Switching from a 34mm Keihin to a 38mm airstryker idol problems

[TonyV]

I upgraded this carb on my TRX250R The jetting was huge it had a 178 main and a 52 pilot i dropped the pilot to a 48 which was still fouling plugs fast and bad so went to a 42 the main jetting is at 165 which I think may be lean by a plug check after dropping the pilot down and not loading the plug up on idle. I have an LRD pipe K&N air filter and a ESR Cool Head. I was told that the pipe called for 2 main jet sizes up and the K&N called for 2 sizes up on the main jet aswell I cannot get this machine to idle I have the idle adjustment all the way in (as far as it goes) and it still idles low for a second then dies but starts right back up do I need to cut this idle adjustment spring maybe?? Im thinking it would help because i hear the idle move when bringing it in and out. has anyoneelse ran into this problem and do you think this 42 pilot is to lean the original pilot in the 34mm carb was a 42 and thats as i said whats now in this 38. I was told to drop it lower and that it was still to rich but i just cant see going lower than what stock (the book) called for.

[GPracer2500]

What is the air screw set at?

[TonyV]

the airscrew at 1 1/2 - 1 3/4 turns I have messed with it with no results thats what is throwing me for a loop

[GPracer2500]

If the pilot circuit is too rich with a 42 than keep going lower. A size X jet in one model carb doesn't always translated directly to the same size in another model carb. Pay close attention to how the engine behaves in response to air screw changes. This can be a big help in figureing out if the pilot jet is the correct size.

Also be SURE that the pilot circuit passages in the carb are squeeky clean. If no amount of carb tuning ever helps than consider that it's not even a carb problem. Leaking crank seals, for example, can cause erratic idling characteristics.

[TonyV]

Ok now Im thinking its the pilot jet because today it fouled yet another plug. Anyone else running this carb on a honda 250R also what are your thoughts on the jetting as said i have an 89 motor fresh rebuild an lrd pipe k&n air filter with a esr cool head 42 pilot 165 main jet clip on needle is on the 2nd groove from top( lean) what are you guys running as far as jetting with these 38 mm carbs??? I know every machine is different but atleast it gives me a little reference on where to aim. Like I said the stock pilot in a 34mm carb was a 45 and the main was i believe a 158 or 160 this fouling plugs thing is crazy i was affraid to go lower in the pilot but im thinking that i have to if its to lean on pilot there would be a dead spot or hesitate due to starving for fuel in worse case scenario. I am also thinking that my main jet will have to be bumped up to a 168 after this pilot problems figured out. But Ill worry about that later.

[wilkin250r]

I don't know about the idle. 42 sounds a bit small. It's possible, just odd. If I got into this realm, I'd be worried about an air leak, bad reeds, or some other problem. Did you do a leakdown test?

165 also sounds a bit small for the main. I think most people running a 38mm are running somewhere close to 180. Do a search in the 250r section and you'll find more information.

For a quick band-aid fix, you can play with the throttle cable adjustment at the thumb throttle. I know many people that use this tactic, just adjust all the slack out so that the slide is still slightly open even at zero throttle. It's not the correct way, but it's very effective, and has very little adverse side-effects. I know some very good racers that still do it this way, because it's easy and hassle-free.