56 Model 62 Coupe acceleration issue (fuel pump?)

[Brent #22313]

Hello,

Im having an issue with acceleration in my 1956 Model 62 Coupe that is new to me:

When approaching around 50 mph, the acceleration dies off, the engine sputters and loses speed momentarily as if the fuel supply is either cut off or flooded.  It runs beautifully 0 to 50 mph with no issues whatsoever.  When it sputters like this, I release the accelerator pedal briefly and then slowly reapply and can cruise along nicely with no problem at < 50 mph.

It has a rebuilt single Carter four barrel that was rebuilt approx one year ago, and whose installation precedes this problem, so I dont think it is the carb (although you never know).  In-line fuel filter is clean and tidy, so I dont think its a crud issue.

I am thinking the fuel pump may be the culprit and might replace it, but thought Id check with the knowledgable folks here for any other ideas.

I greatly appreciate any advice!  Thanks,
Brent

[Lou CLC 19028]

Your carb is starving from lack of fuel. Check the simple things like, is your fuel filter installed upside down(dont ask!), check the fuel line from the pump to carb for kinks and if thats all good then test the fuel pump pressure. Hope that helps....

Lou

[John #22631]

One thing a lot of people overlook because they dont know its there, is the fuel tank sending unit pick-up filter, or sock filter as it is sometimes referred to.

Biggest problem is you must drain and drop the tank and remove the pick-up to get to it. After 60 years, IF it has never been removed or changed, chances are it is blocked solid.
John

[David #19063]

Brent,

Will your car run fine at speeds of 70 & 80 mph?

Under full throttle acceleration, does it cut out prior to shifting out of 1st?

Is the secondary throttle opening properly?

David

[Doug Houston]

The fuel filter on the 56 engine IS upside down! Sort of strange, but it appears that there was no way to mount it bowl down, so its bowl up.

ANYWAY, check your vacuum control on the distributor. It may not be working. A timing light on the harmonic balancer will tell the story if you gun the engine.

This isnt offered as a solution to your question, but you might want to check the timing marks on the flywheel part of the harmonic balancer. They have a habit of breaking loose from the hub, and your timing marks shift and your engine timing is never right. I had it happen on my first 56 back in the fifties. Determine if the top dead center (TDC) mark shows as cylinder #1 is truly at TDC.

[Brent #22313]

Thanks for the reply David.

It shifts out of first ok under full acceleration.  I am not able to reach speeds of 70-80 mph.  The acceleration problem functions as a ceiling on maximum speed.

Thanks,
Brent

[David #19063]

Hi Brent,

That is interesting.  Ill give you some ideas and hopefully others will chime in and give some others as well.

If the car has not received a full tune up lately, that may be a good thing to do whether or not it solves this problem, points, condensor, rotor, cap, plugs (gap them yourself), and plug wires, timing.

I would do the full tune up first.  I am thinking that this will solve the issue.

We have had some people mention weird running issues and it turned out to be a bad coil causing it.

The suggestion that a clogging sock/filter in the gas tank also could be the culprit.

Also check for any vacuum leaks.  Especially on the carb itself.  I once bought a 67 Fury II with the 383-2bbl.  The old lady that had it stopped driving it about 6 years earlier after it started running poorly.  She said she has her shop rebuild the carb way back then.  After a few days, I felt the outsides of the carb with my hands and could feel vacuum from several places where there were gaskets.  A bought a rebuilt kit to rebuild it.  When I took it apart, I saw that the shop rebuilt it using the old gaskets that were broken and cracked.  Ran good after properly rebuilding.

Am I correct in the fact that you did not have this issue before the carb was rebuilt?

Too bad you dont know anyone else with the same car and you could swap the carbs and see if that is the issue.

Keep us updated.

David

[Brent #22313]

Thanks David.

I rebuilt the carb after owning the car for a month (prior owner had installed a heat shield gasket that was leaking, so I took the opportunity to rebuild it).  Both prior to and immediately after the rebuild, I was able to cruise at highway speed with no problem.

I then had the tranny seals replaced and when I got it back this problem was present.  

Tranny seems to be fine, so I dont think it has anything to do with that, just a coincidence.  

The problem coincided with cold weather, so I thought it might be a choke problem (which it still might be).  Ive fiddled around with that with no success.  Are there any tricks to adjusting the carb with the car set in neutral and running at high "speed" to see if the carb is faltering?

I like the idea of tuning it up (simple solutions first, right!).  I cant say that yanking the gas tank to get to the sock filter is something Im really looking forward to :-)

Thanks so much for your time and help.  Im a bit green with mechanics beyond the basics, so your help is greatly appreciated and useful.

Cheers,
Brent

[Rhino 21150]

Im voting for fuel starvation at speed. My Dodge van had a piece of gunk in it (I remooved it and blew through it backwards, the sock got clogged just a little and the short pieces of rubber tubing all sucked just a little air. The truck was about 20 years old at the time, 90,000 miles. On the van the pickup tube did NOT require removing the tank. Chrysler replaced so many floats under warranty they made them easy to replace...

[Brent #22313]

I thought Id let everyone know what turned out to be the source of my fuel starvation at high speeds:

a kinked fuel line!

Somewhere along the way the fuel line was struck pretty good against the frame, reducing its diameter to about 1/3 of what it should have been.  Once the engine started sucking greater amounts of fuel at high speeds, this pinch point couldnt accomodate it and, hence, the starvation.

Spliced in a piece of line and was whizzing down the highway at 70 mph once again!

Thanks to everyone for their help.

Best,
Brent