1981 40hp Mariner Erratic Operation

[63seasprite]

I've got a 1981 Mariner 40 mounted on a 14ft runabout. It starts fine. The engine has spark to both cylinders but never smooths out in idle. It stalls terribly when revved and wants to die. Just removed carb, diassembled, and cleaned. Smoke comes out from the lower cowling assembly. Have not checked compression, but have verified fuel flow is adequate. Installed new plugs, but they are wet when I remove them telling me there's not enough or hot enough spark or too rich fuel mixture. Sounds like it hammers away on 1 cylinder and the 2nd hits erratically causing the motor to jerk hard from side to side. Noticed lots of gas and oil in the test tank. Any ideas? Bad coil? Stator? These were all replaced 2 yrs ago. Thanks,

 

[mellowyellow]

Re: 1981 40hp Mariner Erratic Operation

welcome aboard.<br />first step is to check compression on all cyliders.<br />post results and we'll try to help.<br />M.Y.

 

[63seasprite]

Re: 1981 40hp Mariner Erratic Operation

After reading some other articles similar to mine, let me ask someone this...the tank I'm using is from an old 62 40hp evinrude I used to have and obviously it has the OMC fitting on the tank. I bought a new hose that hooks to the tank, but replaced one end of the hose with a fitting that fits my mariner. Could this be causing the problem, the wrong air / fuel mixture?

 

[mellowyellow]

Re: 1981 40hp Mariner Erratic Operation

not a bad place to start...<br />always start with a new/clean tank w/new gas.<br />eliminates a world of causes IMHO.<br />good luck,<br />M.Y.

 

[63seasprite]

Re: 1981 40hp Mariner Erratic Operation

OK, I checked the compression, both were fine @ around 120psi. While the motor was running, I pulled both plug wires off and each wire caused it to shut off, telling me that they were both firing. Here is an interesting thing I found though...I took my fuel pump apart and found that there is a tear in the outer gasket that goes on top of the diaphragm and the diaphragm has a slight tear in it coming off of the lower right bolt hole. Last night I put it back together and left the fuel line disconnected from the carb. When I cranked the motor, no gas came out. Is that normal or shouldn't it be pumping fuel? Naturally if I squeeze the bulb it shoots out, but not when cranking the motor. I'm thinking that it may be sucking air through those tears in the gasket and diaphragm. They also seem very stretched as well (probably the original). Any ideas?

 

[63seasprite]

Re: 1981 40hp Mariner Erratic Operation

I found the problem I beleive and it's not the fuel system. My top cylinder, if you put a screwdriver or anything within 1/4" of the metal jacket on the end of the plug wire, the spark will ark out to that object. I beleive the spark is grounding out on the block and not firing the plug. If I hold the wire with a screwdriver the right way, the motor speeds up and goes on 2 cylinders. Can I crimp a new wire end onto this wire or do those metal jackets on the existing wires serve another purpose I'm not aware of? I hate to buy an entire new coil just to replace a wire since it's obvious the coil is putting out spark. Can the existing wire be repaired? Any ideas??

 

[25xs Mercury]

Re: 1981 40hp Mariner Erratic Operation

Have you replaced the plugs...? You could completely coat the plug boot in "Liquid Electrical Tape" (marine stores have it) to find out if it's definitely your problem.<br /><br />Now, I am RUNNING home to try the same test on my 1984 Mariner 40hp to see if my erratic running is a spark plug boot.<br /><br />Tom

 

[63seasprite]

Re: 1981 40hp Mariner Erratic Operation

OK, it's been awhile since I've been on here, but now I'm very stumped. I put a new coil and plug boots on along with new plugs. I took the boat out and it ran like a champ for maybe 20min. Then it was starving for gas. I took the carb apart again and found dirt in one of the needle valves. Cleaned and reassembled last night, fired it up in the barrel and it ran great. Shut it off, tried to start it again, nothing. Wouldn't fire at all. Upon looking at it, I see that the stator plate (correct me if I'm wrong), or the smaller round hub under the flywheel had turned so far that it passed the timing screw (there's a screw through a bracket bolted to the side of the block that is supposed to stop the from turning.) The 2 wires that run into this plate are stretched tight. HOW DID THIS HAPPEN? I cannot even begin to think how this happened. I never touched this. More importantly, how to I correct it? I tried turning it back but it doesn't move. I assume I need to remove the flywheel? I'm confused here...