YSM-12

[Steve Miller]

Gordon,I have a 1979 Hunter with a rebuilt YSM-12 engine. The engine runs as good as it ever did, However at top speed I get 3.5 -4.2 knots Max depending on wind speed. I am always the last one out of the harbor and last one back. Very reliable but, can I improve top end speed? Would changing props improve it currently has a two blade prop. Would this be a viable alternative, and what would you recommend? The bottom is clean, and so is the prop. No problem with rpms, just very slow and noisy. Thanks.

 

[John Reid]

Power

I'm no expert but, what the heck, I'll jump out on the limb here and suggest that maybe your engine isn't getting up to as high RPMs as you think it is. Until two years ago I owned the identical model boat (same year) with the identical model engine. It cruised at a solid 5 - 5 1/2 knots and that's with the original two-blade prop. If your engine panel is the same as what I had, there are no gauges (i.e., no tach), so it's not easy to know if your engine is running up to its intended speed.

 

[Roland]

More Power

Have a '77h with a YSB12. Was having problems with slow speed although engine ran fine. Problem was worn transmission pressure plates. Replaced them and now run along fine at 5.5 - 6.5 knots.-RolandFraulein II

 

[Gordon Torresen]

YSM12 boat speed

You should be able to cruise at six without too much problem. The two previous posts cover some of the problems that you might be encountering.You could also be suffering a loss of power from restricted exhaust, although that was probably taken care of when the engine was rebuilt. You did not say if you have ever motored at higher speed. If not, you just may have the wrong prop. There were three different reduction ratios available for that engine so your prop may not be the same as your neighbors. If you want less nebulous answers, give us some more details like gear ratio, max RPM in neutral and under way at max speed.