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08-17-2019, 08:31 PM | #1 |
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The Case of the Gasping Flathead
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?
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08-17-2019, 09:10 PM | #2 |
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Re: The Case of the Gasping Flathead
Weird! Is clamp that tightens the base of the air cleaner to the top of the carb jamming or interfering with the choke?
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08-17-2019, 09:14 PM | #3 |
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Re: The Case of the Gasping Flathead
What Drolston said.
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08-17-2019, 09:17 PM | #4 |
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Re: The Case of the Gasping Flathead
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. Last edited by Tinker; 08-17-2019 at 09:22 PM. |
08-17-2019, 09:17 PM | #5 |
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Re: The Case of the Gasping Flathead
Nope on the choke.
Yes, on oil bath. Ignorant question: How will resetting with a vac gauge help?
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08-17-2019, 09:23 PM | #6 | |
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Re: The Case of the Gasping Flathead
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Quote:
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. Last edited by Tinker; 08-17-2019 at 09:37 PM. |
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08-17-2019, 09:37 PM | #7 |
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Re: The Case of the Gasping Flathead
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?
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08-17-2019, 09:40 PM | #8 |
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Re: The Case of the Gasping Flathead
If you have never used a vacuum gauge. I might start there....
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08-17-2019, 09:44 PM | #9 |
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Re: The Case of the Gasping Flathead
See comment regarding my ignorance.
Thanks for the input. I'll give it a go.
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08-17-2019, 09:48 PM | #10 |
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Re: The Case of the Gasping Flathead
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. Last edited by Tinker; 08-17-2019 at 10:57 PM. |
08-18-2019, 01:21 AM | #11 |
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Re: The Case of the Gasping Flathead
Could the air cleaner body be touching generator/ignition wires?
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08-18-2019, 04:00 AM | #12 |
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Re: The Case of the Gasping Flathead
I did look for that issue and didn't see any evidence of it.
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08-18-2019, 05:31 AM | #13 |
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Re: The Case of the Gasping Flathead
Seems that the culprit for sure is the filter. Did you add too much oil to the reservoir?
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08-18-2019, 06:59 AM | #14 |
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Re: The Case of the Gasping Flathead
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.
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08-18-2019, 07:45 AM | #15 |
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Re: The Case of the Gasping Flathead
Is this the original air cleaner? Can you shoot us some pictures of ac and top of carburetor?
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08-18-2019, 08:04 AM | #16 |
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Re: The Case of the Gasping Flathead
could the base of the aircleaner be full of mouse nest?
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08-18-2019, 08:43 AM | #17 | |
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Re: The Case of the Gasping Flathead
Quote:
(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 Last edited by big job; 08-18-2019 at 08:51 AM. |
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08-18-2019, 09:29 AM | #18 |
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Re: The Case of the Gasping Flathead
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.
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08-19-2019, 06:45 AM | #19 |
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Re: The Case of the Gasping Flathead
Newbie here:
Could the base be interfering with a vacuum line causing a lean condition?
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08-21-2019, 04:27 AM | #20 |
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Re: The Case of the Gasping Flathead
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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08-22-2019, 02:49 AM | #21 |
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Re: The Case of the Gasping Flathead
vacuum should drop to near zero at open throttle but never zero. going from 17 to 13 is not correct. maybe the vacuum is not in the right area. pv wouldn't open on the carbs.
from that video the vacuum is steady. hard to tell from the pictures. being its just armchairing it on the web. Last edited by Tinker; 08-22-2019 at 03:05 AM. |
08-22-2019, 09:52 AM | #22 |
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Re: The Case of the Gasping Flathead
The drop in vacuum is totally dependent on how much the throttle is opened.
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08-22-2019, 01:21 PM | #23 |
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Re: The Case of the Gasping Flathead
Any suggestions?
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08-22-2019, 05:29 PM | #24 |
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Re: The Case of the Gasping Flathead
No, I was just noting that Tinker said a 17 to 13 drop was not correct. It is impossible to say what the drop would be since it totally depends on how far you punch the pedal down. Are you flooring the pedal when you get the 17 to 13 drop?
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08-22-2019, 08:46 PM | #25 |
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Re: The Case of the Gasping Flathead
Listen to Jack.
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08-22-2019, 11:49 PM | #26 |
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Re: The Case of the Gasping Flathead
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08-23-2019, 08:23 AM | #27 |
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Re: The Case of the Gasping Flathead
That would account for a smaller drop.
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08-23-2019, 07:06 PM | #28 |
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Re: The Case of the Gasping Flathead
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08-23-2019, 07:19 PM | #29 |
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Re: The Case of the Gasping Flathead
So do I need to rerun the check at full throttle to have meaningful results?
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08-23-2019, 07:22 PM | #30 |
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Re: The Case of the Gasping Flathead
How are you checking your vacuum?
Yes you can goose the throttle to the floor and check what the vacuum does. Don't leave it to the floor at idle. But it needs to open fully. 17 is still a bit low. you can bring it up to around 19 with the idle/air adjustment screws. Being that the vacuum is steady at 17 idle is a good thing. Just bring it up to 19ish. Set your vacuum with your air clear on too.... its how you are driving the car. . Last edited by Tinker; 08-23-2019 at 07:55 PM. |
08-23-2019, 07:33 PM | #31 |
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Re: The Case of the Gasping Flathead
The video shows that I'm manually moving the throttle while watching the gauge. I'll also adjust the mixture screws.
Thanks for the comments. I appreciate it.
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08-25-2019, 04:36 PM | #32 |
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Re: The Case of the Gasping Flathead
i have a 36 pickup with a 21 stud . its all stock, i had the orignal air cleaner on it. i changed it to one of he little chrome air cleaners, with a K and N filter element.
i could tell the difference as soon as i started to crank over the engine, you could hear it breathe, while cranking. and it ran so much better
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08-25-2019, 08:28 PM | #33 |
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Re: The Case of the Gasping Flathead
As others have mentioned, the original style air filters can be clogged for any number of reasons. Glad you found a solution that meets your needs.
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