I need help!

Pinkston120
Edited Date/Time 3/16/2015 3:04pm
So I have a 2012 kx250f...had one on the intake valves getting tight, soi replaced it. Put everything back together, shimmed it all out and now it won't start? What could be the issue? Any help will greatly be appreciated! Thanks
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markit
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Bogalusa, LA, USA
markit 3/15/2015 8:57pm
3/15/2015 8:57pm
Check your timming.
Pinkston120 3/16/2015 4:13am
3/16/2015 4:13am
I've done that. A buddy said my compression feels low. Could that be the problem?
MicMcDude375 3/16/2015 7:46am
3/16/2015 7:46am
Could be. You could have a valve slightly open. Was the valve you shimmed in acceptable range when you put it back together? And what was it before you shimmed it?
Pinkston120 3/16/2015 8:22am
3/16/2015 8:22am
When I replaced the valve, it was so tight I couldn't even get a .001 feeler in it And that was with the smallest shim I had in my kit from hot cams. So I replaced the valve and now I'm running both at .003.

The Shop

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Paw Paw 271
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Paw Paw 271 3/16/2015 8:47am
3/16/2015 8:47am
.003 is too tight. Re-Shim the valves to the correct clearance.
Did you have the valve seat cut when you replaced it? If not then I would suspect the new valve is leaking due to seat wear. The valves grow in length, but they also pound the seats and the need to be cut when a new valve is installed.

Paw Paw
Pinkston120 3/16/2015 1:47pm
3/16/2015 1:47pm
Shimmed to .15mm now. Valve seats are good. Still not firing. Think I'm going to just get a high compression piston and try that.
BobPA
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BobPA 3/16/2015 1:55pm
3/16/2015 1:55pm
Check for spark and make sure your cam timing is correct. There are a few marks on the flywheel so it is pretty easy to mess it up. They have a compression release built in so they don't have much compression when you're kicking.
mxtech1
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mxtech1 3/16/2015 2:09pm
3/16/2015 2:09pm
Pinkston120 wrote:
Shimmed to .15mm now. Valve seats are good. Still not firing. Think I'm going to just get a high compression piston and try that.
You can't do that and just assume a piston kit will fix it.

If timing, valves, spark, fuel, air, etc have all been ruled out, then your next step needs to be a compression test and a leakdown test to determine what exactly is causing the low compression.

If you were running the bike with zero clearance, there is no possible way that that valve seat doesn't have damage. You'll never get it to run right until you get the valve seats fixed. At a minimum, you should have at least lapped the new valve in the valve seat.

garagedog 3/16/2015 2:12pm
3/16/2015 2:12pm
Is it getting spark?

I bought a KXF that wouldn't start. The cam timing was off by 1 tooth. Triple check it.

Try pull/push starting it?
Pinkston120 3/16/2015 2:17pm
3/16/2015 2:17pm
I never ran it tight. The valve held gas with no leaks and I could see all 3 angles. I'm going to check the timing again
markit
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markit 3/16/2015 2:43pm
3/16/2015 2:43pm
Re
Jakes Dad
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Jakes Dad 3/16/2015 3:04pm
3/16/2015 3:04pm
Paw Paw 271 wrote:
.003 is too tight. Re-Shim the valves to the correct clearance. Did you have the valve seat cut when you replaced it? If not then I...
.003 is too tight. Re-Shim the valves to the correct clearance.
Did you have the valve seat cut when you replaced it? If not then I would suspect the new valve is leaking due to seat wear. The valves grow in length, but they also pound the seats and the need to be cut when a new valve is installed.

Paw Paw
Ding ding ding!
It's a give and take on both sides (valve & seat). Just one of the issues you have to accept running older 4 strokes. It's funny a few of my (4 stroke) buddies give me shit about maintenance on Jake's bike. But I don't have the money to change out bikes every 6 to 8 months like they do. So they hardly ever have those valve train issues.

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