[1963 250 hp 4sps conv] I have been chasing an intermittent stumble under acceleration for a couple of years. It occurs mainly under power and especially while turning to the left. It usually goes away after driving in a straight line for a few seconds. Sometimes it will continue while rowing thru the gears then returns to normal operation. Occasionally, if I stop for a few minutes to tend to something else and let it idle, when I accelerate while pulling back on the road it will stumble thru the gears. My original thoughts were centered on the carb malfunctioning. I shipped it off to a highly recommended vendor after speaking to him about the issue and he concurred it was a strong candidate for a rebuild. I sent it to him and after a lengthy process he returned it to me. He was unable to cite any particular problem he uncovered, but assured me it was in great working order. I installed the carb and took it for a short drive and it appeared to be better than before. I then took it on a 3500 mi road trip that was nearly a mechanical catastrophe for the engine. I filled up the gas tank and hit the road in the morning while the car performed as usual. About150 miles later I unexpectedly ran out of gas. I typically fill up about every 300-350 miles so I thought I must have a fuel leak. I crawled around under the car and the hood and could not find any signs of a leak, so I filled it up after getting enough gas to get to a station. I drove about 600 miles until I got to my buddies house where I could work on it.During this time it was consuming gas at about twice the normal amount, and I was concerned it was keeping the cylinder walls washed down and they weren't oiling properly. We pulled the carb, checked the floats, etc and re-installed. Drove it locally monitoring the gas mileage and discovered it was still twice the norm. We then pulled the carb and disassembled it completely. We discovered that a gasket had been installed incorrectly and wasn't allowing the metering rods to move correctly while accelerating, but it allowed gas to keep pouring into the carb. We flipped the gasket over, the holes for the metering rods lined up correctly, so put it back together and test drove it for 50 miles. The gas consumption returned to the usual 16-20 mpg but the stumble remained. I continued my trip, while staying in touch with the re-builder during this exploratory process, and keeping him informed of the issues. He didn't really have any advice as to solving the problem except ship it back to him. When I discovered the problem and sent him a foto of the gasket's original install he claimed that was the first time that had ever occurred to one of his jobs. I pulled the carb when I got home and sent it to him as he requested. Unfortunately, he wasn't very interested or motivated to solve the problem. After a very lengthy stay in his shop and repeated inquiries from me for its return, he eventually returned it to me with no explanations or insights regarding the repairs. He made it clear he had done all he could, or would, do to that carb. My confidence in him had waned to a point that I didn't desire to do any more business with him, either. That was about 2 years ago and I took a 3,000 mi trip last summer without any carb related issues, other than the persistent stumble.
In an attempt to isolate the cause of the stumble I ran a wire from my coil into the cabin. Today, I hooked up a ground wire to the Z-bar and connected them both to my Tach/Dwell meter temporarily mounted on my steering column. It allowed me to monitor the Dwell while it would stumble, to see if perhaps it was an electrical problem. I did it a number of times and the meter remained steady during the stumbles. I honestly believe it is fuel related and not electrical. It is more of an annoyance more than a problem, except when pulling out into traffic and needing to get up to speed quickly, etc. If I had access to another WCFB that I could install and test with I could confirm that carb is the problem. Alas, I don't have a resource to accomplish that and the cost for another correct one(this is the carb the car was born with) is about $800-$1K. That's a bit pricey for a test piece, unless that is the problem for certain and it needs replaced, which I would do if necessary.
MY QUESTIONS; Are there parts on this WCFB that wear out and can't be repaired/replaced? Has anyone had a similar issue and can share their experiences with me in resolving it? Other than this issue it runs fine, starts without problems,etc. I've been driving this car for nearly 50 years and am familiar with it's peculiarities. I would prefer to solve this one instead of living with it, if possible. Thanks for your time- lib

 

You really have to wonder what kind of job the rebuilder performed when you found a gasket installed incorrectly. A couple of things:
1) Check the accelerator pump.
2) This could be a stumble related to an off-idle circuit issue (progression). A big problem, historically, with Webers, but it is something I would check and see if that circuit/passage is functioning, correctly.

