please help with black max 150

[cdnstudman]

good day all! i am pretty new to boating and recently picked up a 16.6' bowrider with a 1980 black max 150 engine on it. it was running like a bag of poop so after a bit of trouble shooting i decided to replace the carbs with a used set. this has really helped, but still not quite perfect. the carbs i bought used on kjiji, but were off a merc 200. like i said though, they do work and the boat will go 64 kph. from talking to a few people and watching various videos of the black max 150 i see the she should be able to pull about 100 kph on plane. now the question i have is if i would need to change the intake with the new from the 200 as well? i am just not sure if the 2 would have different reeds? any other ideas where to find my missing power?
carbs have been fully cleaned, new pugs, new fuel pump, so all that should be fine.

thanks guys

 

[galamb]

If you have the year correct on the motor then the block sizes were not the same - that's issue number one. An 80 model would have been the "XR2" format - 2 liter block. A 200 has/had a 2.5 liter block, so the carbs were designed to "fuel" a block with 25% more displacement which meant significantly different jets.

Otherwise, the reeds were the same - no issue there.

I'm not even sure how to advise you here. There is pretty much nothing you can modify here or bolt on to make the carbs work with that motor - at least if improving the performance is your goal.

If you still have your original carbs you would be better off rebuilding them. The main jets, air jets and vent jets from the 200 are way out to lunch compared to what your "block wants". There is no way you can stop it from running extremely rich which will do nothing more than carbon up the motor, eat plugs, burn gas and "decrease" your overall performance.

You are just plain missing 32 cubic inches...