I like to start my ice cream truck every week or so in the winter to keep the juices flowing. So it’s been getting harder to start, even on warmish days. I took a peek down the throttle body and pumped the accelerator pedal. Instead of a nice stream of fuel coming out of the little jet on the side, I saw a drippy trickle run down the side. The carb was rebuilt about 3 years ago. Is the jet clogged? Bad accelerator pump? I’ve never taken a carb apart and was reluctant to do so. Last time I did a carb exchange online.
Yeah those 1936 Ford trucks are a pain. Seriously, if it is a carb (oh boy a carb question), if there is no fuel in the bowl, nothing with squirt out when you press the throttle. So the bowl is either drying out or you’ve got a small leak in the bowl or gasket that allows the gas to empty. Now if you have the mechanical fuel pump, that could not be supplying the fuel to fill the bowl also, but it really sounds like the bowl is just leaking the fuel out. Now if you start it and run it, and it hesitates when you step on the gas and need to feather the gas to prevent a stall, that would be an indicator of a worn or dry accelerator pump. The pumps are just a piece of leather on a plunger that can wear over time or dry out from sitting.
Sounds like a carb rebuild is in order again. Ethanol in the gasoline just plays havoc with older carbs. You cannot get the correct materials to survive the ethanol for very long so get used to rebuilding the carb on a regular basis. Sorry.
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My brother added this primer bulb on the suction side of the fuel pump of his '51 Packard. Made it start like a dream after sitting for weeks:
Did you put something like Sta-Bil into the gas last Fall? As fuel deteriorates with time things like this happen, whether it’s a failing accelerator pump, a clogged passage or a leaky float bowl (and of course that float bowl has an open vent, so it dries out pretty quickly just sitting, and then the leather in the accelerator pump dries out too).
Some people put cleaners like Seafoam into their fuel as well. That’s up to you.
Depending where you live, you might be able to find fuel without ethanol.
Clogged jet sounds reasonable to me, can you disconnect the fuel line and spray carb cleaner into the jet while wearing safety glasses and keeping your mouth closed of course, the try and clean it out?
Clogged jet is a good possibility.
So is a bad/torn/split diaphragm or seal in the accelerator pump. Especially with modern fuels, as Mustangman alluded to. The accelerator pump will either be a rubber diaphragm or a small piston with a rubber seal around it. Without knowing more about the engine, I couldn’t guess which it is.
It’s also possible that the float bowl is draining. Possibly due to a submerged float. Thin metallic floats can corrode and leak, and other materials sometimes used can become saturated with fuel. This allows the float to drop, keep the needle valve open, and the bowl can drain. This will also cause flooding when running. Without knowing what was changed in the carb rebuild, I can only suggest this as a possibility.
Or the bowl gasket could be leaking. Again, I can only point to it as a possibility.
Someone who knows carbs needs to look at this hands-on. I guess that’s the bottom line. 
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Wow, thanks for all of the great responses. A couple more things I should have mentioned. I do have a one way valve on the fuel line because I thought that fuel was draining back into the tank. Fuel filter and mechanical fuel pump are new. I was adding Lucas Ethanol Fuel Treatment every tank and recently found ethanol free gas locally. The carb was from an online exchange website that supposedly gives you a completely rebuilt matching carb. I’ve probably only put about 2000 miles on it over 3 seasons. It does sit around a lot. I do add dry gas and sometimes a stabilizer when it sits for a while. I feel like the fuel evaporates out of the bowl quickly, especially when it’s turned off and at full temperature.
It may still be draining out of the bowl, because sometimes in the summer, if it sits for several days, I will pump the gas like 50 times and it will start right up. Maybe the check valve in the fuel line is bad.
I can either order a rebuilt carb from one of the online exchange places, pay to have it rebuilt or try to do it myself (I’ve never done it before). How hard is it to do a rebuild. 3 months until ice cream season!!!
Your ice cream truck looks much nicer, versus the ones that visit my neighborhood . . . !
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Another possibility occurred to me today. If you have an old mechanical fuel pump, the diaphragm may be ruptured. The pump may need replacing.
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What year and GVW vehicle is this? And does it possibly have a manual choke?
The fuel pump is just a year or two old. It’s a 1974 Ford P-350 Straight 6 4.9L 300CID with a single barrel carburetor. It has an automatic hot air choke.
