Fuel delivery confusion and questions...

[Suplexilicious]

Hey guys.

 

I'm going to apologize in advance if these questions have been covered or if it's a simple fix - being a butcher during the holiday season can fry your brain.

[datzenmike]

The previous owner probably thought the mechanical wasn't working because he wasn't getting gas to the carb. Added it and still no gas. Problem is possibly the fuel line is blocked. Pull the hose off the electric pump and direct into a suitable pail. Turn the pump on.... Does gas come out???

 

No..... tank is empty or fuel line blocked. Take hose off inlet to pump and blow back towards the tank to remove blockage.

 

Yes... The outlet hose should go directly to the carb. If it feeds the mechanical pump, disconnect it and connect directly to the carb.

 

Does carb fill up now???

 

Yes.... problem solved

 

No..... the float is stuck, the brass filter on the carb inlet is plugged or the needle valve is stuck shut.

[DanielC]

A common problem with any old vehicle is crap in the gas tank.  A 521 has a pipe, that goes close to the bottom of the tank, and no filter, sock, or any other thing to strain the gas.  If there is crud in the gas tank, and the vehicle is 45 years old, this crud can get sucked up to the fuel pick up pipe, and clog it.  As long as the engine is running, the crud is held there.   A quick way to see id the fuel pick up pipe is clogged, is to blow air backwards from the fuel filter to the gas tank.  

A 521 fuel pump should pump about a quart a minute, at 1,000 RPM.  Obviously, the fuel pick up pipe in the gas tank can reduce this.  another issue, is the rubber hoses between the fuel pump and the gas tank can have a pinhole, and this allows air to be sucked into the fuel lines.  It is also not impossible that the steel fuel lines have a leak. 

If the stock fuel pump is good, and there are no holes in the pipe, or hoses going to the gas tank, and the gas tank is clean, the stock fuel pump is way more that you will need.

 

The L-20-B card should work OK on a L-16.  Not ideal, but OK.

[Suplexilicious]

I figured as much on the secondary pump. I'll get the lines blown out today and update.

 

Would I be best served to track down an L16 carb and use it instead?

[Stoffregen Motorsports]

Track down a Weber DGV instead.

[datzenmike]

The L20B carb is pretty much the same carb as the L16 but the primary and secondary jets will be slightly larger on the L20B. If it runs ok keep it but look for a L16 carb in your spare time. It will probably give better mileage.

 

If getting a weber carb always buy it new.  

[Suplexilicious]

So far I've...

Blown out the solid fuel lines towards the tank.

Replaced fuel filter

Replaced rubber fuel lines

Removed the in-line pump (It was only hooked to ground. No power so I just bypassed it for now.)

Checked mechanical fuel pump to ensure it was functioning.

 

It'll turn over and run briefly with some starter fluid but not otherwise. At this point I'll track down the aforementioned L16 carb, rebuild and install. I'll bet the tank could use some love as well and if I'm feeling ambitious, new hard lines.

 

Two other items of note...

1.) The truck has a block warmer (at least I think it is. Haha)

2.) It is unbearably cold right now - which could be another factor.

[dgi]

You checked the mechanical fuel pump to ensure it was functioning....  did you actually see it spurting gas out of the outlet side?  If so, then fuel should be getting to the carb and filling the float boal.  If it isn't, then the needle valve is stuck.

 

Since you blew the lines back to the tank, remember there is nothing in the lines.   The pump is going to take a bit to suck the gas up to the engine compartment.  It will take more than a brief run on starting fluid.

 

Now, if you haven't seen the gas spurt out of the fuel pump as the King Rat datzenmike suggested above, don't start on the carb until you actually verify the pump is working.

 

I bought a 521 once that had been setting for 12 years.  It ran, but not well, for about 25 miles and then would not start again.  Found that the suction pipe in the tank had a hole in it.  Engine started and ran only until gas in the tank got below that hole.  Then the fuel pump was sucking air, not gas.  Result, engine no run.  Had my radiator shop clean out the tank, reline it, and put in a new suction tube.  Problem solved.

