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07 WR450 Backfiring/No idle

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OK I have been chasing this problem for about 3 months and I'm about to lose my mind. The 450 will start, run, and idle with the choke on no problem. The minute I push the choke in it dies.  If I gas it a bit and continue to give it throttle it will run after I push the choke in but it does backfire. Let off the throttle though and once again it dies.  The bike was sitting for about a year without starting or running.  To get the bike up to snuff and attempt to get it running right I have replaced the cams with hot cams, gotten new exhaust seals, gotten a new rubber insulator for between the carb and motor, gotten all new jets (new GTYR kit) and rebuilt the carb with rebuild kit(piano wire in all holes and blew cleaner with air compressor to make sure clear) cleaned the carb a total of 4 times (thought it was plugged pilot jet passage), brand new plug, did compression leakdown test and tested great, adjusted valves to be in spec (valve job was done last time it was running), tested the charging system and it tested good, and replaced the battery. I started with the mixture screw at 2.5 turns out from lightly seated and tried to adjust it so it would idle with the choke off but no luck.  The only thing I can even begin to think of that I have not replaced is the coil.  I'm just sick of throwing time and money at this thing for nothing.  Anyone have any idea why this bike won't idle off choke or stop backfiring?

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Your problem is that of a lean condition in the pilot circuit; pulling out the choke is confirming this. The problem is in the carb.

That could be caused by:

- partially clogged pilot passage above the pilot jet (ream it and use real solvent/ there os a 90 degree bend up there)

- bad pilot jet (just replace it with a 45 keihin jet)

- compromised body seal (that has melted and is blocking passages)

- hot start that is leaking (due to corrosion, a broken cap, etc)

- choke that is leaking (corrosion, orings etc)

 

You have to bring the carb back to factory specs.... and your body seal sounds like it might be the issue. 

 

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Thank you Krannie for the reply. I have checked, replaced and cleaned everything mentioned except the body seal.  What exactly is that and where is it located?

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That was the issue I had a couple weeks ago my bike would die without the choke all I had to was replace the gasket on the float bowl. it was causing a vacuum leak creating the lean condition 

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Excellent.....I figured it was a lean condition I just couldn't figure out where.  I did not know of a mid-mid-body seal and that's about the only thing I have not done so I bet you are right on the money.  I guess it's off to tear the carb down yet again.  Thank you all for the help!

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Well, I got a mid body gasket kit for the bike got it all back together and started it up.......absolutely no difference at all.  Also something I didn't mention before and I don't know if it matters but I have to open/close the throttle all the way about 15 times as well as pull the choke or it will not start.    Still backfiring like crazy and only idles with the choke out.  Is there any way it could be the coil? I honestly don't even see how it could be the carb because I have taken the carb apart and THOROUGHLY cleaned it a total of 6 times, and every time paying special attention to the pilot jet passages.  I read somewhere on here a bad coil could possibly cause problems like this.  Is there a way to test it with a multimeter? Or maybe the fuel isn't flowing from the tank fast enough?

Edited by TB2Blazer
Missing info

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Hot start seal was replaced and and the crappy plastic nut was replaced with an aluminum one. I have checked for air leaks and can't find any.  I can't remember if I checked the slide seal or not but I just now bypassed the ACV (it looked perfectly fine) and disconnected the tps.  After doing that it made a big difference and doesn't backfire nearly as much but it's still having trouble idling and it's really hard to start. I'm going to play with the idle and see if that helps any. 

Edited by TB2Blazer

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Be sure your ACV delete was done right. There are several methods, a few of which require slow air jet changes.

Make one change at a time and test. Making multiple changes, you will have a much harder time diagnosing. You should reconnect the TPS and test it and confirm it is properly adjusted.

Also, confirm you have no exhaust system leaks., Hold a wet towel over the end of the muffler with the bike idling and listen for hissing. Stock muffler or an open pipe? Open pipes will back fire a lot. A muffler, well muffles.

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Have an 05 with same damn problem. Replaced everything i can think of that would cause this. I threw in the towel. Was working on this for a friend. 

Edited by strokemetwice

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I have stock muffler....already checked for exhaust leaks and replaced the copper gasket.  I cut a piece of inner tube and covered the small rubber o-ring on the air cut (done the same way I did it on all 4 carbs of my CB900C). I did try running it with the cps connected and disconnected and did not notice any difference. I know what you mean stroke......I have done absolutely everything I could possibly imagine and I'm about to push this thing off a bridge.  I have also replaced every single seal, jet, and gasket in the carb twice.  I've thrown a bunch of money and a shit load of time at it and I'm about to the breaking point.......I can honestly say I will never buy another carbeurated bike. 

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20 minutes ago, TB2Blazer said:

I have stock muffler....already checked for exhaust leaks and replaced the copper gasket.  I cut a piece of inner tube and covered the small rubber o-ring on the air cut (done the same way I did it on all 4 carbs of my CB900C). I did try running it with the cps connected and disconnected and did not notice any difference. I know what you mean stroke......I have done absolutely everything I could possibly imagine and I'm about to push this thing off a bridge.  I have also replaced every single seal, jet, and gasket in the carb twice.  I've thrown a bunch of money and a shit load of time at it and I'm about to the breaking point.......I can honestly say I will never buy another carbeurated bike. 

Carbed 2 strokes are great. Have a ouple and always run flawlessly. Carbed four strokes on the other hand should all be put to death. 

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I went through this exact same nightmare with my 2003 WR250F thinking it was a carb or timing issue. I have great respect for William1 but in this case he is dismissing your questioning about being an electrical issue. I spent an assload of money and time on the carb when all along it was the coil. I swapped the coil from my 2003 WR450F that is still sitting around unfixed due to cylinder head issues, and the coil is what the problem was the entire time. I posted my problem as a YouTube video and another guy that had the same problem on his YZ told me to replace the coil, he was right.

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I'm not saying the coil is the for-sure problem, William1 is a wise man that is quite knowledgeable, disregarding the coil when my situation has proven him wrong is an example of the situation. Search my profile and previous posts back in May of last year spreading the word of my scenario. See link below. DO NOT DISMISS THE COIL!  

 

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17 minutes ago, NateInRoundRockTX said:

I'm not saying the coil is the for-sure problem, William1 is a wise man that is quite knowledgeable, disregarding the coil when my situation has proven him wrong is an example of the situation. Search my profile and previous posts back in May of last year spreading the word of my scenario. See link below. DO NOT DISMISS THE COIL!  

For some reason, TT is not copying the link to view. Sorry.

 

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TB2blazer, did you ever figure out what the problem was? I am going through the same problem on my friends bike. luckily i have the same bike, so i am going to put my working carb on his bike this weekend to see what happens. hopefully that will narrow my search down a lot.

 

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After way too much time and money I just took it to a mechanic and after about a month they fixed it but I have no idea what they did. I never even asked them, by that time I was just glad to have it fixed.

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