Battling hesitation

[Jack T]

Hi guys, I’m working on getting a 50 Plymouth special deluxe back on the road, and I’m almost there.

The last issue I’m fighting with, is a nasty hesitation/lag/stumble off idle.

This only occurs when warm, and the automatic choke has opened up.

 

I’ve gone through the following:

- Rebuilt the carter carb, and I’m getting a great spray from the accelerator pump.

- Replaced points, condenser, cap and rotor, plugs and wires.

- Checked vacuum advance at distributor - all ok.

- Measuring around 20in of vacuum at wiper port on manifold.

- Played with base timing - no real change:

 

If I disconnect the auto choke rod, and wire the choke plate almost shut - I have great throttle response. This suggests to me a lean condition, but I’d appreciate any input!

 

Oh and it starts and idles perfectly.

 

[Sam Buchanan]

Just some thoughts:

 

Worn throttle shaft allowing air to be pulled past the shaft creating lean condition?

 

Leaking gaskets at base of carb and/or intake manifold?

 

Problem with centrifugal advance springs or sticking weights?

 

Something still plugged in the carb?

 

Stay with it, I suspect you are very close to getting this sorted out. 

Edited September 14, 2019 by Sam Buchanan

[greg g]

Is the step up valve/jet fully operational? If stuck open due to lack of vacuum signal theough the carb, it will default to the open position cusing a too rich mixture.  What do your spark plugs look like now that they have some running time on them?

[philjafo]

Vacuum leak somewhere, like a leaking gasket under the freshly rebuilt carb.

[Los_Control]

 I would spray some carb cleaner in suspect areas while running. The idle rpm's will change if you find a leak.

Spray around the throttle shaft, base gasket, vacuum ports etc .... do you have vacuum wipers?

 

Just a quick tip to help troubleshoot. It will not help if issue is inside the carb though.

But would help eliminate external sources.

[DJ194950]

i had a similar problem with my 50 Ply.

I did not remove the plug on the drivers side of the carb which  has the mid range? jet screwed inside. I remembered that I had neglected to clean out that very small passage. After I cleaned it and reassembled the car ran perfect at mid range speeds again after several years of neglect.

Just a thought.

 

DJ

[MarcDeSoto]

Back in the 80s, a guy who worked as ship's carpenter on the last iron side ship, The Star of India, in San Diego drove a 1947 Chrysler Windsor business coupe.  He hired me to work on it and it was having a similar problem to yours.  I replaced the fuel pump, fixed a burned valve in the 5th cylinder, and no fix.  He finally took it to a shop and they discovered that he had a tiny little rust hole at the top part of the fuel line where you can't see it sucking air.  Have you replaced your fuel line from the tank to the fuel pump?  

 

 

[Jack T]

Well guys thanks for all the advice.

 

I had another snoop around today and sprayed some brake cleaner around. I did notice a little rise in rpm if I sprayed around the throttle plate shaft. The base gasket etc is all new, and I spent time cleaning the surfaces - so I highly doubt there’s any issues there. Right now, a leak past that shaft seems the most likely culprit.

Which leads me to the question of, can I do anything to resolve that? Finding a direct replacement carb seems impossible.

[Los_Control]

I dont know how or who ... I think the cure is to drill out and then install a new bushing. That will fit the throttle shaft.

I bought a rebuilt Autoline C522 from Rockauto, they are also available from other local auto parts store.

They are asking a core charge, I am afraid that people like me that hoard the old parts, they may run out of core carbs to rebuild  soon.

 

Just saying, I rebuilt mine, then bought a new rebuilt and put my new rebuilt in oil and rags and on a shelf for future use. Nice to have a spare.

I think someday we may run out of cores to rebuild and sell.

The one I bought from Autoline seems to work fine so far.

[DJ194950]

 

One choice.

Others on this frum have tried a 1bbl. carb from a early Ford 6 cyl. mustang I think it was with good results, however They posted this info but never showed and pics etc. Cannot speak about results for either one myself but I was recently thinking about this. Ended up getting my Carter B&B working good. Saved my $$.

 

DJ

[chrysleritis]

Check your ignition coil. I'm glad I did. It's cheap and easy to replace. Mine performed about like your problem sounds. Started with effort, idle a little rough-ish, but the main problem was stumble coming off idle once it was warm. 

[greg g]

Did you read your spark plugs, is your acceleratorpupm passing enough gas?  Where is the linkage set for the accpump stroe, there are three positions.  Did you soak the account pump leather piece in oil before installing it? Did you check your step up circuit?