The Stovebolt Site Forums The Shop Area Engine Shop Vapor Lock?

I'm still working on solving my headlight and horn issues but now have another one to deal with.

I started the truck ('50 217) and let it run for about 5 or 10 minutes before heading out. I drove about a mile to get some gas for the lawn mower. While filling a 2 gallon can I let the truck idle.

At about halfway home the truck started dying as if there was a bog or flat spot in the carburetor. When I let off the gas it smoothed out a little and I continued a short distance before the "bog" happened again and the truck quit. I got it started briefly a couple time by priming it with gas from my mower can.

It started with a lot of difficulty before dying.

It's sitting in the Walmart parking lot now. I'm giving it an hour to cool down before I walk back over there and try to start it.

If it starts and runs, I guess I'll have my answer on the vapor lock question but who knows? The carb is recently rebuilt and the fuel pump is new. New doesn't mean what it used to, though.

I'd appreciate any thoughts on this.

Do these trucks have a propensity for vapor lock? Should I suspect the fuel pump? Did I mess up the carburetor rebuild?

Bad accelerator pump? No fuel squirted when I worked it manually but it may have evaporated out.

Fuel starvation. Dirty tank, rusty lines, clogged fuel filter. Bad fuel pump. Just some areas for you to check.

The entire fuel system is brand new. New tank , new lines, new pump, rebuilt carb.

I don't want to cut the steel lines to install a fuel filter so I intend to thread one in to the outlet at the tank. I'm having trouble finding a male/male adapter to thread into the outlet and into the filter.

Any suggestions? I want to avoid rubber lines and clamps.

Right now the only filter is the strainer in the fuel pump.

It's only had about three fillups since all this was done. Non ethanol fuel

Do you have a vented gas cap on the fuel tank?
Maybe a bit of contaminant in the carburetor needle valve (fuel valve).

After sitting for more than an hour it will only start and run when primed and then conk out. I'm going to disconnect the pump and see if it's working at all. No gas sprays when I worjk the accelerator pump manually so either the fuel pump isn't working or there's something wrong in the carb.

The cap is a new vented cap.

Experiencing a true "vapor lock" where the fuel in the lines boils and becomes a vapor is about as likely as finding a chicken with lips. I've seen it maybe a dozen times in the past 60 years. It's much more likely that you've got a restriction in a line, an air leak on the inlet side of the fuel pump, a bad pump, or some kind of debris in the fuel tank that's blocking the tank outlet periodically. Putting a filter anywhere on the suction side of the pump is probably the worst possble choice- - -it promotes air leaks, and suction on the gas from pulling it through the filter will actually make a vapor lock more likely. The best place to put a filter is at the carburetor inlet, working with pressurized fuel. Do the 3-part test of the fuel pump that I've suggested for years- - - -volume, pressure, and vacuum. If you do that, you'll be one of maybe 5 or 6 stoveboilters who have taken my advice on fuel pump testing in the past nearly 20 years.
Jerry

Yeah I'm in the Walmart parking lot so I don't have all of my equipment. But recent test of the fuel pump indicated two and a half to three PSI. I don't know how much volume it was pumping in a given amount of time but it put about a quart of fuel into a gas can with about 15 to 20 seconds or so of cranking. That was back in the spring when I was trouble shooting the carb.

These numbers are of course are all approximate. Disconnected from the carburetor in the parking lot, it is squirting out fuel, but again I can't get any exact numbers with the limited tools I have on hand.

My initial vote, based on the evidence presented, is a bad condenser.

Second vote would be a leaking fuel fitting between the tank and the pump, Jerry's test should find that.

Before doing anything else, I would change the condenser.

Jon.

Condenser is a Jon Goodman Special.

I checked all fuel line connections, including the one at the tank for leaks.

Engine will start and run when primed but conks out after fuel is used. So it's either the fuel pump not putting out enough, or there's something stuck in the carb.

I would vote for the Carb. if it runs when you prime it, I would think you have spark and just running out of gas after priming. So first thing would be to check for spark and eliminate an electrical issue. You might have to check with priming and running and then again just after it quits. The condenser may just work for a while and quit. What does the screen in the fuel pump look like? Is it clean? Hard to believe with all the new stuff that you have replaced that there would be junk in the new lines. What kind of carb, Carter or rochester? You can get a screw in filter for them or an old school glass bowl one and put it just ahead of the carb. Is there any evidence of flooding around the base of the carb? These are most of the things I dealt with recently caused by a dirty and now replaced tank.

