40 hp Force prop question

Hello guys! New to the forum and new to boating. Just bought a 1977 fiberglass tri-hull with a 1993 Force 40hp outboard. Had it out yesterday and I am very disappointed with the performance. I feel it should do better. with around 600 pounds (people and gear) in the boat, it seems like it is plowing water instead of the bow raising and plaining out like a boat should do at WOT. I do not have a tach in the boat so I do not know what rpm the motor is running at WOT. The prop that is on it know is a 10 3/8 diameter with a 11 1/2 pitch. I can trim it out and it helps a little but not like it should. The motor runs great. Any advice will help and be greatly appreciated.

Re: 40 hp Force prop question

What size tri-hull? Do you know the dry weight.
A lightly loaded test run get us the wot rpm and gps speed.
In the mean time be sure the throttle opens all the way.
Check compression and confirm it is on all cylinders.
You wouldn't be the first to not realize you were on one cylinder except for the lack of power.

Re: 40 hp Force prop question

You are light on hp. You didn't say the boat's length, but even at 15' a 60 was about minimum at the time. A fiberglass monohull semi-vee, pretty much flat transom hull area, built back in the late 60's weighing about 500# dry with 2 people, a couple of 6 gallons cans of gas and tackle would do about 25 with a 40 hp., maybe 27 or so if you are lucky.

Trimming out helps to reduce the hull drag and improve performance as a result, but you still need the ponies to push the load.

Mark

Re: 40 hp Force prop question

Thanks for the responses. I will check to make sure the throttle is open all the way at WOT and check the compression and let you know what I figure out.

Re: 40 hp Force prop question

Hey guys! Now that I have some time off of work, I can dig into this deeper. I do not know the dryweight of the boat, but it is a 15 ft fiberglass tri hull. From all my research I am guessing it is around 650 lbs plus motor.

I did notice that when at WOT, the butterfly is only open about 3/4 of the way. Is there a way to adjust it to open all the way, or does that sound like where it is supposed to be.

Do any of you know what the compression should be at for each cylinder? I can't seem the find that anywhere in my searches.

Again I do not know what RPM the engine is running at WOT, as there is no tachometer.

Thanks for all your help! I will be playing around with this tomorrow.

Re: 40 hp Force prop question

Go over to the Force/Chrysler forum. Read the sticky about synchronizing carbs and timing then watch the video. It will explain how to get wide open throttle.

Do understand that with the mercury controls your engine has, any changes made to idle speed or carb settings REQUIRES re-adjusting the control cable.

Good compression ratio should be up around 145 PSI, but different gauges will give higher or lower readings. The important thing is no more than 10 PSI difference between cylinders.

Also, as mentioned above, you are a little low in the horsepower department. 600 pounds is a heavy load in a 15 foot boat.

Re: 40 hp Force prop question

Now is the time for that lightly loaded test run. An induction tach like a TinyTach for rpm. Be sure to tell them it is going on a outboard.
At the least we need the prop size and the wot gps speed.Some cells have e a gps app.