Mercury Force 120hp Fuel Port Cover Issue and Carb Overflow

[GTMustang]

Hey Guys,

I'm 100% new to boating and I'm 100% new to forums (any forum) and and this was the only spot I saw Mercury and Sterndrive in the same sentence. I have a 120hp Sterndrive force engine that had a blown fuel port cover gasket. I ordered a new one and installed it (it had what looked like a sealing compound on one side) after installing that it seemed to be good for a few startups but now I'm getting a POOF of smoke out of that port cover when the motor first starts and when it shuts down. I don't see that it's blown out again. Should I have put some sort of other sealing compound on it before installing it? Also worth noting is that cylinder has about 30psi on a compression test. All other cylinders have 125ish. Also, my bottom carburetor overflows with fuel and drips off the bottom of the bowl when the engine is running with a little throttle, if i put it back to "neutral" it will idle for about 10-15 seconds and shutdown. I took the bowl off and there was a little bit of corrosion at the bottom, the float moves very freely. Sorry in advance if this needs moved to the right section. Thanks for any input you guys might have!

GTMustang

 

[Scott Danforth]

First, Welcome aboard

unfortunately sterndrive and force are not the same.

would you have a Force L-drive? would have been found on a few bayliners in the 89-91 year range. its basically an outboard motor shoved thru the hull.

it is not an outboard, it is not an I/O (sterndrive) and its a force only with minimal to zero parts support.

The L-drive was made up of a 2 cycle powerhead from an outboard, a "custom" drive unit, connected to a lower unit from an outboard.

They are a bit problematic. the parts you can find are more expensive than either an OB or I/O equivalent.

A bit of history on Force

Chrysler sold its outboard engine division to bayliner who gave them the Force name so they could have a low-cost engine to factory rig their boats

Brunswick purchased bayliner, and the motor division came with it. Brunswick owns Mercury, so they "upgraded" the force line with CDI ignition and a mercury lower gear gase, props, etc. however for years the power head was unique.

it was an entry level, 2nd tier motor brand.

The L-drive was intended to put an inexpensive motor in an entry level boat. unfortunately the market place wanted a bit more performance, reliability, etc. and the concept died shortly after its conception

 

[GTMustang]

First, Welcome aboard

unfortunately sterndrive and force are not the same.

would you have a Force L-drive? would have been found on a few bayliners in the 89-91 year range. its basically an outboard motor shoved thru the hull.

it is not an outboard, it is not an I/O (sterndrive) and its a force only with minimal to zero parts support.

The L-drive was made up of a 2 cycle powerhead from an outboard, a "custom" drive unit, connected to a lower unit from an outboard.

They are a bit problematic. the parts you can find are more expensive than either an OB or I/O equivalent.

Yes, it is a force L-Drive, I should have been more specific. The boat is a 1990 Bayliner Capri (not sure of the sub-model). I can see that parts are pretty limited out there but thankfully so far i haven't needed anything major. As long as this 30psi on the bottom cylinder turns out to be the fuel port cover gasket leaking again I'll be happy. I picked up the boat from a guy at work for $200, so I thought why not try it for 200 bucks there's a lot of items on these boats that sell for some decent money. And the trailer is in great shape. I'm in the boat for about 250 now, I think I'm pretty close to putting it on the water for the first time. Any input is greatly appreciated. (Just saw your edit, thanks for the info!)

GTMustang

 

[flyingscott]

I will bet that 30 psi is going to be more than that fuel gasket. More than likely a bad head gasket or smoked piston. The carb leaking could be a bad needle and seat or a misadjusted float.

 

[GTMustang]

I will bet that 30 psi is going to be more than that fuel gasket. More than likely a bad head gasket or smoked piston. The carb leaking could be a bad needle and seat or a misadjusted float.

I plan on getting a leak down tester this weekend and see if I can tell where its leaking from. Also going to pull that carb off and go through it. REALLY hoping its nothing major with the cylinder having low compression.

 

[pnwboat]

With only 30LBS of compression in that one cylinder, that means you are not getting full power. Usually a broken ring, damaged cylinder walls, or bad piston, is the cause for low compression. Sometimes all 3 things occur together. To correct this you may need to replace the piston and rings. You might have to have the cylinder bored to the next larger size of piston if the cylinder walls have been damaged enough to prevent the rings from sealing.

I would suspect that the reason you're getting a puff of smoke from that cylinder on start up and shutdown is that the ring seal on that cylinder is so bad that you're getting significant amounts of blow-by. The ring seal is no longer confining the pressure of combustion in the combustion chamber and it's blowing past the rings into the crankcase, which is part of the induction system in a 2-stroke motor.

Fuel dripping from the carburetor usually indicates that the needle valve is bad, or debris is caught between the needle valve and seat, or the float is not adjusted correctly.

I've attached some pictures of an L Drive set up and a standard outboard set up.

FORCE L-Drive set up.


Standard FORCE outboard set up.

