VCCA Home Forums TECHNICAL - 1945 AND NEWER 1949-1954 3rd Gear hesitation

Hi,

I have a 1954 Bel air with 1 barrel Rochester. Original 3 on the column.

A couple weeks back I was having an awful hesitation in 1st and 2nd gear only. A new air filter fixed the problem and it ran beautifully for about 300 miles.

Today I am getting a very slight hesitation in 1st and 2nd, but only on occasion. In third at highway speeds I get a noticeable hesitation, on and off.

I am thinking a fuel issue.
I can see the glass fuel filter under the hood filling with gas as I increase the idle speed so I don't think it is the fuel pump.
And it idles beautifully.

It has gotten colder here and was in the low 40s today. Are these carbs sensitive to temp?

Accelerator pump working fine. Both fuel filters are new, timing is good and all ignition components, less the distributor, are new.

Any thoughts?

How old is your fuel? If your gas has ethanol in it, t has a very short storage life (month or two). Also fuel blends change considerably in the fall in many places as the winter blend vaporizes easier so maybe your carb just runs better with a certain fuel/outside temperature combination.

These cars tend to spend a lot of time sitting so common to need the carb cleaned at some point as well.

I expect that your fuel is relatively fresh If you have driven 300 miles after you installed he new air filter.

Tim is correct that you could be experiencing an issue due to the change to winter fuel.

I do not remember the details from your prior thread. When was the carburetor rebuilt?

You also mentioned that both fuel filters were recently changed. If the fuel tank has not been cleaned out recently one of those could already be plugged. Also, some people have reported issues with restricted gas flow with 2 filters in the circuit. The fuel pump can not overcome the resistance of both filters.

Another idea is to temporarily remove the new air filter to see if the problem still exists.

Thank you for the replies.

The tank of fuel is new. I drove about 40 miles on this new tank of gas with no problems. Then, today, on the same gas, things started acting up.

I have driven about 1,000 miles on the 2 fuel filters with no problem. But In will look into that.

I tried running it without the air filter and oddly enough it ran worse.

The car is new to me so I am not sure when the carburetor was rebuilt. The fuel tank was replaced at some point before I bought it. It is one of the plastic (?) types.

What do you think?

Removing the air filter should be a neutral event. Almost seems like it's running lean and removing the air filter makes it worse.

If it has a manual choke, try giving it a bit of choke when driving at the point where you get the hesitation and experiment a bit. Also see if the heat riser valve in the exhaust manifold is free/moving. Cold weather + lean carb + stuck heat riser = lean engine. Maybe just the perfect combination to create something you might notice. Does your engine temperature gauge reach normal operating temperature?

I had a 71 Nova with a carb that acted like this when it was cold.

It's kind of a sudden change so makes me wonder about quality or just that batch of gas. I'd be tempted to drive it and watch it a bit longer and maybe even in warm weather before I'd be convinced there is truly something wrong.

Thanks.

The car has an automatic choke. The heat riser is moving freely. The temperature gauge stays around the middle to a little less than the middle.

Thanks for the advice. I will drive it around a bit under different weather conditions. If it still acts up, do you think adjusting the mixture a little richer might help? It is a Rochester 1 barrel BC

The mixture screw only affects richness at idle, and the spot just the tiniest bit above idle. Not at all past that.

You might want to check the automatic choke. The fact that removing the air cleaner made it worse might be a clue. I agree with Tim that the car should perform the same with and without the air filter.

Unless someone has converted to an electric choke that choke uses a coiled thermostatic spring. As the spring heats it turns the shaft which opens the choke plate.

Do some simple checks on the choke. Make sure it rotates open and closed with only the spring resistance. The shaft and plate should not bind.

Check the heat tube to make sure it is open and passes warm air to the housing.

When the engine is cold the choke plate should snap shut when you open the throttle. When everything is warm the choke plate should firmly be in the vertical position. I have seen a few cases when either choke was adjusted too cold or the spring was weak. The choke plate would be vertical but there was very little resistance to hold it in that position The air flowing over it would try to close it while you were driving. The car would stumble or hesitate. Yet when you stop the car and look the choke is open.

This is how I adjust these chokes. Others might offer there ideas.
- Remove the air cleaner housing.
- With the engine cold loosen the screws that hold the cover on the choke spring housing.
- Hold/block the throttle partially open so the fast idle linkage does not interfere with the choke adjustment.
-Turn the housing cover both ways and watch to confirm that the choke plate does open and close as the spring and cover rotate.
- Rotate the cover so the choke plate is just completely closed. Then move the cover one more index mark to make sure the choke plate is firmly seated.
- Tighten the screws on the cover and see how the car drives.

I really do wonder if a carb rebuild is needed as a long term solution. If that is a Rochester GC they are pretty simple. Nothing like a W1 with all the brass plugs or a RXO.

I will check into that. I also notice a black plastic dial locked into place with screws that says lean and rich. I am reluctant to dial it to more rich because the car was running great until yesterday. I will check the choke adjustment and follow your guidance. What do you think about the lean / rich adjustment?

