Chasing down the allusive stumble

bigd1101

bigd1101

Senior Member
Got the 53 Merc engine back all rebuilt. Had the teapot Holly rebuilt. Checked the vacuum including the distributor vacuum advance. Electronic ignition. New plugs. Still a slight stumble when taking off at a start, all warmed up. I've heard the teapots even rebuilt are finicky devils, but I don't think that's the problem. I moved the tiny rod on the accelerator pump arm forward and that helped a bit, but she just likes to hesitate. Doesn't seem to happen when I'm cruising at 50 or more, when I get on it, just at lower speeds. Replacing the coil just for sheets and giggles.....any thoughts as to what I'm missing?

Don
 
Probably not germane, but I'll throw it out anyway. I had the engine in my Corvette rebuilt and ended up with the same problem. A distinctive stumble when I got on the gas. I fooled around with it for a couple of years, and after going through the carburetor twice, I almost had it licked; down to maybe once every ten times. During one session, I had removed the air cleaner completely. I noticed that the stumble was gone. In an attempt to increase flow through the air cleaner, I stepped up and bought an expensive K&N element. It only made things worse! A little on-line research revealed that the K&N filters were more restrictive than stock. The final solution was to go with a 4" tall 14" element, rather than the stock 3" unit. Since installing it, no more stumble. Luckily, the 4" unit fit under the hood with no modifications. The only thing needed was a longer mounting stud.
 
I don't know if this will apply, since you have an electronic ignition.

I had the same thing in my 53' Merc until recently, when I had the distributor set to factory specks, on a Sun Distributor machine. It involved changing one of the springs and turning the cam post, that holds the other spring, for more tension. By properly setting the curve, it cured numerous little issues, I have been chasing and living with, for years. The car runs better, than it ever has, in 11 years I have owned it. It improved acceleration from a stop and at speed.

I had both my primary distributor and my back up set, on the machine. Well worth the effort.
 
We need a little more information about the electronic ignition you have. Is it a conversion kit in a stock Load-a-Matic distributor or a complete new electronic distributor?
 
tubman said:
We need a little more information about the electronic ignition you have. Is it a conversion kit in a stock Load-a-Matic distributor or a complete new electronic distributor?
Click to expand...

I believe it's a stock distributor with a conversion added (points removed)
 
I've been living with that same annoying stumble on my 52 for years. All original equipment. All I have done is adapt my driving style to give an extra quick pump on the gas pedal when I want to accelerate. The extra gas seems to be all it needs. If I just accelerate gradually it does not seem to hesitate. Its more of a problem when the engine is cold but that is to be expected.
 
RalphG said:
I've been living with that same annoying stumble on my 52 for years. All original equipment. All I have done is adapt my driving style to give an extra quick pump on the gas pedal when I want to accelerate. The extra gas seems to be all it needs. If I just accelerate gradually it does not seem to hesitate. Its more of a problem when the engine is cold but that is to be expected.
Click to expand...

" If I just accelerate gradually, it does not seem to hesitate."

Yes, same symptom with my car. Although I too can live with it, it drives me nuts and I think there HAS to be a solution. Some component I have not replaced or addressed. Like I said, I'm replacing the coil. Maybe a failing regulator? Got to be something.....just frustrating.
 
A vacuum gauge can sometimes help diagnose certain issues.It helped solved some issues for Flathead buddies here.
 

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bigd1101 said:
Got the 53 Merc engine back all rebuilt. Had the teapot Holly rebuilt. Checked the vacuum including the distributor vacuum advance. Electronic ignition. New plugs. Still a slight stumble when taking off at a start, all warmed up. I've heard the teapots even rebuilt are finicky devils, but I don't think that's the problem. I moved the tiny rod on the accelerator pump arm forward and that helped a bit, but she just likes to hesitate. Doesn't seem to happen when I'm cruising at 50 or more, when I get on it, just at lower speeds. Replacing the coil just for sheets and giggles.....any thoughts as to what I'm missing?

Don
Click to expand...
Might be worth checking for a vacuum leak in your wiper motor circuit. Just cap off the vacuum fitting at the intake and see if that makes a difference.
 
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