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weblex

Polaris Sportsman 500 '98 engine slows while opening throttle on idle

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Problem: The ATV starts and runs at idle perfectly. But as soon as I open the throttle, the engine starts to slow down until it stops. On the attached video you can hear the sound of how it works: see video below

Prehistory: there is a Polaris Sportsman 500 1998, which for about 1.5 years stood in repair, including also replacing CDI with one taken from the same ATV. Finally, the vehicles were on wheels, traveled several kilometers and overheated - forgot to fill the antifreeze :) Came back home in small moves. The next trip started well, but after 10 km there was a feeling of a small drop in power (even as the vehicle got warm completely) but still drives. Next trip - the situation is repeated. The next test of ATV through time and a huge loss of power from the very beginning. The engine sneezes, does not want to go more than 5 mph.

What has been done: the carburetor has been replaced with a new one (inexpensive, $ 40), a new spark plug, a new ignition coil, the engine head has been removed, the piston is in good condition, valves were corrected - but the problem was definitely not in them.

Ignition control unit is suspected. Who faced similar? Please help in solving the problem.
Thanks in advance.

 

 

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I would start by rebuilding the oem carb. Put that back on. The cheap carbs are shit.  Check the gap at the pick up coil as well as test the pick up coil.  How’s the fuel delivery system? Pump or gravity ? 

 

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Thanks for the answer. I will clarify: the situation with the eom carburetor was very similar, so I think this part can be ignored. Now the fuel goes through a pump from a plastic bottle - there is pressure, the fuel is constantly in the filter.
The situation is very similar to the fact that with an increase in engine speed, the ignition timing does not changes and the fuel explodes before it should, thereby stopping the engine. So yes, I will look now on the pickup coil, hope I had some old one somewhere.

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Have you tried giving it a little choke while the engine is dying, just to see what happens?

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Ok, I have checked the pickup coil's resistance and it was almost normal. Then connected the choke as it was disconnected while changing the carb and the picture started to change. On the fully opened choke the engine on idle works fine even on big rpm. Seem this is the problem - will try to configure carb's needle position little later.

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Ok guys, I finally defeated the problem and it was that after the overheating the exhaust camshaft was erased. Replacing the camshaft put Polaris back on its feet. Thank you all for your help!

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