Help!...Mechanical Fuel pump only pumps by hand...

[rshearley]

Recent rebuild of a friends 1970 A-4 that had seized and been taken apart in a random fashion... Very frustrating due to multiple frozen/rusted/broken studs and bolts in the head and manifold and water jacket... but thanks Don for all the parts.

Engine finally running well with the exception of the mechanical fuel pump which was rebuilt, pumps fine with the bail but not putting out otherwise.
The pin looks slightly worn on one end and the cam also looks a little worn but not excessive...don't feel any air or vacuum leak using the bail...
Fuel pump tear down today didn't reveal anything aside from the slight pin and cam wear... I have a suspicion that it may be in the housing but I cant see anything and it looks to be in excellent condition throughout...
Any ideas what the most likely culprit is? And also solutions (aside from the expensive obvious ones or the use of a small child to work the bail while motoring...)
Does anyone have any pics of the fuel pump since I have to admit I didn't have a pic when I took it apart today and someone took the manual off the boat...
It looked right from memory but I may have overlooked something.
It makes sense to me to install an electric pump kit if the feeling is the mechanical one is shot but we were hoping to install a new carb since the old one is actually in far worse shape than the pump and at this point we are way over budget...
Trying to get the boat, a Tartan 27, launched asap and motor is pretty important at this point...

PS, been away from the forum for a while since my "new" 1966 Morgan 34... has a Yanmar. (Loud stinky but very reliable!)
Miss the A-4 though... ( Well not after the last week or so!....)
I do enjoy reading the posts. Glad to see so many still going strong despite the ethanol problems... I miss the trips to the airport to get my 100LL...
Fair winds..

Thanks
Rich.

[67c&ccorv]

1.) Is the pushrod in the block?

2.) Is fuel actually getting to the fuel pump?

3.) Are the inlet/outlet valves in the housing oriented in the right direction - they can easily be reversed?

4.) Is the diaphragm ruptured - all it takes is a small pinprick?

5.) Don't think you will find any info on rebuilding the fuel pump in the manual that came with the Atomic 4 from Medalist...unless you are referring to the Moyer Marine Manual?

[Dave Neptune]

Does it hold?

67, you say you can work the pump manually so I am assuming it pumps~correct?
If it does indeed pump once the carb is full and you release the bail does it stay put to maintain it's internal spring pressure or does it collapse back down?

Dave Neptune

[marthur]

Wierdly enough, I had a very similar thing happen some years ago. The darn pump just wasn't pumping after a rebuild. I disassembled it and found nothing wrong. I flipped the check valves over. Then I disassembled and flipped them back to the correct orientation : ) And forever after, it has worked like a charm. To this day I don't even have a working theory.

In your case, assuming it works normally with the priming lever, I would suspect the push rod or rocker assembly first.

[Clucas]

Wierdly enough, I had a very similar thing happen some years ago. The darn pump just wasn't pumping after a rebuild. I disassembled it and found nothing wrong. I flipped the check valves over. Then I disassembled and flipped them back to the correct orientation : ) And forever after, it has worked like a charm. To this day I don't even have a working theory.

In your case, assuming it works normally with the priming lever, I would suspect the push rod or rocker assembly first.

I had an issue with the check valves where they had effectively become shellacked closed and wouldn't operate. I disassembled the pump, removed the valves and poked them with a small screwdriver to unstick them -- once they were free, the pump worked perfectly. I took me several hours of trying virtually everything else before I stumbled on it. In diagnosing, I switched out the racor, the polishing filter, put a priming bulb inline (upstream of the racor), rebuilt the pump (including installing a new diaphragm -- which I first suspected as being being the culprit), new gasket...

I credit the stuck valves to ethanol, but I may be mistaken.

Another potential cause: if you don't have a good seal between the sediment bowl and the upper pump housing, you won't get much fuel through (if any). Replace the rubber gasket there and make certain the bail hasn't deformed the housing to where you can't get a good seal. This is any easy one -- check it first and you can possibly save yourself a lot of time removing and disassembling the pump (unless you're there already...).

Also, while you have the pump off, replace the two mounting bolts with allen-head bolts -- so much easier!

[Clucas]

If you remove and empty the sediment bowl, then put it back and prime using the bail, does the sediment bowl fill with fuel? If you replaced the racor, did you fill it with fuel?

[rshearley]

Thanks!

Thanks for all the help.. Since the pump works fine with the bail I figured it must be a problem with the push rod or cam assembly... It appears the cam is not moving the diaphragm at all.. The diagram really helped.. I was only able to take the pump apart tonight but it appears from a quick look something is wrong with the way the cam connects to the diaphragm piston...
The wear on the cam and push rod leads me to believe it is taking a beating instead of doing its job... I will work on it tomorrow and post an update...
Thanks again... Lots if great info...

[tenders]

I don't have a mechanical fuel pump, but I can appreciate the extent to which that is an EXCELLENT diagram, marthur.

[sastanley]

+1 what tenders said. There are some details that need a diagram and then they make perfect sense.

Personally, I love my mechanical fuel pump..I am a mech fuel pump hoarder..I think I have three now...(and I'll admit to having a spare pushrod..)

[supplej]

Fuel Pump Weep Hole is Spraying Gas

The Weep Hole on the flywheel side of my fuel pump is spraying gas on my 1975 C&C 27. It barely leaks at idle, but sprays and drips at higher RPM.
Thanks to MArthur's Dec 2004 post with a diagram of a fuel pump illustrating the weep hole. Mine has a weep hole on both sides. I've seen photos of fuel pumps without a weep hole.
What is the purpose of this weep hole?
Do you suppose epoxy might seal it?

Jim Supple
Ottawa

[marthur]

Jim, the weep hole is below the fuel pump diaphragm. The fuel is pumped through the pump on the top of the diaphragm. If fuel is leaking from it, you need to replace the diaphragm.