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EFV-8 Club Forum / General Ford Discussion / flathead running poorly

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09-14-2019 @ 2:18 PM
Posts: 45
Joined: Mar 2010
I have a 41 ford 1/2 ton truck with a flathead v 8. I recently got it running kinda. I have been a mechanic professionally my entire working life, so i am not new at this. Engine runs, but backfires. Back to basics, checked compression, 165 plus all 8 cyl's. still backfires. I have the wires in the black metal tubes. Should i run a different wire loom? Also i have installed an inline electric pump for priming and a new pump from Ken Isidor. I have also installed a pressure regulator and gauge ( 0 to 10 psi ) set at 2 pounds. The electric never quits running and after i turn the engine off, the pressure goes to zero after a few seconds. Bad power valve? Any help would be appreciated. BTW, vacuum gauge fluctuates from 13 to 15 pounds like a bad valve

09-14-2019 @ 6:41 PM
Posts: 1100
Joined: Nov 2009
Excellent compression!

Is it backfiring out the exhaust or out the carb? If it's backfiring through the carb you've blown the power valve. Make sure that the spark plug wires are plugged in correctly at the distributor - 1 to 1, 2 to 2, 3 to 3, etc. What are you using as a switch for the electric fuel pump? Given the vacuum reading, you might have sticking valves. Tell us more about the engine. Has it been sitting idle for a long period of time?....

09-15-2019 @ 6:20 AM
Posts: 45
Joined: Mar 2010
bought the engine in 1990. It was setting on an engine stand covered in plastic. It was supposedly overhauled in 1975 and never installed in a vehicle. I bought it because it because it had all the dress up parts that i was looking for Edlebrock intake for 3 deuces, Offenhouser heads and tube headers. Pig in a poke right but i paid less for the engine then it would have cost me for the parts. Also i had the engine that came with the truck, supposedly a 100 horse mercury ( how do you tell? ) that ran fine. I took the crab distributor from the merc and bought 3 carbs in pieces from several swap meets. I dont know what cam is in it or anything else about it. It first ran about 3 years ago and sounded fine. I have checked the distributor and cap and ran a comp test. With high compression, i think i can rule out a stuck valve, also the fuel pressure gauge wont maintain pressure after i shut the engine down, so probably a blown power valve. The secondary carbs are all show for now as the fuel has been stopped at the inlet and they have block off plates below. Not sucking air, i checked with carb cleaner. It has dual exhaust. The vacuum is at 13 to 15 inches and fluctuating erratically. Sounds like a sticking valve.

09-15-2019 @ 7:18 AM
Posts: 743
Joined: Oct 2009
Are you using the 1941 Distributor? Double check the secondary ignition wiring. Make sure that each wire coming out of the distributor is going to the correct spark plug. There might be cross firing taking place. Also check the brush on the bottom of the coil to make sure it is making good consistent contact with the rotor.

09-15-2019 @ 7:56 AM
Posts: 45
Joined: Mar 2010
I am using a crab style distributor with electronic ignition, everything new. Checked the wiring 3x. The wires were put on about 3 years ago, but was only started maybe 4 times since. New internal resistance coil, not hooked up to original resistor. It seems to be coming from the passengers side, dual exhaust.

09-15-2019 @ 8:57 AM
Posts: 6105
Joined: Oct 2009
Varying 13-15 inches vacuum could be normal with a cam that has lots of overlap. The cam manufacturer may have stamped the model number on the end of the cam with the timing gear. That will enable you to determine the cam specs.

The pressure gauge could be going back to 0 because the fuel pump valves are not holding pressure or that the carburetor is leaking fuel or the needle valve in the carburetor is not sealing.

Look down the throat of the carburetor, that is operational, when the engine is idling and when you shut it down. You should not see any fuel entering the throat. All fuel for the engine should be coming from the idle ports below the throttle plate. If you see fuel when the engine is idling, the power valve is leaking or the float level is set too high.

If the truck engine had a 59 stamped on the bell housing, it would have been a 100 HP post war engine that was shared across all vehicles. It gets a little more difficult with the pre-WWII engines. The bore on the Mercury engine was larger (3 3/16") than the Ford engine (3 1/6"). There were some external differences when they were manufactured, but they may not have survived the years.

You never answered the question about where the backfire is, exhaust or intake and when does it occur, accelerating, when you lift your foot from the accelerator pedal or driving at a steady speed.


09-15-2019 @ 12:58 PM
Posts: 45
Joined: Mar 2010
I have not driven the truck yet. Exhaust on passengers side seems to be where the backfire is. I am going to pull carb top to see if it holds fuel. I suspect the power valve might be bad, any suggestions on where to buy reputable replacements?

09-15-2019 @ 1:29 PM
Posts: 1425
Joined: Oct 2009
here is the man you want to contact for CARBURETOR PARTS
Contact: ken isidor - igadore@sbcglobal.net EARLY FORD V8 CLUB MEMBER
I saw you were having problems with bad vacuum reading, this is a cheap fix,
I would suggest using MARVEL MYSTERY OIL, and see if this has any effect on the vacuum reading,
valves sticking from sitting is a common problem with idle engines,
disconnect one spark plug wire at a time, and see if it effects the engine,
if you remove one wire and it make no difference that most likely is the cylinder with the problem
the intake gasket could be also leaking, does the engine wobble when idling ?
using a spray carb cleaner along the edge of gasket and intake and see if there is any difference in idle
be careful not get to much on the hot engine, a few drops will work,
hope this helps 37RAGTOPMAN

09-15-2019 @ 4:26 PM
Posts: 743
Joined: Oct 2009
As you know the firing order for all Flathead Ford V8's is: 1-5-4-8-6-3-7-2. With the crab distributor cap one of the ignition (spark plug) wires for each bank crosses over to the other side of the engine. Looking at the distributor cap from the front, the order of the wires coming out of the cap on the passenger's side are from the top down: #2, #1, #5 & #4; from the top down on the driver's side the order is: Coil, #7, #3, #6 & #8. The rotor mounted on the front of camshaft rotates counter-clockwise. Your electronic ignition may require a larger spark plug gap than the stock system. Hope this helps and that you get your engine running properly.

09-16-2019 @ 6:35 AM
Posts: 45
Joined: Mar 2010
I am going to remove the spark plug wires from the metal tubes they run in and try running them in a different way. Also replacing power valve in carb. i want to take it to the Newport hill climb in October.

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