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Discussion Starter · #1 ·
Yay! Nov 1 and was out riding today not bad for 1st of the year.
I have a 93 AC Mountain Cat 700 EFI and it has started to backfire. New plugs, new gas, gas line antifreeze added. It starts and runs fine but starts to backfire once in a while when I'm cruising at 60-70.

Any ideas of where I should start to look?
 

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I would throw a differnt set of plugs in it just to be sure you dont have a faulty spark plug. I would guess the cylinder miss fires (doesnt fire) and then pushes that air fuel mix into the pipe, then when the other cylinder fires, it sends the nice hot exhaust gasses into the pipe which will ignite the unburned mix from the other cylinder causing what you think is the backfire. I've had this happen on my Triumph more than once.
 

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^^I have also had this happen on my old 500. Change the plugs and see what happens.
 

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Unless your compression is low, dont worry about the rings. Backfiring out the exhaust has more to do with incorrect timing, fouled plugs, than it does with rings. If it were backfiring out the intake then rings would be a possibility, but highly doubtful.
 

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Inspect those cables as well, you may have a cracked or worn one. That would cause a misfire now and then.
 

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Discussion Starter · #11 ·
Hopefully getting close to the problem. Changed plugs and wires - no change.Brought it in to Cat dealer to get a diagnostic done. Compression 115 in both cylinders - was told a little low, but should be OK. Backfiring probably caused by the micro-switch in the throttle - cutting engine in and out. Waiting for a bypass plug before I replace the whole throttle switch ($5 vs $80). That will tell me if it is the switch or not. Here's hoping!
 
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