1996 5.7 Mercruiser Alpha II lumpy and stalling at takeoff.

[subysti]

OK I searched and couldn't seem to find an answer. I have a 96 Larson 194 Lxi with 5.7 LX with Thunderbolt V with 2bbl carb. Was running fine then couple hours in it started to stall when accelerating from idle. Starts right back up no problem but a little lumpy with idle. Engages outdrive at idle fine but when shifting out of idle it wants to stall. If it jam it forward fast it jumps and takes off and seems to run fine at high speeds. Cruised back to dock at 35mph for a few miles fine. Replaced fuel filter and checked carb filter/screen. Pulled 5 of 8 plugs so far and all look good. Pulled distributer cap, looked OK but cleaned anyways. Thought idle/shift switch adjustment but that wouldn't explain lumpy idle. Thought fuel pump/clog but then it should run worse at higher speeds? Gonna pull the last 3 plugs and take a look but would a bad plug or 2 cause it to stall?

 

[alldodge]

Shift interrupter switch would cause idle issues if it was not working correctly or not adjusted properly. The interrupter switch interrupts spark going to the plugs

 

[subysti]

Isn't that switch either on or off. How would it cause a bad idle?

 

[thumpar]

When is the last time the carb was cleaned and rebuilt? The circuits are different for idle and high speed so the idle circuit could be dirty causing the problem.

 

[Phreaq]

Bad linkage adjustment, I think, can cause the switch to activate in neutral. i.e. Bad idle.

If you are in there with a meter, I would love to know the resistance for the switch. when it is closed.

 

[thumpar]

Bad linkage adjustment, I think, can cause the switch to activate in neutral. i.e. Bad idle.

That would kill the engine not cause bad idle.

 

[NHGuy]

Yah, I think the Mercruiser doesn't do a partial ignition interrupt like some others do. Mercruiser is an ignition cutoff. So check out the carb idle circuit. Might have some junk in there.

 

[subysti]

I'm not sure but I may have found the problem. Plug number 8 when I pulled it seemed wet so it may have been a bad connection. I tested the cable with a spark tester and the cable was fine so I reattached it. While I was down there I noticed the return line from the carb to the fuel pump didn't look right. I'm guessing its a return line, it comes from the top of the back of the carb and goes down to the fuel pump. The hose looked to be about 90% plugged up with crap so I cleaned it out. Engine is running and accelerating fine now in the yard, the real test will be under load it the water. I couldn't find that hose anywhere in the service manual.

 

[thumpar]

If you are referring to the clear line it is not a return line. Carbs don't use return lines. It is a tell tail if the fuel pump diaphragm goes out. The pump will dump the extra fuel into the carb instead of the crankcase. There should not be fuel in that line.

 

[alldodge]

Don't see a carb issue, the clogging will not start and stop and cause it to run fine then bad and back again. The switch can be bouncing internally from the vibration. Either way subysti you have a couple issue to try. Good luck and let us know if you can advise of any other issues or need any other opinions/suggestions