3.0L won't start, idle, or run without constantly pumping the throttle

[TSTitans]

Hi all,

I've been trying to get out 1988 Mercruiser 3.0 up and running for a few week. Redid the spark plugs, distributor cap, cables, etc. Electronics seem to be fine. We replaced fuel filters and followed the whole line up to the carb, and it's pumping fuel into the carb. It ran for a few days but then died on the water while idling and wouldn't start again. So I finally took the plunge and rebuilt the carb yesterday with a kit and a bunch of YouTube videos.

When I hooked it back up, I can get it to start if I pump the throttle and/or spray a bunch of starter fluid, but it won't stay on unless I keep pumping the throttle. Even if I open it up and push the throttle forward, it won't keep running. Some notes:
1. When I rebuilt it, I couldn't get the jets out (the top was worn from a previous person trying to unscrew them), but we let it soak for a few days in cleaner and sprayed it out; both jets allow spray to come out fine.
2. I couldn't find a check ball under the accelerator pump and spring. Some forums online said that Mercury had taken those out. The kit came with a couple balls, but I couldn't see a way to install it in the cylinder and have it sit still. The spring isn't as wide as the space, there isn't really any "seat" that would hold it in place, and no clamps/rings that i could find would fit in anywhere there. So I've left it out.
3. The second check ball, underneath the venturi assembly with the T-shaped pin and small spring, I checked and cleaned. This part isn't on the instruction sheet, but a replacement T and spring were included in the kit. I used the old ball.
4. The float bowl fills up ok, I took the assembly back apart to check. Would the adjustment on the float have an effect like this? The bowl was filled to about 1/4" from the rim of the throttle body.
5. Spraying carb cleaner into the jets has it come out the other end into the throttle body, as far as I can tell.
6. Chokes adjusted to be almost fully closed when cold. After trying and starting if for awhile, it was starting to open up more as expected. I think it's set right.
7. There is a screw on the throttle portion of the carb that pushes against a cam that's linked to the choke. I set this, according to one set of instructions, but seating it against the cam with the engine off, then tightening it two full turns. I think it sets the idle RPM. Doesn't seem to matter much since no amount of throttle makes it start or stay on

Any help or suggestions would be appreciated. This is my first boat and first time working on engines/carbs.

 

[TSTitans]

Quick additional notes:
1. When I first started it, I could get it to stay on with the throttle fairly far forward, but it coughed and died after about 30 seconds.
2. I played with the idle mixture screw. Have tried seating + 1 1/4 turns out, 1 1/2, 2. Not sure if it did anything. I've read various numbers on that, so I'm not sure of the right place to put it.

 

[alldodge]

It ran for a few days but then died on the water while idling and wouldn't start again.

First, take the can of starting fluid and put it somewhere you won't be able to find it again.

The motor died and wouldn't restart, so you tried rebuilding the carb. Now it won't stay running without pumping gas down the carb.

I seeing two problems, and thing your first one was the fuel pump or a restriction. Your not getting any gas to the carb, or not enough. Need to install a Tee fitting between the fuel pump and carb and measure pressure (4 to 7 psi). Check your anti siphon valve on top the tank (barbed fitting which the rubber fuel line connects to).

Your other problem is you need to go buy a rebuilt carb, because this one is going to take someone there that can work thru its issues.

 

[TSTitans]

Thanks for the advice!

When I disconnect the fuel line to the carb and run the starter, it spits out fuel very regularly and periodically, so I figured it wasn't a restriction in the line. Also, the fuel bowl is full of gas after I took the airhorn part of the carb off...But I'll check out the pressure measurement with the T...are these parts I can just find at the auto parts store?

The anti-siphon valve - what am I checking for?

I've read, since posting this, to check for vacuum/pressure, although I'm not sure how to do that either. While we were working on the shifting cable and assembly, we had to move the shift cables off the engine block and onto another part of the boat since Mercuiser had discontinued the old neutral cut-off switch and the new plate assembly didn't fit on the engine. We noticed that a few of the screws, including the 2 that held the old switch in place, opened straight into the engine below and would spit out oil when running, so we put the screws back in. I'm wondering if we accidentally missed some other piece that would plug a hole and create the vacuum.

Replacing the carb is probably a long-term solution we'll do, but I need to get this working, if possible, by this weekend for a family trip

 

[alldodge]

You will need a fitting to connect to the carb . Use rubber fuel line and connect one end to the fuel line going to the cab with a clamp. Then install a Tee, more fuel line and clamps. Can also use to fittings, one on carb and the other on the pump with Tee, in between. Another method is get one of these which may be found at an auto store.



The anti siphon valve has a spring and ball inside and if it gets gunk in it, then it will restrict fuel flow. It stops flow in one direction but allows it to flow in the other, but with a slight bit of suction being needed from the pump

we had to move the shift cables off the engine block and onto another part of the boat since Mercuiser had discontinued the old neutral cut-off switch and the new plate assembly didn't fit on the engine

This comment makes me thing of other things. If you moved the shift interrupter switch and its not adjusted correctly, it can keep the motor from firing.

Need to find out when the motor will not start, is it fuel or spark your not getting. If you had a vacuum leak, this would make it run bad, but it should still start. In most cases you will not find a place to get a vacuum reading on a marine motor