kx250f 2008 massive backfires

Gohard
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AU
Gohard
hello,
so im not one to post of forums often but this time im really stumped

ive recently purchased a kx250f 2008 that has been sitting for a long time, i decided to clean the carb change the fuel and do a full service, ever since i have got it has had a massive backfire issue ive played with the mixture screw with 2 1/2 and 3 turn etc and it doesn't help much if any also i checked the valve clearances and everything is in spec, and very very rarely when kicking it over the kickstart will become solid but after abit of constant pressure she will kick over and that wont happen again for a while but will repeat

so im pretty much stumped for the moment if anyone has any suggestions im all ears CHEERS!

also (stock exhaust) and new filter
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omalley
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Snohomish, WA US
omalley 6/27/2020 10:09pm
6/27/2020 10:09pm
Check orientation of the floating plate on the carb slide. It’s easy to put it in upside down. If you do, the bike will start and run but backfire like crazy. Hard to explain, but it actually looks correct when it’s upside down (shape compared to the slide),
Gohard
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AU
Gohard 6/28/2020 1:33am
6/28/2020 1:33am
omalley wrote:
Check orientation of the floating plate on the carb slide. It’s easy to put it in upside down. If you do, the bike will start and...
Check orientation of the floating plate on the carb slide. It’s easy to put it in upside down. If you do, the bike will start and run but backfire like crazy. Hard to explain, but it actually looks correct when it’s upside down (shape compared to the slide),
ill have a look at that asap, but a backfire issue definitely would come from a carb issue and not a mechanical problem
Paw Paw
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Benton, LA US
Paw Paw 6/28/2020 5:37am
6/28/2020 5:37am
Bad exhaust gasket or seal at pipe to head will cause this.
A lean pilot jet or clogged pilot jet will cause this.
A worn cam chain will cause all the issued have stated.

Paw Paw
omalley
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omalley 6/28/2020 7:09am
6/28/2020 7:09am
omalley wrote:
Check orientation of the floating plate on the carb slide. It’s easy to put it in upside down. If you do, the bike will start and...
Check orientation of the floating plate on the carb slide. It’s easy to put it in upside down. If you do, the bike will start and run but backfire like crazy. Hard to explain, but it actually looks correct when it’s upside down (shape compared to the slide),
Gohard wrote:
ill have a look at that asap, but a backfire issue definitely would come from a carb issue and not a mechanical problem
If you’re talking about a single backfire while trying to start, then no. If you’re talking about popping and backfiring while running, it absolutely can come from mechanical issues. Including the floating plate. Been there, done that. Had my carb apart 5+ times before I found it years ago.

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