Yamaha 150 performance

[brokenboat]

My Yamaha is a 1997 that was new in 1998. The compresseion in all 6 cyl. is 120psi. I changed the plugs to what Yamaha recommended (bh7) and it ran terrible. It kind of lopped throught RPM and never seemed to reach wot rpm. I put the bh8 ones back and the problem cleared up. This plug is what is recommended in the lower cowl I found. Was any damage done by using the bh7 plugs? What is the difference anyway?<br /><br />I have noticed what seems to be a loss of power or really WOT. I can't tell by the tachometer because it does not work properly. It is a Faria and they have replaced it 2 times. It will go to what I think is the proper rpm and then fall back to 3000 +-. No change in engine sound. I believe the pole setting is 5. I really don't like these Faria gauges so any thoughts on replacements is welcome. Does anyone know the top rpm for this motor? I don't know the propeller pitch, but the boat is a Cobia 206 sport deck. Motor is original and is steel prop.

 

[brokenboat]

Re: Yamaha 150 performance

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[metalmessiah]

Re: Yamaha 150 performance

if that is an ngk spark plug number then the bh7 is a hotter plug.did the motor seem to overheat when you ran it?that's the only problem I can see. I had some plug issues with a few Yamaha dirt bikes before. they never seemed to like running the reccommended plug, always one number hotter.I ran both bikes for years on a plug one step hotter than what the manual called for.