1996 force 120 intermittent idle issue and hard to start

rhedayi

Seaman Apprentice
Joined
Dec 25, 2023
Messages
39
Hello everyone. Thanks in advance. The prior times I’ve posted I’ve had good advice. Boat is 1996 trophy 2002 with force 120. I’ve put 130 hours since i bought it. Since purchase I’ve done plugs, rebuilt the fuel pump since it was original, replaced fuel filter, added fuel water separator, replaced the lines in the hull and external to the motor (bulb too). Recently i noticed that boat just not running well low rpms. Wot 5200rpm top speed 32-33mph. I don’t keep it there much. Usually I’m in the 4200-4500 rpm range. I would come to a fishing spot and put in idle. Couple times it sputtered and died. Sometimes when idling and going into gear it seems to idle 700. In they past, when stopped for ten fifteen minutes i could crank it over and it would start immediately. Now sometimes i need to give it gas to get it started (even when warm). I just swapped the plugs again and it’s better but still seems a bit off. I did recently change the thermostat and the motor seems to be running real cool according to a temp switch mounted on the block (100 degrees but it’s external not internal). Would a faulty thermostat cause it to run too cold and rough? Water temp and air temp last few trips here in California have been cooler than when boat used to run better. Where do i start with the troubleshooting? Also to note idle sometimes is 800 in neutral and sometimes closer to 1000 which seems odd. Thank you
 

jerryjerry05

Supreme Mariner
Joined
May 7, 2008
Messages
18,057
First step: do a compression and spark test. Looking for the comp to be even on all 4 or real close and the spark to be strong and clear. The actual comp #s varies due to the difference in tools, Cheapo tools= poor results. Harbor Freight tester = low results.
Check the fuel pump diaphragm (even new can go bad)
Next is do a starting fluid test: start and at idle, spray SF around the intake side of the motor. This includes under the carbs and under the coils and pack.
If the spray makes any difference in the way it runs?? then it's sucking air somewhere?? The 4 port covers, the gaskets can start leaking for no reason and make it run poor. A small backfire or cough can cause them to leak.
The first 5 post in this forum has a bunch of things that might help??? Read the posts, maybe something in there might help.
If the spark is questionable? then outboardignition.com has tests for the electrical system. Just need an analog test meter and possibly a DVA Meter for the more complicated results. And asking questions, no matter how silly might help. Good luck.
 

rhedayi

Seaman Apprentice
Joined
Dec 25, 2023
Messages
39
Thank you both. Jerry I’ll need to look at those 5 posts. Jerry what’s a cough in this context?
 
Last edited:

rhedayi

Seaman Apprentice
Joined
Dec 25, 2023
Messages
39
Could the engine running cold due to 110 degree thermostat instead of the oem 130 cause it to run poorly at times? At the end of the trip when i load boat on trailer i put the motor up on the way home. I get fuel leaking onto the transom area. Is that normal? Could it be a symptom of any of this?
 

jerryjerry05

Supreme Mariner
Joined
May 7, 2008
Messages
18,057
Cough: backfire or stutter/miss or kickback through the carb.
The fuel leak is normal. The carbs have fuel left in them and when tilted the fuel leaves the bowl and finds it's way to the well.
The thermo at 110d shouldn't really make much difference other than using more fuel. An engine running at proper temp will get better fuel usage.

Spark plugs: all 4 should look about the same. One "different" plug can mean it's not working right. Post pics of the plugs and the order they came out.
 
Top