O7 rhino 660 runs good,then backfires and stalls.starts every crank,but will run short time then stalls.does not backfire everytime.seems like it runs longer when it sets couple of days.

make, model, year? backfires are spontaneous burning (exploding) of unburnt fuel outside of the combustion chamber. suspect bad spark plug/s, ignition coils, ignition timing, computer, leaking fuel injector, etc. scan for trouble codes, then post back. because the problem is intermittent, problem manifests only when hot (engine at operating temperature) do tests for both cold & hot conditions. test resistances (ohm) of suspected sensors: cam & crankshaft position sensors, ignition coils (if possible),(search the web for the recommended procedures). also test voltages at the computer (search the web for the pin outs of the computer of your car). also check associated relays (like for the fuel pump, etc.) a bad relay may have its coil open when heated, then becomes good again when cold. i suspect the car may have a good fuel delivery but the sparks are not coming in on demand, thus backfiring.

Cutting out at 32mph - Yamaha Rhino Forum - Rhino Forums.net

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If the unit runs normally after it starts it is probably a defective coil that isnt changing timing relative to crank speed. It is running advanced even at slow speeds and that is the backfire. You could also have a slightly bent flywheel key. This is what sets the primary timing so it is always a good idea to check it when you have the engine cover off!

The backfire could be a problem with the distributor cap or plug wires, or lack of fuel. The cap or wires could get damp and short out until the engine gets hot.
The fuel pressure could be low or not steady until the engine warms up.

Honda makes quite good gasoline motors. I doubt it is a valve timing issue but it might be a burned valve or a valve adjustment issue. What does after a while mean? A couple of minutes or 4 hours? Is it running for just a short while and then stops or it runs well for a long time and then stops?

I would guess fuel pump or filter, Tim

its the crank angle sensor not getting the proper voltage. put a 200amp booster on it and itll start right up.

I would carefully go over your wiring, especially any you may have disconnected during the head gasket swap, and check for a loose ground first.

If all your connections are good, then take a voltmeter to your battery, see what it's putting out. (If you can load test it, even better). Sometimes, when a battery get's messed up, it'll start overloading and put out too much power, and burn up fuses/wires.

when its hot and humid you could be having a ignition coil or cable problem.check cables and replace plugs, then take it from there. have your ignition coil tested also. backfiring is a sure sign of an ignition problem

Sounds like the EGR valve is bad.