Mercury 1985 4cyl 75 hp missfire

mercuk

Petty Officer 2nd Class
Joined
Feb 6, 2012
Messages
122
Hi all, Ive noticed something on my engine that it wasn't doing before. For the first say 10 secs of starting it up from cold it sounds like its loosing its spark and running on 2-3 cylinders and I have to throttle up for it to stay running. BUT it only does this for the first 10-15 secs of running then idles fine. Something after 10 secs changes and it will be fine from there on.

I have changed spark plugs, HT leads, checked coils and wiring and I have tested spark from all cyl and have a spark accross a 7/16 gap.....

Any other suggestions out there? Many thanks...
 

snayke62

Cadet
Joined
May 2, 2013
Messages
10
Re: Mercury 1985 4cyl 75 hp missfire

I am no boat expert, but if the spark is good it must be fuel related? like its suckin a little air or loosin its prime somehow maybe. just a thought.
 

mercuk

Petty Officer 2nd Class
Joined
Feb 6, 2012
Messages
122
Re: Mercury 1985 4cyl 75 hp missfire

I am no boat expert, but if the spark is good it must be fuel related? like its suckin a little air or loosin its prime somehow maybe. just a thought.

Thanks for the input. Ive had a think about it and figured one of the carbs is probably not set up right hence why it sounds like it runs on 2/3 cyl and splutery for like 20 secs then all is fine.......

Just seems wierd that it only does it for first 20 secs then seems to sort is self out after that and is fine..
Any other thoughts people??!!!
 

Faztbullet

Supreme Mariner
Joined
Mar 2, 2008
Messages
15,589
Re: Mercury 1985 4cyl 75 hp missfire

Try opening the idle mixture screws 1/8 turn as it could be a lean crankcase backfire....
 

mercuk

Petty Officer 2nd Class
Joined
Feb 6, 2012
Messages
122
Re: Mercury 1985 4cyl 75 hp missfire

Try opening the idle mixture screws 1/8 turn as it could be a lean crankcase backfire....

O.k will do. "lean crankcase backfire" wow, that sounds nasty lol, I will open up the idle mixtures 1/8 and see if that helps the situation. By "open" do you mean counter-clockwise right?!! if not I'll strip the carbs down and see whats going on........

Please remind me which way richens up the mix, clockways right?!.... Thanks
 
Top