No flooding around the base of carb. I detailed the rebuild on this forum back in March. It's been working fine since then. It's a Carter YF.

I have the original glass bowl pump which I may rebuild if I can find a quality kit for it.

The current AutoZone pump deletes the glass bowl. I haven't taken it apart to look inside. I assume it has a filter screen similar to the original pump.

Yes HRL, you're right about the placement of the fuel filter. Are there any short ones that will thread into the carburetor and allow the steel line to screw into it?

Well, Gentlemen, it appears that I have a worn fuel pump cam / eccentric.

I thought I hit pay dirt when I found two cracks in the brass fuel line fitting on the inlet side of the pump. Maybe it was sucking air! Nope. That wasn't it.

No fuel being pumped up to the carburetor at all. New pump - same symptoms. Not a drop reaching the carburetor.

I just got in after working on it and having it towed the block and a half to my house. Haven't looked at the manual yet.

What's involved in replacing the fuel pump cam? Should I just put an electric pump back by the tank? If so what brand/model, etc? It's still a 6 volt system.

If you're talking the 216 in the '50 3100, you'll need to remove the engine, then the pan, harmonic balancer, timing cover, rocker assembly, pushrods, then pull the camshaft out, remove the timing gear, then reassemble.
If you're not concerned about originality, you could put an electric pump in and open up the fuel pump and take the check valves out of it so fuel can just run thru the original fuel pump.

Uggghhh! I was afraid it might be something like that.

Now that the truck is back in my garage after spending more than 24 hours sitting in Walmart parking lot I'll be able to look at it more closely but I can't think of any other reason that fuel isn't pumping out.

Can you or anybody give me the lowdown on what electric pump to purchase?

I assume that it would be installed near the fuel tank outlet. I guess this will take car of my fuel filter dilemma at the same time.

I have the original pump with the glass bowl on top. Can that be made to allow fuel to flow through without pumping? I assume that since the arm isn't pumping anyway I can leave it in place?

How do you know that the fuel pump lobe on the camshaft is worn off? I have doubt that it is.

The only evidence I have is that two fuel pumps don't pump any fuel even though there is fuel at the pump.

I’m sure there are other ways to do it but, if you have a rebuildable pump, disassemble the diaphragm assembly and disconnect the fuel lines. Have someone crank the engine and observe the pump arm to see if it moves. Others will be along shortly with a better way.

The pump I removed squirted out fuel when I worked the arm manually so it was probably still good. I figured it was weak or something and not pumping the to specs. After installing the new pump I removed the fuel line between the carb and pump. No fuel would squirt from it when the starter was pressed..

I had problems with the new mechanical fuel pumps, too much fuel pressure. Every time I would shut the truck off it would flood and wouldn't start for about a half hour (even with a regulator). I installed a Carter electric fuel pump(took the advise from this forum) and installed it with a remote filter down on the frame. Solved my flooding problems and gave me peace of mind with the remote filter. Carter makes 6 volt electrics also.

I may be heading in that direction although I haven't experienced too high a pressure. When I last checked the pressure on the pump I just took off, it was 2.5 psi or so.

I think I'm going to start a new thread on this subject with all the facts laid out from start to finish to make it easier for people to follow and give advice.

I was just letting you know why I went to an electric pump. You asked for experience and what kind of of pump used. I have no regrets switching it over to an electric.

Most all the pumps ( mechanical ) that I have installed in engines, have some spring pressure on them while bolting them on. Maybe I just get unlucky and hit the lobes every time, but you should feel the resistance from the pump arm when bolting to the block. Fuel pump lobes wear off the cam just like lifter lobes do. You should be able see in the opening with a light and mirror or inspection camera and see the lobe. Have someone rotate the engine while you look. They are not big lobes, but you should see if it's damaged or missing.

Adding a small electric pulse pump is pretty straight forward, no need to pull mechanical pump off or apart, the electric will push fuel right through the engine driven pump. Look for one with 2- 3 psi output, anymore and you could run into needle and seat issues which leads to flooding. Use a safety switch with manual override for priming. Safety switch allows pump to run only when oil pressure is present. You will have to get specific information about your engines oiling system from someone else, I don't know much about the early engines. The Chevrolet Vega ( from the 70's ) used an oil pressure/fuel pump switch which is the common one everyone uses now. Most parts houses will be able to get one, or shop online for Vega oil pressure switch. DO NOT just wire the pump to an on/off switch. For a primer switch, use a push button only so the pump only works while holding the switch.

