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Post by kingster on Oct 18, 2014 20:50:46 GMT -5
hey guys my cn250 is backfiring through the carburetor. I have been readjusting my valves and timing all day. whats causing this? i set piston to tdc compression stroke, then adjust valves but im still getting backfire in the carb. i also have the camshaft lined up evenly with the head. The hole in the camshaft is on top with the A on the bottom.
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Post by alleyoop on Oct 18, 2014 21:00:25 GMT -5
You sure your header pipe flange is not leaking? To backfire like that you either have a bad air leak or it is out of time. Badly adjusted valves would not cause backfiring like that. So check for leaks, put up a picture of the carb area if you can.
Check you exhaust pipeing especially where it connects to the motor that is where it would suck in a lot of air and backfire on you.
Alleyoop
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Post by kingster on Oct 18, 2014 21:34:41 GMT -5
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Post by alleyoop on Oct 18, 2014 22:01:01 GMT -5
I see it has what they call a performance carb(which is one with a pumper) and it looks like it has not been used for a while.
The throttle control wheel has not seen a cable attached to it for a while.
Have you checked the timing? the valve setting looks fine but it could be out of time. So bring it up like you did with the screw driver in the plug hole and then check the timing mark on the flywheel to see if it is timed right or if it is out of time for some reason.
Alleyoop'
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Post by kingster on Oct 19, 2014 9:47:46 GMT -5
i went back out and checked the timing again this morning and im still getting backfire, so i took the head off to check the valves. i poured gas through each port and the exhaust and intake valve is leaking gas. so if its leaking gas then i know its leaking air when the engine is trying to crank. could that be the problem?
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Post by alleyoop on Oct 19, 2014 11:34:19 GMT -5
Yes, it will suck in gas and as it is coming up on the compression stroke it is blowing some of the gas past the valve back into the intake and carb.
Alleyoop
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Post by kingster on Oct 19, 2014 11:49:27 GMT -5
thanks for your response, I knew my timing was correct. so do I need to relap the valves or replace them, as they shouldn't be bent. the engine has never jumped time.
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Post by alleyoop on Oct 19, 2014 11:58:54 GMT -5
Try relaping them and check to make sure they seal if not then either get a new head or valves.
Alleyoop
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Post by urbanmadness on Oct 19, 2014 15:13:58 GMT -5
I was thinking leaking intake valve..... but that's rare on these bikes unless you bent the intake valve for some reason or it's sticking....
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Post by kingster on Oct 20, 2014 10:31:03 GMT -5
yea both intake and exhaust valve were leaking. they are not bent, they just wont seat well after I relaped them. so I ordered a new pair hopefully they will seat.
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Post by alleyoop on Oct 20, 2014 12:31:59 GMT -5
Good luck hope that fixes it and it cranks right up.
Alleyoop
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Post by kingster on Oct 23, 2014 19:58:55 GMT -5
hey guys just an update I installed my new valves(lapped them) and now I get backfire through the exhaust with a flame and the backfire is loud!!!!
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Post by alleyoop on Oct 23, 2014 20:44:11 GMT -5
Well now it is leaking where it attachs to the head, That is a very common cause , did you put in a new exhaust gasket?
Alleyoop
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Post by kingster on Oct 23, 2014 20:50:15 GMT -5
no I don't have an gasket there. I just tightened the exhaust bolt.
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Post by alleyoop on Oct 23, 2014 20:52:37 GMT -5
There is you problem.
Alleyoop
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..BAD TO THE BONE..
