Posts
18
Joined
7/6/2018
Location
Kingsport, TN
US
Edited Date/Time
5/12/2019 5:59pm
I just rebuilt my 1996 rm250 that I recently bought. It has the original PJ Carb with pro circuit pipe, fmf silencer and a new vforce 3 reed block. I have the jetting close to dialed in. I have a 55 pilot jet and 170 main. It idles fine, runs great on the main and in between, but the issue I'm having is when I just Crack the throttle open a little bit it loads up. It sputter pretty bad and wants to stall, if I open the throttle more past a half or so it clears up and runs great. I'm pretty sure it a rich condition because pulling the choke makes it worse. I dropped the pilot to a 52, that made it seem to lean but made no difference with the off idle issue. I have tried three different needles and different clip positions and nothing seems to help. I don't have alot of experience with tuning carbs, I'm hoping someone can steer me in the right direction.
Set the idle a little high with the air screw 1 1/2 turns out. Now, slowly turn the screw inward until the engine "misses" a little. then go the other way until it misses again. Your best setting is between those two points. If you cannot get the bike to miss but you have screwed the air screw all the way in, your pilot is too lean. If the opposite is true and you cannot get it to miss after going two full turns out, the pilot is too rich.
I suspect a clogged pilot, however. Double check that you can see sunlight through the hole. If that jet is plugged up, small throttle openings will make the bike starve for fuel and cut out. The symptoms would clear up with larger throttle openings once the needle and main come into play, somewhere near 1/4 to 1/2 throttle.
Also I forgot to mention that the carb has been cleaned thoroughly. Every time I take it off I make sure to blast the jets with some air and/or carb cleaner.
PawPaw
The Shop
Paw Paw
If you want to use the single taper needle, like what you have in the carb now, I recommend a CEJ needle in the #3 clip position a 48 or 45 pilot and a 175/172 main to start out with.
Pit Row
Currently I have the CEJ needle on the second clip with 48pj and 170mj. The engine starts easy and runs great with good power. The only thing that concerns me, it seems to have a bit of a deceleration pop. The best way I can describe this is after I rev it and the rpms are coming back down it’s kind of like you hit the throttle just for a very split second. It acted the same with both a 45 and 48 pilot, and now that I think about it, I tried 45 pilot on 2nd and 3rd clip with no change but I didn’t try the 48 pilot on 3rd clip. It just seems a little bit lean to me. I’m not sure if this is something I should even be concerned with, and if it is, I’m not sure where I should go with my next needle. Do I keep the Cxx series or go down to a Dxx. Then should I stay in the CEx, DEx. I know it I will need to go richer just not sure which letter to go richer on.
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