I believe I have this right - on my '1983 W250, I see 3-4 lines down along the passenger side of frame just ahead of the rear wheel. I want to plumb in a pusher (rotary vane style) fuel pump strictly for priming carb as my truck often sits idle for weeks at at a time. I assume the largest diameter line is the fuel outlet line, i.e. that line that supplies fuel to the mechanical pump, carb etc? I see a few other lines of smaller diameter (not brake lines) that must be vent lines, correct? Thanks!

 

Yep, the big one should be the feed line to the pump. Keep in mind, that the pump for a carb only puts out 3-7 PSI, so, careful what you install upstream from that.

 

Thanks, yep, it is a low psi pump, thanks again

 

How is the mechanical pump going to get fuel from the one in the tank if it's off(not pumping)? A rotary vane pump will block a vacuum from the output side. If you are going to go threw all that i think it would make more sense to just run a electric pump with a regulator.

 

These rotary style pumps flow through just fine, they offer no resistance when not operating, now if the rain will stop long enough for me to get under my truck and install this pump, run the wiring, switch and relay . . .

 

Update: Installed the Edelbrock pump as low as I could get it below tank along passenger side frame rail. I did not have time to wire in the momentary switch, relay and fuse but did ground pump and powered up pump temporarily to battery to prime - worked great! truck ran fine per normal with mechanical pump pulling fuel easily through pump. Will wire up the rest tomorrow and report back.

 

UPDATE: Wired in a nice momentary bush button switch and grabbed power on the switch side from the cigarette lighter so momentary switch is essentially a "switched" setup. Used a 4 pin relay, have a fused circuit from battery positive to #30 on the relay. Truck sat for almost 5 days, normally this results in a little cranking but today, pushed button for 5 seconds to prime and the little 318 fired right off immediately!

 

Quote:
Originally Posted by Moparite
How is the mechanical pump going to get fuel from the one in the tank if it's off(not pumping)? A rotary vane pump will block a vacuum from the output side. If you are going to go threw all that i think it would make more sense to just run a electric pump with a regulator.

These rotary style pumps flow through just fine, they offer no resistance when not operating, now if the rain will stop long enough for me to get under my truck and install this pump, run the wiring, switch and relay . . .
Seems a fine solution, my '85 has the same problem. Ignore the negativity of the spelling wizards and parrots. Nicely done.