Starting problems - fuel pump? What next?

[unipus]

I've got me a 710K that doesn't want to start anymore. Starting was originally fairly quick + crisp, and I'd noticed was starting to take longer and longer to prime, especially after left to sit for more than a couple days. No surprise there, especially since I generally am forced to park it somewhat facing uphill.

But after leaving it for about two weeks, it no longer started at all. So I've dug deep into the engine for the first time ever. I checked the fuel filter, which is pretty new and pretty clean, and the spark plugs all look pretty good. I pulled off the manifold and poured in some carb cleaner, then tried pouring gasoline directly into the carb. It DOES try to start after that.

So, I went ahead and ordered a VW replacement fuel pump. For $30 it seems like I might as well replace it, since I know nothing about what shape the old one is in and it seemed like a likely culprit. I replaced that tonight, with a couple potential issues: the one I got is a somewhat different style than the one that was in there. It looks like this:



Whereas the old one has the two line ports side-by-side and facing forward. But I figured it's here and I might as well give it a shot. Since the lines now have to run to the rear, rather than the front, I took the opportunity to shorten the line from the filter by bypassing the Y to the heater altogether... I remember reading that the heater itself is sometimes a problem and probably ought to be gotten rid of regardless. So it's out of the loop now.

And, well... it almost sorta works? It still wouldn't start initially, even after a good 30 seconds of cranking. So I once again gave the carb a little shot of juice, and that combined with a little gas was actually enough to get it into an idle... but a pretty rough one that died a few times. In addition to belching smoke out of both carbs at one point and backfiring super sharply on two other occasions, which is fun. That's when I decided to stop before the neighbors come looking for me.

So... where am I at now? I've still got the air filter and the manifold off... do I just need to get those back on and give it some time? Is that pump just not gonna cut it? Or is there something still fouled up I need to be hunting for?


When replying, remember to respond as if speaking to a particularly slow child with basically zero automotive experience. Slightly helpfully the only other car I've ever worked on was a 1968 Karmann Ghia, but I'm still essentially an idiot.

[Hotzenplotz]

unipus

you can easily verify the function of the fuel pump.
on the driver side of the carbs you have the fuel hose coming from the pump.
It is attached with a bolt with a 17 mm hex head. Loosen that bolt one at a time, remove the central lead from coli to distributor and try to start.
this allows air to excape the system. if you have fuel leaking from the bolt your pump is ok.

Next would be to check the floater valve (hopefully a correctly translated term) to ensure fuel gets into the intake from the carbs.
but one step after another

[audiocontr]

To add to Hotz - Disconnect fuel at Carbs and pump into a plastic bottle to ensure fuel is flowing. My guess is an obstruction in the fuel line somewhere between the tank and pump... possibly even red flakes

[Jimm391730]

A common problem with these older trucks is that the fuel line develops cracks; sometimes small enough that fuel won't leak, but air will. If the hose between the tank and the pump has even the tiniest air leak then air will get sucked in and the pump will never prime well. If in doubt replace the fuel hoses.

[edzz]

No offence, however you have physically verified that you have sufficient gas in the tank. I've known of more than one time people trying to hunt down fuel problems just to find they are out of gas.

If you drop the tank to replace the hoses don't overlook the opportunity to replace the cork gaskets for the fuel level sending unit and the fuel pick-up tube. They are known to dry out and crack over time adding to the in cab gas smell.

[unipus]

Yes, there's fuel! I figured that might be part of the problem because when I last parked it it was on R, so I gave it a full gas can just to check that box off...

[Twin Pinzies]

Did you check the plugs? They get fouled, ya know.

[Texas710]

First thing would be to replace all fuel lines and clamps, I like the fuel injection clamps if you can find them. I recently did this and it made a big difference in starting. I used gates fuel line, good stuff and you can get one that is ethanol friendly. Next I would swap out a fuel filter with new, they are only a few bucks. Easy enough to verify if the pump is working.

Then, you might want to verify your timing or advance is not out of sorts. If it's backfiring through the carbs, might need to be checked. Those are my 2 cents

[unipus]

All right, thanks guys. Heading out of town for a little bit but will look at the lines and then I guess ignition after I return.