kep1113

1956 Buick Special hesitation issue

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Hello everyone,  my son recently acquired a 1956 Buick Special, 322 V-8.  It is still very warm here in Florida and we were battling vapor lock issues, so we bypassed the stock mechanical fuel pump, installed an electric pump, and that seems to have resolved that problem.  The car seems to run fine as it is warming up.  However, when it is fully warmed up it begins hesitating when accelerating from a stop.  He has to "butterfly" the accelerator pedal (maybe that's not the right term, but you probably know what I mean!).  The original Carter carburetor was rebuilt and the accelerator pump appears to be working as it should - when the pedal is pressed there are two jets of gas pumped into the carb throat.

 

Has anyone else experienced this issue?  Thanks!!

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I think "feathering" the throttle is the term you were looking for... Was a pressure regulator installed with the electric pump? Sounds like the pressure may be too high and it's flooding a little.

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See how it runs when the weather gets cooler.  The recent hurricanes resulted in giving the oil companies permission to produce the more volatile winter blend gas.  I too have vapor lock (if not using the electric fuel pump), along with hesitation and percolation.  In the meantime set the idle mixture screws as lean (turned in) as it will run well...that helps to keep the transition from idle to increased rpm a little smoother.

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Thanks for the responses.   I don't think the fuel pressure is too high.  We installed a clear fuel filter just before the carb and the pump keeps fuel flowing but not enough to completely fill the filter while the engine is running.  As for the fuel itself, that could be an issue.  We do have access to non-ethanol gasoline, but I'm not sure if that makes a difference or not.  We will try leaning out the carburetors and see what happens.

 

By the way, my son just turned 16 and this is his first car so he's learning a lot... as am I.  I appreciate any input we can get.  I did a broad Google search on the issue, but got only questions about late model Buicks, so that wasn't much help.  Fortunately, we have a 1956 shop manual which helps immensely, but obviously it can't address every issue.

 

I was going to insert a picture but I don't have one handy.  Will do it soon.  Thanks again.

 

 

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You can't base the pressure off what you see in the filter. The stock pump puts out 4-6 psi at the carb. A pressure gauge is the only way to tell you where you sit. If you're too low, you may be starving the carb and if you're too high, you'll be flooding the carb. Also do you have any paper work on the carb rebuild? If the fuel pump pressure is okay and ethanol is not an issue (that's all I can run in mine), then there may be some carb cleaning that needs to be done.

 

Looking forward to seeing those pictures!

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Is the fuel pressure gauge something I can get at any auto parts store?   

 

Will double-check the carb mounting bolts.

 

Here's a quick pic of the proud owner.  According to the plate under the hood, it was originally grey & white.IMG_1512.JPG.8d2ba1d0fccea6e7a68b98e0d0fa3b3f.JPG

 

 

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Sometimes the gauges get coupled with a vacuum gauge. My local NAPA had them on the shelf last I was in town. Old car tuning tools can be found cheap at swap meets but its probably a little too late in the year now. A vacuum gauge, tachometer/dwell meter and dial back timing light are a must to get the car from "it runs ok" to "I know what works best and how to get there". Good luck! 

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Lucky kid!  I was fortunate to land a '54 my senior year of high school, and it has been a blast with Buicks ever since.

 

Rebuild the mechanical pump, and wire the electric one to use only when necessary, such as after a long sitting or vapor problems...

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18 hours ago, kep1113 said:

Is the fuel pressure gauge something I can get at any auto parts store?   

 

Will double-check the carb mounting bolts.

 

Here's a quick pic of the proud owner.  According to the plate under the hood, it was originally grey & white.IMG_1512.JPG.8d2ba1d0fccea6e7a68b98e0d0fa3b3f.JPG

 

 

Lucky boy , not bad for a first car 😊

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I too have that hesitation problem with my '55 Century.  When I rebuilt the engine, I installed a new vacuum advance, rebuilt the carburetor, I am running ethanol-free gas (90 octane), and have adjusted the carburetor as Old-Tank suggests.  I have just learned to live with it.  I think it is "the nature of the beast" with modern gas formulation.

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Just now, old-tank said:

Confused...

 

 

At least for me, vacuum measured across the wiper system has a 2-3 drop in vacuum when hooked up. Putting a one way check valve before the system ensures any type of loss will not change the dynamics of the engine.

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The vacuum advance plate in the distributor requires lubrication at least once every 50'years or so.  A little (few drops) of clean motor oil will help the plate move freely.  There is a hole in the plate and actually says "oil here" if I remember correctly.  Made the problems on my 56 Special go away.

 

Matt

Edited by jackofalltrades70 (see edit history)
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Thanks for all the input... it is greatly appreciated.  I don't think we've investigated the lubrication of the vacuum advance so that might be an issue.

 

One more question (for now).  I'm pretty sure the idle speed is in the ballpark of where it should be, but when he shifts from park to reverse the shift is so abrupt that it makes the tires "bark".  That can't be good, right?  Do you think this is simply a symptom of 61 year old transmission that probably needs to be rebuilt?

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1. I don't get how the tires bark if the brakes are on when shifting into R.  If the brakes aren't on, I don't get why they aren't.

2. Rather than guess about the idle speed, measure it.  That kind of abrupt engagement sounds like a high idle.

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No, the Idle speed should be lower.  The factory setting is 450 RPM when at full operating temperature.  However I have set my 56 Super to 500 RPM.

 

As mentioned by Konga Man, the brakes should be employed when shifting to reverse.  One practice I use is to hold the brakes tight, and just relieve the pressure on them as I am putting the car in reverse.  This seems to reduce the shock of the shift.  I will caution that if you don't be careful, dropping the car into reverse when the idle is high may cause the strut rod that holds the reverse band to drop out of place. Of course, this means no reverse till the rod is reinstalled.

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2 hours ago, JohnD1956 said:

No, the Idle speed should be lower.  The factory setting is 450 RPM when at full operating temperature.  However I have set my 56 Super to 500 RPM.

 

I may need to recheck this, but I'm pretty sure it's 450RPM in gear. My grandpa always set the idle to 600RPM in park, which drops to around 450-500 in drive.

 

Again, eye-balling or "winging it" on a vintage engine is not the best route to go. You really need to get the right tools to know what you're doing with that old engine. Get a $20 tach off Ebay and verify dwell, then get a timing light and verify 5 degrees on the balancer with the advance unhooked, then verify the advance works, then verify RPM. Get a vacuum gauge to dial in the carb idle with the tach in tandem and you will be set.

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We finally had a chance to do a little more investigation into the hesitation issue.  We hooked up the Halloween fog machine to the vacuum port on the manifold and discovered some leakage from around a few of the carb hold-down bolts, so I guess the gasket is shot.  We also saw smoke coming out of this hole in the side of the carburetor (see pic, the hole between and below the two screws holding the top half to the bottom).  The Carter WGD diagrams don't really help much in terms of identifying what this hole is for, but I assume it is supposed to be plugged, right?  Can anyone shed light on this?  Thanks again!!IMG_8058.thumb.JPG.d84c2e363820453a4a19f95d7c57963f.JPG

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If you already have a 1956 Shop Manual,just buy a Product Service Bullentins book ,a lot of tip and things that are missing in the Shop Manual can you find in this book.Usualle cost around $30-40 on e-bay,well worth the money.

Leif in Sweden.

Buick 1956 Product Service Bulletin..JPG

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