if you raise the sleeve,and it loses too much torque to reliably launch the boat, you can drop the sleeve back down. if you cut the exhaust higher and it loses to much torque, then you buy a new piston and liner. i'd probably try the shim first. sometimes the only way to know for shure is to try something. also, if you put too many shims under the liner, you can lose the fit,and torque. you can sometimes get the fit back by squeezing the liner or by re grooving the piston. another thing to rember is to maintain the head clearance at about .006. also check your head volume and compression ratio. the little motors need 10 to 1 or a little higher to make good torque. if your volume is too high, cut the head down to raise the compression ratio,then raise the sleeve, and i would grind the top of the case ports, if the're showing up in the port windows. use a hot plug, like a 1L, and don't over cool. sometimes running water will put the fire out. sometimes these things are as hard to set up as a cup car.
what pipe are you running on your 12 boat martin? i am using the mac 2.5 pipe and want to try something else to get some more speed outta it and maybe more torque? i am using a os 12 5 port tz.. thanks
terry
terry,
i am running any browns 12 pipe right now, glenn quarles has a nice one also..
steve,
head clearance is .006, and running temps about 180, i tried it with water cooling it definently put the fire out..using odonnel 89 plugs in it now they sem to work well..i think first i will fix the case ports and see where that gets me..im not having any problems with torque right now and its been pretty hot out..compression ratio is 10.5 the fit is also still tight, i raised the liner before running it in..
basicly if i raise just the exhaust or the whole liner im going to lose some torque correct? but which do you think will get me more rpm ? or is the rpm tied mostly to just the exhaust timing?
what are considered high timing #s for these little motors..are they close to 21 numbers?
next question is the rotor timing on this motor, the duration is 201 with it closing at 57 , im sure this is hurting top end also..would it be a good idea to try a later closing like 65..
thanks Martin