1988 15 HP force questions

[hunterope]

All.. Hope you can help me out a bit. First off, the motor I have run's well, but doesn't push my 14 footer much faster then 9 MPH. Not a very heavy boat (old sea king). I've fiddled with the trim etc.. No improvement. It's a 2 blade prop. Would a 3 blade improve my speed and if so, where can I get a used one? Also, I've noticed that my fuel consumption is extremely high for the distance I travel with it. I'm talking about a gallon to a mile. Is this normal? If not, what do you think may be the issue with me burning so much fuel?

 

[Frank Acampora]

Re: 1988 15 HP force questions

If it is a light aluminum hull, and if it will not get up on plane, then yes, top speed is too low. And yes, it sounds like you are using too much fuel.

I don't think a prop change will do much for you unless the pitch on the existing one is so low that the engine is turning excessively high RPM.

First thing to do would be to read the numbers on the prop and see if it is the correct one for your application. The guys over at the prop forum will tell you, but be aware that they will want more info like current RPM, boat weight, etc.

SO; If the prop is correct, now it is time to check compression, fuel pump and carb settings

 

[hunterope]

Re: 1988 15 HP force questions

Thanks for the reply. I'm not able to get an RPM on it, but I do know that when running on the river I did some testing for speed via GPG. Up river I managed 9.2 MPH, down river I got 10.4. I took the average and got 9.8. I would think that a 15 HP would do a bit better then this with my rig. Capacity is rated at 750. This is an older SeaKing, the aluminum is pretty thick come to think about it. I've not added much in the way of weight to it. The fuel thing has me baffled, but I'm a bit more worried about the speed. I'll look tonight to get some #'s off of it when I get home. The motor starts pretty easy (1 or 2 pulls) when cold. Do you think that I'm possibly running on one cylinder? I'd think the motor would sputter and die if so?

 

[Old Gamefisher]

Re: 1988 15 HP force questions

Hunterope,

Get a Tiny Tach. It's VERY easy to install; I put one on my 15hp Force in about 5 minutes (it involves clamping a ground wire under an existing bolt or nut, and wrapping an antenna wire around a spark plug cable. Remove the nylon plug on the front of the engine: it's above and to the left of the gear shift as you look at the gear shift. Run the wire through the hole, and seal the hole with a rubber grommet that you've placed in a hole you've drilled in the nylon plug (you'll have to slit them both to accomodate the wire). You can get the grommet, and new nylon plugs, at Lowe's (strange but true, they had nylon plugs that fit exactly - hardware section, in the drawers). Leave some slack in the wire, and figure out where you want to mount the tiny little display.

The link: http://www.tinytach.com/tinytach/index.php

It cost about $40, and has been worth every penny.

It sounds like the wrong prop is on that motor. The tach will tell you quickly. My 15 hp pushes my 14' tinny at 20 knots at 5500 RPM at WOT with an 8 x 6 3-blade aluminum prop. It burns amazingly little gas, a lot less than what you're getting. I'll leave the rest of the discussion to the prop forum, but getting that tach should be your first step.

 

[hunterope]

Re: 1988 15 HP force questions

I've got the #'s from my prop this AM. To dark to pull it when I got home last night. 8 1/4 DX 8 1/4 P

My model # is 225 - 581500

I checked my spline's and they appear to be perfect. When I bought the motor and did a once over on it, it appeared that the motor was run maybe 2 or 3 times. Prop was / is almost mint. No paint wear or chipping. Wasn't a repaint job on it either. Like I stated earlier in the posts it's a 2 blade.

I did a spark test on both top and bottom wires and I'm getting a super bright blue spark. I don't have a compression guage but both top and bottom blow by my thumb prett easy and I'm pressing very hard. I'd like to think I'm a bit stronger then your average guy hand strength wise (i know that's no true test). I'm thnking that I've just got a very heavy boat and with me, the dog and the decoys(about 35 pounds) gun and gear, that it's about what I'm going to get out of her. I had a 9.8 HP merc that would do 8 to 9 mph on the same boat.
As far as gas comsumption, I'm stumpped. I guess it's just a pig. I do tend to run her wide open most of the time once I get into deep water.

All in all, i'm pleased with the motor but with the post's I'm seeing of 20 mph I guess I'm just looking for better performance out of the bigger motor.

Any suggestions to tweek her are more then welcome and appreciated. I did notice that there arn't a lot of post's out there for this motor. Maybe I should sell her and get an old merc again. Thanks guys.

 

[moparman]

Re: 1988 15 HP force questions

I'm not a prop expert, but it sounds like your prop pitch is off some what,and you need one more blade on that prop. Do as old game fisher suggested, and check the rpm to find out for sure, I would have thought you would have been able to get at least15-18 mph out of your combo,but until you know your rpm it will be a guessing game to figure out. hope this helps in your quest for more SPEED[ LOL].... MOPARMAN ............... ROLL TIDE

 

[hunterope]

Re: 1988 15 HP force questions

Got an RPM on it this AM. 5300 wide open. Going about 11 to 12 mph without anyone but me in the boat. I called up Mecury (who made the force that year) and the tech guy told me I need a 3 blade prop. They have them, but they want way to much for my budget. He also stated that there are 3 different options to choose from. One is the original prop I have on the boat 8 1/4 dx 8 1/4 P. He also stated 2 others but I didn't bring the paper home from work. One was a 9 x 7 1/4 (think that would be to big for clearence with the cav plate) but like I stated before, I'm no expert on the force. The old Merc's I'm pretty savy with though. Does anyone one know where I could get another "used/inexpensive" prop for this bad boy? I know the motor has more potential in it then what I'm getting out of it.