Jetting an '83 KDX250

[fred99999au]

Hi All. My mates 83 KDX is nearly there and we are hoping to launch it for its maiden voyage at Cooka.

He has just got a new carby from Tom at MikuniOz but we think he has ordered the wrong carby.

He has ordered a 34mm VM roundslide. Measuring the bore on the manifold side of the carb, it is a bit over 33mm from memory. The old carby is supposed to be a 37mm bore, but we have no guarantee that that carb was any good either. In fact we could ride it but it carried on and was worn and we had to push start it.

We have a 250 main jet, a R6 needle jet, a 3.0 slide cutaway and a 60 pilot with a good 6FJ43 nedle.

We have kicked it and kicked it but the bastard wont start.

Pushed it up and down the street a few times and got a couple of farts, but nothing to ride home about (see what I did there??).

Just so happens I have a new VM38 carb here, so we swapped the jets and needles into that and we can kick start it now and it idles ok at 1.5 turns out on the airscrew.

We've marked the throttle grip at closed, 1/4, 1/2, 3/4 and WOT so we know where we are in relation to carb circuits.

We can kick the bike and it starts when cold with the choke, and without choke when warm. When riding it, we can get to 1/4 throttle and then it dies. If at just under 1/4 throttle I throw the choke on and open it up a bit it makes me wobble and my eyes water as I can see what I'm going to hit. Let it drop below 1/4 throttle and it dies.

This suggests to me that it is way lean.

Is the 38mm carb too big for this bike? Any suggestions about needle jet site that would be better with the 38mm carb? Are there better options?

Is there a chart of needle jets in order of size?

Cheers,

Fred.

[80-85 husky]

where is the needle clip? put it at the bottom of the needle (full rich) and see what happens... some one who knows what to do will show up soon
what about the float level? ok? and is the tap giving you enough fuel flow??

[fred99999au]

Thanks mate. needle is in the middle clip, but I reckon it is nore than one jet size out. I guess we could richen the needle up and see if it gets any better...

[rocketfrog]

Did Mikuniatoz suggest the 34mm? sounds small for a 250.

[fred99999au]

no, unfortunately, my mate suggested it. Tom has quite helpful in the past, so I was surprised when the carb was so small.

[80-85 husky]

mate just put a new mikuni on his PE, it was rich all over (so clowns don't seize it and blame the carb) the air mixture screw was xthreaded and snapped off ...so off to the machine shop....

[rocketfrog]

Hmmm, that size and jetting sounds more apt for a 125. I have what I believe to be a KX250 Mikuni here if you want to give it a go. I got it thrown in with a bunch of Yamaha stuff from a Kawasaki guy on the forum here, its of no use to me, so send me your address and a few bucks for post and I will swing it your way if you want.