2000 Mercruiser 4.3 2bbl refuses to stay started for more than 5-6 seconds

[Porschesolutions]

I’ve lost my second summer now due to this bargain boat buy.

I have a low hour VIP runabout with a 4.3 Mercruiser with a Gen2 Alpha.

Due to mis-tune last year and a dishonest past owner, I ended up with a warped head, mixed fluids, and roasted water shutters, so I just performed a valve job, rebuilt the carburetor, replaced the fuel, oil, gear lube, impeller, plugs, cap, rotor, wires, oil, water shutters, etc- it’s ready to start.

Mixture screw is 1.25 turned out from fully seated.

Idle cam is two full turns in from initial contact.

Timing is roughly 10D BTDC

Disty, wires, rotor are all set for 1-6-5-4-3-2, confirmed compression stroke and via timing light. Mk

Fuel filter is recent and pump is strong when bridged- I pumped out the tank via simply removing the hard line into the carb and powering the pump, it flows well!

Problem is, boat won’t start for more than 5-6 seconds, then dies. I give it a two pumps and start it up over and over to no avail- it’s like the pump works when cranking but shuts off once it catches. I can do this for an hour straight.

I read that there’s a pump cut that engages when OP is low, though OP can be “ok” idling at a mere 4psi so I dunno. I plan to re-bridge the fuel pump tonight and see if it starts in case there’s an active interrupt, otherwise I’m out of ideas.

ok i ran the pump off the battery and it does the same thing.

last night, started the boat with the battery directly powering the pump- no difference.

Verified compression one last time at 160psii across the board.

Anything I might have missed???

 

[poconojoe]

All that work and now this problem...must be frustrating.
Carb problem? I don't know a whole lot about carbs, but maybe the float bowl is emptying and not filling back up or not fast enough? How about that little screen filter at the fuel inlet on the carb?
Let's see what the experts say....

 

[tpenfield]

Didn’t see anything about carb cleaning or rebuild.

 

[Scott Danforth]

if your oil pressure is only 4psi, you have two issues.

first is that idle oil pressure should be much higher. minimum is 10 psi for every 1000 RPM. you have an internal engine issue as I have never actually witnessed a motor that had that little of oil pressure without a spun bearing or seriously worn out bearings. at idle, the pump flows 2-3 times the oil flow needed to maintain pressure against the internal pump regulator spring unless you have a spun bearing or two

second, the fuel pump shut off is 7 psi.

if this is the motor that you seriously overheated to warp a head, I believe you will find that the bearings are gone.

 

[alldodge]

started the boat with the battery directly powering the pump- no difference.

I think you have an electrical issue not fuel

What is the motor serial number?
Do you have a Merc or TKS carb?

Connect a voltmeter on the + side of the coil

 

[kulle]

could it be the oil pressure switch, that is failing to send 12v to fuel pump and you are only burning the fuel from pumping bthrottle?

 

[nola mike]

Didn’t see anything about carb cleaning or rebuild.

"... rebuilt the carburetor..."