[Suplexilicious]

You checked the mechanical fuel pump to ensure it was functioning....  did you actually see it spurting gas out of the outlet side?  If so, then fuel should be getting to the carb and filling the float boal.  If it isn't, then the needle valve is stuck.

 

Since you blew the lines back to the tank, remember there is nothing in the lines.   The pump is going to take a bit to suck the gas up to the engine compartment.  It will take more than a brief run on starting fluid.

 

Now, if you haven't seen the gas spurt out of the fuel pump as the King Rat datzenmike suggested above, don't start on the carb until you actually verify the pump is working.

 

I bought a 521 once that had been setting for 12 years.  It ran, but not well, for about 25 miles and then would not start again.  Found that the suction pipe in the tank had a hole in it.  Engine started and ran only until gas in the tank got below that hole.  Then the fuel pump was sucking air, not gas.  Result, engine no run.  Had my radiator shop clean out the tank, reline it, and put in a new suction tube.  Problem solved.

Yeah, I pulled the lines off and watched the mechanical pump spurt fuel on the outlet side. I couldn't figure out why there was fuel in the lines between the fuel pump and the carb but none in the filter or the line from the filter to the pump (I had a bunch of leftover clear tubing from my kart and riding mower projects. It makes diagnosing said fuel problems a little easier. And yes, I'll be replacing it with the standard black lines).

 

I then tried to blow out the hard lines again and SHABAM!, it fired right up. I guess my first attempt was piss poor.

 

So now that I've figured out this little hiccup, Im assuming that my tank is the culprit and needs some proper treatment. I'll call some radiator shops next week.

 

While I'm on the subject, are there any larger tanks out there that'll swap into a 521?

 

Thanks again everyone! I love Ratsun and its members.

[DanielC]

A 521 gas tank is suspended under the bed.  There is not a lot of room under the bed, but possibly a slightly larger one could fit.  A stock 521 tank holds 10.8 gallons, and a 521 should get at least 20 MPG, giving you a range of over 200 miles per tank.

 

I have not heard of a larger tank for a 521, and I have been messing around with them since the early 1970's.  Early 620 trucks had a gas tank mounted on the right side, not left like a 521, and it might be possible to put a second gas tank there, but then you would need to figure out where to put the muffler.

 

If you are going to drop the gas tank out of your 521, go and put some penetrating oil on the bolts that hold the gas tank.  And then remove the tank the next day.

There is a trap door in the bed of the 521, so you can get access to the fuel gauge sender connections, and the hose for the fuel line pick up tube.

Check the condition of the fuel filler hose before you start the project.  It may not survive gas tank removal.   However, the 521 was built using inch measurements, and you should be able to get fuel filler hose at a good auto parts store.  You probably also have evaporative emissions control on your truck.  That can be identified by a filler neck held to the bed with three screws, and a cover ahead of the left rear wheel well, for a vapor separator tank.

[Suplexilicious]

 

If you are going to drop the gas tank out of your 521, go and put some penetrating oil on the bolts that hold the gas tank.  And then remove the tank the next day.

There is a trap door in the bed of the 521, so you can get access to the fuel gauge sender connections, and the hose for the fuel line pick up tube.

Check the condition of the fuel filler hose before you start the project.  It may not survive gas tank removal.   However, the 521 was built using inch measurements, and you should be able to get fuel filler hose at a good auto parts store.  You probably also have evaporative emissions control on your truck.  That can be identified by a filler neck held to the bed with three screws, and a cover ahead of the left rear wheel well, for a vapor separator tank.

Yeah, I've got the cover ahead of the wheel well. When I tried removing it (6 weeks ago), It didn't matter how much penetrating oil I used. I think I broke off every screw holding it on. Haha. That said, I think I'll start soaking the tank bolts.

 

I will look into the filler hose because if the rest of the truck is any indication, it'll need it.

 

Thanks DanielC.

[Stoffregen Motorsports]

I normally use a MAP gas torch to heat the offending hardware but I dare you to try on a fuel tank.