I bought a fmf megamax II for my wheeler, and after finally sealing up a leak it had, it is still popping everytime I let off the gas. Ive messed around with the idle screw, but i dont know where the air screw is. I read that u should set both back all the way then turn them about 2 1/2 turns. Would this help? Im thinking about just sending it in to the dealership, but i dont want to spend the money for labor. Id appreciate any suggestions.

 

unless the popping is really bad, i would say its normal. My bike does that too and its jetted pretty close to perfect. it only does it when i go full throttle top speed and then let off. most say its normal

 

I've read elsewhere on a motorcycle forum that 4 strokes backfire some - naturally. And yours may always did but with a stock pipe you did not hear it but with an aftermarket pipe with less muffle you may hear it now. This was from a pretty knowledgable mechanic on that forum ... and I found the same on my bike.

 

It is lean on the pilot jet or the air screw. Turn the air screw out a 1/4 at a time and see if it goes away. If it takes more than a turn, bump up the pilot jet one size.

On any Honda carb I've had in my hands, the air screw is on the bottom of the carb on the engine side of the slide. It should be almost flush and made of brass and require a flat screw driver.

 

I dont think it needs to be jetted since on the fmf web site it says it should run fine with stock jetting. I noticed today that it only pops at low rpm or when its rolling down a hill. Jokerguy, u might be right about hearing it more with the new pipe cuz it always did pop a little. This might be a really dumb question, but is the idle screw and the air screw the same thing? Ive been adjusting what the manual calls the idle screw.

 

this is exactly right besides the screw is a fuel screw, not an air screw. an air screw and a fuel screw do the opposite of each other. the fuel screw you turn out to richen the mixture and the air screw you turn in to richen the mixture.

 

fmf may say you don't HAVE to do anything. well, you don't! however, not rejetting may cause the exact same problem your having. does the bike run fine? sure it does. so, rejetting isn't manditory. however, for best performance you should jet it. also, i can't imagine the megamax flows much more than stock. they tend to be very restrictive exhaust systems. however, i would turn the fuel screw (it will probably be a bronze colored screw on the very bottom of the carb that you adjust with a flatblade screwdriver) out in 1/4 turn increments at a time. like others mentioned, if you have to go out more than 1 turn from where you started, bump up the pilot jet to the next size. i would put money that the bike quits popping or greatly diminishes the problem after doing this. however, it is common for a 4-stroke to act like this.


the fuel screw and idle screw are NOT the same thing. the idle screw will raise or lower your idle. the fuel screw will fine tune in the air/fuel ratio around idle to 1/4 throttle or so.