ok i just got my FMF factory 4 slip on muffler and mid pipe put on with the required jetting and after u let it warm up and if i rev it pretty high flames come out the muffler i dunno if thats normal or not cuz s/o told me it was b.c it doesnt have a spark arrester on it but i have no idea so is this normal or do i got a problem?

thanks

 

Sounds like your running rich. So the excess fuel is coming out the pipe in flames. Check your plug, it most likely is black.

 

thats impossible if i was runnin rich it wouldnt cut out when i give it the gas real quick but idk

 

It will cut out if you are running rich. Your dumping more fuel then what the engine can burn. Your air/fuel mixture won't be right so it will cut out on you.

 

so i should adjust the air fuel mixture?

 

What jetting did you use? Did you put a pilot jet in too? The best way to tell is doing a plug check.

 

i used a 162 MJ cuz thats wut FMF requires with the pipe and i never put a different pilot jet

 

Do you have the lid on or off? That jetting does seem low for your mods.

 

This should help you. I found this info.

pilot 45 (biggest in the gytr jet kit for the YFZ450) airscrew 2 and mainjet 165 (Biggest in the Yamaha jet kit)and needle clip stock #4 is my advice to anyone buying a 450 right off the shelf, if you remove the baffle and the airbox lid then put the needle on #5 clip.

IF YOU BUY A PIPE then get a 170 mainjet at least usually unless you are at altitude of several thousand feet..

THAT IS ALL YOU HAVE TO KNOW! Popping and crackling and a little hesitation, is not much problem it won't hurt anything, and your tail pipe will glow RED! It is cool at night! Don't melt your pants. This won't cost you any money except a 6 dollar pilot and a 4 dollar mainjet.

The first change is alway a bigger mainjet then one up on the needle clip, then a bigger mainjet again. When you think you have it right, then you need to take out your spark plug and put in a new one. check the old one and see what color the electrodes are. This tells you if you are jetted safely. If there is a LOT OF WHITE or chalk color on the electrodes, then you are runniing too hot and too lean.

If the electrodes look BLACK and like PENCIL LEAD COLOR you are too rich and need to go down a main jet and try again. Or down a needle clip. CHANGE ONLY ONE THING AT A TIME. IF you have the cam mod you should run pilot 48.
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NEVER go below a PILOT OF 45! for any reason.
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NEVER go below a mainjet of 165 for any reason. NEVER put your needle clip below #4 for any reason on the STOCK NEEDLE!

CLIP 4 means the fourth clip counting from the big fat end. The closes notch to the big fat end is clip # 1 this is danger zone clip #2 is danger zone and clip #3 is danger zone if you do any mods clip #4 is safe for simple mods and so is clip 5 and 6.
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Looking at the plug, you will see that a good plug is light brown.

if you have white on the electrodes then you are too lean, that means your jet numbers are a little bit low, so put in one bigger one. either a mianjet or another clip up on the needle. DO NOT JUST KEEP PUTTING IN BIGGER AND BIGGER MAINJETS! the rule of thumb is FIRST put in one mainjet, THEN GO UP ON THE NEEDLE TO #4 then go u 1-2 more mainjets. then go up to #5 on the needle then go up 1 mainjet. then go up to #6 then go up 1-2 mainjets. Don't just go up only on mainjets, youll get way out of balance.

AFTER GOING UP TWO CLIPS ON THE NEEDLE YOU MUST GO UP ON THE PILOT BY ONE or you will get hesitation. IF IT WILL NOT START then go down on the pilot by one.

Hope this helps ... i used these methods to jet mine and it is good advise found in here Jet index

 

i have my airbox lid on and all i got is a pipe and K&N filter and FMF even says that a 162 MJ is the required one and dirt wheels even did the pipe shootout and it was a 162 MJ i havent yet adjusted the air/fuel mixture screw or put the needle clip at the #4 but im ganna be doin that soon