mercury outboard wont start

[belizesailor]

Originally Posted by Buzzman

Can't believe no-one suggested checking the plug gap.....and grounding against block while turning over to check for spark.

Air. Fuel. Spark.

Not rocket science.

Suck, squeeze, bang, blow...that's what makes the engine go! [emoji16]

[Houtrib]

Mercury 15 hp 2 stroke 1995. Ran well on test two days ago on mixture of old (2017) and less old fuel (premium and stabilised). Today would not idle but was able to run for 45 minutes at cruising revs to get where I wanted to be. Removed low speed mixture screw (with concentric spring) and hosed out threaded recess and associated very small airways with aerosol carburettor cleaner. Replaced low speed mixture screw. Screwed in firm but not tight then backed out 1.5 turns. Motor idled fine - job done.
I hate stripping the carbie. The choke assembly is always difficult to refit. The above was done, pitching in a dinghy, swinging on a mooring. The low speed mixture screw is brass and about 40 mm long. Its size and the fact that the concentric spring is a firm fit on the screw reduces the risk of losing it overboard. Final tuning will be done when calm.

[radsailor]

It looks like I have come to the right place.

I have a 5 year old 4hp 4 stroke mercury outboard that worked fine until about six weeks ago, although in order to start it I had to have the throttle wide open. Once started it ran smooth and quiet.

Now, sometimes it starts on the first pull and runs great. The majority of the time, it will try to start on the first pull and on the 30th pull, but will not get beyond a sputter or sometimes a few seconds of very very low speed running, but then dies.

I have it hooked up to a new external tank with new fuel line, quick connect at motor end and new bulb. Ethanol fuel with treatment. I also tried filling the internal tank with ethanol free fuel, but same problem.

The marina mechanic told me it was because it was cold (Southern Virginia). I lived in New England for 40 years and never had trouble starting my snow blower in much much colder weather.

I spoke with a mercury mechanic on the phone who thought it might be a tear in the fuel pump diaphragm or a problem with the carburetor. I know nothing about engines. I just cannot see how either of these problems fit what I am observing. Again, if I get it started, it runs great.