Jump to content

2005 backfiring at idle


Recommended Posts

I am hoping someone on this forum can help me with an idle issue I am having with my brothers 05 450F. First some background. The bike was purchased used and the previous owner had the carb cleaned and felt that all it needed was some "adjustment" to correct the idle issue. When my brother brought the bike over for me to look at the fuel screw was turned three turns out so I initially thought that the pilot jet or circuit was plugged up. We took the carb off, removed all the jets (main/pilot) and fuel screw and used compressed air to verify that all the passages flowed air and blew out the jets and set the fuel screw to 1.75 turns out. After reinstalling the carb the bike runs identically as before. Turning the fuel screw in or out has little to no effect on the idle or backfire condition. If you pull out the choke it runs great (and of course idles way high) with no back firing.

The bike start great hot or cold and idles fine with the choke on but as soon as you turn the choke off it idles very eradically and backfires through the exhaust as evident by the flame coming out of the silencer when it back fires.

I assumed that since it does all this at idle that it would be the idle circuit but know I am stumped. I have checked for air leaks and that the hot start is not unseating and there are no exhaust leaks. Could it be the exhaust valves even though it start first or second kick hot or cold? Any insight will be helpful. If I have to I will pull the carb off my 02 450 to eleminate carb issues but I rather not since I just got it back together. Thanks for any and all help!

Link to comment
Share on other sites

My son's '05 recently started backfiring and sputtering. It starts and idles fine, but twisting the throttle causes backfiring. We pulled the carb and cleaned it thoroughly (it was pretty dirty). Put it back on, and it still backfires. So we then did what we should have done first - checked the valve clearance. Sure enough, the left intake is zero'd out. My advice to you is to check the valves if you haven't already done so. That may not be your issue, but it's easy enough to check just to rule it out.

Link to comment
Share on other sites

mine did the same and I checked the valves and they were not zeroed out but I did reshim them to spec. Checked timing perfect. Cleaned carb no help. I got some jetting advice and put in a smaller pilot jet ( no good). I put in a larger one and all is good. When I got the bike it had a 160 MJ and a 45 PJ. I have changed both to a 172 MJ and a 48 PJ. It will backfire if bursting the throttle on decel but when riding with a load it backfires very little. I think this is mostly caused from the Yoshimura pipe it has on it.

So to make this long story short trying upping the PJ. get a couple different ones they are only like 5 bucks a piece. I went up 8 from stock on the PJ and 2 from stock on the MJ. it idles down to nothing and starts pretty easy even with it being only in the 40s here.

Hope this helps

Jason

Link to comment
Share on other sites

Mine did the same thing after cleaning the carb. It was fine previous. I had the slide plate on upside down. It looks like it fits better that way and I cleaned the carb two more times and still put it on upside down. It would start and run but backfire as soon as I hit the throttle. If the carb is clean and the valves are in spec, it's the throttle plate or the valve timing.

Link to comment
Share on other sites

Make sure you didnt put the slide in the carby in the wrong way as in 180degrees out. This is so easy to do because it fits perfectly both ways. I did this on my cousins 05 crf 450. It was hard to start and running bad down low so i checked the valves and sure enough both inlets were riding so i reshimmed them to spec and kicked her in the guts (still the same) ,oh must be the carby i thought ,pulled it off and removed everything you can possibly remove and cleaned the hell out of it and it was proper dirty believe me so i was totally convinced that was the problem ,put it all back together and to be sure nothing ever gets back in there i removed the tank cleaned it out and fitted a fuel filter ,started her up again (even worse). Pulled the carby off again thinking somehow something has found its way back in there but it was spotless so i started to assemble the carby again and got putting the slide in when i realised that i had put the slide back in 180 degrees out after cleaning the first time ,started her up and now runs better than it ever did.

Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Reply with:

×
×
  • Create New...