[Flamin 250]

Hello Honda people!
Got a 87 trx250x fourtrax with ( very loud) exhaust and intake. I'm doing a carb rebuild and figured I should throw larger jets in since it has the increased air flow. I looked at the plug and it does not appear to be running lean however it does run poorly reguardless and gets very hot with backfires.
My questions are what size main and pilot jets? Perhaps 128 and 40? How many turns on the needles?
Thanks!!!

 

[SamUK]

Carb tuning is all down to spark plug color, have you looked at the sticky thread on this forum, 'plug chop'? That will explain a lot for you.

If your carb is jetted properly the amount of turns out on the pilot would usually remain between 2 and 3.

 

[Flamin 250]

Sure thing! Plug appeared to be black as if running just right

 

[SamUK]

Sure thing! Plug appeared to be black as if running just right

Plug shouldn't be black if it's running right..!!

It should be a light 'tea' (sand) color throughout. Black suggests a carbon build up, to much fuel basically. This could be a choke (enrichment valve) issue, a blocked or dirty carb or the wrong jets.

 

[Flamin 250]

Hmm okay I think I found my answer here. I am almost certain the carb is clogged up because it isn't running lean in this case so it must be plugged up. The jets on the carb are OEM. I thought that typically with an exhaust and intake that the jets should be replaced with slightly larger ones to compensate for the more fuel needed to compensate the free flow. There could not be too much fuel because the carb hasn't been touched but then again I don't know the quads history. The choke works fine so It can't be that. How could it run rich if the carb is clogged? Im certain it is because the quad is harder to start when warm and it does not idle well. I plan to pull the carb off, clean it, rebuild it and throw in slightly larger jets because in theory, I can tune it to the correct mixture with larger jets rather than starve for fuel with the OEM ones. Am I still on the right track here?