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I got a 1998 gp1200 just rebuilt the engine (complete) 84.5 xpro"s I used a (riva) performance head (stock but modified to increase compression)Boat runs great ,I just decieded i would check compression to see where it was at.I got 115psi on all three cylinders.(snapon guage)I have looked down the cylinders with my bore scope ,cylinder walls look good.I only have about 15-20 hrs on engine.Got the gasket set from you.What do you think could be the cause for the low compression? too thick of a head gasket?I dont no thecc for the rive head ,but the combustion cambers were smaller than the stock ones.I know its a riva part but i cant get any help from them,they wont return my emails.Any ideas?
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Was the throttle open or closed? Battery fully charge to allow engine to crank at speed?***1100 Venture***<br />OE head mod-- by Riva Yamaha<br />Wiseco (+ .5mm)<br />True-welded crank<br />Riva F/A+ Jet kit<br />Boyeson Power reeds<br />Riva 1100 CDI<br />NGK plugs- BR8HS<br />R&D Aqua-Vein<br />Solas 14-21 Super Camber//Impros<br />Riva rideplate<br />Amsoil "AIO" @ 50:1 pre-mix, currently KLOTZ Ski-Craft<br />MOBIL-1 grease in the pump<br />Sears Diehard<br /><br /> Dream-meter shows 65---- GPS says 54.2 mph best, 9/14/02 @ 850 ft elevation -
There is only one gasket.
I suspect your gauge or testing method is faulty - verify with another gauge or have a shop do the test.SBT Tech Support is here to help with your problems.
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Replace the Scrader valve in the guage hose.Bill O'Neal WCM
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Double checked with a Matco gauge same readings ,Put a little oil in cylinder ,same readings.Im using one of your cranks and the xpros.Could their be a piston hight difference than stock this was not checked when motor was built.Im going to pull the head and look.But if i dont find anything how much can i shave this head ,Would like to come up with a psi around 140-150.I have heard you can seperate the head gasket to gain compression ,but that doesnt sound like the right way to do it.Oh battery is good and throtle was open when checking compression.Comment
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It's Pro-X, and I've never heard of them being that far off. What clearance and ring gap did you set it to?SBT Tech Support is here to help with your problems.
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