2.5 mercruizer not running on all cylinders

[adam1psu]

today my 1980 2.5l (chevy) with a mercruizer drive worked fine all day getting to and from fishing locations. I turned it over to head for the docks. When the engine started I heard a loud pop sounding like a backfire. the engine idoled rough for about 10 seconds then shut down. It now is not running on all for cylinders for i can smell gas in the exhaust and it will not stay running for more than a few seconds. I am going to tear into it tomorow starting with the ignition electronics to find the problem. any suggestions? one other thing the last three times i had it on the water i could smell a burnt rubber smell at high rmp. i thought it was my coupler slipping but now i think it is electrical. any suggestions will be appreciated- thanks

 

[Don S]

Re: 2.5 mercruizer not running on all cylinders

First thing to do would be to pull the spark plugs and look at them.
See if there is water, physical damage, one looking a lot different than the others.
Check your fuel filter/water seperator for water.
Make sure you have spark on all 4 plugs.
The burnt rubber may be lack of cooling water and burning of the exhaust hose.
You are there, look!

 

[Boatist]

Re: 2.5 mercruizer not running on all cylinders

I agree with Don.
Don't assume it electrical and start throwing parts at it. Instead troubleshoot it and find the problem then fix the problem.
While you have the plugs out Check for spark to each plug. Also do a compression check and make sure you have proper compression on all cylinders. Then put a timing light on it and make sure it is in time.

You can pull the plug wires one at a time and see if they all make the same amount of difference. If one makes no different then that is the bad cylinder.

Fuel is the hardest thing to check so do it last after you have made sure the compression and spark are good.

 

[adam1psu]

Re: 2.5 mercruizer not running on all cylinders

thanks for the info, it was an easy fix one plug had the insulation cracked on it. the rubber smell might be from the plug arching inside the rubber boot. as far as the exhaust hose burning the engine stays cool so im pretty sure it is not the problem.

Can anyone tell me the correct spark plug gap for this engine? thanks again guys.

 

[180shabah]

Re: 2.5 mercruizer not running on all cylinders

That'll do it. Glad it was simple.