2004 sportster compression test

[fixin]

On a 947 Rotax,how do you do the compression test.Throttle all the way open,or closed.I get different results.
100 closed
125 open

 

[drtbikeril]

Either way, it seems kind of low. Each cylinder should be typically 3-5 psi within range of the other. I always do it with the throttle closed, granted their is enough oil in the cylinder to keep it lubed.

Is the engine warm or cold?

 

[jsp]

I've always been told to do it with the throttles wide open. Not for as a lubrication precaution. But then the engine can get the air needed to give accurate numbers.

But yes like said above. Those number seem quite low. Was there a reason you were doing the test? Engine lacking power or not running quite right?

 

[Robj]

Always do it with throttle wide open. Regarding the numbers, check the specs, because 125 is low for some engines, but not for others.

 

[fixin]

Cold engine.
Engine runs rough,sounds like it's missing.Only wants to get up to 5600 rpms.Also new plugs have like a white ash on them.
Wondering maybe head gasket?
cylinders are within 2 lbs of each other.

 

[Dr Honda]

You do the test on a cold engine... throttle open... and no extra oil in the cyl's.

A 951 engine should only be 135 PSI on a fresh rebuild. So... 125, is still OK.


White ash on the plugs isn't good. I'd pull the carbs and check them out. Also, you want to verify that there are no air leaks in the fuel system, and make sure your reed valves aren't broken.

Do you still have gray Tempo fuel lines?

 

[fixin]

Black lawrence ind. fuel lines.After google,I'm thinking the ash could be from the seadoo fuel cleaner/conditioner I put in it.
You said 951 engine,is that the same as 947 engine?

 

[Dr Honda]

.....

You said 951 engine,is that the same as 947 engine?

Yep.

We also call the 717cc engine the "720", and the 787cc engine the "800".

 

[fixin]

Any suggestions of were to go from here?

 

[Dr Honda]

Any suggestions of were to go from here?

Did you pull the carbs, and clean them yet? Did you look at the reed valves while you had the carbs off?