Marvel Carb Modification Gone Bad

[petew]

I inherited a Marvel carb that two of my friends had tried to get functioning properly.
Ran it through my ultrasonic cleaner , replaced the worn throttle shaft and put it back together with parts from Dave Renner.
My results were similar to what my friends had experienced, it ran like crap.
Very lean at idle and if you opened the mixture screw more than 1/4 turn it would die and not restart.
While I was rebuilding I noticed that it had a modification done to change the bowl vent to allow an air filter to be used .
The modification consisted of milling a slot across the idle passage hole ,the other hole behind it and then blocking the factory vent with a screw in plug.
That slot caused the mixture screw to pull air instead of fuel .
So that led to my very lean at idle and low speed problems.

As a repair i reconstructed the slotted bulkhead with JB Weld and then filed it down to what it would have looked like before the modification .
Removed the plug in the side of the carb to restore the original vent and then put it back on the car.

That fixed it and the carb now performs perfectly.

Dave Renner does a similar modification but his procedure doesn’t ruin the seal between the bowl and the carb top maintaining the idle passage seal , so the mixture screw flows fuel as it should not air !

I spoke with Dave and shared pictures about the mod on my carb and my planned fix.

Thought I would share in case any of you stumble across a similar “improvement “ on a Marvel Carb .

[Y-Blockhead]

Job job, oviously someone in the past did not understand how a marvel works.

[ursus]

I have found similar "improvements" to Zenith carbs that seem to defy logic. I wonder how well the JB Weld holds up to continuous exposure to gasoline?

[petew]

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Originally Posted by ursus

I have found similar "improvements" to Zenith carbs that seem to defy logic. I wonder how well the JB Weld holds up to continuous exposure to gasoline?

Once cured it is impervious to gasoline , so says the manufacturer of JB weld.
I have used it previously for repairs similar to this and have never had a problem after years in service.