Compatible powerheads for Force 70 HP

[MrMarty51]

i tried doing a search for the information but didnt do much good with that so, I went through about 40 pages of threads and seen nothing there too, on the info I am seeking.
new member here, but not new to boats and such, mainly new to the Force powerplants.
The model number is 708A92A. Just wondering if there is a power head that can be purchased that would have a bit more power, something that would bolt to this lower unit.
i think this unit is getting rather tired. My son just bought this Maxum 1700 RX and we are still trying to sort it all out. We had it on the water last weekend and with two children and two adults loaded into the boat it just did not seem to want to plane up.
after we got home and pulled the cover, two of the sparking plug wires had black electrical tape arojnd the plug boots and the plugs were fuel soaked.
right now we are waiting for some carb gaskets to get here then we shall get the carb back together and see how it does with new boots on the plug wires and new plugs.
I did do a compression test on the cold engine, cyl1 was 100, two at 000 and three at 125. After we get it warmed up and run some decarbon stuff through it I’ll rerun the compression test and hope it does come up on that no. 2.
anyhow, I am curious if it comes to replacing the power head if there would be a more powerful option.

 

[Nordin]

The numbers from the compression test confirm that the engine is tired.
Zero at number two indicate either a blown head gasket or a blown piston/stuck piston rings.
Try to remove the head and check the gasket and pistons.

There are no more powerful power head to bolt on to the leg.
The 70Hp 3 cylinder engine fed with one carb was really not a good design.
Feeding 3 cylinders with one carb is not easy to design.

 

[jerryjerry05]

You need to get a complete motor.
No other blocks will swap.
That motor was only made for 1 year and discontinued.
Poor design, poor performance etc.
It was a mix of Force and Mercury parts.
The transom clamps, Mercury
The linkage, Force.

You can swap to any of the later Mercury/Force motors.
Stay away from the 70 and 75

In the search for more power???
The only answer: get a BIGGER motor.

 

[MrMarty51]

Thank You for the information. I’ll pull the head and see what is up with that cylinder. Probably no sense in even putting the carb back together.
i was online yesterday evening looking at some used engines. Kind of a tough time figuring out if a person could trust the dealer or people selling them.
there is one store here that sells motorcycles and boats so not a lot to pick from. Might ne worth a trip to Minnesota or Wisconsin and do some scouting in those areas.
I been wanting to do some exploring over in that direction anyway. Thinking I should sell my place here and buy something on a lake over there.

 

[jerryjerry05]

Just make sure what ever you buy has good compression
and spark on each cylinder.

 

[MrMarty51]

Just make sure what ever you buy has good compression
and spark on each cylinder.

We sure will.
The son is talking about going with a four stroke if this engine is non salvageable.
I found some information on the Maxum Boats and it appears that this 1700XR is suppose to be able to handle up to 115 horse, it said Merc, or, 120 horse Force.
I imagine that a four stroke will be some bit heavier than a two stroke so that too may have to be taken into consideration.
Have to find a weight comparison chart of sorts and get it figured out.
I do have a question on the Tillotson carb that's on this engine but I will start a different thread for that, with a pic too. LOL
I thank everyone that has responded to this thread and I will try to be of help in mechanicals where I can.

 

[MrMarty51]

Welp, the verdict is in. Got the carb kit and put the carb together and installed, adjusted according to the book.
The son got some Mercury Power Tune, we run that through the engine, let the engine die out with a good fog of that in the cylinders then goofed off for a couple of hours. Fired up the engine and run some more through the intake and out the exhaust. It is a very small pond that we went to, the only pond in about fifty or more miles. We cast off from shore and run the boat around and around. It did plane up and engine running way better than the first venture out with it. Boat would even plane up. Running at just under 5200 RPMs full throttle and timing right on 32 degrees, yeah, timing light was working with the solid core wires, the wipe off of the pickup must have helped.
loaded the boat and got it back to the garage, pulled spark plugs, run compression test, cylinder 2 as dead as ever. Popped the head, deeeep gouge in the chlinder, all three pistons was failing along the top of the lands.
not a good day for the boy child. Welp, so much for the old Force 70 HP.
on to a better enjun for sure now.

 

[MrMarty51]

Piston from problem hole.

 

[roscoe]

ouch

 

[MrMarty51]

Yeah. Sad to say the least.