That Old Merc… AGAIN!

See original thread, if you wanna….

http://www.idofishing.com/forum/showflat.php/Number/817628/fpart/1/old-merc-fuel-delivery-issues

Alright, guys… I’m back to square 1. Here’s the current status:

Carbs were completely cleaned out
New carb kits (gaskets, needles, seats)
New tank
New fuel lines throughout
New filter

It ran perfectly one time after all this.
It came down to the pump diaphragm.

After running it, a leaf spring on the trailer broke, and it had been sitting for a fwe weeks.

Got the spring fixed, took it out last Tuesday night.

Had to feather the choke to warm her up… it was about 44º at the time.

Ran perfectly after warming up.

Sat again for a week, tried to show it to a potential buyer yesterday, and NOTHING.

It took no time firing up, but I could only keep it running on full choke.
LOTS AND LOTS of heavy exhaust, and an occasional misfire.

Buyer is still interested, but I need to figure it out first.

OKAY-

After that debacle, I emptied out the tank, put in new gas/oil/seafoam.
Results were the same.

Changed the plugs next.

A-HA!

I have successfully exchanged one problem for another!

I didn’t have to choke it anymore.
Instead, I’m back to the ORIGINAL problem…
Must keep priming to keep it running!!

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Here are my observations-

1) Bowls fill when primed
2) Bowls empty when vent screws are taken out
3) I can spray carb cleaner through the (whatever those are, reed blocks? see pic) and I get a full stream out the vents, so I know those are clear
4) The floats are floating
5) The needle valves are valving
6) The fuel pump diaphragm shows no signs of flaws
7) The new plugs show signs of firing (I did not actually check for spark yet)

I’m sure I missed some things.

So, what next?

Any ideas?

I’m going to pull the distributor cap and inspect/clean the points and rotor tonight, then check if I’m getting spark on all 3.

It’s running SUPER rough, and the thick smoke tells me it’s running rich (odd, considering I have to prime MORE gas in just to keep it running). I’ve already messed around with the idle adjust needles PLENTY enough, and could only make the problem worse. I’m still getting the occasional misfire, generally at higher RPMs (in neutral).

Basically, running rich, and not picking up new fuel.

If I’m not running on all 3 cyl all the time, will that affect the ability of the fuel pump to do it’s thing? Would that also account for the smoke?

Man, I gotta get this thing going so I can get it sold!

What is the compression on each of the cyclinders?

i had a problem like that, went thru and changed many items . No help. Another mechanic checked the carb bowl, found a micro-crack.. Used dye-penetrant testing to see crack.. Replaced carb bowl and good to go, no problems. Hope is helps

Newexplorer

Quote:

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i had a problem like that, went thru and changed many items . No help. Another mechanic checked the carb bowl, found a micro-crack.. Used dye-penetrant testing to see crack.. Replaced carb bowl and good to go, no problems. Hope is helps

Newexplorer

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I HOPE that’s not it.

The bowl and carb are one cast unit on this thing.

I haven’t compression tested it yet.

Thought of a couple other options which I’m about to go check into.

Okay, aside from the smoke, it appears as though it starved of fuel. I’ve been getting into the habit of disconnecting the fuel line from the tank when I’m ready to get off the water, and letting the motor burn up the rest of the fuel in the lines.

Last night, when I did this, I noticed that the motor had no problem pulling the rest of the fuel. ALL of the fuel in the line… all the way down to the tank connection.

I’m thinking it might be sucking air, and I have to replace the connection to the tank.

My other possibility regarding the fuel… I did not replace the check valve in the fuel pump.

The fuel line connections and that check valve are the only things that have not been replaced in the fuel sys.

Time to go play in the rain!

Idle is good now, and no more smoke, after more fine-tuning of the idle adjust.

Still isn’t picking up fuel, but I think I have it narrowed down to the stupid primer bulb!

Firing on all 3, still haven’t checked the compression… but it seems to be running great as long as there’s gas present.

There IS still a cough every once in a while, however.

I think I need to stop buying Atwood primer bulbs…