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I have a 04 Polaris 500 ranger. Runs good for the first 10 minutes then lacks power after warm up????replaced fuel pump, new spark plug, not sure what to do next??
 

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So, good power when cold, lacks power when warm. Possibly carb issues, leaning out. When cold the engine get a richer mixture than when warm. Like Rangerwhit says carb cleaning, check fuel pressure/volume.
If that doesn't fix it it may be the engine is worn. Do a compression test cold then one warm. If you see a significant difference (lower compression when warm) that may well be the problem.
Cold and warm cylinder leak down test will provide a better diagnosis.
 

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Also check the coil, they like to fail when warm, look for carbon trails on it.
Also check the coil, they like to fail when warm, look for carbon trails on it.
cleaning
Thank you everyone for the help!! I checked all fuel lines, new pump, filter and cleaned carb. Machine runs the best it ever has but now only after removing and cleaning carb , runs good at initial test run then hour later it's back to choking out and blue smoke!! Really hate cleaning carb just to ride!
 

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Discussion Starter #7
Compression tests ok, a good carburetor cleaning fixes it until next time machine is driven,?? Very frustrating lol
 

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How is the carb getting dirty? Take tank off and clean it?


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Yep. If you haven't dumped the tank and wiped the bottom with a rag i would do so.
 

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Blue smoke is oil, 99% of the time. Fuel system problems shouldn't cause blue smoke. Rich conditions cause black smoke.
It may not be that carburetor cleaning is fixing the problem, but rather that when the engine is cold/cool, the oil hasn't thinned and/or metal internals of the engine haven't reached the temperature where oil makes it into the combustion chamber. It may be that running good after a cab cleaning is merely coincidence.
When was the last oil change? Oil may be thinned by fuel leaking into the crankcase when you initially had carb problems. Smell the oil, does it smell like gasoline?
Did you do your compression test with the engine warm and throttle fully open? Compression tests are not all that reliable as a measure of wear. Cold compression tests are less reliable.
A cylinder leak down test is a far better, more accurate test of cylinder sealing than a compression test.
When oil gets hot it gets thinner and may be making it past the valve guides if they are worn or the valve guide seals are bad. This will be more evident when accelerating after periods of idling or after deceleration using compression to brake. The latter causes a high vacuum condition in the combustion chamber and will pull oil past worn rings or valve guides/seals.
Fully warmed engines will open any cracks in cylinders/pistons if they are present and can allow oil to enter the cylinder. Higher engine temperatures also can increase clearances between the cylinder and piston and widen ring gaps.
Check your crankcase breather to be sure it is clean and operating properly. If it isn't oil can be drawn from the crankcase to the cylinder and burned.
If you are burning oil it should be evident on the spark plug. As soon as you see blue smoke shut down and pull the plug. Waiting until smoke clears up may allow the plug to self clean (burn of oil deposits) unless you are consuming a considerable quantity of oil.
 

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I have a 04 Polaris 500 ranger. Runs good for the first 10 minutes then lacks power after warm up????replaced fuel pump, new spark plug, not sure what to do next??
When was the last time the valve lash was checked/adjusted ?
 
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