kx125412

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Mar 30, 2006
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Please don't put this in the mini forum I just never get answers there. Two minutes ago my brother had his bike warming up just setting the idle and stuff not really doing anything and he shuts it off. I check the plug because its been running rich, and its oily and black. But it ran two seconds ago so he goes to start and PFT, it backfires and a bunch of white exhaust comes out of the pipe. Being too rich couldn't cause this sudden backfiring could it? I tried starting it a couple times and the same pop happened.
 

kx125412

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Mar 30, 2006
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I don't thinks its that because we got this bike back in december I think. And riding around the backyard slow and spinning in the snow and it still started. We had it out last weekend and my brother was just going slow second gear on the road since it was his first bike, again still starting fine. Just today it decided to backfire and not start.
 

slowgsxr97

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Feb 24, 2007
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Thats what my 04 predator did. running fine, then the next weekend it wouldnt start and backfired...turned out the intake valves were tight. I adjusted them and started and ran perfect.
 

kx125412

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Mar 30, 2006
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Could it be its getting way to much fuel into the cylinder. It backfired again today and sprayed the shop door.


This is why I hate 4-strokes :|
 

Ol'89r

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kx125412 said:
Could it be its getting way to much fuel into the cylinder. It backfired again today and sprayed the shop door.
This is why I hate 4-strokes :|



This is why 4-strokes are getting such a bad name. People are either too lazy or too freekin stupid to check the obvious. :whoa: CHECK YOUR DAMN VALVES. :bang:

Or, I guess you could continue to run it until you hear the answer that you are looking for or do damage to your engine. Then you can come back and tell us how much 4-strokes suck. :yell:
 

slowgsxr97

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Feb 24, 2007
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kx125412 said:
Could it be its getting way to much fuel into the cylinder. It backfired again today and sprayed the shop door.


This is why I hate 4-strokes :|

If your not sure how to check the valves, Learn, or pay someone who does. You will be tons of money ahead in the long wrong. :nod:
 

TimberPig

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Jan 19, 2006
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slowgsxr97 said:
If your not sure how to check the valves, Learn, or pay someone who does. You will be tons of money ahead in the long wrong. :nod:

Exactly, setting the valves on an XR is probably about the easiest you're going to get. No shims to mess with, just good old rocker tappets, with screw and locknut adjusters. Can't get much simpler than that. TDC, check the clearance (2 thousandths of an inch I believe) on the intake, repeat on the exhaust, and adjust as required.
 

Patman

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kx125412 said:
Please don't put this in the mini forum I just never get answers there.
Or perhaps you get an answer but it's not the one you want to hear? Look Spanky your answer is here.
Ol'89r said:
People are either too lazy or too freekin stupid to check the obvious. :whoa: CHECK YOUR DAMN VALVES.
And if you would have posted this in the mini forum I would have posted the same thing with the little tidbit that the neighbor kid had exactly the same problem you describe on his XR80 which I fixed by ADJUSTING THE VALVES on his bike. The process took me 30 minutes because I also pulled his carb and cleaned it.
 

kx125412

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Whoaa alright how do I go about settting the valves the only 4 stroke experience I have is tearing down a briggs and stratton lawn mower.
 

Patman

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I'll post the XR80 proceedure & specs when my son and I get back from riding, if I don't forget ;)
 

Ol'89r

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kx125412 said:
Whoaa alright how do I go about settting the valves QUOTE]

Remove the spark plug, the valve cover caps and the dyno cover. Rotate the engine until both valves open and close and the piston comes up to top dead center. (TDC). Take a small screwdriver and carefully put it in the spark plug hole and feel the piston come up to TDC. Check on the side of the flywheel and there should be a line marked 'T'. When you feel the piston at TDC the 'T' line should line up with the pointer on the case.

At this point, both valves should be closed and both rocker arms should have clearance. Take a feeler gauge and check between the rocker arm and the top of the valve. There should be .002 thousands clearance on the intake valve and .003 on the exhaust. If the clearance is not correct, loosen the lock nut on the adjuster screw and re-adjust the clearance. Tighten the lock nut and recheck the clearance. If everything checks ok, reassemble the engine and fire it up.

It's a good idea to purchase a service manual. It will give you the specs and explain in detail how to do these things.

Tight valves may not be the problem but it is necessary to check certain things first before troubleshooting other problems. If the valves are tight, your engine won't run right no matter what else you do.

Patman.
I did this out of memory :yikes: so, could you check your manual and verify the specs.
 

TimberPig

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Jan 19, 2006
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Ol'89r said:
kx125412 said:
Whoaa alright how do I go about settting the valves QUOTE]

Remove the spark plug, the valve cover caps and the dyno cover. Rotate the engine until both valves open and close and the piston comes up to top dead center. (TDC). Take a small screwdriver and carefully put it in the spark plug hole and feel the piston come up to TDC. Check on the side of the flywheel and there should be a line marked 'T'. When you feel the piston at TDC the 'T' line should line up with the pointer on the case.

At this point, both valves should be closed and both rocker arms should have clearance. Take a feeler gauge and check between the rocker arm and the top of the valve. There should be .002 thousands clearance on the intake valve and .003 on the exhaust. If the clearance is not correct, loosen the lock nut on the adjuster screw and re-adjust the clearance. Tighten the lock nut and recheck the clearance. If everything checks ok, reassemble the engine and fire it up.

It's a good idea to purchase a service manual. It will give you the specs and explain in detail how to do these things.

Tight valves may not be the problem but it is necessary to check certain things first before troubleshooting other problems. If the valves are tight, your engine won't run right no matter what else you do.

Patman.
I did this out of memory :yikes: so, could you check your manual and verify the specs.


Other than the valve cover being removed as a unit (no caps on the XR/XL 75-100's), that is pretty much straight from the manual.
 

Patman

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Ol'89r said:
kx125412 said:
Patman.
I did this out of memory :yikes: so, could you check your manual and verify the specs.
yeah the specs are dead on Terry. i'm one handing it right now so your post saved me a lot of pecking. :cool:
 

kx125412

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Mar 30, 2006
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So does it matter what stroke its on or it just has to be TDC? Also, the only reason I was asking other questions was I wanted to eliminate some other things before digging into the engine. I know this isn't a big deal to you guys but i'm used to two strokes and the simplicity of it all.
 

TimberPig

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Jan 19, 2006
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kx125412 said:
So does it matter what stroke its on or it just has to be TDC? Also, the only reason I was asking other questions was I wanted to eliminate some other things before digging into the engine. I know this isn't a big deal to you guys but i'm used to two strokes and the simplicity of it all.

TDC on the compression stroke. If you time at TDC anywhere else, you'll be way off. If the valves are depressed, it isn't TDC on the compression stroke.

You really are a clueless 2 stroke man when it comes to 4 strokes, because XR's are almost as simple as a 2 stroke. There is very little to making them go, beyond that in a 2 stroke.
 

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