Force 120 HP questions

[mattsmall1972]

My buddy just bought a used boat with what is supposed to be a 120hp Force motor. We took it out the other day to give it a good run and have a few questions about the motor:

1) The engine takes off really well but the top end seems kind of low - 30mph/5000rpm. It is possible that this is an incorrect prop for the engine? I don't know what the prop is offhand but we can find out. Or is it possible that there's a 120hp cover on a 90hp engine?

2) There's no serial number tag on the engine that we can find (I've already searched these forums). Is there any other way that the serial number to get the hp/year?

3) The engine is a cold-natured - a bit hard to start and it stalls on initial takeoff. Is there anything we should check/adjust/change to get this a little bit warmer?

Thanks for your help.

 

[mattsmall1972]

Re: Force 120 HP questions

Picture of boat:

 

[mattsmall1972]

Re: Force 120 HP questions

<bump>
Anyone?

 

[roscoe]

Re: Force 120 HP questions

90 hp is a 3 cylinder engine.
120 hp is a 4 cylinder engine.

Rpm are good for wot.
Hard to tell how much that boat would weigh, but 30 mph is about right.


I doubt that you are down a cylinder if you are hitting 5000 rpm, but it never hurts to check spark and compression. If nothing else, you will have baseline info for future diagnostics.


As for the stalling, a good carb cleaning, and idle adjustment should take care of it.

Proper starting procedure should make it come to life in 10-15 seconds.


There is no conventional choke on that motor.
There is a fuel enrichment valve, that releases fuel directly into the intake manifold.

Open fuel tank vent

Check the kill switch, place in "run" position

Squeeze fuel primer bulb till firm.

Advance the throttle 3/4 way, without putting it in gear. -- This is done by either pushing a button in the center of the controls, or pulling the shift handle toward the driver, or raising the fast idle lever, all depending on what control unit you have.

Activate the choke (fuel enrichment valve) by pushing in on the key. The valve is only open while the key is being pushed in.

Turn the key to start while continuing to hold the key in.

Release the key and choke when it starts.

3-5 seconds of "choke", is usually enough.

Be ready to pull the throttle back toward the idle/neutral position, when the engine starts and the revs increase.

Continue to pull the throttle back as the engine warms up.

You should not have to use the choke much, if at all, once the engine has warmed up.

 

[mattsmall1972]

Re: Force 120 HP questions

Thanks, this answers my questions fully.
The boat weights about 1700lbs as it came from the factory in 1985 without the motor.
It's being checked over by a mechanic who is going to clean the carbs as well.
It does sound like the engine is really in quite good shape and we'll follow your advice for starting.

Thanks again!