Kx450f backfire after rebuild

lambo609
Profile picture for user lambo609
Posts
3
Joined
11/3/2021
Location
Mays Landing, NJ, USA
lambo609
2017 kx450f Last weekend my bike died . Piston cracked down the middle . Replaced the piston today . Cylinder appeared to be good . Could still see cross hatching and there were no imperfections I could see or feel . After putting it all back together I went to start it and it fired right up two kicks no problem . It idkes and won’t die when I rev it but it backfires repeatedly and sounds terrible .
I’ve rebuilt more then a couple top ends . First time doing the kx450 but rebuilt the kx250f several times . Just looking for some insight . Fairly certain the timings good and I’m pretty sure it would not start right up if timing was off

Any suggestions would be much appreciated
|
Paw Paw 271
Profile picture for user Paw Paw 271
Posts
3632
Joined
4/3/2013
Location
Benton, LA, USA
Paw Paw 271 11/4/2021 7:09am
11/4/2021 7:09am
Did you replace the cam chain?
Have you check the fuel filter and pump for dirt?
Have you cleaned the injector?

PawPaw
1
kb228
Profile picture for user kb228
Posts
6153
Joined
1/31/2018
Location
Mansfield, OH, USA
kb228 11/4/2021 7:58am
11/4/2021 7:58am
Id look into an exhaust leak. Replace the copper gasket and check the connection to the muffler. It wont run if its 1 tooth off and as long as you didnt mix up your shims it should run the same as before.

Did you bump the tps by accident during disassembly?
1
lambo609
Profile picture for user lambo609
Posts
3
Joined
11/3/2021
Location
Mays Landing, NJ, USA
lambo609 11/4/2021 3:59pm
11/4/2021 3:59pm
kb228 wrote:
Id look into an exhaust leak. Replace the copper gasket and check the connection to the muffler. It wont run if its 1 tooth off and...
Id look into an exhaust leak. Replace the copper gasket and check the connection to the muffler. It wont run if its 1 tooth off and as long as you didnt mix up your shims it should run the same as before.

Did you bump the tps by accident during disassembly?
I was honestly thinking tps might be the issue. I don’t know if I knocked it or not to be honest . I know there pretty sensitive but I’m not to sure how to even troubleshoot one .
PK27RACING
Profile picture for user PK27RACING
Posts
118
Joined
10/22/2012
Location
Louisville, KY, USA
PK27RACING 11/5/2021 6:18pm
11/5/2021 6:18pm
Exhaust leak or valves. Do a leakdown test.

The Shop

See All »
hubbardmx50
Profile picture for user hubbardmx50
Posts
2837
Joined
11/17/2016
Location
Rancho Cucamonga, CA, USA
hubbardmx50 11/6/2021 10:34am
11/6/2021 10:34am
Made sure all connectors are plugged in? MAP sensor, air temp, water temp?
Grovesy98
Profile picture for user Grovesy98
Posts
246
Joined
10/14/2019
Location
GB
Grovesy98 11/6/2021 4:28pm
11/6/2021 4:28pm
I had a 18 KXF450 skip a tooth on the timing and it still ran, just popped and was a bit erratic. Turned out the cam chain was toast after only 30hrs
mshea397
Profile picture for user mshea397
Posts
161
Joined
12/18/2018
Location
Prior Lake, MN, USA
Fantasy
531st
mshea397 11/6/2021 6:36pm
11/6/2021 6:36pm
check the cam timing. i was a tooth off on my 2013 and it ran how you described.
Leeham
Profile picture for user Leeham
Posts
1160
Joined
10/29/2018
Location
Rochester, WA, USA
Leeham 11/8/2021 1:13pm
11/8/2021 1:13pm
Check timing and clearances. Make sure tensioner is working. Then after that maybe do leakdown and check connections.

Post a reply to: Kx450f backfire after rebuild