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power drop off

ronnnbeem

New member
i have a 1987 force 125 2cycl outboard that i bought at the beginning of the summer. I have replaced the head gasket,reed valves plugs,cleaned and rebuilt both carbs,and changed the primer pump. i put it in the water this weekend and it started great. it went right to wot and gave me a top speed of close to fifty mph. i had never seen this kind of power out of it before,however after maintaining that speed for about ten minutes it slowly lost power as if it was running out of gas and died. it started right back up but wouldnt let me push the throttle past about one third of the way,but it maintained that speed great. im thinking i have a ignition module heating up and breaking down.i would appreciate any help or advice with this problem
 
What is the compression?

How old is the gas?

Did you suck up some dirty gas?
 
Last edited:
How much oil did you mix with the gas?
Do a compression test.
Check the fuel pump diaphragm.
Check the connections on the fuel lines.
Any old Force/Chrysler connectors can suck air while they seem good.
Check the vent line for clogs, bugs get in their and make nests blocking it off.
Ethanol can be a problem too, melting the inside of the lines.
The "new" squeezie can be bad. There is a check valve that can block the flow.
I've encountered them bad right out of the box.
 
have not done a compression test since changing the head gasket,but the boat seems to run great until it heats up thats when i start seeing the power drop off. i have not changed the fuel pump since i bought it. i have had it out several times this year it has been a work in progress. im using a 50:1 ratio of oil to gas and the gas is fresh, ive checked the lines and changed the primer ball and checked the fuel screen on the pump it was clean. the power drop off has always been an issue thats why ive been changing parts. is there another fuel filter other than the one on the motor i dont see an apperant one.
 
Sounds like you solved your problem.
You didn't mention it getting hot!!!!
Test the overheat buzzer.
Change the impeller.
Check the thermostat.
 
i have a 1987 force 125 2cycl outboard that i bought at the beginning of the summer. I have replaced the head gasket,reed valves plugs,cleaned and rebuilt both carbs,and changed the primer pump. i put it in the water this weekend and it started great. it went right to wot and gave me a top speed of close to fifty mph. i had never seen this kind of power out of it before,however after maintaining that speed for about ten minutes it slowly lost power as if it was running out of gas and died. it started right back up but wouldnt let me push the throttle past about one third of the way,but it maintained that speed great. im thinking i have a ignition module heating up and breaking down.i would appreciate any help or advice with this problem

You are describing a definte fuel starvation problem. I see this engine is on a 1987 Bayliner 1910 Center console. You have several potential problem spots that I have encounter before on these boats. All of the other responses are good "look ats" But here are some other suggestion you might consider suince this has "always been an issue".

1) The Carbs on this modle have a inlet needle seat that is a neoprene insert in the body of the carb that is prone to swelling by the current gasolines. You need a minimum diameter if this opening of at least .058" to maintain a constant fuel level in the carb fuel bowl. Due to the swellig of the needle seat, this opening will close down and will cause a starvation condition. If you are lucky it will do as you are discribing by giving you a warning. If you are unlucky the symtom will be a scorched piston and lost of compression. Compression on these engines ran right at 150 psi new. This is a problem that came apparent in September 1989 when the fuel formulation changed. The response from Mercury/Force was a change in the inlet needle seat to a solid seat with a Viton tip on the needle in the 1990 modle. They offered no retro fit to the earlier modles. We initiated a fit retro during our Anual service program using OEM parts from Walboro and machined the carb body to accept the solid seat with a viton tip. This was an in house progam only.

2) This modle also came with an anti siphon valve in the fuel pick up at the tank. The antisiphon valve is a required saftey feature that stops the free flow of fuel from the tank in case a siphon condition during a fire should occure. The siphon valve is a check valve in side the fuel barb at your fuel tank that is spring loaded. I have seen these valves that require way to much draw pressure to open them. If the neoprene fuel pumps diaphram has been hardened by the current fuels, the fuel pump will not develop enough suction to over come this valve to deliver fuel to your engine. You can adjust this valve by altering the tension on the spring inside the valve. I have had mechanics that just remove the check valve not realizing, understanding or even caring that they are there for a reason. Do not remove the antisiphon feature. This condition can be also accented by the screen at the end of the fuel pickup down inside the tank. Not all of these boats had a screen on the end of the pick up but it is something that can cause your same problem.

I hope this helps you and that the ghost in the Force will no longer be with you.
 
Anti siphon valve on an outboard???
Not on any boat I've seen???
The pump isn't strong enough to pull past the valve.
 
My 21 has 2 fuel pickups in the tank.
Neither has a valve.
The fuel pump isn't strong enough to pull past a valve.
If he had a I/O he'd have a valve.
 
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