1978 150 horse mercury black max on 1978 sea star 18ft tri hull

[CharlieB]

Re: 1978 150 horse mercury black max on 1978 sea star 18ft tri hull

The Michigan prop has numbers on it somewhere, you just have to look a lot closer.

Sometimes they are stamped inside the hub area and may be dirty, you need to wipe it off and look closely. It will either have the size and pitch or a part # that can be looked up in the Michigan book.

Before spending money on a new prop, you may want to check for a hot blue spark, 7/16 inch, check compression, maybe clean the carbs and rebuild the fuel pump. You want to be sure your motor is running at its best before spending money on a prop. You would hate to buy a prop, then later after a tune up find out the new prop is too small!

 

[sutor623]

Re: 1978 150 horse mercury black max on 1978 sea star 18ft tri hull

No im new to 2 strokes... Im guessing i shouldnt have done that? Whats got me wondering is why it will run those rpms with no load but wont do the 5500 it should in the water

Any motor at top end with no load is going to wind up faster than a motor without a load. And you shouldn't rev these guys up past 1500rpms or so without a load.

 

[m.qualls89]

Re: 1978 150 horse mercury black max on 1978 sea star 18ft tri hull

The michigan prop had the numbers spm 319 stamped inside the hub but i cant get any info from them even from the marine store. The fuel pump was just replaced by the previous owner. It runs great with the michigan prop but i have to hold the throttle back. On closer inspection the bigger prop is a 13 3/4 x 21 pitch not 24 i found out though. The spark plugs seem to be goid but they are the perma gap plugs that are just flat and i cant check a gap on them...

 

[m.qualls89]

Re: 1978 150 horse mercury black max on 1978 sea star 18ft tri hull

Also when i checked the compression the highest compression on one cylinder i got was 120 psi and the lowest 110 psi with no leakdown