question about a 250x

[bigman1391]

my friend has a 1988 honda 250x. he jus got a pipe for it andit is backfiring. he needs the jet we live in levittown pa and dont kno the elevation here so wat size main jet wuld he need to get????

[ghak99]

What kind of pipe is it and is there any other mods to the motor? When does it backfire?

[bigman1391]

its a dg pipe.. and it backfires after you let off the gas...

[bradley300]

if it backfires when you let off, your too lean, find out what main jet is in it, and buy the next 4 or 5 sizes, change them out from smallest to biggest until it quits backfiring. and save the jets you dont use, you'll need to re jet again in the winter

[plkmonster2]

Um, actually, the main jet has nothing to do once you let off. Buy the next size or two up pilot jet. This controls the idle fuel mixture, and pops when you let off becuase the pilot can't supply enough fuel. Either unscrew your mixture screw 1/2-1 turn out, but if it still pops, buy the next size up on the pilot.

[wilkin250r]

Here's the question. How far are you letting off the gas?

If you're talking about letting go of the throttle completely, then the slide is closed, and the carb is running on the idle circuit, even if you're still going 35 miles per hour (but obviously you are slowing down).

Remember, the carb doesn't know if the engine is running at 750rpm or 5000rpm. All it knows is throttle position. So if the throttle position is closed, then you are running on the idle circuit, which is the pilot jet. You may not need a bigger pilot, you can probably just adjust your mixture screw. If the mixture screw doesn't fix it, you need a bigger pilot. Consult your manual for mixture screw adjustment and/or pilot jet replacement.

Now, if you are talking about letting off the throttle from full throttle dropping to half throttle(not fully closed), then you are running off the needle. You would need to raise your needle by lowering the clip on the needle. Again, consult your manual.