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EFV-8 Club Forum / General Ford Discussion / Poor engine performance

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Posted By Discussion Topic: Poor engine performance

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01-12-2019 @ 3:02 PM
Posts: 56
Joined: Oct 2014
I need your good advice here. I have a 1950 Ford Fordor with a flathead V8 and three speed manual tranny with overdrive. The engine is not original. It is a Mercury flathead with 8MC on the heads.

Here is the problem; engine performance is poor. Here are the symptoms:
1. The engine starts without difficulty. However, when idling, the engine will shake, yet it will idle smoothly.
2. While drive at various speeds, the engine will run fine; no missing, coughing, or bogging down.
3. When accelerating the engine has no power. Even a gentle hill is a challenge to ascend. When more acceleration is applied the engine will shutter and lumber along with no appreciable acceleration.

So, if this were your car, where would you start with your diagnosis; points, plugs, timing, spark wires, etc, etc? What am I leaving out?
Please advise. Your help will be greatly appreciated.
PS: The overdrive system works fine. It engages and disengages as it should.

01-12-2019 @ 5:23 PM
Posts: 88
Joined: Feb 2016
Hi....Sounds like it's starving for gas. BT

01-12-2019 @ 7:17 PM
Posts: 964
Joined: Nov 2009
Sounds like you're only running on 4 cylinders - no gas to the other 4. Could be carb jet clogged - only half the carb is working. From your picture, it looks to be a fairly new/fresh carb but that doesn't mean it should be eliminated as the cause of the problem. Were it my car, I'd start my diagnosis at the carb...

This message was edited by MG on 1-13-19 @ 11:08 AM

01-12-2019 @ 9:34 PM
Posts: 643
Joined: Oct 2009
I would start with a compression check of all the cylinders. Does the engine smoke or use oil? It could be worn out and lacking in power. Do a vacuum test on the engine to determine it's health.
There could be a restriction in the air cleaner or the exhaust system that limits airflow through the engine at speeds above idle.

01-13-2019 @ 4:52 AM
Posts: 56
Joined: Oct 2014
Buckawho, MG, and Crazycar,
Thank you for responding so promptly. You three have probably nailed it for me. Here's why, what I didn't say in my original post is that I recently changed carburetors to a newly rebuilt one. The new one is still a Holley 94 (correct for this engine) but it was a re-built carburetor that I bought and assumed it would be a good carburetor. But, the first problem I had with this carburetor was that the power piston would not pump very much gas into the main jets. The spray of gas was very anemic if any came out at all. So, I took it a part and found that the spring attached to the power piston was not attached-it was just sitting inside the power piston sleeve, meaning the power piston never correctly traveled up and down to deliver the requisite amount of additional gas when needed. I corrected the spring problem and it sprays gas as it should. However, maybe there are other problems with this carburetor that I am not aware of. After your posts here I am thinking I will take off the new carburetor, repair the leaky power piston in the original carburetor (the reason I switched carburetors in the first place) and see if the performance returns to normal.

Actually, before swapping out the old carburetor for the re-built one, the car ran fine with plenty of power. The problem with the old carburetor was it leaked gas on the manifold from the power piston-not a safe condition.

Thank you for your thoughts here.
PS to Crazycar: No smoke or extreme oil consumption. A compression test would be good to do. Compression is always a key vital sign of an engine's health.

ken ct.
01-13-2019 @ 1:21 PM
Posts: 1372
Joined: Jan 2010
If this is a true Merc. engine it would have a back draft Holley carb on it. Not a Holley 94 on it. It also has a port on the front of carb for dist vacume line. What have you really got there ??? ken ct.

40 Coupe
01-14-2019 @ 4:54 AM
Posts: 1116
Joined: Oct 2009
Where does your distributor get it's vacuum from?

ken ct.
01-14-2019 @ 1:25 PM
Posts: 1372
Joined: Jan 2010
Good question Coupe. ken ct He has the wrong carb on there if its a true Merc. engine and manifold. Could be a diff sourse for vacume ??

02-05-2019 @ 12:26 PM
Posts: 6513
Joined: Oct 2009
See my post regarding loss of power.

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