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2000 Polaris Sportsman 500 Backfire Only No Start
Good evening! I have a 2000 sportsman 500 that will only backfire out the intake and will not run. i have put a cam and rockers in it, as the old rockers wore a groove from the decompression hall. Motor shows 120 PSI with the new cam (i feel like this is high). The motor does have spark. It doesn’t seem to want to do anything but throw a fireball out the intake. It’s my first polaris quad and i’m not sure where to go now. Any help is appreciated!
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Timing way off?Good evening! I have a 2000 sportsman 500 that will only backfire out the intake and will not run. i have put a cam and rockers in it, as the old rockers wore a groove from the decompression hall. Motor shows 120 PSI with the new cam (i feel like this is high). The motor does have spark. It doesn’t seem to want to do anything but throw a fireball out the intake. It’s my first polaris quad and i’m not sure where to go now. Any help is appreciated!
Checked and double checked and i also had a screwdriver in the plug hole to verify TDC.Timing way off?
TDC will happen twice, compression and exhaust. You might be off 180* with timing.
So it matters what stroke you set TDC? Which would it be then, compression or exhaust stroke? I thought TDC was TDC was TDC.TDC will happen twice, compression and exhaust. You might be off 180* with timing.
Also if timing was 180 off, wouldn’t i have poor compression?TDC will happen twice, compression and exhaust. You might be off 180* with timing.
Example:
- Intake: Also known as induction or suction. This stroke of the piston begins at top dead center (T.D.C.) and ends at bottom dead center (B.D.C.). In this stroke the intake valve must be in the open position while the piston pulls an air-fuel mixture into the cylinder by producing a partial vacuum (negative pressure) in the cylinder through its downward motion.
- Compression: This stroke begins at B.D.C, or just at the end of the suction stroke, and ends at T.D.C. In this stroke the piston compresses the air-fuel mixture in preparation for ignition during the power stroke (below). Both the intake and exhaust valves are closed during this stage.
- Combustion: Also known as power or ignition. This is the start of the second revolution of the four stroke cycle. At this point the crankshaft has completed a full 360 degree revolution. While the piston is at T.D.C. (the end of the compression stroke) the compressed air-fuel mixture is ignited by a spark plug (in a gasoline engine) or by heat generated by high compression (diesel engines), forcefully returning the piston to B.D.C. This stroke produces mechanical work from the engine to turn the crankshaft.
- Exhaust: Also known as outlet. During the exhaust stroke, the piston, once again, returns from B.D.C. to T.D.C. while the exhaust valve is open. This action expels the spent air-fuel mixture through the exhaust port.
Yeah i knew the strokes and what their purposes were, and i’ve set timing before on other quads and never had an issue. Also, when i bought this quad it had the same backfiring problem.Example:
- Intake: Also known as induction or suction. This stroke of the piston begins at top dead center (T.D.C.) and ends at bottom dead center (B.D.C.). In this stroke the intake valve must be in the open position while the piston pulls an air-fuel mixture into the cylinder by producing a partial vacuum (negative pressure) in the cylinder through its downward motion.
- Compression: This stroke begins at B.D.C, or just at the end of the suction stroke, and ends at T.D.C. In this stroke the piston compresses the air-fuel mixture in preparation for ignition during the power stroke (below). Both the intake and exhaust valves are closed during this stage.
- Combustion: Also known as power or ignition. This is the start of the second revolution of the four stroke cycle. At this point the crankshaft has completed a full 360 degree revolution. While the piston is at T.D.C. (the end of the compression stroke) the compressed air-fuel mixture is ignited by a spark plug (in a gasoline engine) or by heat generated by high compression (diesel engines), forcefully returning the piston to B.D.C. This stroke produces mechanical work from the engine to turn the crankshaft.
- Exhaust: Also known as outlet. During the exhaust stroke, the piston, once again, returns from B.D.C. to T.D.C. while the exhaust valve is open. This action expels the spent air-fuel mixture through the exhaust port.
Spark timing is set by the flywheel - a sheared fly wheel key will cause improper spark timing even if the cam timing is correct, but if you set the cam using flywheel marks without verifying that the TDC mark coincided with the position of the piston
Checked and the flywheel is correct with the strokeSpark timing is set by the flywheel - a sheared fly wheel key will cause improper spark timing even if the cam timing is correct, but if you set the cam using flywheel marks without verifying that the TDC mark coincided with the position of the piston
Sooo i checked it all over and spun the timing 180 and tried there and i’m having the same issue. It wont even fire if i put starting fluid directly down the spark plug hole. Compression reads 130 and i know there is good blue spark.
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