If I do a compression test what should the meter read? 01 Yamaha Raptor

 

[img]i/expressions/face-icon-small-confused.gif[/img] Leak down & commpression are 2 compleatly diffrent things.[img]i/expressions/face-icon-small-blush.gif[/img]You don't say how old your Quad is but from the pic above your name I am guessing it's a raptor.

On a new Raptor the leak down should be less than 5% over 10% & you may have problems. It could be anything from a too tight valve to worn rings or a burnt valve. If your leak down is too high listen to the exaust, intake & crankcase vent to hear where the air is leaking past. If it's coming out the exaust check exaust valves, If you can hear it in the airbox check the intake valves, if you hear air leaking through the crank caes breather hose check rings & cylinder.

Compression on a new Raptor With 9.5 to 1 compression should be around 150 LBS, 100 LBS or lower may mean the same probs as above. Rember to hold the throttle wide open when cranking to get proper compression.

All these numbers are aproximate I haven't done a leak down or compression on my Raptor But have done many on race cars. If you think your getting a bad reading check with someone who has done this on a Raptor.

 

The Raptor has an internal RPM activated decompression device and you can not check compression by turning it over with the starter. You will only get about 85psi when doing it this way. Not sure why you are checking compression but the intake valves will tighten on a Raptor causing low compression and loss of power!!. This is a very common problem. Hope this helps.

 

wow i took my raptor in to a local shop here in town and had them check some things, one was a compression test, they called me back saying i only got 80-85 psi. if that " would be the right compression" i'm going to be pissed cause i just paid 160 buck to redo my valves

so 2strokeDiehard how do you do a correct compression test on the raptor ???

 

disturbed660: I'd be disturbed too! Was it a yamaha shop? If so go back & politly raise HE!! they should have known better!2strokediehard: would the decompression device also give a false reading on a leakdown test?

 

Just need to be sure the valves are closed, Its an extra pin that pops out on the cam. It is out until a certain RPM is reached.

You would have to spin the motor over I think 800-900 RPM to get an accurate reading. only way to really do it I guess is to tow it down the road and let the clutch out while in gear for a moment to get a reading. Not a very "high tech" way but short of a high speed external starter only way to do it I guess.

Did that shop just adjust the valves or reseat them? They probable were out of adjustment if there was many hours on it. But I would be hesitant to go back!

 

when doing a compression test on a stock raptor you should get a reading of 181 psi at sea level w/ a min of 149psi at sea level & max of 192psi at sea level on a stock bike.yes you will only get a reading of about 85psi if you dont do it right.first ground plug lead when cranking,make sure battery is at full charge,then crank over engine w/electric starter w/ throotle fully open until reading on gauge stabilizes this will overide the decompression unit on the cam to give you an accurate reading of about 180psi at sea level.To disturbed660 i would change shops asap cause they dont know how to work on bikes

 

Not related to Raptors - but should all compression tests on 4 strokes or two strokes be done with the throttle fulley open? Isnt this a "wet" test? Only did cars before now so I'm curious. Just tested my 350x and was pretty disapointed. Shop did it in Nov. and said it was 245 (12:1 piston)just did it myself with foot crank and only got 120. I have reason to suspect a problem which is why I am testing it, Would like to hear back.

 

I was wondering if it will still work on a Raptor that is not stock, and I'm not at sea level. I have it jetted, Uni foam air filter, White Bro's E-series pipe. Thanks

 

hckycoach: Yes all compression tests should be done with the throttle wide open. You must let enough air in to fill the cyl to get an accurate reading. If you don't it can make a large diffrence.

smith31 it should work on a mod quad.