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yamaha vmax 200 HPDI compression

Kubota guy

New member
I have a Yamaha Vmax 200 HPDI outboard. Wondering what the compression should be on it? I am getting
between 90 and 95 psi per cylinder. This seems low to me but the motor seems to run ok other then a slight miss.
 
If all cylinders are equal, it is fine.

Slight miss is also acceptable, these engines run like normal 2-stroke engines (not as a E-tec or a 4-stroke).

You could install new spark plugs and decarbonize the engine with Engine Tuner (Evinrude)/Power Tuner (Mercury), that could help a lot if carbon is the issue.
 
120 is better. If you aren't running Yamaha RING FREE I would start. Possibly even do a shock treatment. Those motors run on 4 cylinders in neutral so that may be your miss but otherwise throughout the rpm range you should not be missing unless there is a problem. You may have some intermittent spark plug bridging when you start with the ring free but that should clear up as the motor cleans up.
 
Super low compression unit. I have a pair on my 28 Bertram. The only thing that is high pressure on a HPDI is the fuel rail pressure. Thanks Martin Yes PRBMAN is correct with his ring free. I would also be running Seafoam, your unit will loveit and you cannot overdose it.
 
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