The "lean to rich" is the choke adjustment only. Sould be set about in the center position. When cold and the engine not runing the choke should be completely shut. When stsrting the engine vacuum will open it slightly and after aabout 15 minutes the choke should be fully open.

I took off the 2nd (in the engine compartment) fuel filter. The choke opens and closes without any resistance as does the heat riser. Choke plate snaps shut when I open and close it so it feels like the spring is in great shape.

When the engine is warm the throttle opens but it is not open to the completely vertical and most open position. However, to move it completely open isn't much movement.

The car idles beautifully but I notice it will eventually stall when I take off the air filter.

When the engine is cold it fires right up. It seems like it runs worse the more it warms up.

It may be time for a carburetor rebuild but I think I will drive through most of this tank of gas first.

I think you mean that the choke plate does not open to a full vertical position. It should be firmly open in that position when the engine is at operating temperature.

That is the issue I was describing. My suspicion is that if you increase the engine speed by opening the throttle with the air cleaner removed you will see the choke plate start to close. The air flow will push it closed because that plate is by design off-center on the shaft.

The fix is to turn the cover towards lean or possibly replace the coiled flat spring in the choke housing.

The trick is that the spring has to have a full range of travel from cold to hot. It must hold the choke plate closed when cold and hold it completely open when warm.

Your troubleshooting steps are helping.

I thing the carburetor should be removed and rebuit/adjusted by some one that knows what they are doing.

Thanks, I will try moving it toward lean. If that fixes it I will look into a new spring, if I can find one.
Yes, I wouldn't doubt that the carb should be rebuilt, it certainly wouldn't hurt. The car is new to me so I don't know its history.

Is the adjustment a small adjustment at a time?

Pick a time when the ambient is between 65 and 70 degrees F., and the engine is cold.

Loosen the three screws that hold the choke cover so it may be rotated.

With one hand, rotate the throttle to the wide-open position, release it, and move and hold it approximately 1/2 open.

With your second hand, rotate the choke cover in the direction of "lean" until the choke plate drops open.

Then (still holding the throttle), rotate the choke cover in the direction of "rich" until the choke plate just touches closed, with NO tension.

With your third hand , tighten the three retaining screws.

Start the engine, and run for 15 minutes or so. Remove the air cleaner, and observe the position of the choke plate. It should be completely vertical. If not, you have other issues, probably in the vacuum circuit evacuating the choke housing, and allowing hot air to flow to the choke housing (but one thing at a time, adjust the choke, and test).

Jon.

And remember that hesitation and Rochester type B go together.

Just one of the several reasons Carter sold more than 1 million type YF carburetors to disgruntled Chevrolet owners.

Jon.

Well, I went to adjust the black choke cover to lean and it was completely loose. I got the car to operating temperature, took the air cleaner off and adjusted the black choke cover to the lean position until the throttle snapped completely open. Now the car idles beautifully without the air cleaner. Prior to doing that, the car would stall as soon as I removed the air cleaner. So, I think that problem is solved; the choke cover was completely loose, and now it idles well without the air cleaner.

But...... I took it out for a run and it is hesitating worse than ever, I almost broke down. It must be a 2 or more pronged issue.

You adjusted the automatic choke exactly incorectly....it is done with a cold engine

I will look at it again tomorrow. It has been a long time since I messed with one of these chokes. I'll get it right!

Up here in the "great white north",
where summer and winter temperatures vary widely...

We used to have to tweek the choke a few notches from season to season all the time when we were running Rochester Quadrajets.
Counter-intuitively, you adjusted to leaner in the winter and richer in the summer.
This was of course because in really cold weather the air flowing to the choke spring was a fair bit cooler and would never completely pull the choke open.
Thus, in the winter, we set leaner.
Also, when you tried to start a small block Chev that wasn't plugged in at 30 or 40 below, they would fire and keep kicking over but never quite run until you stuck a screw driver in the choke to hold it open a bit. Again... you had to set the choke leaner when the temperature dropped.

Long story short, 1 setting on a Rochester Quadrajet choke would not work in all conditions.

The one Chev six we had with a single barrel Rochester was a little 230.
Dad put a manual choke on that during the first winter.

If you understand how an automatic choke works and it is working correctly you will have no problems.

Same with a Rochester carbuetor. ....except some of the early 1950-1951 models.

Well...
We understood how they worked but,
the design just didn't handle conditions that varied as much as they do here very well unless you knew enough to adjust a little between seasons.
And a driver who knows and has "a feel" for his or her engine will equal or better an automatic choke any day. If an engine doesn't start right off for some reason (gas a little off for example) an automatic choke will never think or experiment it's way past the problem. Just keeps trying the same thing revolution after revolution.

If it dosen't start right off to prevent flooding you push the accelerator to the floor. This opens the choke slightly to prevent flooding.
We do get -25 Deg. weather here.

We knew all about that.
Also knew that when you did that you pumped an accelerator well full of gasoline right into the manifold that didn't help things any.

Then it was standard proceedure to tow the car in, installnew plugs, change the oil because if was full of gas and hope the owner learden something.
With todays fuel injected cars any on can start them when cold, strart right up and they drive off without a hickup