Compression Testing

[panici33]

I learned something interesting today from a Yoshi tech that I thought I might share with everyone...

I was asking about compression testing my quad with a high compression piston and whether there is a certain psi that I need to have with that type of piston. The manual for the LTR states that a stock compression test should read 114psi, nothing less. So my thinking was that I have to have a greater psi with the hcp...well I was wrong. The guy at Yoshi said because the bike has an automatic decompressioner (that thing on the exhaust cam), the hcp will not matter; if it's 114psi I am good.

By the way, I called JE Piston first and asked them the same question when I finally got to talk to a human being, and the gentlemen had no answer and referred me to Yoshimura.

[Jeremy]

Thats correct. Disable the decompresser somehow and try to start it. Your battery or leg will not be happy.

[ElderGeek]

Same thing on YFZs, Found that out when I was going to do a leakdown test.

Good Info!!

[l1tech]

Pretty much all 4 stroke quads have some sort of decompressor to bleed off compression so that they can spin fast enough to start, some are automatic adn some have to be set...Hondas up until 08 have decompressors that you manually adjust to set the cranking compression.

[l1tech]

Same thing on YFZs, Found that out when I was going to do a leakdown test.

Good Info!!

Should have no affect on a leakdown test as all the valves are closed

[ElderGeek]

I will need to confirm but I read or was told I had to manually disingage the comp release. It's due for a valve lash check this summer. I'll check it out then.

[Coondog #77]

I actually had to remove my auto decamp system on my 400ex when I changed to the hot cam. There was a plunger with a spring. Just pulled it out. Couldn't tell you if the psi went up but it started just fine