1950 Roadmaster is hard to start.

My 1950 Roadmaster is hard to start. When it has been run recently it starts OK. But, if not, I have to pump it 10 or 20 times to get it to start. It has a professionally rebuilt carburetor and fuel pump. Otherwise, it runs fine. Any suggestions?
 
It sounds like the gas is evaporating, leaking down into the manifold or running back to the tank. Easiest soloution is add an electric fuel pump which would eliminate the problem.

What I do after the car had sat for a while is crank the engine 2 or 3 times until I see oil pressure bump the gauge then I set the choke to start the engine and crank it again and it starts instantly with no stumble. This has 2 advantages, 1) it keeps the engine from starting while starved for oil and 2) it allows the fuel pump to send fuel to the carb filling the float bowl and allowing the engine to start right up.

Every engine and fuel system is different so it may take more cranks to achieve the balance but this starting system has worked for me with every carburetored vehicle I've owned after it has sat for a while.
 
Thanks for your quick response. I have electric fuel pumps on some of my other cars and maybe that is the best idea. But, I am thinking I may just need a check valve on the carburetor. About the choke. Isn't it automatic on my stromberg? I don't think I have a manual choke??.
 
Yes a check valve would work if drain back is the issue. Some Rochester carbs have them built into the fuel filter. Even automatic chokes have to be set by flooring the pedal once when cold. Until that is done the engine won't start up until there is a lot of gas built up in the manifold but that is stumbly and not a smooth start.
 
Explain how a carburetor can "drain back"?

If the fuel tank isn't vented when hot some of the fuel vaporizes and it creates pressure in the tank. When cooled down say at night the fuel condenses and that creates a light vacuum situation in the fuel line pulling the gas back to the tank hence drain back. It will take a couple of cranks of the engine working the fuel pump to return the fuel to the carb.
 
Exactly what is this "flooring" step? Maybe that is part of my problem. I do "pump" it now. Do I do it with the ignition off? If not, it tries to start.
 
Exactly what is this "flooring" step? Maybe that is part of my problem. I do "pump" it now. Do I do it with the ignition off? If not, it tries to start.
Ok, let's look at this on your car. After it has cooled down overnight after a hot run, without touching the throttle or linkage or gas pedal, remove the air cleaner. The choke should be open. With the key off rotate the linkage to wide open and the choke blade should close and after release it should be on the fast idle cam. Doing this you have also delivered a shot of fuel from the accelerator pump if the bowl has fuel in it.
Push to the floor once and turn the key on and proceed with normal starting. Most engines will fire and run right away.
 
I have always wondered about this fuel drain back issue. I have heard old car people complain about it for years. It seems to me that there should still be fuel in the float bowl enough to start the engine... assuming that the needle and seat are in good condition. How does the air get into the line so that it can drain back?
 
It does not and can not drain back. After a hot run with todays very volatile fuel the gas in the bowl will boil or percolate over into the manifold, leaving it empty for start up the next day. The valves in the fuel pump will prevent any drain back in the line.
 
It does not and can not drain back. After a hot run with todays very volatile fuel the gas in the bowl will boil or percolate over into the manifold, leaving it empty for start up the next day. The valves in the fuel pump will prevent any drain back in the line.

Your so wrong for so many reasons I'm not even going to waste my time.
Do yourself a favor and do some research about fuel systems from that period of time before giving wrong absolute answers.
 
First, my credentials are dubious at best. I have lit myself on fire twice, the car I was working on at least a half a dozen times, and had the entire floor of my garage in flames at least once... all over fuel troubles. In my own defense, I was left unsupervised for extended periods of time.

Now, it seems to me that if the car starts well after having been recently driven, then the float bowl has to be full at that point. It cannot drain back from within the bowl on most carburetors because (usually) the needle and seat are in the upper portion of the float bowl... and the bowl is vented, so really, the fuel should not be able to jump the air gap uphill to return to the fuel line and "drain back".

This in no way indicates that there could not be a problem with the fuel pump, even a rebuilt one.

So this leads to a different question. Why is the fuel bowl empty at all? Pumping the throttle with an empty fuel bowl is largely ineffectual, you cannot pump fuel that isn't in there. This also indicates that the fuel bowl is empty.

Over a long enough time line, the fuel will evaporate through the carburetor vent.
Just simple evaporation over time seems like the most likely answer.

If it were actually percolating away in there, a bit faster, sure... but I am assuming we are talking a longer time line than just once the car has cooled down again. If it were to fail to start readily at that (early) point, a phenolic spacer under the carburetor might be the answer. I don't think Buick used them, so I rather doubt that they felt that it was necessary. If Buick did use such a thing, perhaps some knowledgeable person could chime in and let us know.

Now, assuming that the fuel has just evaporated, there is that other issue with the fuel pump. Modern fuels, especially ethanol, tends to absorb water which can form rust scale in the fuel tank. Unless someone has installed a fuel filter in between the tank and the fuel pump, I can imagine that a check ball in the pump could have a bit of rust sticking to it that might prevent it from developing enough vacuum to draw fuel at engine cranking speed, and still be entirely adequate once the engine starts. I have had that exact problem before with vehicles that sat for extended periods of time with ethanol in the tank. An issue with rust scale in the check valve would certainly slow fuel down on its path to the carburetor.

Either way, or perhaps even both... it would seem that the solution could be to install an electric fuel pump with a filter between the pump and the gasoline tank.

Just my two cents. It doesn't make me right. Tough to diagnose these things when you aren't there to play around with the car.
 
I appreciate all the input. I have electric fuel pumps in a couple of my other cars and maybe I will put one in the Roadmaster if I have to. What is the consensus on full time use or only when starting. I run my others full time.
 
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