Marvel Carb Adjustments?
 

Last year I picked up a virtually unused Marvel carburetor, and today I got around to inspecting it, cleaning it up, and installing it. It works pretty well- it gives plenty of power and does not have any tendency to make the engine die when decelerating. But there is one funny thing: I have to leave the GAV about 2 turns open. This seems to be the best setting for idle, normal driving, and full-power driving.

Is this normal for these carbs? Before I messed with the carb, I noticed that the shoulder of the GAV needle was bottoming out on its housing. Also, the housing was only partially screwed into the carb body. So I screwed the housing fully into the body, and then the needle tip was seating in the valve before running out of threads.

So I am wondering: is the housing is supposed to be only partially screwed into the body, and is the needle supposed to bottom out? Perhaps in the factory the housing was screwed into the body with the needle bottomed out on it until the mixture was correct, and then sealed in that position?

I'd love to hear what the Marvel aficionados have to say...

Doug

Re: Marvel Carb Adjustments?
 

I just installed a Marvel this afternoon. It is raining so I'm unable to road test. I also noticed that I'm running at least 2 turns on the GAV to get a smooth idle. My Zenith and Tilly's idled with the GAV only slightly cracked open (CCW). Please let me know what else you find on this carb as I've heard it is even a better "goer" than my now leaking Tilly.

I screwed the GAV "nut" all the way into the body, and snugged the GAV needle carefully to the bottom of the housing. Anything approaching 1.25 or less turns of the GAV kills the engine.

Had a few dead spiders in the float bowl, so I went over the guts with WD 40 and compressed air, all the small openings work, and the float valve adjustment tab seems very easy to adjust for correct fuel level. No gush of gas from the intake when the bowl first filled. Also, this seems to not run rich when I put an Air Maze on the intake. My Tilly and Zenith were notorious for black smoke from too little air, so in the words of Carl Spangler, "....so I got that goin' for me!"

I also noticed that when I shut off the gas under the dash, the engine ran for 2 minutes before running dry. My Zenith and Tilly usually took a third the time to run dry.

The mixture screw seems to have a greater impact on smoothness at idle and stopping the "galloping" I get with a Zenith, but again, I haven't road tested yet. Standing there, I was thinking that this might be a more thirsty Carb than I'm used too. Time will tell.

I'll check back to see what you've found, I have high hopes for a good runner during the summer months, maybe the GAV will run more closed as the temperature rises (and humidity soars).

Air/Spark/Gas, how much easier can it get.

Re: Marvel Carb Adjustments?
 

Your observations sound pretty consistent with mine. The Marvel's fuel bowl is definitely bigger than a Zenith's.

I was running the GAV 2 1/4 turns open, but the engine would simply die if I closed it down 3/4 of a turn. On a Zenith, that would suggest that something was very messed up, but like I said before, the carb seemed to run well at high speed, low speed, and idle.

Doug

Re: Marvel Carb Adjustments?
 

Ran 15 miles today. This carb is 50% better on performance than my professionally rebuilt Zenith, and 10% better than my old leaky Tilly.

I replaced the gaskets with a kit from Mike's A Fordable. There were three washer/gaskets (fiber?). I put the largest under the big bolt that comes up at an angle from the bottom of the carb near the float bowl. Not sure about the use of the other two. Did you use them?

No leaks (yet!).

Also did not put any "O" rings or washers on the fuel line fitting.

I've run both of these questions back to Erich to make sure I'm making full use of the whole $8 I spent to get the best running carb I've ever had!

Still took 1 minute to drain the fuel line on shut down, but this does not cause a problem because I back up an incline into a 1920's carriage house, and the Zenith would often run dry before I finished parking.

How's yours running?

Re: Marvel Carb Adjustments?
 

