Hesitation at speed

[CowboyConnor]

I cannot figure out what to do about the way my car is acting up. Accelerating, it has no problem.  Holding speed at 30-40 mph, it has no problem.  Holding a speed anything higher than that it starts to hesitate and seems to not know really what to do. (It sort of bucks back and forth very subtly).  After awhile it even bogs down and even with my foot on the pedal it will stall out.  I am no car expert and have the wedding I built this car for coming up so I would like to get it running well.  Any tips would help.  also, i am running dual carbs from langdon with 3.5lbs of pressure from an electric fuel pump.  

Thanks

[plymjim]

This may be repetitive but check the pigtail wire in your

distributor. You have a stock distributor, I assume. When

it advances the insulation on this tiny wire can rub it's

self bare & temporarily ground out on the housing.

Simple & inexpensive place to begin your search.

Good luck, hope you find your problem.

[knuckleharley]

Have you checked your fuel filter?

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

[CowboyConnor]

I will look into that Plymjim.

Yes, i have a clear filter right by carbs.  Seems fine and fills fast when key is turned.

[greg g]

Next time it does this. Pull over safely shut the engine off.  Take the top off one the carbs and see how much fuel is in the float bowl.  You may have pressure, but I think stock is 5 or 6 psi.  You might have flow, but you may not be getting proper volume to sustain cruising speeds.  Try blowing some compressed air back through the fuel line into the tank.  You should be able to hear air bubbles coming through the tank.  The test for volume with the stock pump is about eight ounces for 12 strokes of the fuel pump. The cam which powers the stock pump rotates at 1/2 crankshaft speed.  So 12 strokes would require 24 engine revolutions.  If your car idles at 500 rpm's, that is about 8 revolutions per second.  Run your pump for three seconds and see how much gas it puts into a container.

Where is the pump in relation to the gas tank?

 

 

Edited September 27, 2016 by greg g

[knuckleharley]

4 hours ago, CowboyConnor said:

I will look into that Plymjim.

Yes, i have a clear filter right by carbs.  Seems fine and fills fast when key is turned.

If you have to crank the engine over to fill your fuel filter,that is a good first clue as to where your problem lies. The fuel filter should remain full after the engine shuts down.

[CowboyConnor]

Even with an electric fuel pump Knuckleharley?

it takes a split second once key is turned get fuel to the carbs. 

 

Right in front of the rear axle. Seems to work great. 

[greg g]

Seems to work great is not a valid measurement of actual performance.

[Plymouthy Adams]

not posting to start an argument, yet, seems to be something wrong is more than valid and warrants further investigation....I cannot ever say it enough..when you do not know what is wrong, prove what is right...by this elimination we usually are able to resolve the wrong more quickly and at a lesser cost overall..

 

 

[Jeff Balazs]

It has been my experience that "bucking " at speed is usually a fuel delivery problem. You may want to do a better test on that fuel pump. Get a decent size gas can...say a gallon.....and time how long it takes your pump to fill it. Could be the line between the pump and the carbs is restricted or the tank vent is not working correctly.

Jeff

[knuckleharley]

4 hours ago, CowboyConnor said:

Even with an electric fuel pump Knuckleharley?

it takes a split second once key is turned get fuel to the carbs. 

 

Right in front of the rear axle. Seems to work great. 

Yes,even with an electric fuel pump. They do the exact same thing the mechanical fuel pumps do,they just do it in a different way.

For one thing,the restriction may be further forward,and not in the fuel tank.

Or it could be a pin hole in the fuel line towards the front of the car that makes your line lose pressure.

The one thing I know is that gas is not supposed to run back down your fuel line once you stop the engine, ESPECIALLY not if you are running dual carbs on an aluminum intake and the intake is not bolted to the exhaust manifold. The fuel doesn't really run back down the line in those cases,it just gets hot enough to turn into vapor and disappear, Some people explain that by saying the carbs :"boil out".

Your fuel pressure gauge should be mounted up high close to your carbs. If it's not,mount it there. If it is,how much fuel pressure does it hold while running,and does it seem to spike and drop back,or is the pressure steady?

[Plymouthy Adams]

don't forget point bounce..the problem at high rotation when the spring force to close the points is less than specified by the manufactuer

[Captain Neon]

Even after sitting 6 months during the winter, my fuel filter is usually still full of gasoline.