Does anybody know the correct procedure for checking compression on a Raptor?

The spec is 181psi but I am getting 90psi.

I think the reason for the low compression is the compression release but the service manual does not give any information about disabling the compression release before testing compression.

I am putting 45 RWhp to the ground out of a stock 660cc engine (pipe and carb mods only)so I would find it hard to believe that I have that much compression loss.

Any information would be appreciated.

 

The raptor has a centrifugal compression release. At low (starter assisted) RPMs the compression is released. As soon as the RPMs build there is full compression. From what I understand, a good fully charged battery is needed to get the RPMs high enough to dis-engage the release. I hear that if ya attach a battery charger to the battery for the compression check it will get the proper RPMs for the test.

Please let me know how it turns out -

 

Make sure the valves are properly adjusted,
Warm the engine up fully,
attach a battery charger to get it spinning fast enough to override the decompression device &
make sure you hold the throttle wide open when your cranking.
That should give you a correct reading.

If your getting 45 HP you should have plenty of compression.

Do not leave the battery charger on boost for a long period of time or you can fry the battery.

 

Thanks for the replies.

I'll give your suggestions a try.

I know that I did not have the throttle wide open when I checked it.

 

Holding the throttle open will make a big diffrence! Those puppies need to breath to get the right readings!