Technical GMC 228 fuel pump drama

so im working on this 1946 gmc 228. Fuel pump leaking bad. Lots of gas in crank case. Drained and refilled with new oil. Put new Carter pump from Napa on. No pump. Good supply of gas at pump. Nothing out other side. Return pump. Install another from Napa. No pump. Clamped in vise and tested. Shoots gas across shop. Has free play ( slack ) before it pumps. Original pump feels like it pumps immediately. It’s like the fp lobe on the cam only moves arm enough to still be in slack. Not enough to pump. Anyone else have this issue? If so what did you do to correct it? Thanks in advance

 

Once had a 57 chevy 283 with electric pump that over time failed, happened to have a new mechanical pump on the shelf so thought it to be a logical choice but not to be, as I discovered the cam lobe was compromised.

 

Did you check the throw movement of the original to the new one before taking it and did the arm of the new one look EXACTLY the same as the replacement? Did the old one work but just leak? There are diaphragms for these if it’s a screw together. You’ve proved the new one works but does it work farther in on the stroke.
With a mirror and light you can see in the hole an rotate the engine to see it there is any lobe damage which would be extremely rare on this style of pump actuator.

 

I drove it into the shop with old pump. I can feel the lobe thru hole. It feels smooth.

 

Old one worked but leaked terribly. Got to point it didn’t wanna start just moving it around shop. The replacement Napa pumps are different. . They have a laminated arm. Original was stamped. Cannot find anything available that doesn’t look like the ones from Napa. ( Carter). Airtex looks just like one from Napa too. Yeah I think the pump action is to deep in the stroke. No tag on the old pump. Rebuilding may be best but not sure if I can get correct kit Plus they’re all lout of stock.

 

Is the arm the same shape and length?

 

Check with Chevrolet’s of the 40’s they list pump repair kits and the GMC’s are real close to the later Chevrolet’s.

 

• Just went thru the same problem on a '54 248. Even though the Chev 6 pump looks identical, they don't interchange due to differences in the arm. On your engine, rebuilding a single action GMC core would likely be the best way to go. Make sure the party selling the kit specifies "Ethanol Proof".
• The diaphragms in '50s-'60s NOS & NORS kits made of cotton & tar will fail immediately. Buy new production.

 

Which carter pump did they give the M751?
That is listed as a Chevy 217 & 235 pump also.

 

Can you swap old stamped arm onto new pump?

Sent from my SM-G950U using The H.A.M.B. mobile app

 

send the original out to be rebuilt. Arthur Gould does all my rebuilding. I stopped buying new Chinese junk.

 

Not sure. I sent the new one back. I think rebuilding old one is best

 

Unsure. It had a Napa part number. Built by carter though ( in Mexico)