85 Hp Force Motor

[Hefe707]

I recently bought (my first boat) a 86 Bayliner Capri 16' with a 85 hp Force motor. The motor and boat are very clean. After the purchase I took it to the mechanic and he lubed the steering and cables and changed the impeller and lower end gear fluid. He said everything checked out good, runs smooth. I take the boat out every weekend to local fresh water lakes. Starts up, a little cold blooded, but seems to be reliable. I hear people say that their 85 hp motors will go 30-40mph but my top speed has been 22mph at full throttle, if i push the throttle down as hard as I can it starts to run a little rough. I would like to improve mph's to pull skiers, hoping someone can point me in the right direction to solve this problem. Thanks!

 

[MWBROWN]

Re: 85 Hp Force Motor

I have a 1984 Bayliner Fish and Ski with an 85 Hp Force.
With a stainless prop 17 x 13 1/4 with 2"cup I get 37.5 with full tank, 2 big guys and gear. 5500 rpm. GPS speed. My full WOT sounds rough also.
If I back off just a little, 5000 to 5200 the engine sounds like it could run forever.

Did he check the compression?
What pitch prop do you have?
What is your RPM?
How is your speed measured?

Good Luck,

Mike

 

[steelespike]

Re: 85 Hp Force Motor

Your performance should be right in the area of MWBrowns.Check the prop size.Should be on the barrel of prop -- X -- (diameter X pitch)There are some simple things you can check.Look in the carbs to see if the butterflys are open all the way.Check the compression.(be sure plug wires are grounded or kill circuit is closed) before cranking. The antiventilation plate(just above the prop) should be about even with the bottom of the boat.Is prop in good shape?

 

[kadesdad07]

Re: 85 Hp Force Motor

At full throttle what were the RPM?s? That way you can determine if it is an engine issue or your prop.

 

[Hefe707]

Re: 85 Hp Force Motor

I'm not sure what pitch my prop is I will check it out. What pitch prop is recomended for faster speeds. I looked online and it seems that there are different styles, It has an exhaust above the prop but does it also release exhaust through the prop as well (any recommendations for a good prop ).
The boat does not have a tach installed, so i'm not sure what rpms i'm getting , is it a good idea to install one. The compresion is good, but i will check the butterflies in the carbs.
Thanks for all the replies

 

[kadesdad07]

Re: 85 Hp Force Motor

.I would want an RPM gauge, but it is your boat and money spent. Speedo gauges are never accurate. I used my friends GPS unit to figure out mine. Anyway if you buy a new prop and it is the engine not getting to full RPM then you may buy it for nothing. If you decide to buy a new prop used an online guide to help decide what is best for your application. The pitch of a prop will change speed and RPM. The higher the pitch 20, 21, 23 so on the higher your speed, but will change the torque. So you may be able to go 60 mph, but it will take you a country mile to get up to speed. If you want to pull a skier you want something in the middle, good torque and speed. Let us know what you decide and if it makes the difference.

 

[Hefe707]

Re: 85 Hp Force Motor

thank you very much for the advice i'm off to the garage!

 

[Frank Acampora]

Re: 85 Hp Force Motor

That engine on that boat can not swing a big prop. There is no prop for faster speeds. FOR EXAMPLE: if you are using a 19 inch pitch prop and turning the recommended 5000 RPM, then changing to either a 17 or 21 pitch prop will drop the speed. With the 17, the engine will turn faster but the boat will be slightly slower. With the 21, the engine will turn slower, not develop its full horsepower and the boat will go slower.

You should PROBABLY swing a 17 pitch prop and depending on load, possibly even a 19. You should be getting around 35-38 MPH. 22 is way too low.

Before you run out and get another prop, you really need to find out why the boat is going too slow. It is possible that the engine has something wrong but it is also possible that you really simply have the incorrect prop. Or, your prop may be damaged enough to affect performance. It is also possible that you have a lot of water inside the hull weighing it down. Dirty, rough bottom--all these things need to be checked.

As an example, I rebuilt a Force 125 for a fellow. It was on an 18 foot bass boat. With his original prop, the engine turned 6000 RPM and the boat did 40 MPH. I switched him to a 19 pitch stainless (one of my favorites) And the RPM immediately dropped to 5000-5500 (I forget exactly) and speed went up to 47 MPH. ---A 7 MPH gain just from changing the prop.

Usually, for tubing, you don't change props. But for skiing, it is common to use a prop with 2 inches less pitch so you get a good strong quick acceleration to pull the skier up fast.

But you MUST have a tachometer and a reasonably accurate speedometer to (A). Find out baseline performance, and (B) test other props against it.

 

[raekmike]

Re: 85 Hp Force Motor

Hefe,
We had the same problem when we bought our 85 bayliner capri with an 85hp force. When we first took it out it did between 20 and 25mph at wot. We thought it was great being our first boat and all, but we went over a good size wake and shook the boat a bit and all of a sudden the rpm's went way up and the boat sped up fast for about 3 seconds then went back down to the 20mph range. Hmm we thought? after a few days of moving around coils and checking wiring and compression and everything a newbie could I looked up under the flywheel and saw one of the wires coming down had rubbed on the spinning flywheel and rubbed through! Not exactly sure what that wire is called but it was toast. Spliced that wire together and o.m.g. now we had some speed.
The motor was running on 2 cylinders the whole time and it was running great we thought, It wasn't sputtering or smoking or doing anything weird, It just wasn't getting spark to 1 cylinder. Just might be one more thing to check if you havn't already.....


By the way,
Ours is also a 16' capri and consistantly get 37mph at wot with 2, 200lb guys and our fishin gear. The prop is the original white aluminum and we have a sting ray hydrofoil to pop us right up out of the water.