Yes, I understand. I have no problem using an electric pump if necessary. I will be doing more research to find out exactly what's going on with this particular situation.

Did you start a new thread on electric fuel pump or vapor lock? It's been major hot in west TN the past few weeks. Yesterday a few of our club members were taking a cruise up to KY, about 65 miles one way. My '49' 3100 made it about 30 miles and started to jerk. It only got worse the next 2 miles. It was about 95 degrees. I stopped and let the truck cool down for about an hr. Still jerked a bit on the way back home. The info I've found say's install an electric fuel pump and wrap the original steel fuel lines with a thermal tape or replace it with a rubber hose with nylon. This thread says a pump with 2-3 psi. Add push button to the pump to get the fuel to the carb. Do I bypass the mechanical fuel pump? Any thing I'm missing.

Thanks, Cyril

Hi Cyril,

No, I haven't yet. I gotr sidetracked on two other repairs so the truck situation had to wait.

It's now appearing that I have a fuel pump/carburetor issue but I have more investigating to do.

Yes, the fuel pressure for the 216 should be about 2-3 lbs.

Place the electric pump back by the fuel tank. It can push straight through the mechanical pump. The electric pump is useful for priming after the truck sits for a while. When you are experiencing the vapor lock problem an electric pump can help to push fresh "cold" fuel to the carburetor.

I'm not sure insulating the fuel line will work. It will eventually heat up and then hold the heat. Try the elctric pump first and see what hapens.

Dumping cold water on the fuel pump can often alleviate vapor lock, at least temporarily.

I'm aware of a classic car tour where one of the cars experience vapor lock. The fuel pump was cooled down by dumping cold water on it. Then a small melon was cut in half and placed over the fuel pump to insulate it. The guy was able to complete the tour.

Maybe take a few small cantaloupes with you on the next drive. Check the manual, though. I think Chevrolet recommends acorn squash instead.

I found this on Amazon

https://www.amazon.com/CarBole-Universal-2-3-5P-S-I-Operating-Self-Priming/dp/B01IR6BNKY/ref=sr_1_3?crid=3VAZ8653TXERT&keywords=Electric+Fuel+Pump+12V%2C+2-3+PSI+Micro+Low+Pressure+Fuel+Transfer+Pump+for+Gasoline&qid=1658096552&s=automotive&sprefix=electric+fuel+pump+12v%2C+2-3+psi+micro+low+pressure+fuel+transfer+pump+for+gasoline+%2Cautomotive%2C130&sr=1-3

I wouldn't buy that one. It says it can't be used with ethanol fuel. Look for one compatible with ethanol.

This on is also 12v. You'll need 6v unless you've converted to 12v.

Mr Gasket has a wide range of electric pumps. I used one on my Toronado. It was about $25 at Auto Zone.

Take the punp off and rig a magnetic base dial indicastor so the plunger bears against the cam lobe. Turn the engine (by hand if possible) by removing the spark plugs and pulling on the fan blade. In two turns of the crankshaft the pump cam lobe will make one full cycle. I've got a few camshafts I can set up in my lathe and give you a specification for what a normal amount of lobe lift should be. It's far more likely thst you're getting "new" pumps that are defective, given where they're most likely coming from.
Jerry

Yes Jerry, I believe you're right. I'll post updates soon. I've been on other projects.

Take a look at the "failed" pump picture. That little wear spot is only on the edge of the arm. Upon close examination I found that the three leaf stack that makes up the pump arm isn't put together correctly. The three leaves aren't even with each other on the mating surface (about 1/64th off) so the leaf at the rear is the only one making contact with the cam.

I intend to check the entire cam lobe, however to be sure.

Thanks for the chuckle.

We have a gallon thinner can with a 12v electric pump strapped to the carrying handle with a big hose clamp. There is an inlet tube from pump through a hole punched in the top of the can and the outlet is a rubber hose that runs to carb. Our "starter pack" also has a 12v small battery (motorcycle, mower) in case vehicle has different voltage. Has been used hundreds of times for reasons ranging from no tank on vehicle to not wanting to pump what might be in tank/lines into carb. In your case it would fire the engine so you could conduct any test you desired. It can even be used to find how many miles one will go on an EXACT gallon of gas. Very handy tool.