1990 Force 120hp starts but wont sustain

[Droop]

Hello everyone,

I recently came upon this site, and you guys have helped me TONS so far, but im still having some issues getting my motor going.
Little bit of backstory bought this boat, with the previous owner saying that all it needs is a throttle tune. it still hasnt gotten a throttle tune, and that very well could be it. (they replaced the throttle and shifter cables)

So with a fresh battery i can get it to turn over and fire, and when i give her some gas it will even sustain for about 3 seconds, then it cuts out. It seems to be backfiring maybe? i will post a video of it tomorrow. (battery is on trickle charger) Any ideas to get her dialed in? and able to sustain idle?

Cheers,
Blake

 

[roscoe]

Re: 1990 Force 120hp starts but wont sustain

Welcome to iboats Droop.


Do you know any history on the motor? Perhaps anything the seller mentioned doing?

Start with the basics.
Check for spark on all plugs.
Check the compression on each cylinder.

If those are ok, it leaves timing, fuel delivery, and starting procedure..

So, check the timing, but don't adjust anything just yet.

Is fuel getting to both carbs?
Does fuel leak out of the carbs?
Is the choke working?

Is it "sneezing" through the carb? Or is it more of a traditional backfire?

If its a sneeze, carbs are either dirty or set too lean on the fuel/air mixture.
If its a backfire, could be timing is off, possibly caused by broken key between the flywheel and the crankshaft.
This could be caused by excessive backfiring, or by not having the flywheel torqued to spec if it was ever removed.

Starting procedure:

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 by pushing in on the key. The choke only works while the key is being pushed and held 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.

Engine should start within 10 seconds of turning the key.


Keep the info coming.
Provide as much detail as possible.

And most importantly, if you are going to own and maintain an outboard, you should buy a repair manual.
Either a factory service manual, or a Clymer Force repair manual. It is filled with tons of info and specs, test procedures, tuning tips, etc.
You can get a lot of info here on the forum, but the technical data is best gotten from the manual.

 

[Droop]

Re: 1990 Force 120hp starts but wont sustain

Thanks for the reply roscoe and thank you for the welcome


So the motor is less backfiring as it is sneezing. Thats likely an issue of the carbs. I already had a marine specialist come look at it early on memorial day weekend, but all he had was an hour, and i wasnt even present. He did tell me he thought my carbs looked a bit dirty, and that he drained my carb pools.

Another thing, I have tried your startup procedure, with the boat in neutral, and the throttle forward i could get it to actually start and maintain, it ran hard, and sounded good, no typical clunks or valve chatter as you can often hear. I need to do a real spark test, and engine compression though, or have those tests run.

Any idea on where to get a factory service manual for a 1990 force 120?

Thanks for your help,
I will keep you posted on where this goes!
-Blake

 

[roscoe]

Re: 1990 Force 120hp starts but wont sustain

You can usually find one on ebay.

Remember that all the ignition components changed in late 1991, so you should really try to get a manual for a 1990 model.

The Clymer repair manual is pretty decent and is probably a little more informative, giving more detailed explanations, if you are new to 2-cycle outboard motors.

 

[Droop]

Re: 1990 Force 120hp starts but wont sustain

Roscoe,

Followed your startup procedure, got her going and sustaining, shes still sneezing a bit, and gets a little rough from here to there, I feel like the carbs are dirty, gonna give my guy a call and have those badboys cleaned out and she should be right as rain.

Thanks for your help.
-Blake

 

[jerryjerry05]

Re: 1990 Force 120hp starts but wont sustain

Sneezing at idle is the air mixture.
The carbs have a screw(with spring)on them.
Turn them both in till it stops.Remember the turns and post them(so we can see).
Then turn them out 1 and 1/16th out.Leave them there.That's the factory way.
Sneezing at speed could be the reeds or the recirc system clogged.
High speed jets clogged,clean carbs.

 

[Droop]

Re: 1990 Force 120hp starts but wont sustain

Welp,

got the compression test done today,

turns out we have spark on all cylinders, and the results of the compression test are

145
145
0
145

:/ there goes that motor. time to find a running force 120-125 in the puget sound.

Thanks for your help everyone.

 

[Jiggz]

Re: 1990 Force 120hp starts but wont sustain

When you decide to remove the head and check on the gasket can you post some pics? I'm just intrigued that it read zero.

 

[bentle]

Re: 1990 Force 120hp starts but wont sustain

Seriously post some pics of that cylinder.
0 compression??
Did you perform it yourself or did a mech. do it?