3 ltr merc hard start, run rich, stall at idle

[Marpet]

95 merc 3 ltr, aplha 1 EST ignition

First the background...

Purchased the boat in early Aug, used. Ran it a few times with no issues. Ran well, pulled well, idled well. Replaced tach, crossed wires and the boat wouldn't start (grounded out the coil = weak spark). Finally figured out the problem and unhooked the new tach(fried) and got the boat running. Black smoke at start but cleared up and idled smooth and well on driveway. Took boat to lake this weekend, fired right up but then noticed it was bogging down at all throttle positions (if left there long enough), wouldn't idle without stall, and required 15 to 20 seconds of cranking with throttle wide open to start. Was noticing some miss firing later in the day and decided to finally pull the boat off. Also, even idleing at increased rpm, black smoke and fuel smell present.
When looking for the initial problem (crossed wires on tach), I regapped the plugs, checked the rotor and distributor, checked spark(good) on all cylinders and the coil, pulled the fuel screen on the carb and cleaned, pulled the distributor module and verified ground, added fuel stabilizer for this last trip, ran 92 octane gas with no ethanol.
So, any ideas on the hard start, the idling issues, etc.
I think it's fuel delivery related, maybe carb rebuild but why just bad all of a sudden?
Where should I start?

Great forum guys, keep up the good work.

Marpet

 

[cr2k]

Re: 3 ltr merc hard start, run rich, stall at idle

That definitely sounds like a carb issue. Float sticking.

 

[fat fanny]

Re: 3 ltr merc hard start, run rich, stall at idle

most definatlely getting to much fuel

 

[Bondo]

Re: 3 ltr merc hard start, run rich, stall at idle

I think it's fuel delivery related, maybe carb rebuild

Ayuh,... I can agree with That...

 

[Don S]

Re: 3 ltr merc hard start, run rich, stall at idle

Does the choke open when it warms up?

There is a clear hose that goes from the fuel pump to the carb. This hose should have nothing in it. All it's there for is if the fuel pump diaphram fails, fuel is pumped to the carb and not the bilge. If your fuel pump fails, it could be pumping raw gas directily into your carb, and causing your problem.

 

[Marpet]

Re: 3 ltr merc hard start, run rich, stall at idle

Choke is wide open, and the clear line is...clear. Brand new fuel pump, so I will assume for now that it is not the problem. Will check the float.

Thanks for the quick replies.

Gord

 

[Marpet]

Re: 3 ltr merc hard start, run rich, stall at idle

Checked the float and it measured 9/16 from the reference point to the gasket (or where the gasket would be if there), need a new gasket so can't put it back together. I'm trying to understand how it works, if the float is stuck in the up position, then that would slow the flow of gas to the bowl, and opposite if stuck down? If that is the case then I need to check the drop and the weight to see if there is a hole in the float?
Nothing else out of the ordinary, some small sediment in the bowl but the jets seemed fine and if they were restricted, wouldn't that give mean a lean situation and not a rich one?
Any other ideas?

Gord

 

[Marpet]

Re: 3 ltr merc hard start, run rich, stall at idle

I should also mention, when driving to the lake, I hit a curb pretty hard. Hard enough to stop and check the tire and rim for damage. The boat bounced pretty hard on the trailer. It's probably unlikely but would that be enough to knock the carb out of tune? I can't see it but thought it would be worth mentioning.
The lake is a hours highway drive from home so I would figure that the jarring from the curb would be shaken off by the time we got to the lake. The float would drop if stuck up and rise if stuck down.

gord

 

[T-Bone Coug]

Re: 3 ltr merc hard start, run rich, stall at idle

Checked the float and it measured 9/16 from the reference point to the gasket (or where the gasket would be if there), need a new gasket so can't put it back together. I'm trying to understand how it works, if the float is stuck in the up position, then that would slow the flow of gas to the bowl, and opposite if stuck down? If that is the case then I need to check the drop and the weight to see if there is a hole in the float?
Nothing else out of the ordinary, some small sediment in the bowl but the jets seemed fine and if they were restricted, wouldn't that give mean a lean situation and not a rich one?
Any other ideas?

Gord

When float is up, fuel should completely stop flowing. The needle under the float tang should shut off fuel when the float is properly adjusted at 9/16". If your needle is the spring loaded version, then your current adjustment is correct. If you have a solid needle the measurement should be 3/8". If you are already adjusted to spec and are still flooding, then you either have a bad needle/seat or a bad float. If this is the case I would suggest a complete rebuild of the carb (including new alcohol resistant float) to ensure everything is clean and sediment free.

 

[Marpet]

Re: 3 ltr merc hard start, run rich, stall at idle

Have the carb rebuild on order. Will do the rebuild and then see where I stand.
Unsure why it came on so quick but a rebuilt carb can't hurt. Hopefully it gets here soon, starting to get cold.

Gord