rough idle 1985 merc 140

[michaeli84]

I recently was having truoble starting my boat. I had to put the throttle all the way down for it to start and then back off it so it wont over rev. I seen that when the throttle was in the neutral position the choke was closed. When i put the throotle lever all the way down it would open up just about 1/8 in and the engine would fire right up. So i took the choke off another carb i had (the same style of course) and swaped them. When i did it i put too much tension on the choke i guess. When i took the boat out i was trolling for about 30 min at 1100rpm. When i went to speed up it started bogging bad almost like it was missing when i gave it gas. I took it back in slowly and came home and took the choke apart and read the manual and put it back the right way. I pulled the spark plugs and they were black with carbon. i previously cleaned them befor this last run. I turned the mixture screw to try and lean it out a little but it dont seem to make a difference. After putting everything back the way it was now i have a rough idle and i cant get it to smooth out. I replaced the water seperater also cause it was overdue. However when i put it to throttle only and rev it up it is very smooth. What should i do to fix this problem. It had a full tune up this season and the carb was rebuilt 2 seasons ago i use startron in the gas sometimes and mrvel mystery oil some time but not together. Sorry it is so long i wanted to be detailed so you can be accurate with your input thank you mike.

 

[Don S]

Re: rough idle 1985 merc 140

Does the choke plate open when the engine is warm?

Do you have an electric choke? Has it ever worked since the rebuild of the carb?

 

[michaeli84]

Re: rough idle 1985 merc 140

Yes, its an electric choke and it was working. When boat is at normal temp it is open all the way. I need to know how to adjust the mixture. Also, i forgot to add when i changed the water separater, i put the gas in a clear glass and their was not any water but there appeared to be alot of rust particles floating around. Maybe that could have had something to do with it also? thanx mike

 

[Don S]

Re: rough idle 1985 merc 140

when i changed the water separater, i put the gas in a clear glass and their was not any water but there appeared to be alot of rust particles floating around. Maybe that could have had something to do with it also?

Hopefully you didn't reuse that filter.

I just rebuilt a carb that really didn't look that bad inside, but it had a rough idle I could clear up by adjusting the mixture screw out about 3 and a half turns. But when you brought it back to idle it always died.
After the rebuild and the proper idle mixture, it works great. Final mixture has to be done on the boat with it running at idle.

 

[michaeli84]

Re: rough idle 1985 merc 140

no/ i did not use the old one i replaced it with a bigger one. When i adjust the mixture what do i do whilr turning that needle? just listen for it to smooth out? whar way is rich and what way is lean? When do i know its just right? Thanx