 

[GTMustang]

With only 30LBS of compression in that one cylinder, that means you are not getting full power. Usually a broken ring, damaged cylinder walls, or bad piston, is the cause for low compression. Sometimes all 3 things occur together. To correct this you may need to replace the piston and rings. You might have to have the cylinder bored to the next larger size of piston if the cylinder walls have been damaged enough to prevent the rings from sealing.

I would suspect that the reason you're getting a puff of smoke from that cylinder on start up and shutdown is that the ring seal on that cylinder is so bad that you're getting significant amounts of blow-by. The ring seal is no longer confining the pressure of combustion in the combustion chamber and it's blowing past the rings into the crankcase, which is part of the induction system in a 2-stroke motor.

Fuel dripping from the carburetor usually indicates that the needle valve is bad, or debris is caught between the needle valve and seat, or the float is not adjusted correctly.

I've attached some pictures of an L Drive set up and a standard outboard set up.

FORCE L-Drive set up.


Standard FORCE outboard set up.

WELL SHOOT, now you guys have me worried. I know its just the reality of the situation. The darn thing runs pretty stinkin' smooth so I didn't think something pretty major could be wrong with it. I will get a leakdown tester this weekend and keep my fingers crossed that it's nothing to major. I've watched quite a few videos on those things and know what to listen for for certain leaks. It doesn't seem like there's much to these engines to rebuild unless of course machining is needed. Are items for these engines just really hard to find? Or really expensive?

 

[Scott Danforth]

the exhaust hose is like $220. the rest of the part number are NLA

same goes for most of the drive parts

 

[GTMustang]

the exhaust hose is like $220. the rest of the part number are NLA

same goes for most of the drive parts

I hate to give up on it now, I got it so cheap. At least i think it was cheap? I'll call a mechanic buddy and see if he works on boats and prepare for the worst HAHA! Do the leak down test this weekend and go from there.

 

[GTMustang]

Thanks for all the replies guys, I will post an update here what I find on the bottom cylinder this weekend. If anyone has had any experience taking these force engines out and apart and have any tips or tricks let me know. Thanks again!

 

[pnwboat]

There are numerous Forum members here that have taken these motors apart (for the first time) and successfully completed repairs. If you're a DIY'er, then you shouldn't have too much trouble working on these motors. They're 2-stoke, old school design and fairly simple.

 

[jerryjerry05]

30# is probably a bunch wrong.
​Don't bother with a leakdown, just remove the head and check the gasket.

Fuel back through the carb could be the bad piston??.
​Could be the reeds??
​The poof of smoke (backfire) is the engine telling you that it's sucking air and the fuel air ratio is off and somethings wrong.

I just rebuilt a 125(same as a 120) and it's fairly easy.
​Just gotta make sure the crank locating pins fit in the bearing hole.
And the pistons aren't in backwards.

Make a signature for the bottom of your posts and include your location.
You might be close to someone who can help???

 

[GTMustang]

30# is probably a bunch wrong.
​Don't bother with a leakdown, just remove the head and check the gasket.

Fuel back through the carb could be the bad piston??.
​Could be the reeds??
​The poof of smoke (backfire) is the engine telling you that it's sucking air and the fuel air ratio is off and somethings wrong.

I just rebuilt a 125(same as a 120) and it's fairly easy.
​Just gotta make sure the crank locating pins fit in the bearing hole.
And the pistons aren't in backwards.

Make a signature for the bottom of your posts and include your location.
You might be close to someone who can help???

Will do, the only reason I'm wanting to do a leakdown test is to get a general idea of where the problem is coming from. If a leakdown isn't the way to go then maybe I will pull the head and see what I can see. Can you point me in the direction of a good rebuild setup? The poof of smoke doesn't sound like a backfire, it actually doesnt make much noise at all besides a woosh of air and the smoke of course, the poof of smoke actually comes out of that exhaust port cover, like maybe the gasket has went bad again. Thanks for the info Jerry!

 

[jerryjerry05]

Believe me the poof is a backfire, it doesn't have to be loud.

​At 30# there won't be much to leak.
​The leak down usually tells the condition of the rings and valves(no valves)
Remove that cover and check the condition of the side of the piston.
If the boats ever been in salt water?? Then it can be a lot harder.
​The exhaust chest has MANY (25) 1/4-20 X3 screws. They can seize and twist off very easy.
​You can remove it to check the other side.Be careful.

 

[GTMustang]

Figured I would post an update since I sold the boat and the guy who bought it was able to take the engine apart and figure out what was wrong with it. He said that it looked like the water pump had failed and melted the bottom piston. He has since got a new engine for it and re-upholstered and put in new carpet, has it running and out on the water again. Thanks for all the help guys and sorry it took so long to give an update.

 

[jerryjerry05]

Thanks,
Usually the melted piston isn't from an overheat but an air leak somewhere?
Sucking air on 1 piston can cause it to get so hot it then melts that piston.

Glad he's got to use it.