[rog]

my 98 vmax 600 is reading 115 in one and 110 in the other. It runs great, but I'd like to see 120 and 120. what can or should I do

 

[magislander]

get your cylinders inspected,serviced if needed, new pistons,rings,pins,and bearings if they bad.you'll need gaskets too.

 

[mosabi]

115 and 110 is fairly good. If the sled runs good like you said I would not fix whats not broken. My 85 has 110 and 90 and it runs great.

 

[yamadad4]

i would suggest using a second comp tester for comparison. you may be surprised at the variance between gauges. also, the testing procedure can factor in a few pounds as well. engine hot? cold? etc.

depending on mileage and overall condition of the engine, as mosabi mentioned a fresh top end can help considerably. if the sled is fairly low miled and seems to be in good running condition and you are comfortable with the compression test, order a high altitude head gasket from your yamaha dealer. its a thinner gasket and will bump your compression up. it would any head gasket from the mtn specific twins.

the only downside to this is you will need to run premium fuel, min 91 octane. and i would always carry some octane boost if you frequently buy gas along the trailways.

 

[rog]

I will try another tester. It has 5100 miles so I'm assuming that the gasket swap might not be a good idea then?

 

[yamadad4]

at 5100 miles and if its never been rebuilt on the top end, your getting close to needing a freshen up anyway. your sled would probably go another couple thousand miles and still run good without a freshen up.

if you decide to to a top end rebuild you will need a new head gasket anyway. that would be the time to swap for the thinner one. or if you had to pull the head for any reason.just dont forget about the premium fuel.

do you know the history of your sled? has it ever had a top end done?

 

[smokingcrater]

what altitude? Barometric pressure can have a HUGE impact on compression results.