Mercury 1150

[jason1150]

Took my boat out this weekend and could only get my rpm's to 4200 and speed to 30mph, I just put the tach on so I could get this information, I'm running a 17 pitch prop, tried turning my max spark advance just a tiny bit to see what would happen and I got 4300 rpm and 32mph, was wondering what my max rpm's,mph should be, what size prop should I run on a 16ft ski boat, How far should my motor sit out of the water? I want this sucker to scream without exploding, would like to go 45mph, does this motor need to be timed on the water or what? thanks for your time reading this, any help would be greatly appreciated, thanks, Jason

 

[achris]

Re: Mercury 1150

You didn't give us a serial number or year, and there were 2 variants of that engine, a distributored engine and a non distibutored engine.

Both have a maximum revs at WOT of 5000-5500. Any less and you run a very high risk of burning pistons.

The distributored engine has a maximum timing setting of 21* with the engine running.

The non distributored engine has maximum timing advance of 20* at cranking revs.

On both engines if you over advance the timing you will punch holes in the pistons.

The fact that you are only making 4200-4300 is of serious concern. On a 16' ski boat that engine with a 17" prop should fly. You should be getting well into the 5500 area with a speed of around 38 knots (43mph, if you must use landlubber terminology). I would start at the very basics. Check compressions, check spark, check carb sync, change filters, new fuel, new plugs, the works.

Chris.......

 

[jason1150]

Re: Mercury 1150

oops, it's a 71 1150 with a distributor, do you think it could be not getting enough spark? It idles(around 800), starts, and runs fine. I've already sync'd the carbs and did the timing like clams has described, I will go back over everything again. Jason

 

[75TowerOfPower]

Re: Mercury 1150

How many people were onboard and do you happen to know if the boat is in good shape?

I know I gained some MPH because I had water logged foam and a soaked floor, I trimmed off about 400 pounds.

 

[jason1150]

Re: Mercury 1150

okay, went over my timing and carb sync today and everything looks good, had a guy come out and look at my boat and he says everything is set up right and that the motor is just worn out, that it's a restricted 135hp and that the only thing I could do is enjoy it or rebuild it to a 135, does this sound right, I did a compression test and got 135 to 140 psi on all cylinders, maybe it's the prop?

 

[achris]

Re: Mercury 1150

okay, went over my timing and carb sync today and everything looks good, had a guy come out and look at my boat and he says everything is set up right and that the motor is just worn out

With compressions of 135-140 on all cylinders, just not true...

that it's a restricted 135hp

No. The engine block family ranges from 90hp to 150hp, but it's not done by restricting any of them. It's done with different pistons and different carbs.

and that the only thing I could do is enjoy it or rebuild it to a 135, does this sound right

Not even remotely

I did a compression test and got 135 to 140 psi on all cylinders, maybe it's the prop?

Maybe, but usually a dinged up prop will increase revs and decrease speed.

I would certainly try a smaller (pitch) prop.

 

[jason1150]

Re: Mercury 1150

thanks chris, I really like this motor, what size prop do you think I should try, 11",13",15", 17p,16p,15,? 2 blade, 3 blade, 4 blade, so many to choose, I know it's hard to guess with the limited information I've given, is there a prop calculator you could recommend, my year motor does not jive with most calculators, I don't know the weight of the boat, it's a tahiti style, I would like to get the rpm's in the proper range and of coarse speed, one more, does this motor have a power band? does it step up like my 2 stroke dirtbike does at high rpm, thanks again, Jason

 

[achris]

Re: Mercury 1150

Since you're currently running a 17, I'd throw a 15 on and see what the difference is. I would expect an increase of about 400-600 revs. If you get a lot less than that it would point to an engine problem.

Chris..............

 

[CV16]

Re: Mercury 1150

I also have a 16' ski boat. Mine has a 73 1500 on it. With 4 adults on board, I get 5600 rps running an aluminum 17 pitch prop. With just me in the boat, I can run a 23. If I were you, I'd try to borrow a 13 & 15 to try out.