Primer bulb on Yanmar Diesel

[bact0ee]

I have a primer bulb on my Yanmar diesel (54 hp) and after about a hour or so it will collapse when running at 2500 rpm. When it collapses it shuts off the fuel and the engine dies. I recently tried running at 2000 rpm and the problem went away.

Has the bulb wore out to where it cannot handle the suction at this rpm or is there another culprit.

Appreciate any thoughts. Thinking of removing this bulb from the system. It is between the fuel tank and the racor.

[SY Harmony]

Theres no need for a bulb. The engine has a lift pump with a priming function

[gonesail]

my 3gm bulb never collapsed. you should try replacing it.

[MicHughV]

I can't think of a reason to have a primer bulb inline on your diesel fuel delivery line prior to the Racor.

This is a first for me. The engine lift pump should be able to suck the fuel out of the tank.
Some engines will have an electrical fuel pump feed the mechanical fuel pump.

Primer bulbs are more commonly seen on outboard motors.

Regardless, a primer bulb should not fail above a certain rpm.

Is this primer bulb "original equipment ?" or was it placed there by somebody.

[Snore]

Check racor, it is likely clogged. High ROM needs more fuel, racor cannot supply, injector pump pulls vacuum, bulb collapses. When you see it you assum blurb, but real fault is clogged filter, or other impediment to fuel flow.


PS I HATE primer bulbs below deck! Spend $100 and wire in a lift pump. It should turn on with ignition. This will also make changing filter much easier.

[ScottRhodes13]

Since the bulb is between the fuel tank and the Racor, a clogged Racor would not cause the bulb to collapse. It's more likely a clogged intake in the fuel tank or a bad vent.

[stormalong]

Primer bulbs are very handy. They move a lot more fuel than the mechanical lift pump lever. they fill my racor and on-engine filters in no time. No wiring and simple plumbing. Just make the primer bulb the highest thing in your fuel system. That way a broken primer bulb won't siphon fuel into your bilge.

I have had a primer bulb in my fuel system for many years without problems. I carry a spare but have not had to use it (yet).

I agree with ScottRhodes13. Look for blocked pickup or clogged vent.

[Snore]

Originally Posted by ScottRhodes13

Since the bulb is between the fuel tank and the Racor, a clogged Racor would not cause the bulb to collapse. It's more likely a clogged intake in the fuel tank or a bad vent.

Yes you are right!

Must be something in pickup tube or impingement in fuel line or perhaps a clogged vent line.

[MicHughV]

I was in an anchorage once, where I met a guy having fuel delivery issues, so I went over to troubleshoot and help.
Despite an entire morning in the engine room, we could not solve the issue.
Frustrated, I climbed back into my dink to leave, when right at eye level I noticed the vent line for the fuel tank.
Of interest, was that some mud dobber wasps had been trying to build a nest there, and had clogged the vent shut. This was quickly removed....and voila....problem solved.

Fuel delivery issues usually always involve a blockage somewhere, the trick is to find it.

[FPNC]

Some fuel pickup tubes have screens at the bottom or anti-siphon type ball valves built into the top. If either one starts to block from debris, it will cause the suction in the fuel line to increase. Both the screen and the anti siphon valve can be removed. They are not required for diesel applications.

[bact0ee]

Originally Posted by MicHughV

I can't think of a reason to have a primer bulb inline on your diesel fuel delivery line prior to the Racor.

This is a first for me. The engine lift pump should be able to suck the fuel out of the tank.
Some engines will have an electrical fuel pump feed the mechanical fuel pump.

Primer bulbs are more commonly seen on outboard motors.

Regardless, a primer bulb should not fail above a certain rpm.

Is this primer bulb "original equipment ?" or was it placed there by somebody.

Bulb was in place when we bought the boat. Not sure if it is original equipment or not.

[MicHughV]

I can't think of a time when I've ever seen a primer bulb on a diesel intake line. It's possible off course, but I've never seen one.

As I see it, you have two options (a) remove it (b) replace it.

If the rpm problem persist, after removal or replacement, you'll have to start looking elsewhere.
As stated above, many other possibilities, clogged Racor, etc...it becomes a process of elimination.
Replacing it would be the simple option, otherwise you'll have to mate the two ends of the fuel line together with a pipe.

Remember too, once removed or replaced, you'll have to bleed the system.
Some Yanmar's are self-bleeding, check your manual, I believe your engine is one of them, but not sure, but it makes me wonder why there is a primer bulb in the first place.

[SY Harmony]

Originally Posted by MicHughV

Remember too, once removed or replaced, you'll have to bleed the system.
Some Yanmar's are self-bleeding, check your manual, I believe your engine is one of them, but not sure, but it makes me wonder why there is a primer bulb in the first place.

Old habits die hard

[noelex 77]

Primer bulbs are not uncommon on a marine diesel.

The best idea is to plumb them with isolation valves so they are effectively removed from the system when not being used. This removes the concern about the rubber bulb splitting, the check valves jamming closed or the low fire rating of the bulb.

In this case, the bulb provided an alert to another problem in the system (vacuum on the inlet side), but the isolation valves are still a good idea.

[donradcliffe]

Your primer bulb is doing its job. Its is telling you that there is a blockage upstream of the bulb that is creating a vacuum. The blockage could be in a joint or valve in the fuel line, the fuel pickup tube, or the tank vent.

The quick and dirty solution could be to turn the bulb around and blow the blockage back into the tank. The better solution would be to take things apart. In any case its time to add Biobor to the tank if you haven't been using it.