1991 Mercruiser 3.0 - Starts, won't stay running

[SGaynor]

I just bought last week a 1991 Bayliner Capri 1850 with a Mercruiser 3.0 (Serial #: D428186) When I bought it, it fired up and ran in the guy's driveway on muffs. He had rebuilt the carburetor, installed a electric fuel pump prior to the mechanical pump, but it had not been in the water for a couple of years.

A week later, I went to start it to get the oil warmed to change it and it won't stay running. It starts and runs for about 5-10 seconds at most, then dies. I'm going to do a complete tune up on it and see if that helps.

However, while I was doing some initial troubleshooting, I found that the voltage at the coil was 5.5V. Searching tells me that it could be 12v or 6v depending on the ignition. It has a purple wire coming to it, is that the resistor wire? What should the voltage be?

And why doesn't anyone carry the tune up kits for that motor (part #: 18-5262)? Any idea on a cross reference part?

 

[alldodge]

Your serial number says you have points. You should have 12V when cranking and 6V to 9V when running.

Since the fuel pump has been replaced with electric, I think your either running out of fuel, or loosing connection. Start with fuel and when it dies see if you can pump the throttle and tell if any gas is going down the throat of the carb

 

[SGaynor]

So to clarify, I should have 6-9V with the key in the on position (not cranking)? I've only got 5.5V...ignition switch issue?

On the fuel side, there were some leaking connections between the tank and the pump - the electric pump was cavitating. I fixed those leaks and the pump is quiet now. I do have fuel going into the carb barrels. Is it possible the mechanical fuel pump is failing/has failed? It did seem that it would run out of fuel, but I fixed the pump issue and am using new gas. Problem remains.

 

[alldodge]

Don't bother with what voltage your getting right now, need to find out if your loosing spark or fuel. You crank the motor and it starts then dies shortly after. I would be looking to see if your carb has any gas left in it. If this is the case then need to look at the system, pump, lines, filter (inside the pump), anti-siphon valve and tank.

Check you fuel pressure to see if your getting 4 to 7 psi at the carb. If fuel system checks out then check for spark

 

[bruceb58]

You are saying this boat has a electrical pump in addition to its mechanical pump? I would be getting rid of the electric pump.

If he thinks he needed an electric pump, you may want to run the engine from a portable can through just the mechanical pump first.

 

[SGaynor]

At the risk of asking a noob question: How can I check the fuel pressure at the Carb with the hard line there?

I tried to eliminate all the components in the fuel system - removed the line from the tank to the electric pump (with a filter in-line), and put a line from the electric pump directly into a gas can - that should remove the tank, anti-siphon valve (although the one there is just a brass barbed fitting - no valve; yeah, on the list to fix), the gas, and the filter from the equation. There is a small filter at the front of the electric pump that I removed and blew through it - no resistance whatsoever.

So that leaves the electric pump --> mechanical pump --> Carb.

I know I'm getting fuel to the carb, but am I getting enough? Is there another place there can be a restriction, ie, in the carb itself? That was supposed to be rebuilt.

Bruce - Yes, that's the set up. I thought about bypassing the electric pump, but didn't do that. I will now.

 

[alldodge]

You need a Tee fitting to go between the carb and hard line. Can get one which is made to do it or make one out of fittings and gas hose.

My initial thought was the carb is getting just very little gas and then it stops getting more. Take the electric fuel pump and go straight to the carb, this will rule out gas. You can even run the pump until the carb is full, the turn it off. It will take a few minutes before it dies with a full bowl.

 

[Bondo]

Ayuh,.... To test the fuel pump itself, just dead head the line into the gauge, 'n see how many psi yer gettin',....

Alot easier than the whole t-fittin' mes,....

 

[SGaynor]

So, I'm not sure what the exact problem was, but I changed out the filter in the mechanical pump (interestingly, the one that was there was a ceramic type, see pic), checked the pump vacuum and outlet pressure - all good. Then I replaced the plugs, wires, points, condenser, cap, rotor, coil. It's now running. But, it seems that there was bad gas in the tank. I was doing my troubleshooting/tuning using gas out of a 5 gal can; when I hooked it up to the tank, it bogged down and stumbled/died. Put the gas can back on - runs like a champ.

So, I pumped the gas out of the tank (about 12 gal) and tomorrow I'll put fresh gas in it and see what's what.

One more question though - I tried putting an in-line fuel filter/water separator (the Attwood from WallyWorld) , but it seems that I'm not getting fuel drawn out of the tank/into the filter. Any suggestions? Do I have to fill the filter with gas first?

 

[alldodge]

Do I have to fill the filter with gas first?

Yes, prefill the filter. Also make sure the inlet and outlet are going in the right direction

 

[SGaynor]

Thanks on the prefill. I've got the lines going to the right places. But....

Update: Took the boat to the lake and it promptly died. Then the starter was chattering and not turning the motor over. Had to get towed in the 50 yrds back to the boat ramp by guy in jet ski. Sigh...

When I got it back home and looked it over, I realized a few things: fuel was pouring out of the carb venturis, the fuel inlet line at the carb was leaking (and the brass nut on the fuel line itself was thrashed), and the radio was on (it's tied directly to the battery).

So...recharged the battery and cleaned up the ground/positive starter lines (ended up replacing the ground) to deal with the starter, and tried tapping the carb (assuming a stuck float). Got it running, but only when I held the choke open (last Saturday it was hot and was usually open). Looks like the previous owner either did a **** job on the carb rebuild or just didn't do it.

I'm taking it to a boat yard to get the carb rebuilt and the metal fuel line replaced. That's something that's well within my capabilities, I just don't have time this weekend; got other projects that need attending to, and I want to get this thing on the water. So, for the ~$300 parts/labor I was quoted for the rebuild...