The Case of the Gasping Flathead

FortyNiner

FortyNiner

Well-known member
Welcome back flatty fans. Today's web episode is the Case of Gasping Flathead. A little background:

'46 Tudor - bone stock resto

A 59AB that has been recently rebuilt
- bored .030 over
- original cam and crank

Original 94 carb expertly rebuilt by our own Charlie NY.

Engine has was started and has been run a number of times - almost all under power moving the car during various shake down cycles (about 30 miles worth). Motor typically fired quickly and carb was adjusted to lower and smooth the idle.

All of this was done without the air cleaner in place.

[If this thing had audio, the background music would now change to a lower, minor key]

Seemingly finishing the debugging phase. I installed the original oil bath air cleaner that had been washed and refreshed.

Instantly, the engine was a very hard starter. After firing, it would not rev, would not develop any power, and would slowly grind to a halt.

I removed the top of the air cleaner. No change.

i removed the base of the air cleaner. Everything is suddenly happy - quick start, revs are back, power to move the car, and it maintains the fire.

So, since I would clearly want an air cleaner, my question:

What do I do to allow the engine to run with the air cleaner in place?
 
Weird! Is clamp that tightens the base of the air cleaner to the top of the carb jamming or interfering with the choke?
 
Set your carb by vacuum at idle with the air cleaner on. Oil bath? Thinking your lacking air.


My thinking is you want to put a vacuum gauge on the carb at what you are running.
 
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FortyNiner said:
Nope on the choke.

Yes, on oil bath.

Ignorant question: How will resetting with a vac gauge help?
Click to expand...


NOT IGNORANT. How will it not? How do you tune your motor? You need a healthy intake vacuum on a motor. A vacuum gauge is your friend.


A combustion engine is basically a air pump. A vacuum guage can tell you everything from a vacuum leak, sticky valves, too poor rings. Before computers.


Motor just needs air, fuel, and spark basically.
 
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Fair enough. Since the engine will not stay lit with the cleaner on, I'll need to check for vac readings without it. Any issues starting with this approach?
 
I don't mean to ever be rude. It's the internet. Besides I said your are not ignorant. Just not familiar maybe.

Lots of guys here with more experience and knowledge then me, big dogs. I get corrected all the time.

A vacuum gauge is used to set a new carb on a motor. Early motors off the intake. 18-19 lbs is close to good.

Best of luck and look forward to your next question. only way to learn.


You could take a few days and read searches on vacuum readings too.
 
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Oil for the bath is slightly below the fill line. The gasping condition is the same with only the bottom of the filter in place.
 
FortyNiner said:
Oil for the bath is slightly below the fill line. The gasping condition is the same with only the bottom of the filter in place.
Click to expand...

The bottom is the housing with oil & the top one is the filter. With the top
(filter removed) you should plainly see down the carb if this housing is
causing the choke to close as someone already mentioned. I picture my
air cleaner as I type this & and I can't see anything that would cause that.
HOW EVER, I have seen many times the filter with the screen with its
steel wool was washed in gas that disturbed gunk and just not cleaned
correctly and installed and barely would run at all Just could be. Is your
air cleaner stamped "Front" because I have seen some that the bottom
has stamped indentations to clear things. I don't have a parts book to
cross air cleaner numbers for cars maybe Bill the number dummy, he hangs
out in the FTE large truck forums...I'll look at my air cleaner (46 59A)
today and get back. sam

What Drolstom said is my guess
 
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Yes, the housing has 'front' embossed into it and it faces forward.

The housing does have a recess for the clamp to nest.

I'll take another look at the choke position. It has been a head scratcher.
 
Episode Two: Return of the Rumble

In today's episode our hapless poser mechanic is baffled by the disappearance of the problem he whined about in the first post. After reinstalling the air cleaner housing, the flatty fired up repeatedly without any issues. Prompting our non-hero to loose the dramatic exclamation of, "Huh".

Prior to this development, I did put a vacuum gauge on and found the idle reading of a steady 17 with revs showing a quick drop to 13 before returning to 17. This was with the cleaner completely off the carb. Reinstalling the cleaner assembly didn't change the readings.

So, on the original issue, again I'm clueless. I tried to recreate the problem by moving things into different positions. Nothing. I looked for interference points with the choke and linkage. Double nothing. Vacuum lines? Nope. Conclusion? User error.

Having demonstrated my lack of mechanical chops, I am most interested in reaction to the vacuum readings. They looked like this in real time:

https://youtu.be/pSaWAsctLlY

I also need to work on my movie making skills.

Still shot and view underneath the housing showing absolutely nothing causing any sort of problem.
 

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