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Installed FMF on 70 - now it pops a lot...insight?

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My son wanted his bike ('05 CRF70) to sound like mine (450R), so I got him a full FMF exhuast...

His bike is near-new, and runs dead perfect.

Install went fine, starts right up, etc.

Bike still runs ok, but now pops/chugs on hard accelerations, and pops ALOT on hard DECELLERATIONS...like chop the throttle off after pinning it...and it pops like crazy.

I'm sure i need to adjust the carb or something, but have no idea what to adjust...

Tips?

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You're running lean, you need to rejet the mains and pilot larger and readjust your air screw. The manufacturer should have a helpline that will give you base line starting points, and go from there.

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You will need a bigger main jet. You may be able to keep the same pilot jet and turn up your fuel mixture screw a bit. After you get rid of the popping then you can work on the bog if you still have it. May just need to raise the needle a notch after your rejet.

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Thanks for the responses...I've read these, as well as researched other sites, searched in THIS forum, etc, etc...the general concensus is that I raise the needle 1 notch (lower the clip, right?), then mess with the fuel/air screw, and polish it off with fine-tuning the idle....right?

Are there any standard "open the airbox" type recommended mods? It's completely stock, other than the pipe right now...

ps: couple general questions:

*how often do ya'll change the oil on these?

*how often do you change the oil filter (is there an oil filter?)

*how often do you clean the air filter?

*what are the stock sprocket sizes? Does anyone gear them down a little? At first my son wouldn't get out of 1st gear...now he pretty much only likes 2nd gear, which usually tends to be a bit high...

What are the top mods for a beginner rider?

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