04 RMZ250 Backfiring Need help

Hi to all, My name is Island and I have just purchase my first dirtbike a used 04 rmz250. To me the bike runs fine starts up on first or second kick but it has some backfire, i put new plug, and changed oil and coolant. I have read most of your forum for the rmz250 and from what i read its like the valves need to be adjusted or the jetting? I'am not very sure i really need your help. If i have to adjust the valves, what are the filler gages sizes? and if the jetting what size do i use? It has an after market full exhaust and perfomance airfilter. Thank you very much you help will be greatly appreciated.    

whats up island and WELCOME i am alex, i have a 2008 yz250f race bike. I was just talking to my mech the other day about back fireing, since i have a high preformance bike and so do you in a way, he says back firing is normal in some cases, like my aribox is moddified so that more air flow can get thru, so my bike back fires quite often, my mech asked me is your bike hard to start up cold or hot i said no usually about 3 kicks does the job sometimes less and my mech said does it sound funny i said no, so if you awnserd all those question the same as i did, then you bike is probly fine. If your still not sure then ya go ahead and check i was still thining about getting mined checked. hope this helped.  
--------------------
Autismspeaks.org   check it out
--------------------
life in the fast rut!!!!
--------------------
my rides- 2008 yz250f fully modified, use to be j-laws bike
        &
IT400 1979 yamaha!!!
--------------------
Home: SO CAL

Thanks Alex know i can ride with out worrying to much.   I'am gonna check my jets thow see what i have in there. Thanks again  

Ya, a backfire generally (not always) occurs when there is too much fuel in the chamber. Not a huge deal, but it will probably progress to a bigger problem. My good friend Alex is bang on.  

Welcome island.
Dose it do it at high RPM then letting off the throttle quick?
Check for a air leak around the carb and air box.
Also check for a exhaust leak.
Both types of leaks will cause backfire and sence you just got the bike it would be a good idea to check the valve clearance. Its not hard to do if you got the manual.  
---------------------------

I love this dirt stuff.

pojp58:
Welcome island.
Dose it do it at high RPM then letting off the throttle quick?
Check for a air leak around the carb and air box.
Also check for a exhaust leak.
Both types of leaks will cause backfire and sence you just got the bike it would be a good idea to check the valve clearance. Its not hard to do if you got the manual.

i fully agree with POP, he is absolutley right on this, if you have time to check might as well. Like when you here a back fire its just a big loud ace !!!!!POP&BANG!!!!! right??? well when my bike when i ride it, it will only back fire after a ride it and get the motor fully hot, i mean its hard to say if my bike back fires because its not loud its like i will be going and then when i am coasting in to my car it will just do 1 buuuuuuuuuuuuu ba buuuuu but its not a loud BANG!! its just a little baa so i am really not sure now. LOL My bike does not do it always ether, But my mech drove my bike and said it was normal so i guess i will trust him, so POP maybe you could tell me.  
--------------------
Autismspeaks.org   check it out
--------------------
life in the fast rut!!!!
--------------------
my rides- 2008 yz250f fully modified, use to be j-laws bike
        &
IT400 1979 yamaha!!!
--------------------
Home: SO CAL

Put in a new plug then run it and read it. The plug itself can cause back fire.  
-------------------


DIABETES SUX!

yzwoods:
Put in a new plug then run it and read it. The plug itself can cause back fire.

Thanks Woods i will probly try that.  
--------------------
Autismspeaks.org   check it out
--------------------
life in the fast rut!!!!
--------------------
my rides- 2008 yz250f fully modified, use to be j-laws bike
        &
IT400 1979 yamaha!!!
--------------------
Home: SO CAL

ive ridden a 4str bike with badly adjusted valves and backfired regularly...a 1976 ttr 500 which i ALMOST had for 350 bucks but someone else came and offered 360 so i didnt want to get in a bidding war right there so i just said forget it and drove away and got my DT...but anyways this bike would backfire occasionally on the test drives i took it on...it think it was usually on deceleration after high RPM and it wasnt some little pop...it was a HUGE embarassing POWWWW ...unmistakable  
1978 Yamaha 175 MX
Northern Ontario
Canada
31 yrs young
WHEELIES!
Yaaaayyyyyy!

DT_Jason:
ive ridden a 4str bike with badly adjusted valves and backfired regularly...a 1976 ttr 500 which i ALMOST had for 350 bucks but someone else came and offered 360 so i didnt want to get in a bidding war right there so i just said forget it and drove away and got my DT...but anyways this bike would backfire occasionally on the test drives i took it on...it think it was usually on deceleration after high RPM and it wasnt some little pop...it was a HUGE embarassing POWWWW ...unmistakable

SHEESH!!!!!  
--------------------
Autismspeaks.org   check it out
--------------------
life in the fast rut!!!!
--------------------
my rides- 2008 yz250f fully modified, use to be j-laws bike
        &
IT400 1979 yamaha!!!
--------------------
Home: SO CAL

Hi, Yes there is a hair line crack on my header where it hit the shock i will mig that as soon as i borrow my mig back from my co-worker. lol Thanks everyone you all have been a great help thank for the warm welcome.  

How did your header hit the shock?  
---------------------------

I love this dirt stuff.

Its actually the header pipe its a larger pipe from the stock. its a full performance exhaust.  

The hairline crack will cause a backfire.  
---------------------------

I love this dirt stuff.