When I hit the gas pedal, should there be a nice steady stream of fuel from the jet, or is it normally a trickle? I feel like it’s clogged or accelerator pump gasket is shot.
It should be a fine but clearly visible spray.
A stream means the orifice is too large. A trickle suggests exactly what you suspect… that the orifice is plugged or that the accelerator pump is bad.
I don’t know which yours has, but the accelerator pump will either be diaphragmatic or a pump. Both have rubbery bits (a diaphragm or a pump piston seal) that if bad will prevent the pump from creating the necessary pressure for the spray. In some designs the accelerator pump is internal to the carb, in some it’s external, the body of the pump being integrated into the carb body casting but the pump itself serviceable without dismantling the carb.
My suggestion on this is to write down the make and model of the carb and look on the manufacturer’s website for an exploded view drawing. That’ll show you all the details. I know that most carb manufacturers offer these documents for carbs going way back. It’s also possible that you can purchase the individual rubbery bits that you need to fix the accelerator pump directly from the website.
NOTE: before doing all this, it might be wise to check to ensure that the accelerator pump linkage isn’t gummed up. Years ago I was having difficulty with my '89 Toyota 22R engine, determined it to be a nonfunctioning accelerator pump, and traced the problem to linkage outside of the carb sticking in the ON position. I flushed the linkage with a solvent and fixed it. A few years later, I found the same root cause for a friend’s carbed pickup and fixed it with a simple solvent flush.
Once again, if there is no fuel in the float bowl, there will be no stream of fuel from the accelerator pump, or if the leather has dried out. Doesn’t mean its a bad pump but no fuel in the bowl. Is there fuel in the bowl and still the fuel just trickles out? If no fuel in the bowl, the bowl could be porous, a leak in the plug in the bottom if there is one, or maybe the gasket leaking if there is one there. Its been a while so can’t remember, but its not rocket science. No point chasing fathom problems when it is simply out of fuel.
The truck may have an Autolite carburetor which has the accelerator pump on the outside of the bowl and if it is ruptured it will leak but it may have a Carter carburetor which has the accelerator pump at the bottom of the bowl. Both carburetors deliver the accelerator pump discharge through the bowl to throttle cover gasket which may have failed. But with the engine next to the seat it seems awfully easy to operate the choke by hand after priming the carburetor to get the engine to fire up long enough to determine if the fuel pump is working. Both of the possible carburetors are beyond most beginner DIYers though.
Just a wild shot in the dark here, grab the top of the carburetor and twist it. If it wiggles the throttle to bowl screws have worked loose.
Can you post the make & model off the carb here? It should be on the side of the carb body.
I have a carb’d Ford truck too. When it is hard to start, try squirting (carefully) a couple tablespoons or so of gasoline down the throat of the carb first, then see if it will start. If it pops and starts and runs fine then, that means the basic carb is working ok, but either the accel pump isn’t working or there’s not enough gas in the fuel bowl, like maybe it evaporated. On my truck’s carb it isn’t possible for the gas in the bowl to leak back into the tank, at least I don’t think it is. You can probably pop the top off the carb and peek into the fuel bowl to see if there’s gas in there. That’s what I do when this happens. If there’s plenty of gas in the fuel bowl, but not much comes out where you’re looking when working the accel pump, I think you’re looking at a faulty accel pump. The diaphragms can start to leak on those. I’ve had to replace that part several times over the years. It’s always leaked gas a little visibly out the front of the carb tho on mine when this happens.
I got to thinking, another way for gasoline to mysteriously disappear out of the fuel bowl is if the power valve is leaking. I had that happen recently on my truck in fact. Replacing the power valve fixed it straight away. About the only way to prove that is happening is to remove the carb from the engine, then fill the fuel bowl and see if anything is dripping out the bottom of the carb. When the PV leaks, it drips gasoline into the intake manifold, so no visible leak. One symptom however is that the engine is hard to start when it is already warmed up, like if you drive for 15 minutes, shut it off, then attempt to start it 15-30 minutes later, as the gasoline dripping into the intake manifold makes it flooded. Holding the accel pedal to the floor is the workaround.
Before going down this route, make sure your carb even uses a power valve of course. Early Ford carbs may not use them, don’t know.
Ooh I like this idea! The OP may want to consider adding an electric booster pump or just eliminating the mechanical pump completely. The electric pump will allow him to prime the carb before starting.
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Or he could fix the problem… 
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