 

I would replace the fuel filter at the tank.
Good luck

 

After squinting to read that tale of woe (try double spacing or a few paragraphs next time) I quoted what I believe is the salient portion.

The WCFB is very similar to the Rochester 4G and they were used interchangeably on GM assembly lines. Both have floats that are situated very close to the bowl sides and can easily drag upon them and cause your symptoms. Otherwise both carbs (WCFB & 4G) are some of the least problematic carbs out there. The other thing to look at is a hung up exhaust crossover that is making the intake and carb too hot.

If those check out I would take another look at ignition. One bad plug wire or plug insulator can cause a stumble that could be easily mistaken for a fuel problem. If you have access to someone with an ignition analyzer or oscilloscope it would be easy enough to rule out ignition and if you rule out ignition you will know that your WCFB needs expert experienced hands such as Robert Kunz.

Dan

 

Carter had a bulletin # 497 dated 4/18/1956 subject wcfb cutting out on left hand turns. the following link talks about it WCFB stumble | Chevy Tri Five Forum It has you add a bushing/tube to help seal the vacuum pasage from the bowl to the top.

i hope this helps Henry @ olescarb

 

Amazing knowledge! I have determined I am too old to learn everything and thus we depend on those that do like Henry and are kind enough to share.

 

I pulled the carb and installed the 5/16" tubing as described in the old service bulletin. While I had it apart I couldn't see any obvious signs of where the floats might have been in contact with the carb body or similar issues. I recently took it out for a long drive on my back roads test track and the problem remains unabated. I am nearly convinced that it is related to the carb but am willing to try more to isolate/confirm that is the problem. My latest potential test would to be to cut in a "T" on the fuel line to the carb, between the fuel pump and the carb inlet. A long line could be ran into the cabin where I would be able to view the pressure in real time. I could then monitor the fuel delivery to the carb when it stumbles. I don't know if it would be able to confirm the fuel pressure and the necessary amount of fuel is being delivered when it is stumbling. I have a difficult time imagining that the problem is in the delivery side/ tank as the symptom is short in duration. There is too much fuel in the line from the tank to the carb, in my estimation, to be affected immediately if there is a partial blockage arising while cornering. It seems there should be enough fuel in the bowls of carb to run it for 5-8 seconds unless the pressure drops off entirely. Hence the fuel pressure gauge to monitor that situation. The engine continues to start, run, and get good mileage as usual. If I could resolve this annoyance it would be a relief. I don't have a problem with replacing the original carb if that is the issue. I just don't want to spend about $1k for a test carb and find it doesn't solve the problem. Any additional suggestions are welcome- lib

 

When is the last time the engine had a tune up, spark plug wires etc. Look closely for a small vacuum leak possibly at the hose that connects to the vacuum advance control. How much vacuum at idle? How about the gaskets under the carfburetor, is the carburetor flat on the bottom without any hot slot damage?

 

There is a little tube kit that stops that stumble on left turns, I have them in 2x4 set up stopped the problem, a for member, Frankie, brought them to my attention several years ago, Frankie is sharp on the WCFB'S.

Bill

 

The issue has been resolved to my satisfaction and relief. As often is the case, it was a combination of smaller problems that lead up to the major symptoms. The main repairs were adjusting the carb's float levels (they were too low) and the distributor needed new springs (worn out) and re-curved. Henry at Ole's Carbs did the diagnosis and the repairs to the parts. He also installed the vacuum advance corrector that he and Lars invented on my distributor. I removed the parts from my car and delivered them to his shop after his diagnosis. I picked them back up the following week, installed them, and the car fired right off. I made a couple of test runs to be sure the stumble was cured and took it back to him the following week and he put the final tune on it. The biggest change I noticed is that it rev's faster in the 3000-5000 RPM band and pulls harder thru all gears. It still runs at the same temps on the freeway or in town as before the changes were made. I'm probably going on a road trip next month for a few daze and see how it behaves at different elevations and climates. Thanks for everyone's helpful input and advice in helping me get this annoyance cured- lib

 

Fantastic!
and Thanks for closings the loop with your final solutions.