Have 2 300exs both have been piped and jeted is it normal to have popping when you let out on gas or is jet wrong

 

i have a 2000 300ex with pipe and k&n filter and it pops when i let off the gas i'm not jetted i think i need to be though. i don't think its a problem though

 

If its popping when you let up it needs the carb to be cleaned and re jetted - it should under engine compression braking make a smooth sounding exhaust tone if the carbs jets are clean and of proper size. Also don't forget there is 2 jets not just 1

 

do not drive with a perf pipe til jetted, i blew my atv up because of that

 

I was re-reading your post and didn't catch the fact that not only are you now piped but also put a K&N filter. When it comes to the type of mods you've done if you don't re-jet it chances are you've actually lost HP&Torque and just gained noise once you take care of it you will notice a BIG difference from idle to full throttle. There are a few easy ways you can fix the problem-#1) A 2000 300ex came stock with a #38 low speed and a #122 main I would at the very least jump up to a #130&#40 and go from there up or down depending on your plug reading. #2) K&N sells a carb kit for your application that comes with very easy to follow directions, the kit will contain all the required parts cheaply(prob. under $30. off ebay) and cuts down on the guesswork. #3) You can call K&N's 1-800# or your brand pipes 1-800# and tell them what you have for a set-up(pipe&filter) and they should gladly give you a starting point. DO NOT run it down the trail till you fix it or you will burn up a piston---Once you put in the larger jets make sure you have a couple of NEW plugs so you can ride and check them to make sure you are turning the plug a nice tan to black color, if its black thats not all that bad just so long as its not black and WET, because if its darker then tan then it will be safer come winter. Personally I like the K&N kits but anyway will work--Here is a good link with photo's to show you how to properly read a plug and tell how you how your engine is running----
http://www.totallyamaha.com/sn...tion%20%20Overview.htm

 

Deceleration backfire indicates a lean condition. Did this just start??? If so, you carb is dirty or the air filter or you have an air leak in the intake.

If it was doing this all along, then the jetting is wrong.

 

It has always done it I took out my plug and looked at it and looked at link above and its a nice tan so it should be jetted right runs real good

 

I'd still pop a new plug in and check it because it could have been running richer and the "lean burn" turned it tan. Usually when I have a small motor that is running good and all of a sudden starts popping when I let off of the gas, I first just unscrew the bleeder on the float bowl and let it drain out the fuel and by doing this it lets whatever little bit of crap thats in there out BUT thats a 50/50 chance--if it still does it then you have to take off the bowl and clean BOTH jets and problem solved-usually. Do you have any holes or bad gaskets in your exhaust system? this will sometimes also cause a popping sound under the conditions described.

 

I dont think I have bad gaskets the exhaust is good one I havent worked on the other I just gave a complete rebuild on the motor. So after I put in new plug how long should I run it and then check it

 

lean pilot, adjust a/f mix screw.