91 KX250 Jetting Help

[zrad]

Good Evening Ladies and Gents! 

Ive been beating my head off a brick wall for two days trying to get this carb sorted out. The bike has a massive bog from about 1/8 throttle to wot. It will not enter powerband. I've checked compression cold 175psi,  cleaned carb six times, checked power valve operation and timing, inspected and flipped reeds, looked for air leaks. I've tried multiple jetting configurations from 150-160 mains and 52-58 pilot jets. Bike has FMF Fatty and silencer and I'm at 3000ft above sea level. One thing I haven't done is check the float height but the bike isn't dumping fuel out over flow so I assumed it was ok. Idle screw has little affect and choke does nothing. What makes me suspect the float is I was messing with the idle screw/fuel screw when the petcock was closed I seemed to gain control with the fuel screw and choke plunger when the carb was about half way out of fuel. It revved good and seemed ok then ran out of fuel..

ANY SUGGESTIONS? I'm at wits end with this thing! 

[Pigsfly]

Must set the float height first buddy .

slow jet maybe to rich ,try a 45 or lower , main is a bit to lean for my liking maybe bump that up to 180 

this is considering all is well with the engine, but my gut feeling also is the reeds are past there used by date 

 

 

[zrad]

Thanks Johnny, I'll set the float height tonight and take another run at jetting. 

[zrad]

Float height set. Reeds double checked again and they are in great shape and are an aftermarket carbon fibre set. A tiny little gap on the ends from warpage but I'm talking about a very insignificant amount. I played with jetting again, this time going on a broader range and included the needle jet. Still running like a giant heap of crap, with a huge bog throughout the entire ramp range, smoking a lot too. Anyone have any guesses? I tried a couple different plugs, br8es and br9eg

[zrad]

I just replaced the reeds and repacked the silencer......still running like a heap. 

 

Anyone else have have any ideas?

[Singletrack_rider]

We need some more info.

Was the bike running fine and this problem just started.

Does the bike start easily and idles good.

Did you do some other work on the bike and then the problem happened. 

It may not even be the carb.

[zrad]

Bought the bike like this. It starts good (1st kick). Won't idle long without manipulating the throttle. Wouldn't one think that when I shut off the fuel and run it down a bit, the fact that it finds a sweet spot and runs good then runs out of fuel, would indicate the the problem lies within the carb?

[Singletrack_rider]

I had a similar problem on a kx500. Float level was good, bike ran like crap no matter what I did. This was a used bike that I had just bought myself.

Ended up the carb was bad. The needle had worn the brass needle jet . It made the hole oversize and ovol. Pull the carb , remove the bowl and the main jet. 

Take your needle without the clip on and try to slide it thru the hole it goes in. See ith the needle passes thru. The part of the needle at the clip grooves is .115" the same size of the hole in the carb.

If the clip area slides into the hole hold it up to a light and look for light between the needle and the needle jet hole.

On my kx carb the hole was about .008 big in some areas.

On these older bikes this is a common problem that is overlooked and never diagnosed. 

If this is not the problem we will go from there.

[zrad]

It slides into the needle jet but I don't see any light through it

[zrad]

I should mention also that I get a fair amount of fuel splashing back into the air box while running. The new reeds didn't seem to help this issue either.

[CJ KX250]

Did you ever figure out the problem?