Hey guys, i am pretty new on this forum. Had a question I wonder if you can help me with:

I am loking at raptor (2003). It has a HOT CAM Stage 2, LTE exhaust. I want to check the compresion on it prior to purchasing.


Does anyone know what it should be at with these mods:

 

9.5-10.5:1 maybe. why do u need to know?

 

It the piston is stock, it should be 9.2:1. As far as PSI goes, I'm not sure.

-Brandon

 

Because I want to make sure she is running at her best before i buy the bike.

 

Thanks for the replies guys

 

if you mean you want to check by like putting a compression guage, i dont think you can do that accuratly because of the Auto-Decompression Mechinism. as for the compression ratio, that could be anyones guess, stock is 9.2:1 if hes running stock piston, but their are anywhere from 10.75:1 up to 14:1 on the market, 11:1 being the greatest compression for pump gas( 92octane). Only the owner knows if he installed an aftermarket piston.

 

Compression on a stock machine should be around 180psi. An engine with a lot of hours may show less, and the stage 2 hc could also slightly reduce the compression.

 

according to yamaha service manual, a stock machine at sea level has 181 psi with engine warm and throttle wide open while cranking with fully charged battery. range is from min. 149psi to 192 psi max. Like maddog said, the reading could be a little less with the aftermarket cam.