1987 250X Poor Running Top End

[Cool Honda Man]

We have recently rebuilt our 1987 Honda 250x. At the same time we put on a FMX Mega Max 2 muffler and a K & N Filter. The problem is that above 3/4 throttle it looses power and begins to pop and backfire. It came with a 125 main jet. We went up to a 132 main jet. The needle jet clip is on the 3rd position. Still no improvement!!!! We are frustrated in Utah at 4200 feet elevation.
Any ideas?

[buster369]

run it wide open and take out the plug and look at its color. Get back to me and i'll try to help

[flipstick04]

sounds like you need to go up one more. but ya, check the plug and post again.

[Cool Honda Man]

Well, we found out the problem... We went and bought a 120 main jet. That fixed the problem it runs like a charm. Thanks for your help!

[buster369]

That sounds like a low jet just make sure its not to lean the plug would be white or gray because u'll burn a whole in ur piston

[bigjeep310]

i got a 87 s50x stock motor and carb, cobra exhuast and header and a uni filter what should my jetting be at and what is the stock jetting ?

Mine is doing the same thing after 1/2 to 3/4 throttle it boggs down and trys to shut off

Thanks


JL

[400ex men]

man im runin a 160 M in my 250x but im all mods tho:)

[dork]

That sounds like a low jet just make sure its not to lean the plug would be white or gray because u'll burn a whole in ur piston

look at the elevation, 4200 ft. a 120 is enough jet for the thinner air. the honda manual says to use the high altitude jetting from about 3000ft and up.