Engine Hesitation on Take Off - 1955

[D.Yaros]

On take off from a dead stop there is a slight engine hesitation/stumble when stepping on the gas.  We are talking a second or less.  Then the car runs just fine.  This condition is repeatable.

Had one place tell me it is a bad carburetor accelerator pump diaphragm; most likely caused by modern day ethanol laced fuel.

Problem with this theory, to me, is that I rebuilt the carb using an ethanol compatible kit from Daytona Parts Co.

Anyone else with this situation?

Is the likely culprit, carb, vacuum, transmission, linkage or what?  What do you guys think? 

Need advice.  Thanks.

[Jon S]

Leather accelerator pump plungers are not affected by Ethanol.  It "sounds like" you need to enrichen the accelerator pump shot just a spec (give it more gas) to compensate for the Ethanol fuel volatility.  I had the same problem with my 1973 Lincoln and that cured it.  Unfortunately, the adjustment hole is on the accelerator pump shaft on your carburetor requiring you to open the carburetor.  My Motorcraft adjustment was external.

Ethanol gas is creating problems these cars never had.  Also adding 4 oz of Marvel Mystery Oil to your tank improves the volatility of the Ethanol gas.  I also add Tetra ethyl lead to increase the octane.

[CEC #20099]

Dave: Are you SURE your Hydramatic is in First Gear, & not Second, from a dead stop. ??

c. chleboun #20099

[The Tassie Devil(le)]

Plus, also check the timing with a timing light.   And if the Distributor advance is working correctly.

Bruce.

[D.Yaros]

Distributor vacuum advance newly rebuilt, so it is working.  Timing is set properly.

Jon S. said:  Leather accelerator pump plungers are not affected by Ethanol.  It "sounds like" you need to enrichen the accelerator pump shot just a spec (give it more gas) to compensate for the Ethanol fuel volatility.  I had the same problem with my 1973 Lincoln and that cured it.  Unfortunately, the adjustment hole is on the accelerator pump shaft on your carburetor requiring you to open the carburetor.  My Motorcraft adjustment was external.

Thanks guys.

My pump plunger is not leather.  It came in a rebuild kit from Daytona Parts Co. and is supposed to be ethanol compatible.

Have not heard and am not aware of adjustment for the "accelerator pump shot."  This might bear further investigation.  Where may one learn more about this?

Am I certain it is in first gear.  Am not expert, but would say yes with 99% certainty.  I am certain the car is in "D".

[walt chomosh #23510]

Dave,
  One day I pulled out of my driveway and my 55CDV fell flat onto it's face when shifting into second!(Rochester 4GC) No power what-so-ever unless I really "gave it the gas". I turned to my shop manual and read about the "part throttle circuit" which helps provide additional fuel to meet engine requirements. A quick disassembly and through cleaning of all passages was in order and sure enough,the car "ran like a Cadillac" once again! Hope this helps!...walt..tulsa,ok 

[D.Yaros]

Reporting back on this:

Car is back and the referenced hesitation is gone!

Cause was vacuum, both the distributor vacuum advance and vacuum hoses.  Hoses were dry, brittle and cracked.  All replaced.  Mechanic reported that distributor vacuum advance arm pinched, in a bind, and not able to travel freely as required.

I suspect that was the real culprit.

At any rate, car drives like a Caddy should now!

[walt chomosh #23510]

Dave,
  Glad to hear your car is running well again! The vacumn advance must work properly to ensure best performance. The diaphrams do go bad though(along with centrifical advance pivot points)and I had mine rebuilt(vacumn advance) at Terell Machine in Texas. There is probably other rebuilders around.....I struggled to find an aftermarket unit that would work in the 1955 distributor but struck out....walt...tulsa,ok

[D.Yaros]

Walt,

Terrill Machine did the rebuild on my distributor vacuum advance.  Great outfit!  No problems with their work.  Problem was my not re-installing it properly.