Sudden Death at Mid-RPM

[rodttu02]

I'm writing this message as we float to shore and want to say thanks in advance for any help I can get. Long story short, I recently bought a boat with a 1990 Force 120 that hadn't ran in a decade. Did all the recommended maintenance - new plugs, water pump, fuel lines, cleaned the tank, etc. We have taken the boat out about a half dozen times and the boat has ran well. However, we took it out today and it ran great at first. Then we start out across the lake and the engine started to run a little rough and the just died. It feels like it ran out of gas, but we have 25 gallons in the tank. The engine will crank and fire, but won't stay running. It seems like it is starving for gas. The bulb is pumping gas, so I am out of ideas. Any body got any wisdom? Thanks!!!

 

[dst87mcssac]

Re: Sudden Death at Mid-RPM

I am really not an expert on this motors, but here are some ideas:

#1) Could it of vapor locked in the heat?

#2) Check your gas tank vent. Is it open? Sometimes they have a ball inside that hangs up.

#2) Bad fuel pump diaphram.

Just trying to help,

Donald

 

[foodfisher]

Re: Sudden Death at Mid-RPM

Junk in the carbs? Look and see. Filters are a good thing.

 

[rodttu02]

Re: Sudden Death at Mid-RPM

Thanks for the ideas guys! I believe the issue was plain and simply out of gas... At first i thought a bad primer bulb was the culprit. However, I guess the engine is way worse on fuel consumption that I thought. My girlfriend was bringing the boat around from a public dock to the house and got turned around. She was running wide-open for about an hour and burned up 6 gallons. Does that sound right? I'm wondering if i should take the boat to a mechanic and let them give the carbs a look. Seems quite excessive to me. I also have to note that the fuel guage wasn't working, but i believe i have that fixed after pulling the tank...

 

[dst87mcssac]

Re: Sudden Death at Mid-RPM

My 75 HP Force drinks a lot of gas. These motors are know for using gas. My inboard Ski Boat with a 351W and Four barrel carb uses less gas than my 22' pontoon boat. You will notice a big difference in fuel consumption between 2/3 Rds throttle and full throttle . The Forces use a 1950's design Chrysler Engine Head with Mercury lower and Electronics. They are not very efficient but easy to work on.

JMO,

Donald

 

[rodttu02]

Re: Sudden Death at Mid-RPM

Donald,

I have to agree with your opinion, these are NOT fuel efficient engines. However, I think I still think mine is in the excessive category. We ran through 30+ gallons in 3 days. The other reason I still believe I have an issue is the gas/oil sheen that comes up to the surface after the engine is shut off or idling. I have replaced the spark plugs, used sea-foam, adjusted the carbs to the manual specs, etc. to no success. The boat runs great, but seems to be dumping fuel out of the exhaust. I'm just about out of ideas and believe I may just need to take it to a mechanic.

Thanks,

jerrod

 

[aladin_sane]

Re: Sudden Death at Mid-RPM

Take a look at the carbs with the engine running on the lake with the cowl off. sounds to me like you have fuel coming out the vent on the carb. Could be a float or needle problem.

 

[rodttu02]

Re: Sudden Death at Mid-RPM

I did that this weekend and didn't notice anything leaking from the intake side of the engine. I tried several different settings with the one and only adjustment screw on the carbs. Nothing seemed to get rid of the sheen. However, it did seem to get a little better with the screws backed out farther, rather than when they were cranked down to the one turn recommended by the manual. This seems backward to me. Is this not a fuel/air needle and the farther it is turned out, the more gas will be fed to the engine? I'm definitely not that well versed in carb tuning.

 

[stubtail]

Re: Sudden Death at Mid-RPM

You mentioned some of the maintenance performed - plugs, impeller and fuel lines, but as Donald suggested, how about the fuel pump diaphragm? If it is perforated it will allow fuel directly into the crankcase, allow the excess raw fuel to exit unburned via the exhaust and adversely affect engine operation.

 

[labawg]

Re: Sudden Death at Mid-RPM

There seems to be a consensus at least for Chrysler/Force of Hp/10@WOT=GPH. For example my 1984 125hp at WOT(5200 RPM) does burn between 10 to 12 gallons per hour, depending upon the water conditions.

 

[rodttu02]

Re: Sudden Death at Mid-RPM

Stubtail - No, I did not change the diaphram and completely overlooked that part of Donald's post, DUH! I'm going to order one today and see if that fixes the problem.

Labawg - I'm coming to the realization that this engine is a fuel hog. There's nothing cheap about boat ownership, so this is just one of those things. As Donald mentions in a later post, I'm going to keep my arm out of it and cruise at about 2/3rds throttle. I really don't have 10-15k laying around for a new outboard!

 

[labawg]

Re: Sudden Death at Mid-RPM

Fuel Saver mode will save a lot of gas. These motors were designed when fuel was cheap and people didn't care about how much they burned.

 

[rodttu02]

Re: Sudden Death at Mid-RPM

When you say "Fuel Saver mode," do you mean 2/3rds throttle? If I'm missing some sort of setting, I'd be glad to switch over to that!

I recently sold my 3/4 ton diesel and paid cash for an older, low mileage 1/2 ton. My pocket would be taking a serious beating if I still had that diesel AND this boat...