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Discussion Starter #1
The machine is a 2000 Grizzly. Stopped running one day and tracked it to the CDI. Bought a used one (as the eBay/ amazon ones did NOT work). Plugged it in, started right up, idled excellently. As soon as I got to 1/3 throttle all the way to wide open, it pops through the carb. There’s no back firing through the exhaust... it’s all through the carb. I’ve changed jets, needle height, float... sprayed starting fluid around the carb testing for vacuum leaks,everything. Timing mark corresponds to TDC. Valves were adjusted to factory specs, replaced the coil.
could it be the CDI? It almost is like hitting a rev limiter... this damn thing is driving me nuts!!!!
Thank you!
 

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Welcome from Colorado.
Did you find t.d.c. and with the straw down the plug hole trick rock the crank back and forth to check for slack in the timing chain?
At t.d.c. if you feel the straw move with the slightest turn on the crank nut the rocker arm should move and the lash change.
 

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Discussion Starter #3
Thanks for the welcome, Jim! If timing was off, wouldn’t idle quality be off? It’s strange... if I start it, let it run for a minute and then go direct to wide open throttle, it revs right up correctly to high RPM, then, almost immediately, it then begins to pop through the carb and seems like it goes into limp mode misfiring, popping, etc. If I let it idle for another minute, I can open it up again and it does the same thing....
 

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If there is a slack timing chain the engine will not be consistent, and checking the chain is not something that requires anything to be altered. I don't know how little a chain needs to stretch to affect timing, but rocking the crank a few degrees lets you see how sensitive these thing are when right. Any slack can prevent the valve from closing thus the pop back through the intake.
As for a rev limiter failure, ground it and see what happens. Then if you want that feature replace it. As it go to high r.p.m. I don't think this is your problem.
Another thing, when adjusting the valves did you use an angled feeler gauge? A straight one tends to prevent proper setting for the thickness used. I set my valves to the wide side of the range.
 

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Discussion Starter #5
Looked at everything today. Timing marks all lined up with TDC. Valves were within the factory specs. Honestly, I don't know what else it could be. Maybe it's the CDI.
 

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You started this discussion with a used cdi, and as your bike will go to high engine r.p.m.'s I'm thinking you have another bad cdi. Its lime the engine vibrations cause it to fail, a rev-limiter would prevent it from ever getting to high r.p.m.'s.
You said you determined the old one was bad, do you have a f.s.m. with valves to check?
One thing I've never thought about is when the rev limiter is working to de-tune the engine does it advance or retard the timing?
I would think it retards the timing so the engine does not fire on the compression side of the stroke, like your bike is doing with fire back through the intake.
As you do have fire, just not in time, this problem is different than the bike just cutting off. (the reason for the replacement cdi.)
A stretched chain will retard timing, did you do the straw down the plug hole trick to confirm t.d.c., to then see how the valves where timed to the crank?
 
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