It is still back firing! HELP!


18 replies to this topic
  • goalpostcasualty

Posted May 17, 2007 - 03:05 PM

#1

Ok... I have a 04 yz450. I recently posted a thread entitled "yz450 revving problem". Let me sum it up for you. The bike ran great for the first week I had it. Left it sitting for a few days after my last ride and came back and tried riding it again but it was popping and back firing. It also was sputtering when I got on the gas towards mid to high rpms. Idles great... no problem there. So I cleaned the carb a little bit. Checked the air filter and it was all fine. So i went a got about 5 gallons of 93 octane and added a whole bottle of octane boost to it and changed out the gas for the new higher octane gas... still popping and backfiring bad, and sputtering and popping while i am on the gas. I pulled the plug it was black as night so I changed it and it ran for about 1.5 hours and it basically ran like it was before the problems started. I left it for a couple more days came back today and It was worse than it was the first time. Popping and backfiring really bad and sputtering and popping while i was won the gas... idle still perfect. I pull that plug that only had at most maybe 2 hours on it... again totally black! Whats my problem? Is it the gas with the octane boost or what? I mean i don't think the fuel mixture could have all of a sudden got that bad because I never adjusted it. PLEASE HELP!

  • 02YZ426

Posted May 17, 2007 - 04:31 PM

#2

Well I don't think your supposed to use octane boost for starters. Is your jetting stock or close to it? Maybe you spark plug boot is bad. Have you tried cleaning your carb yet?

  • goalpostcasualty

Posted May 17, 2007 - 05:19 PM

#3

I didn't scrub the carb or anything but i did spray it down with carb cleaner and my jets are stock. I think i am going to drain the gas out and put 89 in it or just regular 93. I don't know about the spark boot. i dont think there is any visual way to check those.

  • goalpostcasualty

Posted May 18, 2007 - 07:33 PM

#4

Ok... i just took the carb off and checked it and it was clean enough to eat out of. Not any grim or build up or nothing. I checked all the jets and needles and they are all fine. Since the spark plugs were black when I took them out i did however turn the fuel screw on the bottom of the carb from 3 turns from all the way in to 2.5 from all the way in. I put it all back together clean the spark plug put fresh gas( regular 93 without octane boost) and fired it up. Still runs like crap. idles great but when you rev it up it sputters and pops like crazy and backfires really bad (even had a little bit of a fire coming out of the exhaust it was backfiring so bad). I don't know what the heck to do! Like i said it all of a sudden started running like this. I didnt change anything. What is wrong?!?! PLEASE HELP!

  • 02YZ426

Posted May 18, 2007 - 07:38 PM

#5

Maybe its time to check your valve clearances. Also while your in there check your cam timing and make sure it hasn't jumped.

  • Maximus83

Posted May 19, 2007 - 08:23 AM

#6

Maybe your exhaust valve isnt closing all the way, that will cause popping and backfiring. Like the above says, check your clearances. Stuff might have tightened up on you in there also. Did you check to make sure your hotstart has some play in it? The lever shouldnt be tight against the mount. No octane boost, especially not an entire bottle. Premium pump is all you need my friend. I was told a black sooty plug means your running rich. Try one lower jet on your main. Dont just be turning your fuel screw blindly either. Speed up the idle, screw it all the way in and then slowly turn it out until the bike sputters or slows idle, then turn it back a couple clicks to where the exhaust note sounds crisp and the engine is idling fastest. Also, if you have the cash, try the Zip Ty carb mod for $100. Suppose to eliminate the back firing problem, if the rest of your bike is in spec that is. I'm not sure what other advice was given to you in the other thread so maybe this is all repeat...problem with starting mulitple threads, same problem.

  • BC3

Posted May 19, 2007 - 09:13 AM

#7

Sounds like an elect. problem....check all your connections (unplug and plug
the connectors to make sure their clean) Also check your choke to make sure it's sealing when closed...Something is causing the plug to foul.....That's where
I would start....Good luck

  • grayracer513

Posted May 19, 2007 - 09:17 AM

#8

Sounds like an elect. problem....check all your connections (unplug and plug
the connectors to make sure their clean) Also check your choke to make sure it's sealing when closed...Something is causing the plug to foul.....That's where
I would start....Good luck

Yep. Black sooty plugs are also a symptom of bad ignition quality, and the soot is conductive.

  • goalpostcasualty

Posted May 19, 2007 - 05:48 PM

#9

Ok i'll get on it right away. What all is involved in checking the my valve tolerences and the timing? I haven't done that before on a bike.

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  • Maximus83

Posted May 19, 2007 - 06:15 PM

#10

Get a manual. You can get CD versions off ebay for like $10.

  • grayracer513

Posted May 19, 2007 - 08:19 PM

#11

Or right here, right now, for free:

http://www.yamahaown...ook.com.au/?r=0

  • goalpostcasualty

Posted May 20, 2007 - 11:45 AM

#12

ok... i was still totally stumped about this whole thing right... so i went out and put a new spark plug in and just let it sit and idle for about 5-7 minutes. I revved it up a few times (still backfiring and popping bad when its not idleing but like i said it idles perfect) then I immediately pulled the plug out... and low and behold it was totally black and seemed to be soaked with oil! I assume it was oil at least. So i am really stumped now but i assume that this is a valid piece of info for you pros so whats wrong?!?! Why is my spark plug soaked with oil?

  • tnl

Posted May 20, 2007 - 12:53 PM

#13

I'm no expert but: How about your exhaust? Is the midpipe clamp tight? Was your bike blowing smoke out of the exhaust if your plug was covered in oil I would think it would be? Or is it fuel?

  • goalpostcasualty

Posted May 20, 2007 - 07:27 PM

#14

Thats a good point... the bike has never blown smoke. Not one time has it so I guess you are right it must not be oil. But the plug came out soaking wet but i guess it could have been a mixture of fuel and soot. The exhaust pipe if on very well. I checked it right off the bat when i started having problems. What might the problem be then if it isnt oil?

  • grayracer513

Posted May 20, 2007 - 07:47 PM

#15

If the ignition is poor, the plug will be wet. The wetness can also be too much fuel, or the simple fact that you didn't really ever get the plug up to operating temperature so it could clean itself. Don't get thrown off the track by something like this.

  • Pezman04wrx

Posted May 21, 2007 - 02:28 AM

#16

How's your hot start holding up where it mounts to the carb? ... The damn little plastic nut gets stripped and causes problems galore ... It's at least worth a quick once over ...

  • goalpostcasualty

Posted May 21, 2007 - 04:36 AM

#17

Well the hot start seems to be fine. It has plenty of slack but i haven't checked where it connects to the motor. Anything yall could recommend before i end up having to take it apart and check everything?

  • poynedexter

Posted May 21, 2007 - 04:46 AM

#18

How's your hot start holding up where it mounts to the carb? ... The damn little plastic nut gets stripped and causes problems galore ... It's at least worth a quick once over ...


water in the hot start. its real common. disconnect it and blow down with compressed air (dont blow dirt down there). blow down the disconnected cable and leave to dry. i'll bet thats your problem. hot start lean/ wet = popping and spitting

  • goalpostcasualty

Posted May 21, 2007 - 05:09 AM

#19

ok... ill give that a try when i get home from work. I really hope thats the problem because i am tired of having no bike to ride. This SUCKS!





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