I have a marvel " Rayfield " on my 30 coupe...and when I got it I took the carb off and cleaned it and it runs real good. The starting procedure is the same as the original carb, One turn open when cold and 1/4 turn when warmed up. It just sounds like if you have to open it that much to get it th run right...there's a blockage somewere. I could be wrong...but I think there is a removable jet under the needle on the fuel mixture rod. If you haven't had it out yet, there may be something blocking it. Just a thought.
I'd like to find someone who has info. on the Rayfield, I hear people mention the marvel carb, but never the rayfield part. If anyone has the info on this carb please let me know. Thanks and good luck.
Stan

Re: Marvel Carb Adjustments?
 

I've got my GAV at about 1 1/2 turns has run great for the last 35 years.I'm thinkin it's a keeper even if not "correct"

Re: Marvel Carb Adjustments?
 

Re: Marvel Carb Adjustments?
 

I also have a well rebuilt Zenith, but I consistently got "bowl slosh" and fuel starvation when approaching a right hand turn. The Marvel (and Tilly) don't seem to have this problem.

Do the Allstate and Rayfield seem "thirstier" than a Zenith? I coming at this from the perspective of using far more GAV than the Zenith would ever allow, but I'm sure that this is a miniscule extra amount through the carb; however gas is at $3.75 without booze and climbing!

Re: Marvel Carb Adjustments?
 

Re: Marvel Carb Adjustments?
 

Re: Marvel Carb Adjustments?
 

Thanks for the reference to the other thread. You carb looks exactly lile mine. Fortunately mine is very lightly used- I think somebody installed it once, took it off after a few days, and it sat around ever since. The pot metal body has a thin uniform layer of grey oxidation, but no grease or dirt.

It looks like yours has the GAV needle holder (the hex brass thing) screwed fully down into the body. And it runs OK with the GAV a half-turn open?

The GAV holder on mine was unscrewed out of the body maybe three turns, and I instinctively tightened it up. Afterwards, I found that I had to open the GAV about 2.5 turns to get it to run well. If I close the GAV down to 2 turns open, the car simply dies, whether at idle or on the road. So now I suspect that the holder had been properly adjusted in the factory. (BTW, I removed the main jet from the bottom, and it was totally clean.)

I look forward to using this carb, even though I have Zenith that has a new throttle shaft, flowed jets, a nice paint job, etc. The design looks quite elegant: The main jet also seems to serve as a secondary well, and by having the float hinged sideways instead of fore-and-aft, might be less affected by deceleration and acceleration and going up and down hills.

Doug

Re: Marvel Carb Adjustments?
 

I have a Marvel-Schebler on my 1931 sedan. The carburetor has been on the car and in service since 1949. Never a problem. Better performance than most Zenith carbs I see in operation.

For starting, when cold weather, that would be up to 40 or so degrees, the GAV is opened a full to 1 1/2 turns open. Once started the GAV is gradually reduced till it is open 3/4 to 1 turn. In warm weather, above 40 degrees then the GAV is usually opened 3/4 turn.

Once the engine is warmed up the GAV is closed for idle when the spark is fully retarded. Advance the spark and the GAV is opened about 3/4 turn. On the road at any speed the GAV is usually run at around 1/4 to 1/2 turn open.

Gas mileage stays around 17 mpg no matter what the average road speed may be up to 55 mph.

I would not consider any carb other than the Marvel-Schebler. Have tried rebuilt Zenith carbs and Tillison. Neither of these carburetors can come close to the performance of the M-S.

Re: Marvel Carb Adjustments?
 

My experience with the Marvel. GAV- 1/4 to 1/2 turns open. Rarely any need to adjust the GAV. Just a momentary pull on the choke during cold start. I like it so much I bought a spare, just in case.

Re: Marvel Carb Adjustments?
 

Get rid of copper fuel line. Copper can work harden then fracture.
Bob

Re: Marvel Carb Adjustments?
 

You do realize you're giving advice to the original poster who started this thread in 2011?

David Serrano

Re: Marvel Carb Adjustments?
 

I thought you might be interested in reading this web page:
https://www.fordbarn.com/forum/showt...ferrerid=16136