1997 Force 120

[jasonbradmorris]

I bought a Tidecraft Wildfire 120. It has a 2 stroke Force made by Mercury Marine on the back. I am having a very particular problem.

A little over 2 years ago, I was on the water at a sizable lake, and I noticed that the motor wanted to die at full throttle. I would ease back to 3/4 throttle and it would be fine. I just couldn't run wide open. What I found odd about this was that it came after a fuel change. It had some older gas mixed at 50:1 when I got there. I ran all of the gas out of it and had to refuel. The aforementioned problem started immediately after.

The same gas was in the tank about a month ago. I take the boat out to a local river and NEVER HAD A SINGLE PROBLEM out of it. I fished a tournament this past weekend. On Saturday, I had the problem again. It would not want to run at full throttle. I eased it back and didn't give it another thought. On Sunday, however, just as soon at the boat would plane out, the motor would start to hesitate, sputter, and want to die. If I put the boat into neutral, it wouldn't die. It idles fine. It will start fine. It will full throttle up until the plane, but once it planes out...DEATH TO FORWARD MOMENTUM.

If anyone has any ideas on why the motor likes old gas and not the newer, better stuff, I am all ears. I replaced the plugs. The bulb is not deflated after running the motor. I am out of ideas on what this could be. Please help.

Brad M.

 

[pnwboat]

Re: 1997 Force 120

Sounds like you might have a fuel supply issue. Just want to make sure that I understand what you're saying. From what I gather, you said the problem started right after you ran out of gas? If so, you probably sucked some debris up into the fuel lines. Do you have an in-line fuel filter between the fuel pump and carburetors? If so replace it. You may also have to replace the fuel pump diaphragm too. It may have gotten some crud in there too.

 

[jasonbradmorris]

Re: 1997 Force 120

I did not run OUT of gas. I was running low and pulled into the Marina to refuel. I was not completely out. The thing that was giving me the most head scratching is the old gas/new gas thing. It may just be a huge coincidence, but it I dont know. Also, where can I find a diagram of the engine or repair manual online?

 

[pnwboat]

Re: 1997 Force 120

OK, thanks for the clarification. Sounds like the motor is running too lean (not enough fuel) at wide open throttle. First thing you probably want to look at is the fuel pump. Replace the diaphragm and check valves. If it's the square shaped pump, the fuel pump kit contains all of these components.

Someone recently posted a link to some manuals on line, however, I've not used them. There are hard copy manuals available through IBoats, and many other sources that you can order.

 

[jasonbradmorris]

Re: 1997 Force 120

Thanks for the help. I am ABSOLUTELY not a mechanic, and this is my first venture into fixing my own boat motor. I am not sure what the fuel pump looks like or where it is located. I opened up the hood/cover and traced out the path of my fuel line. From the primer bulb, it goes into a fuel filter and then into a square place on the right side of the motor. From there, it goes into my 2 carbs, but there is a small round piece that is connected, via rubber hoses about 8 inches away from the carbs on the left side of the motor. I am ASSUMING that the square piece on the right side of the motor is the fuel pump, but I do not know what the other piece is on the right side.. It is about 2 inches long and smaller than a travel size Tylenol bottle.

I guess that I just need to buy a repair manual and hope for the best.

 

[pnwboat]

Re: 1997 Force 120

Yes, the square thing on the side is the fuel pump. The other little thing that you are describing is probably the "fuel enrichment solenoid". Basically it's the choke for the carburetors. It squirts extra gas into the engine to make it easier to start when it's cold.

 

[jasonbradmorris]

Re: 1997 Force 120

Do you have any thoughts on why it would run right with 2 year old gas in it and not newer, better gas TWICE!!

 

[pnwboat]

Re: 1997 Force 120

I don't think that the gas itself really has anything to do with it, although it's always good practice to use fresh gas. I would suspect that the real cause of your problem is something in the fuel supply to the motor. It was probably just coincidence that it ran better twice with old fuel.

 

[jasonbradmorris]

Re: 1997 Force 120

ok. I finished taking apart EVERYTHING that I could get my wrench on and found NOTHING wrong with anything that I checked. The seals for the carb bowls were bad and I will be replacing them in a few moments. I took the pump apart and no no damage to the diaphragm or any trash. I pulled off the filter next. It didnt show any signs of being clogged, dirty, or contaminated. I pulled the bowls off the carbs to check for debris in them and didnt find anything there either. I am not finding any dry rot on any hoses. I am at a loss here. There doesnt seem to be anything wrong with anything that I am looking at.

 

[pnwboat]

Re: 1997 Force 120

It's hard to tell if the rubber diaphragm in the fuel pump is working the way it should unless you find an obvious tear. If the rubber diaphragm is soft and pliable, then it is probably OK. If it's gotten stiff and not as pliable from age, then it may not work as well and could be causing a problem when the fuel demand increases.

There is one other possibility that I didn't think of and that was the fuel tank vent. As the motor sucks the fuel out of the tank, the vent allows air into the tank so that it doesn't create a vacuum in the tank. You can test this by simply opening the gas cap slightly to allow air into the gas tank.

 

[73Chrysler105]

Re: 1997 Force 120

There is one other possibility that I didn't think of and that was the fuel tank vent. As the motor sucks the fuel out of the tank, the vent allows air into the tank so that it doesn't create a vacuum in the tank. You can test this by simply opening the gas cap slightly to allow air into the gas tank.

I have forgotten to open the vent on my tanks a few times and always cant seem to figure out why it wont run full throttle. Thats when we came up with the name for the boat "Operator Error"

Check the vents even if you dont have to open them yourself they may be plugged and not allowing enough air in.

Chris
73 Galaxie Works Tri Hull
73 Chrysler 105 HP Outboard

 

[jasonbradmorris]

Re: 1997 Force 120

Took it out this weekend, all the vents worked perfect. The diaphragm in the fuel pump is not hard, cracked, broken, or any of those things. I bought a new fuel filter and plugs. My carbs are clean and working fine.

I am out of ideas. I do not have the $500 for the rough estimate that the local marine mechanic gave me to take a look at the problem.