#4 cylinder not firing

[michaeli84]

I was trying to get a smooth idle on my 140 merc today and just couldnt get it smooth. Finally , it seemed like it wasnt firing on al cylinders. I began pulling off plug wires while the engine was running. 1 2 3 responded by running rough but when reconnected went back to normal. However, when i pulled #4 nothing happened. I pulled the plug out and checked it and it looked fine. I then turned the motor with the plug out to see if any water came out but none did. These plugs are only a year old what do you think caused this to happen? I took an old plug from the previous tune up cleaned it up and popped it in, reconnected the wire, fired it up, and began pulling wires again this time it stumbled when i pulled the wire off. I want to know how/why that plug went bad and if the engine will be ok. I got it to idle very smooth once i fixed that problem. What could have caused this to happen? Also, i pull the plugs and clean them after every 4 hours or so. I noticed that they are heavily carbon fouled everytime. The spark is strong and the mixture is not too rich and the only time i idle alot is when im warming up on routine starts during the week for maybe 10 min at a time just to keep everything lubed and moving. Is this normal? Should i not start it up every other day like i have? well thats all for now thank you guys for your help!

 

[Don S]

Re: #4 cylinder not firing

Do a compression check, check the plug wire, swap the spark plugs from a good cylinder to the bad and see if it changes.
Could be the carb adjusted wrong or needing rebuilt.

 

[michaeli84]

Re: #4 cylinder not firing

I put a new plug in there and now its firing. When i put the choke on wrong the last run the motor run like crap. Now i fixed the chocke and cleaned the carb the feul line feul filter and changed the water separator. do you think when the choke was messed and i ran it thats what made that plug stop working and the cylinder to stop firing?

 

[Don S]

Re: #4 cylinder not firing

Full tune ups should happen to a marine engine yearly so they run at their best. Especially if they set for 8 or 9 months of the year while winterized.
How old were your spark plugs? or do you even know?

 

[michaeli84]

Re: #4 cylinder not firing

I stated in my post not even a year. I basically do a mini tune up after every use and i go out in the bay once a week. I just take the distrubutor cap off and clean the plate and sand the points and clean all the connections to the coil starter alternator cleah carb filter and change oil and filter every 10 hours and substitute one quart with marvel mystery oil. I put it in the fuel tank also and always keep a full tank of gas. Oh and clean plugs and blow everything out with compressed air. I also claen any rust and paint it I spend alot of time taking care of the motor cause i want to be able to trust it when i go out fishing near the ocean.DONT WANT TO GET STUCK OUT THERE !!!