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Capt Oblivious #1425747 Sat Oct 02 2021 11:19 PM
Joined: Jun 2021
Posts: 59
Ok - so progress has been made, but we're not quite there yet. I installed a new 25 gallon Spectre tank meant for a 76 C30 at the rear of the frame behind the axle. I am using the Spectre sending unit specified for that tank, and then an inline Airtex E8251 pump just forward of the tank mounted to the frame rail (I picked that pump after googling and finding it recommended for use in these old trucks). I still have the mechanical fuel pump (new) installed. I have the fuel pump running off a fuse panel - basically it turns on when I turn the key on - there is no low oil pressure or high fuel pressure switch installed (I didn't think it was going to be necessary). Unfortunately - the electric fuel pump is overpowering the float and blowing fuel everywhere. Now why did I install an electric pump? Well - it seems that my mechanical pump is not pumping enough at all. I can prime the bowl with the electric pump, yank the fuse when I see it flooding, and then start the engine, and it will seem to run only long enough to drain the carb bowl, then it dies. I can then verify the bowl is empty by looking down the throat and lifting the throttle rod - and seeing that I do NOT get a squirt of fuel.

So what's the matter with my setup? I was sure the electric fuel pump was going to solve my low fuel pressure woes, but now I have the opposite problem.

Capt Oblivious #1425775 Sun Oct 03 2021 12:48 PM
Joined: Sep 2015
Posts: 104
The only problem is you forgot the fuel pressure regulator. Get one from Speedway, Jegs etc. I believe you need only about 3 psi for these old trucks so make sure to check the ratings so you get the appropriate piece.


Capt Oblivious #1425786 Sun Oct 03 2021 02:39 PM
Joined: Feb 2000
Posts: 4,566
The problem is the mechanical pump is bad or the lobe on the cam is worn off enough the pump arm is not moving. As for the electric pump, put a momentary push button in line, use it only for priming the carburetor, there's no reason to run it full time. See if fuel will siphon from the tank to a pan lower then the tank. If it does, your mechanical should be able to pull fuel through it and work as normal.

Capt Oblivious #1425796 Sun Oct 03 2021 05:30 PM
Joined: Jun 2021
Posts: 59
Joe - I guess it could be a worn off cam lobe, but the engine's top end didn't really lend itself to that level of wear. The mechanical pump is brand new. I now have a 1-6psi regulator and gauge to put in and will report back.

Capt Oblivious #1425798 Sun Oct 03 2021 06:04 PM
Joined: Jun 2021
Posts: 59
Welp, installed a Mr Gasket adjustable regulator and gauge, can confirm <2psi going into mechanical fuel pump (engine off, key on), and it's still blowing fuel out of the carb.

Capt Oblivious #1425805 Sun Oct 03 2021 08:54 PM
Joined: Jun 2021
Posts: 59
Pulled the carb down again. Removed and reset the seat, reset the float height ( i had set it when I rebuilt it about a month ago, but it was way off) to 1/2". Started right up, no flooding. Now I get to fix everything else that's wrong with this... water hoses, alternator mount and wiring, etc etc 🤣

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