Mechanical fuel pump question

A friend has a 1950's Chris Craft With fuel issues. I removed the fuel pump and submerged the inlet in a cup full of gas and manually pumped the lever and gas came out the outlet. The motor runs with ether (i know thats unsafe and not a good idea but it is his boat and he was in charge of that). All lines appear to be unobstructed. We blew in the tank fill and gas came out the supply line. After reinstalling the pump and cranking the motor the glass bowl would not fill with gas. My question is why does it pump gas while pumping it with my fingers but not when run by the lobe? Also, can mechanical pumps get weak or do they either pump or not pump? Would a stuck float not allow the pump to do its job?

The line fitting at the carb was very tight and I didnt feel like breaking it so i did not take that off. I should have done that though.

I couldnt tell if the pump arm was moving from the eccentric lobe. the lobe itself was moving.

The boat ran great ,last year so i assume its pump related or a float stuck.

Bill,
Here's the Then and Now website. They have the kits but also rebuild pumps.

Bill,
When your friend gets to the point of screwing the two halves of the body together with the new diaphragm between them there is one procedure he needs to be aware of. The arm needs to be compressed so it partially stretches the diaphragm and then the screws are tightened. The pre stretch greatly extends the life of the rubber diaphragm Without the pre stretch, the rubber is stretched with every stroke.

Bill,
Just partial. I'd say so it stretches the diaphragm about 1/4 inch from flat.

To update this thread the fuel pump kit was successful. The old diaphragm appeared to be in perfect working order but certainly was not. Put it back together and the old girl fired up beautifully!

Model year 53 but built in 51. 22’ CC Custom Sedan. CC Marine straight 6 ML engine. I uploaded pictures here a while back. I can’t find the thread though.

Bingo! Thanks Ken!

Mechanical fuel pumps rarely die
Gas lines do from ethanol
Replace the rubber gas lines and the vacuum will stop and you will get fuel
Maybe the fix but it’s cheap and easy troubleshoot
Mine would start then die under load I tried everything
Old timer at parts store told me to change the file line and it worked

1987don wrote: Mechanical fuel pumps rarely die Gas lines do from ethanol Replace the rubber gas lines and the vacuum will stop and you will get fuel Maybe the fix but it’s cheap and easy troubleshoot Mine would start then die under load I tried everything Old timer at parts store told me to change the file line and it worked

Did you bother reading the whole thread?

His issue was fixed with a new fuel pump

Looking at your old posts, you seem to think that replacing the fuel line is the cure all for every fuel issue out there.

It's a good suggestion but it sure ain't the problem every time

Does it accelerate smoothly, no skipping or hesitation, no funny noises............just slow?

Maybe as a start, check the timing at idle around 10 degrees BTDC and watch it advance as the engine speed increases.

Should end up in the 30 range at around 4000 rpm's with the stock Prestolite distributor

Since Pete dug up your old thread from 2014, maybe somebody stole your ACME prop   

Hi Don

If it's not bogging or hesitating, the accelerator pump is most likely not an issue.

Check the thread in the link below from a couple of years ago

It gives an easy way to check that your secondaries are opening on the carburetor. Just need a zip tie.

As it mentions in the thread, they don't open all the way on a 351 with a 600 cfm carburetor, but you can check that the zip tie moved on the shaft to verify that they're at least opening some

Also as mentioned the boat lost a few hundred RPM, lost some acceleration and lost a few MPH.

It's worth sacrificing a zip tie to find out

link

I still think it's the fuel pump.