I posted this in the tech forums but no replies hopefully someone here can clear up a few stupid questions I have!




1st of all don't flame me too bad! I am not very mechanically inclined but willing to try.

OK, so I am reading the manual on how to perform a compression test on a 2006 Heritage and it mentions a throttle plate. Specifically it states "with the throttle plate in the wide open position crank engine continuously 5 to 7 compression strokes"

Is that just holding the throttle wide open? I can't find a throttle plate in the manual? Sorry if this seems stupid to u but I would like some help here

Also can u do the test without opening up the throttle? I guess what I mean is what difference does it make

 

The throttle plater is the butterfly valve in the throat of the carburetor which controls the amount of air/fuel mixture entering the engine. The throttle is held wide open on the test to get the maxiumum amount of air in to the cylinder for a true reading. Also engine needs to be at operating temperature..

 

So, with the EFI u don't have that and just hold the throttle wide open i guess??

 

There is a throttle plate in a carburetor and also in the EFI throttle body. Yes, you hold the throttle wide open when tesing compression. Failure to hold the throttle open will result in lower readings, as muchas 10-15 psi. The motor does not have to be at operating temperature to test cranking compression; you can check it hot or cold. The hot readings may read a bit higher than the cold but not much.

 

Thanks for the info!

What kind of compression numbers should the bike get? Manual says anything over 90psi is fine but damn isn't that a low number? The bike doesn't have any motor work done so I am curious as to what I should expect?

 

+1 curios too. I suppose it depends how it was broke in.

 

Assuming motor is stokc and depending on mileage and the condition of the top end, you should see somewhere between 150psi and 160psi with not more than a 10% differential between the two cylinders.

 

Assuming motor is stock and depending on mileage and the condition of the top end, you should see somewhere between 150psi and 160psi with not more than a 10% differential between the two cylinders.

 

Thanks djl I appreciate the info. Hopefully I will be close to that when I try it later tonight.