mercruiser 120 missing, stalling

[captainnate]

My 1972 mercruiser 120 was giving me some problems a couple days ago. I had my 1972 Starcraft Nova pretty well loaded, 5 adults in the boat with one adult being pulled on a tube. At about 3,300 rpms it would quickly drop in rpms like I was pulling the trottle back. It did this twice, and then was hard to start. I gave it ten minutes or so and it fired up again. I kept it between 1,000 and 1,200 rpms back to the ramp. Even at those low rpms the motor is consistently running a little rough and missing at times. I bought a tune up kit and i have some new spark plugs. I guess I will start there, and see what happens. thanks for any suggestions.

Nate

 

[Bondo]

My 1972 mercruiser 120 was giving me some problems a couple days ago. I had my 1972 Starcraft Nova pretty well loaded, 5 adults in the boat with one adult being pulled on a tube. At about 3,300 rpms it would quickly drop in rpms like I was pulling the trottle back. It did this twice, and then was hard to start. I gave it ten minutes or so and it fired up again. I kept it between 1,000 and 1,200 rpms back to the ramp. Even at those low rpms the motor is consistently running a little rough and missing at times. I bought a tune up kit and i have some new spark plugs. I guess I will start there, and see what happens. thanks for any suggestions.

Nate

Ayuh,.... Sounds like it's runnin' outa Gas,.... Check the fuel filters,...

 

[captainnate]

I will do it. thanks

 

[captainnate]

Here is an update on my progress. A coworker and I worked on the boat yesterday in the driveway, on muffs. I bought a tune-up kit off Iboats and installed it's contents: cap, rotor, condenser and points. We also noticed that wire coming out the side of the distributor going to the coil was in very poor shape. If you touch the wire lightly it would cause the engine to stumble and sometimes stall. We fashioned a new wire, and replaced what was probably the original wire (42 years old). After a few headaches with the dwell and timing we finally got it running well. We set the time to 8 degrees, but I'm not 100% that is correct; anybody know? It is either 6 or 8 according to the manual. It is a 1972 with a Delco distributor. The engine is running much better now, and not missing like it was before.

 

[MikDee]

Then you found your problem, good work! Let us know if there's any other issues.

 

[captainnate]

Okay, so since my last post I have had the boat to the lake twice. She runs really nice at higher rpm's now. At idle it runs well, but there seems to be extra vibration in the back of the boat by the engine. Don't get me wrong, the engine is idling smoother, but there is some vibration. Maybe I need to just adjust the idle a little, not sure. Sometimes I think I need a new shift cable, but then again the boat shifts better now that the engine is running better. Thanks for the input.

 

[captainnate]

It looks like I still have a problem. I had the boat out on Saginaw Bay a couple days ago, and it worked fine until I was almost back to the launch. The engine sounded like somebody was pulling the throttle back, and then it died. I restarted it after a couple tries and made it back to the launch while doing no more than 1,200 rpms. From all my web based research it seems to be either a fuel problem or maybe the ignition coil. I ordered a new coil, hopefully that will do it. I had a mechanic working on the engine a few years ago, and I think he put in an automotive coil. I don't know what the difference would be between an automotive and marine coil?

Anybody have a similar problem?

 

[Bondo]

It looks like I still have a problem. I had the boat out on Saginaw Bay a couple days ago, and it worked fine until I was almost back to the launch. The engine sounded like somebody was pulling the throttle back, and then it died. I restarted it after a couple tries and made it back to the launch while doing no more than 1,200 rpms. From all my web based research it seems to be either a fuel problem or maybe the ignition coil. I ordered a new coil, hopefully that will do it. I had a mechanic working on the engine a few years ago, and I think he put in an automotive coil. I don't know what the difference would be between an automotive and marine coil?

Anybody have a similar problem?

Ayuh,.... Have ya checked, 'n change the fuel Filters since this started,..??

Ya oughta plumb in a canister type filter, just ahead of the fuel pump,...
They make catchin' Water, 'n crud much Easier,...