Engine hesitation

Gezer

Gezer

Member
Engine is a 51 EAB Flathead. I Have let it warm up and set the timing with a timing light. Mark hits the pointer every time. When I step on the gas, it hesitates. It acts like it is starving for gas. I give it a couple pumps and it seems to recover. What should I be checking and in what order?
 
Sounds like the accelerator pump is not functioning... Sometimes - depending on the carb - the leather cup on the pump plunger dries up and refuses to start working again. Ethanol in the fuel doesn't help matters. You may be able to just disassemble, massage the cup with a little bit of oil to make it swell up a bit. Otherwise you may just have to service it with a new pump.
 
Randy has given you an excellent and probable cause for your hesitation. There are several more possible causes:
Non functioning power valve.
Main jet restriction.
Non functioning ignition advance.

In that order, starting with Randy's suggestion.
 
Will it do it in the driveway in neutral - or only under load? You might want to just pull the air cleaner (with the engine off at first) and when you work the throttle mechanism, do you see a good squirt of fuel into the venturis? You can also do this with it running - just be careful, have some glasses on and all that jazz. Usually if an accel pump is not working, you can easily check it out in the driveway - even with the engine off.
 
Sounds very similar to my 52 Merc. It will stall if I step on it from idle. Slow and gradual acceleration will work (when its hot) but also a couple of pumps on the pedal will give it that little extra gas it needs to really take off. The accel pump appears to deliver a good shot of gas both sides when I observe it but it seems like not enough. I've gotten used to driving it this way so have not done anything to the carburetor.
 
I have the same problem with a 50 Merc. I'm going to send the carb to Charlie NY, soon as I can get things together.
 
If you close the choke slightly and the hesitation gets better, you pretty well know that it's a lean condition due to accelerator pump issues...
 
Thanks all,
Not sure why, But the problem went away on its own. I'll drive it awhile and see if it stays away.
 
Be sure that the carb is correct for your engine. Units that match the year of the car often draw vacuum for the advance above the venturi. Raw manifold vacuum will produce a hesitation if the vacuum is not drawn properly, or if the diaphragm in the advance is not holding vacuum, a common problem with old units, making advance slow or non existent.
 
Gezer said:
Thanks all,
Not sure why, But the problem went away on its own. I'll drive it awhile and see if it stays away.
Click to expand...

You probly had a sticky valve that freed up. The use of Marvel Mystery Oil
usually prevents this and will make it go away in most cases. G.M.
 
Thanks for the help. I thought the problem went away but seams to have gotten worse.
I put a riser under the carb thinking heat might be a contributor causing vapor lock. I also added the Marvel mystery oil and pulled the Accel. pump on the 51 EAB Ford Carb. The Accec. pump looks new and the cup is plastic or (blue) rubber. It is in very good condition with no stiffness or nicks. The car idles fine in the driveway. Under load it all of the sudden starts missing. Pulling the choke helps but seams to flood if pulled too far and then I have to keep adjusting it to keep it running. It has completely stalled in traffic. I can hold the speed around 30 max and it goes for a longer time with out cutting out. Could there be an electrical issue too?
Sorry for the book, searching for solutions.
Thanks
 
Gezer said:
Thanks for the help. I thought the problem went away but seams to have gotten worse.
I put a riser under the carb thinking heat might be a contributor causing vapor lock. I also added the Marvel mystery oil and pulled the Accel. pump on the 51 EAB Ford Carb. The Accec. pump looks new and the cup is plastic or (blue) rubber. It is in very good condition with no stiffness or nicks. The car idles fine in the driveway. Under load it all of the sudden starts missing. Pulling the choke helps but seams to flood if pulled too far and then I have to keep adjusting it to keep it running. It has completely stalled in traffic. I can hold the speed around 30 max and it goes for a longer time with out cutting out. Could there be an electrical issue too?
Sorry for the book, searching for solutions.
Thanks
Click to expand...


Seeing it runs good a 30 MPH it sounds like the float level could be set
to low and you run out of fuel. Check the float level. G.M.
Also check flow from fuel pump.
 
I will check that. But the car has run great with no changes up till recently.
in the drive way it idles fine but when you step on it from an idle it hesitates then reves up.
 
who sells accelerator pumps for a ford carb on a 51 EAB engine. I tried Drake but he only has Stromberg.
 
With the car NOT running, pull the air cleaner and take a flashlight and look down the throat of the carb. Then, either pull the throttle linkage like you've floored it or have somebody do this in the car. You should see two distinct streams/shots of fuel being sprayed down into the carb. There is a little nozzle on the float side of the venturi area above the air/gas boosters that sprays the fuel. If you don't see those sprays of fuel, then you have some issue with the accel pump circuit. It could be the pump, the float level, something plugged up, etc.. This is where I'd start.
 
Fuel starvation prior to the carb is possible. An air leak into the suction side of the fuel delivery system can do weird things. If the line between the tank and pump has any flexible portions there may be a crack. They won't leak fuel so much as draw in air. Crap in the fuel tank that gets drawn into the pick up tube is another maybe. The pump might be getting weak. The fuel cap vent may not be venting properly.


On the heat related side for electricals, the ignition condenser may be going bad. There is no rhyme or reason to the way they can act when they are bad. If it has a ballast resistor, the resistance level should be checked. The ignition coil may be suffering from old age or quality problems too.


Always check the easiest thing first and work your way forward from there.
 
Last edited:
Well guys.... After all the input(which U really thank you for) Rotowrenchs' suggestion to check the input fuel line for tight fittings. Bing go. There was no sign of leaking bit the fitting on the mechanical pump was very loose. Makes me think that I forgot to tighten it when I installed the new pump.
Again thanks, very much. Runs smooth as silk now,
 
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