force 120 outboard

[buckeyedwt1]

My outboard motor on my bayliner is 1997 force 120. It ran great until yesterday. The top speed on water is now about 7 MPH. The rpm meter reads nornal and the throttle appears normal too. It was a little rough to start. The linkage appears normal too. Is this maybe a power head problem? Could too rich oil cause this problem?

 

[maxum247]

Re: force 120 outboard

My outboard motor on my bayliner is 1997 force 120. It ran great until yesterday. The top speed on water is now about 7 MPH. The rpm meter reads nornal and the throttle appears normal too. It was a little rough to start. The linkage appears normal too. Is this maybe a power head problem? Could too rich oil cause this problem?

When you say the (rpm meter reads normal), are you saying that the engine is reaching full rpm (like 5000 rpm) at full throttle, if so could be the rubber center in the propeller hub is spun.

If not reaching full rpm, could be several things.

If useing a portable tank did you have the screw vent open?
Air leak in fuel line
Fuel filter dirty or clogged
Incorrect fuel-oil mixture
Fuel pump pressure, pump may need rebuilding
Throttle valve that operates improperly
Carburetor passages clogged or dirty
Carburetor out of adjustment
Defective or fouled sparkplug, if engine is missing
C-D Ignition Components Failed, if engine is missing

If the head gasket is bad and leaking, the plug on the leaking cylinder will look like new and show water drops on the plug after about 10 minutes run time.

Good Luck!

 

[roscoe]

Re: force 120 outboard

My guess is the tank vent, OR.... your prop has spun on the hub.

Try a different prop.

Extra oil is not going to do this.

 

[buckeyedwt1]

Re: force 120 outboard

It is definitely not the prop. I tried a new one and I get the same result. The tank is internal. Where would I find the tank vent?

 

[maxum247]

Re: force 120 outboard

It is definitely not the prop. I tried a new one and I get the same result. The tank is internal. Where would I find the tank vent?

It's about a 3/4" hose running from the gas tank to the transom area, usually with a little chrome scupper mounted to the outside of the hull area that vents the gas fumes as the gas is sloshing around or the gas tank is being filled at the gas pump. You can here the air rushing out when filling the gas tank if the vent hose is not obstructed.

 

[racer-x]

Re: force 120 outboard

Sounds like my 120 when one cylinder went bad (suspected ring problem) and lost all compression (about 5 psi)
Max speed was 5 mph and the engine wouldn't climb in rpm's.
Let me know what the diagnosis is.

 

[buckeyedwt1]

Re: force 120 outboard

The tank vent has no blockage and appears to be working. I get plenty of rpms. It will go all the way up to 5000. I will try a compression check next and make sure it is is firing correctly. Any other ideas?

 

[maxum247]

Re: force 120 outboard

How did the sparkplugs look when you pulled them, any signs of water?

 

[racer-x]

Re: force 120 outboard

With 5000 rpm's, and no speed, I would think the engine is running okay, and there is a driveline issue. I would think the prop hub has issues..... but I am new to boating! I am very interested in this thread!

 

[maxum247]

Re: force 120 outboard

The tank vent has no blockage and appears to be working. I get plenty of rpms. It will go all the way up to 5000. I will try a compression check next and make sure it is is firing correctly. Any other ideas?

Did compression check out ok?

 

[buckeyedwt1]

Re: force 120 outboard

I had one at 140 and the other three were at 150. I also put in new spark plugs. If it were a linkage problem, where would I adjust? at the motor end or at the throttle and gear selector end?

 

[maxum247]

Re: force 120 outboard

I had one at 140 and the other three were at 150. I also put in new spark plugs. If it were a linkage problem, where would I adjust? at the motor end or at the throttle and gear selector end?

Compression, she sounds good!
adjust linkage at the motor!

Take a sample of the lower unit oil in a clear jar let it settle for awhile and see if there's metal flake in the bottom of the jar.

 

[buckeyedwt1]

Re: force 120 outboard

a sample of the oil doesn't show any metal shavings or particles. it was dark though. doesn't the lower unit call for marine gear oil about 80 weight or so? i

 

[maxum247]

Re: force 120 outboard

a sample of the oil doesn't show any metal shavings or particles. it was dark though. doesn't the lower unit call for marine gear oil about 80 weight or so? i

That's great news, no metal!

SAE 80-90 is a common multigrade gear lubricant.

Spun propeller hub or something in the lower unit or the drive shaft slipping somewhere.
I'd say shift cable adjustment but it seems like you'd notice a grinding noise the lower unit.
I guess the clutch dog could be worn and grabbing enough to give you the 7 mph but I thought for sure if that were the case there would be signs of metal flake in the lower unit oil and you would here the clutch dog grinding on the gear, unless the water and engine noise muffle the grinding so it can't be heard.

Was the prop you tried new as in brand new or was it new used?

 

[buckeyedwt1]

Re: force 120 outboard

It was a different prop but there is no visible or obvious damage to the rubber insert on the inside of the prop. it is fixed and there is no slippage even after clamping it on a vice and trying to turn it . Is this something that i need to have checked by a professional?

 

[maxum247]

Re: force 120 outboard

It was a different prop but there is no visible or obvious damage to the rubber insert on the inside of the prop. it is fixed and there is no slippage even after clamping it on a vice and trying to turn it . Is this something that i need to have checked by a professional?

Draw a heavy straight line with a permanent marker across the hub and splined sleeve in the hub end were the nut goes, put the prop on and put the boat in the water and run around for a few minutes and duplicate the 7 mph conditon at full throttle, trailer the boat, take the prop off and see if the marks still line up, if not the hub is spun.