little polishing to them so they will at least stay smooth as long as the old man keeps the bike pinned and tapped, (clears throat!!!) lol. But it really worked well and I got most of the little crannies. I only used half of one and they kinda go away quickly.

The leaving gas on and leaking is a normal 2 stroke thing

Get a can of Permatex spray gasket remover, some nitrile gloves, wire brush and a can of brake clean.

Spray the gasket remover on all the carbonized parts and let it sit a bit, scrub with the brush and wipe off with some paper towels. Repeat. When it's pretty much clean finish with brake clean (or mineral spirits) and lightly lube with 2 stroke oil.

If they don't look like this, they aren't clean yet.


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