Need help on 1997 120 hp force ob

Tends to take a while to get it started.

Under throttle it runs great but when idling in neutral or low speed it dies.
It may take a few minutes to get it started again.

If I kill it and start it right back up it fires right up but the longer it sits before starting the harder it is to start.

On one occasion after it had died in idle, I was attempting to start it and tried to throttle it as it was trying to turn over. The motor died as I increased throttle but this usually does not happen. Every other time increasing throttle helps to get it started.


Would like to solve this problem but I am not very knowledgeable when it comes to working on such things.

That being said I have already replaced the fuel filter and rebuilt the fuel pump just to rule them out.

Not sure where to go from there though.

Any help would be greatly appreciated.

Re: Need help on 1997 120 hp force ob

Have you ever performed a decarb to clean the carbon out of your engine? If not, I suggest you go to the maintenance FAQ and look on page 2 to see how its done. Also, clean your plugs regularly as these engines tend to foul them more often than other engines.

Re: Need help on 1997 120 hp force ob

That's funny cause i'm having the same problem but I haven't had any luck either. In fact, I haven't had any luck having someone respond. Besides that point, I also replaced my fuel filters and make sure my plugs are clean. I still have the same problem. It doesn't stay running after bringing it back to neutral.

Re: Need help on 1997 120 hp force ob

Royal 50,

Have you checked to see that your carb/timing sync is still good? How about compression and timing checks? Have you done them?

Re: Need help on 1997 120 hp force ob

I know my compression is good cause I had someone replace my seals and they did a test and everything was good. As far as the carb timing, I haven't yet, but that's on my list to do next. Thank you.

Re: Need help on 1997 120 hp force ob

So today I pour a can of seafoam into my gas tank and I fired it up and let it run for about 10 minutes or so. I stopped the motor and then started it up again and I let it run some more. Of course it was running good cause usually my problem happens in the water. So my neighbor tells me, maybe you should level your motor as you would out on the lake. So I dropped my trailer jack down and level my motor all the way and I couldn't believe it. This time when I went to start it, the motor backfired and it didn't start. After a couple of times it finally did and just ran fine. So i'm not sure why that would make a difference but my neighbor thought that maybe the seafoam is starting to clean in there like it should. I'm going to run the motor some more tomorrow and see how it does.

Re: Need help on 1997 120 hp force ob

I would at least do fuel pump diaphram kit, maybe carb kits in your case. Im having a similar problem stalling at idle. Racking my brain seems after I run awhile the fuel pump stops pumping. Im thinking maybe I have a restriction in carb somewhere stoping the fuel. I may tear down carb and have a look, I rebuilt mine 7 years ago. Make sure you tighten down fuel pump real good! Been playing with my rig alot so far havent figured it out. I did notice by putting mightyvac on my fuel pump pulse it increase fuel pressure and then my idle went up go figure 400 rpm. Thought I had everything figured out then it stalled on me. Im wondering if also im running fuel tank low and introducing air in system. Does anyone know how air escapes through carb like a relief valve that might be hung closed?

Re: Need help on 1997 120 hp force ob

The angle of the engine only affects one thing, the fuel level in the carbs. Have you ever rebuilt your carbs before? If not, now is the time to put in new needle valves and adjust the float level.

Re: Need help on 1997 120 hp force ob

I never rebuilt these carbs. I only own this boat for about a year. This summer is actually my second summer taking it out. Like I said, today I'm going to run the motor some more and let that seafoam do it's thing ans see how it runs, maybe even taking it out on the lake and see. If it's still idling bad, then I'll look into the carbs. Thanks guys.