Any old Force 2 stroke guys out here

[Scott 352]

I've recently obtained a Force 70 horse 2 stroke 91 by Mercury Marine and in 86 glasstream 15 ft bass boat price was right it gets me going at about 43 mile an hour I am trying to be able to hit 60 with my setup is that possible

[FMP]

That's a big jump. That 70 is a big carb single TC, the 90 is a triple, 3 smaller WB carb. You could cut the head for 165 psi , jetting it up a bit, do the cages and reeds, square the transfers, raise a bit and square the ex ports, set the timing at 34° wot running, 35.5°-36° cranking, cut the transfer cover surfaces down a bit, lift the motor and set it back, get a good prop and hope for the best. Or find a 90 and do the above, bolts right(check adapter/spacer year) same weight or find a 4cyl and do the above with about 35 lbs more weight.

With the 70, two/three cylinders are on an upstroke at the same time, 120° crank spacing. When one cylinder is near max intake through the carb the next cylinder is also on it's upstroke, that carb although the larger TC is in competition between the two cylinders. Not sure how much rpm that is limiting but it's happening.
As a comparison, the triple cylinder 25hp lightning Force also shared one carb, that motor does turn impressive rpm into the 6500+ range, so maybe your 70 will as well.
On the 90, three TC adapters made for the 90 in place of the WB would improve high rpm as well in race tune but the 90 with three WB carbs is a good runner.
Better check compression first and see how things look on the 70.

[Merc 2.5]

Wow..... so these ole forces can b a runner huh?? Whod a thunk it, would like to see or hear one

[Scott 352]

Wow..... so these ole forces can b a runner huh?? Whod a thunk it, would like to see or hear one

Mine runs about 40 and is not set right. I lifted 31/2 inches and put smart tabs on and redid the carb. And I'm up to 43 now. Trying to hit 65 70 mph. Can't afford a new motor so I have to build one I have . Machine shop can be cheap and I can do the tear down and put back. A grand or 2 is cheaper 10 grand for a new motor. And it's fun to build

[BOATMANBLUES]

if you are gonna spend 2 grand , just buy an old johnson / evinrude v4....you will be light years ahead of that force...
if you ever get any rpms out of it , it will break the ring lands off the pistons , even with stock head and compression...
JMO after working on junker motors for too many years....

[Scott 352]

if you are gonna spend 2 grand , just buy an old johnson / evinrude v4....you will be light years ahead of that force...
if you ever get any rpms out of it , it will break the ring lands off the pistons , even with stock head and compression...
JMO after working on junker motors for too many years....

Everything is 4 to 5 grand for anything decent out here by me here in Florida And I already have the force. I'm just trying to keep up with these wkend warrior in these bass tournaments . Don't like the way they smirk and laugh at me and my boat. I just want something me and my 9 yr old daughter to conden with.

[Merc 2.5]

Mine runs about 40 and is not set right. I lifted 31/2 inches and put smart tabs on and redid the carb. And I'm up to 43 now. Trying to hit 65 70 mph. Can't afford a new motor so I have to build one I have . Machine shop can be cheap and I can do the tear down and put back. A grand or 2 is cheaper 10 grand for a new motor. And it's fun to build

I do agree with all that ,but that's a mighty big jump, I'm curious as to what u gain, 20 or 25 mph will b hard to get I believe, just make damn sure ur machine shop guy really knows his chit!! I c ur n Florida, and can give u sum names and info if needed

[Merc 2.5]

Everything is 4 to 5 grand for anything decent out here by me here in Florida And I already have the force. I'm just trying to keep up with these wkend warrior in these bass tournaments . Don't like the way they smirk and laugh at me and my boat. I just want something me and my 9 yr old daughter to conden with.

I've been there and really chaps it ass but when u take ur 2k$ boat and smoke and 20 or 30k boat, makes it all worth it, I've got prolly 4k$ maybe little more n mine and it will shame those 20ft 50k tritons and stratus and such

[Scott 352]

Yes please. That would be much appreciated.

[Scott 352]

They have 2018 z21 nitro with 250 merks on the back. 65000 boats and they are better than me because of it. So I told my daughter that they are and I can build are up. And I have my work cut out for me.

[Merc 2.5]

Well nitros suck neway, had lots prob with hulls, now u will never out run one them 250s with ur 70 but if that's what u want. Build er up!

[FMP]

Wow..... so these ole forces can b a runner huh?? Whod a thunk it, would like to see or hear one

The triples during the early 90s did well in competition. They were modified, ports, chambers sized, etc . Ran very strong, Mike Wienandt of WPT had good results. Only a 1/2 V6 Merc could get around them at the way top end of a long straight away.

Similar, the triple CHRYSLER Bill Edwards. Has a 70-75mph on a 15'.

Here's one the triples , tunning runs
https://m.youtube.com/watch?v=jtiAF2fWK7I

https://m.youtube.com/watch?v=Q-3_pBF7QR4

[Scott 352]

Not so much out run but out perform they can't reach there top end so if I can hit my Mark I can shut them up on the water by out performing them by hitting that 55 60 mph I can take the inside as well witch is what they can run. I've built many street rods but this is my first outboard

[FMP]

It's going to take every bit of smarts to hit your goals, but fun trying.

Is it the one piece side bullet water intake lower unit or Merc style?

[Scott 352]

Merk style... It looks like I might just have to find a bigger motor to hit my goals. So I'm starting to find a 120 force or something similar but to. Going to go with a 2 stroke tho