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Help! '05 Ranger 500 carb engine with too much compression?

This is a discussion on Help! '05 Ranger 500 carb engine with too much compression? within the Ranger Problems & Solutions forums, part of the Polaris Ranger Forums category; Last night I pulled the rocker assembly and found that there is a small groove in the exhaust rocker from the decompressor ball. So that ...

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Thread: Help! '05 Ranger 500 carb engine with too much compression?

  1. #21
    Starting Member wrench's Avatar
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    Last night I pulled the rocker assembly and found that there is a small groove in the exhaust rocker from the decompressor ball. So that explains the high compression at start (180psi checked with 2 different gauges). I didn't find anything in the manual about compression without the decompressor operating. So it is hard to see if having too much compressor when running is the issue, but 180psi seem pretty high for a low performance 4 stroke.

    I also moved the cam 1 pin forward last night, the dowel on the cam seems to be more in line with the crank now and the 2 punch marks on the cam gear are at the top. It is hard for me to believe that there is no reference marks on the block or head for aligning center line of the crank or to reference cam gear location. Most 4 strokes I have rebuilt, you set the piston at tdc then make sure the cam lobes are up or down depending on tappet or rocker style, then you align the punch marks on the cam gear(s) with the top of the head. Simple as that. This you have have to look at an angle because of how the engine is mounted, then you have to draw an imaginary line with the center of the crank that you can't see unless you pull the flywheel cover off.....

    What is this I have read about priming the oil pump? Is that really necessary? I did not do that. There is definitely oil getting to the valve train.

    I checked the exhaust last night, it is clear.

    It has a new spark plug. How do these CV carbs work? I wonder if it isn't getting vacuum to open the slide and allow fuel flow?

    Again, other than smoking badly, this thing ran good before rebuild.

  2. #22
    (Steve) 1000+ Member pyromedic's Avatar
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    If it was running good prior to rebuild (other than smoking), and you haven't done anything to the carbs it doesn't make sense that the carbs are the problem. CV carbs work pretty much like any other carb except that as the throttle valve is opened vacuum is applied to a chamber above the slide to open the slide and provide fuel/air mixture to the engine. The advantage of CV carbs is that they automatically adjust for altitude changes. Mixture adjustments are made pretty much the same way they are in all slide valve type carburetors.

    If the carbs are in good operating condition and the slides are not opening it's because there is insufficient vacuum to open them.

    I am not familiar with your specific engine. Is there a way to adjust ignition timing? Retarded ignition timing will cause low vacuum.

    IMHO, something is amiss with the reassembly. Perhaps something to do with ignition timing. Unfortunately, since I have no experience with this specific engine I cannot be of much help. Perhaps careful re-reading of the manual or someone on the Forum with expertise will come to the rescue.
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  3. #23
    1000+ Member Rangerwhit's Avatar
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    This video might help...

    wrench likes this.
    2007 Ranger 500 (Carb)

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  5. #24
    Starting Member wrench's Avatar
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    Thank you, all I did to the carb was pull the bowl off and clean the jets and put it back together. The pilot screw is plugged so i can't make adjustments there, and also shouldn't need it.

    I have no idea what to check next.

  6. #25
    1000+ Member Rangerwhit's Avatar
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    You check the vent line to atmosphere, diaphragm and slide/needle? I had to use needle nose vice grips to remove screws on diaphram. Drilled a small hole in brass plug and used a screw to pull out plug on pilot. A good cleaning and inspection is where I would be going at this point.
    2007 Ranger 500 (Carb)

  7. #26
    Starting Member wrench's Avatar
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    Yes, I have had the diaphragm out, got the screws out with my impact driver. Pilot should only effect idle and low rpm range though. And again, it ran fine before rebuild. The high compression is what's throwing me. Seems like the thing is just pinging and can't make any power. I have cleaned the carb and jets.

  8. #27
    (Rock) 1000+ Member rocknroll's Avatar
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    Does it run any differently after you changed the cam timing?

  9. #28
    Starting Member wrench's Avatar
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    No sir, it does not.

  10. #29
    RJ
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    (Rod) Elite Member RJ's Avatar
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    Is it a the 2x4 or 4x4?
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  11. #30
    Starting Member wrench's Avatar
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    It is a 4x4 ranger 500 carb

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