1991 4.3 mercruiser intermittent starting issue

[Billy-bob]

Hi all, I having been having starting issue with my boat. Most times it starts fine, will run great, restart after hours of running etc. But a few times usually after a few days of sitting, it just wont start. Spraying quick start will work, then cut off as it uses it up., so getting ignition. Then I go the next day and no issue at all. Rebuilt carb, new ignition sensor and module, new cap, new rotor, wires etc. I'm at a loss since this only shows up at times. I even took it to a marine mech, of course it ran fine and he couldn't fine any issue. He found the timing off and corrected than, but weeks later same issues again! Could it be the interrupter switch acting up? seems to turn off and on in the right position? If it was an all the time problem it would be easier to figure out, since it's only a here and there issue I'm at a loss! This is a cold start issue so i don't see vapor lock being the problem.

 

[Bondo]

Ayuh,..... Welcome Aboard,.... It's a lack of fuel, not ignition, so it's the carb, not electrical,.....

Which carb ya got on it,..??

 

[Billy-bob]

mercarb 2 barrel, just rebuilt, had the float reset to the right height too. But again this is just a sometimes issue

 

[Bondo]

Ayuh,..... If yer not givin' it some throttle when restartin',.....

I'll chalk it up to operator error,....

It's a carb, not Efi,....

 

[Billy-bob]

It aint that, I know how to start it, have had the boat for years, I'm not a young guy so carbs and chokes etc and in my blood. It's just that this is here and there, most times i have no issues whatsoever starting, cold or warm. Also, quick start will ingnite. Is it possible to have vapor lock when cold? or could a partial blocked vent cause it to only sometimes have issue? as i said, i can run in all day on 85f weather with no issues at all

 

[Chris51280]

What kind is your fuel pump. mech or elec? If your boat is standing for awhile, check next time if you have fuel in the carb chamber. Maybe its slowly leaking out and when you want to start it, its empty and needs to be filled again. How long does it take you to get it started after it sat for a while?

 

[Billy-bob]

mechanical pump, when this happens I can't seem to start it at all. I'll let it sit 10-20 mins, even come back later in the day, still nothing, but then the next day, no issue, starts like a charm!

 

[Chris51280]

I had almost a similar scenario. Mine ran fine for half an hour on the water. after 1 hour, nothing. No fuel. Towed back to the marina and then I was told that I had an empty float chamber. Either because of dirt or a stuck float.
So sometimes I guess there are just the little things that keep you from enjoying boating.
I think you got either a carb gremlin or an electrical connection that is intermittent.
Maybe next time when it won't start at all, check for spark.
When you say it wont start at all, did you try spray gas in the carb manually to see if it will fire?

 

[Chris51280]

[No message]

 

[THenning]

When this happened on my 1978 with the Mechanical fuel pump the culprit was the white ethanol crap getting stuck in the anti siphon valve at the fuel tank. Was a pain to figure out.