1950s Bucking at low rpms

[Fitzy]

My brother just purchased a beautiful 1952 Series 62 sedan and is having a bucking at low rpms. for example:
We can get it to do it when you press on the accelerator while the car is at idle. Also when driving it, barely pressing on the accelerator it'll buck till you give it more gas. Let off the accelerator and it'll back fire.
We've come to the conclusion that its spark. We changed the distributor cap and rotor. still the same.
It seems like it goes away when it warms up. So now we're thinking of changing the Ignition Coil and the condensor. If that doesn't fix it than change out the points. Any other ideas?
Also thought maybe its bad gas. We put in stabil and seafoam and have driven it and filled it up a couple of times with 93.
Thankyou.
Jason Fitzgerald

[E Masters]

It may be idle mixtures are a little lean.

[novetti]

Check the Carburetor Accelerator pump squirt.

[35-709]

Also check the vacuum advance.  When it fails it causes a vacuum leak which can cause a backfire on deceleration and will also cause a stumble on acceleration.

[Julien Abrahams]

x2 on the subbestions that were already given. I would check the vacuum advance first. Check if it holds vacuum. Also check timing to see where it is at. It cannot hurt to check.

[D. Mailan]

Also agree with all posts above.

I would also add, checking your fuel pump. If your fuel pump is not supplying enough adequate fuel, issues like sputtering and poor/no acceleration could happen.

Absolutely check timing and most importantly vacuum advance mechanism.

Spray some carb cleaner around the base of the carburetor to see if the idle changed. That would indicate a vacuum leak. Carburetor mixtures are incredibly important.

Best of luck
Derick

[TJ Hopland]

I would also get a dwell meter hooked up and make sure its steady especially when this is happening.  You could have a cracked ground or coil wire in the distributor that looses contact in some advance positions but holds in others.  As soon as it gets to the dead spot the vacuum changes which makes it move to the position it makes contact again.   You could also have a wear issue in the main shaft letting the cam the points ride on wobble around and depending on the rpm if the dwell time is reasonable and on time or not.  Dwell should be very steady throughout the rpm range.   

[Fitzy]

What we have done so far: cap and rotor, coil and condensor. Timing was checked. Did need to be advanced.  Checked vacuum advanced. But how do you exactly check it though? One of my brothers said he checked it but want to mention on how to do it and see if he did do it that way.
We are thinking of changing the points. Also emptying the tank, dropping it and replacing the sender cause the fuel gauge doesn't work. Replacing the inline fuel filter also.
We think it may have bad fuel in it. Thanks for the suggestions. keep them coming.

Jason Fitzgerald

[V63]

Stale fuel can cause the valves to stick (seize) in their guides, diluting does not work because the old fuel is condensed and heavier. If in doubt stop running it or the fix is often removing the heads. No fun there.

[Julien Abrahams]

First remove most of the old fuel (how old is the fuel? And put new fuel in it. A couple of gallons will do.
Then start the engine and let it warm up.
Does it make any difference if the engine is cold or up to operating temperature with regard to the bucking?
If it for example only does it when it is cold it could be fuel-air mixture problem (caused by an incorrect fucntioning choke).
Also check the accelration pump. Shut the car off and while looking down the carb, operate the throttle lever. Two jets of fuel should squirt down the throat of the carb.

The vacuum advance can be checked relatively easily. Unscrew it from the carburetor and put a tight fitting hose over it. Take of the distributor cap and suck on the hose. The base plate should move and when you block airflow with your tongue it should stay in position. If it does not move or does not stay in place, that it is most likely very hard to draw a vacuum which means that the diaphragm has ruptured inside (and need to to be repaired).
Another method is to put a small vacuum pump on the hose, run the engine and check the timing. Pull vacuum and see if the timing advances.

[TJ Hopland]

You replaced all that ignition stuff but not the points?  They are kinda important and the part that often causes the most problems.  If you run alot they wear.  If you don't run much they corrode.   

Here is an example of the sort of hand vacuum pump you could use to check the vacuum advance.  You can check that its actually advancing and that its maintaining electrical contact while it goes through its range.  Tools like this are a must have for anyone working on their own cars and have many uses.  With this and a dwell meter you can just about eliminate ignition as your possible problem.           



https://www.harborfreight.com/brake-bleeder-and-vacuum-pump-kit-63391.html?_br_psugg_q=brake+bleeding+tools

[Fitzy]

Ok thankyou everyone. We've decided to upgrade to electronic ignition instead of points. We took the carb off and cleaned everything. Jets also.

Jason Fitzgerald

[Fitzy]

Update!!! Removed points and put in Electronic Ignition and bucking stopped. Car drives perfect now!!

Jason fitzgerald

[Julien Abrahams]

So the problem was either a worn distributor shaft or simply worn or maladjusted points?

[James Landi]

or may well have been a bad condenser.  I've purchased new ones that are BAD, out of the box.