2007 Honda CRF250R factory main jet

I recently purchased a 2007 Honda CRF250R. It was "popping" or "backfiring", and I was told that the bike had been run in Colorado the week before and had a new main jet put in it for the high alltitude. I'm from oklahoma, so I went to Honda dealership and asked for a factory stock main jet, they provided me with a 160 main jet. When I went to replace the main jet, I discovered that it was a 172 main jet. Does anyone know what the main or stock jet is for a 2007 Honda CRF250R? From what I can find the factory stock jet should be a 175 but Iam not sure. Also the bike is very hard to start and I dont know why.

main jet has nothing to do with what happens when the throttle is closed.

if its hard to start you need to check the valves.

i think stock was 172.

Thank you for replying. I'm new to this and have little or no mechanical knowledge. Would the valves be making the "popping" noise when I release the throttle? Also, the "popping" noise seems to diminish after about 5 minutes of running when the 160 main jet was installed. Would running the 160 main jet be harmfull to the engine? What do I need to tell my mechanic to check?

he needs to check the valve clearance and make sure the pilot jet and pilot circuit passages are clear.

Thanks Eddie, I've owned the bike for a week now, and plan on having it serviced by Honda. Besides what you have already said to have the mechanic look at, is there anything else that you would suggest having a look at on a used bike. My goal is good bike that runs will and is mechanically sound. I'm 38 and have no plans on racing and no plans on boosting performance.

NCYR #4, 160 mj, 40 pj, 70 leak, 2 1/4 fs - '04

NCYQ #3, 172 mj, 42 pj, 70 leak, 1 3/4 fs - '05

NHFS #3, 172 mj, 40 pj, 55 leak, 1 3/4 fs - '06

NKBT #3, 175 mj, 42 pj, 70 leak, 2 1/4 fs - '07

NMGU #3, 188 mj, 42 pj, 70 leak, 1 7/8 fs - '08


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