The Ford Barn

Ggmac · 10-28-2021, 04:05 AM

Where do you live ? Sorry if I missed it in the post . At what rpm is your flat spot ?

FlatheadTed · 10-28-2021, 03:01 PM

Check the Valve timing ,? remove the manifold to sight the valves at same time check the gasket ,use the Zip tie method or a wire to find TDC ,does it smooth out with the Choke out as 51 Merc suggested,

Ross F-1 · 10-28-2021, 04:49 PM

Maybe I missed it, but did you verify the advance mechanism is working?

Speedbump47 · 10-30-2021, 11:35 PM

Did have distributor apart to clean and check. All seemed good.
Will try what Flathead Ted suggests and report back.
Thanks Mike

Speedbump47 · 12-15-2021, 07:40 PM

G'day all
Update...
Put on new carb and new e-fire distributor.

NO CHANGE!

Still have only 11 to 12 vacuum at idle. Does swing a little between 11 and 13

Comments have indicated valve timing could be the problem.

Are there any other suggestions before I start tearing the engine apart.

Thanks

Bill OH · 12-15-2021, 08:08 PM

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I would remove the intake manifold, turn it upside down and pour gasoline in the heat riser until the riser is full. Watch that gasoline level to see if it falls away however slight. You are looking for a cracked intake manifold in its heat riser. 11 inches of vacuum sure indicates a leak - should be around 18 inches with a stock cam. Using gasoline instead of water - gasoline will flow thru a crack much easier. Give it a try!

Crankster · 12-15-2021, 08:10 PM

I don't speak Flathead, but with an OHV engine there are simple "non-invasive" methods of checking valve timing. I'd expect there are ways on a Flathead, too. Incorrect (late) valve timing will definitely cause low manifold vacuum.

Ross F-1 · 12-16-2021, 02:56 PM

A real longshot, but there was a gorgeous yellow 48 Merc convertible in a shop here I visited. It had similar issues including the low vacuum. The mechanic pulled the intake and found someone had cracked off the edge of one cylinder's intake port, presumably while taking out valves. The intake had nothing to seat against there, so it leaked. Wondering if the car's owner had it buttoned up and sold it as-is, vs an expensive repair...

10-28-2021, 04:05 AM	#21
Ggmac Senior Member Join Date: Jul 2016 Location: Lake worth Florida Posts: 1,087	Re: Flat spot that just won't go away Where do you live ? Sorry if I missed it in the post . At what rpm is your flat spot ?

10-28-2021, 03:01 PM	#22
FlatheadTed Senior Member Join Date: May 2010 Location: Auckland Posts: 4,700	Re: Flat spot that just won't go away Check the Valve timing ,? remove the manifold to sight the valves at same time check the gasket ,use the Zip tie method or a wire to find TDC ,does it smooth out with the Choke out as 51 Merc suggested, __________________ http://www.flatheadted.com Flathead Ted brake Floaters , Last edited by FlatheadTed; 10-28-2021 at 05:49 PM.

10-28-2021, 04:49 PM	#23
Ross F-1 Senior Member Join Date: Nov 2010 Location: NM Posts: 2,438	Re: Flat spot that just won't go away Maybe I missed it, but did you verify the advance mechanism is working? __________________ '52 F-1, EAB flathead

10-30-2021, 11:35 PM	#24
Speedbump47 Junior Member Join Date: Sep 2021 Posts: 5	Re: Flat spot that just won't go away Did have distributor apart to clean and check. All seemed good. Will try what Flathead Ted suggests and report back. Thanks Mike

12-15-2021, 07:40 PM	#25
Speedbump47 Junior Member Join Date: Sep 2021 Posts: 5	Re: Flat spot that just won't go away G'day all Update... Put on new carb and new e-fire distributor. NO CHANGE! Still have only 11 to 12 vacuum at idle. Does swing a little between 11 and 13 Comments have indicated valve timing could be the problem. Are there any other suggestions before I start tearing the engine apart. Thanks

12-15-2021, 08:08 PM	#26
Bill OH Senior Member Join Date: May 2010 Posts: 425	Re: Flat spot that just won't go away Sponsored Links (Register now to hide all advertisements) I would remove the intake manifold, turn it upside down and pour gasoline in the heat riser until the riser is full. Watch that gasoline level to see if it falls away however slight. You are looking for a cracked intake manifold in its heat riser. 11 inches of vacuum sure indicates a leak - should be around 18 inches with a stock cam. Using gasoline instead of water - gasoline will flow thru a crack much easier. Give it a try!

12-15-2021, 08:10 PM	#27
Crankster Senior Member Join Date: Oct 2017 Posts: 563	Re: Flat spot that just won't go away I don't speak Flathead, but with an OHV engine there are simple "non-invasive" methods of checking valve timing. I'd expect there are ways on a Flathead, too. Incorrect (late) valve timing will definitely cause low manifold vacuum.

12-16-2021, 02:56 PM	#28
Ross F-1 Senior Member Join Date: Nov 2010 Location: NM Posts: 2,438	Re: Flat spot that just won't go away A real longshot, but there was a gorgeous yellow 48 Merc convertible in a shop here I visited. It had similar issues including the low vacuum. The mechanic pulled the intake and found someone had cracked off the edge of one cylinder's intake port, presumably while taking out valves. The intake had nothing to seat against there, so it leaked. Wondering if the car's owner had it buttoned up and sold it as-is, vs an expensive repair... __________________ '52 F-1, EAB flathead