Mercury won't stay running unless primer bulb is squeezed

[SilverSS07]

Fired up my new to me 1988 Mercury 200 today for the first time since buying it. Started and runs great but will die if the primer bulb isn't squeezed. Before I bought the engine I ran all new fuel line from the tank, new fuel water separator, and new primer bulb. All fittings double clamped. Can't find any leaks anywhere or hear any sucking noises. Primer bulb fills up fast. If I pump the bulb and let it sit for a while without starting it stays firm. The guy I bought the engine from said he had replaced the diaphragm in the fuel pump among other things. When I bought it we ran the engine for a few minutes on a stand off a portable tank and it was fine. I plan on going tomorrow and getting a double barb to hook the fuel line straight from the tank to the engine and see if that changes anything but wondering if anyone had any other thoughts. Thanks.

 

[Alumarine]

That usually indicates that the fuel pump needs rebuilding.
Maybe he didn't do it right.

 

[GA_Boater]

+1 on the fuel pump. If squeezing the bulb keeps it running, 99 times out of 100, it's the pump. In my case, time 100 was a sticky check valve.

 

[SilverSS07]

I took it apart real quick tonight to look at it and didn't see any tears in the diaphragm or anything obvious. Also forgot to mention that I could see air bubbles in the fuel line going from the pump (put clear line on there). Could the check valves in the pump be causing it? GA boater do you mean the check valve in the primer bulb? It's just aggravating to me... seemed to be working fine when I bought the motor about a month ago...

 

[GA_Boater]

I'm not 100% sure of the construction of your fuel pump. but mine has 2 check valves inside the pump. They're are held in place with a double "Y" plate. One of them was sticking and the fuel pressure didn't hold while the motor was running.

 

[SilverSS07]

Yes mine has those check valves as well. Thanks.

 

[GA_Boater]

The valves are installed opposite each other. The inlet valve opens on the in stroke and the outlet closes. On the out stroke, the outlet opens and the inlet valve closes.

I sucked and blew through then to get the correct orientation. That's when I found the sticky one.

 

[GA_Boater]

Forgot about the air bubbles. The O-ring on the tank connector can wear too. Often makes for :champagne fuel.

 

[SilverSS07]

The tank is below deck. The fitting for the hose is welded on.

 

[racerone]

Test run it on a seperate / portable tank.

 

[Teamster]

I've seen brand new primer bulbs be faulty right out of the box,..

 

[SilverSS07]

I don't have a portable tank so I filled up a 1 gallon can and stuck the hose in, same primer, and hooked it up. It stayed running. Can still see some very tiny air bubbles but no big ones. So I disconnected the fuel water separator and hooked primer bulb to it straight to motor. Saw some bigger bubbles again and it died. Then it started raining again. If the rain stops I'm going to unscrew the fitting that goes into the welded bung on the tank and look at it. It's an aluminum fitting... I've got a brass one I can try also.

 

[SilverSS07]

Ok I removed the fitting from the tank with the anti drainback valve in it, used a plain brass fitting, and ran a hose straight to the engine. Stays running. Is it normal to see a small amount of tiny bubbles? The drainback valve seems to be working. It moves if I push it with a screwdriver. So I guess that leaves the hose from the tank to the water separator. Not sure what could have happened to it since it's brand new.

 

[quicktach]

When you looked at the diaphram - if it had ripples in it's surface, it likely needs replacing.

 

[SilverSS07]

I went ahead and ordered new diaphragm and check valves. Seems worth the $12 just to know it's new and rule it out. Honestly can't find anything else. I don't recall any ripples in it but it certainly didn't appear to be new. I just looked at it real quick to see if I saw any tears. The diaphragm was bowed out where the spring pushes against it.

 

[SilverSS07]

Think I may have found the problem. When I got the rebuild kit I had extra gaskets. Looking at the diagram I'm supposed to have a pulse chamber. Not one there...

 

[SilverSS07]

Will different styles of fuel pumps work properly on my engine? I can't find the part I need. Everywhere I look it says no longer available. The parts manual shows 3 different styles of fuel pumps on the engine...