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EFV-8 Club Forum / General Ford Discussion / Miss under Part Throttle

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Discussion Topic: Miss under Part Throttle

JayChicago

08-04-2016 @ 12:21 PM

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Hello all. I am relatively new to the club, and this is my first posting here. I just bought a 40 Ford Standard two door sedan, a garage find, nearly all original, 48,000 miles. This is my first flathead so I am on a steep learning curve, and enjoying every minute of it ! (Well, most of the time I'm enjoying it)

I say "garage find" because the seller put on only 307 miles in 29 years of ownership! He kept it as a trophy in his attached garage, but never drove it due to lots of drivability/reliability issues that I am now trying to work through. (He also has a 64 T-Bird and a 66 Lincoln that he does drive)

After resolving a couple major ignition system issues, now addressing a couple issues that I could use some advice from experience. Any suggestions or trouble shooting tips would be appreciated.

1. Slight bucking at part throttle cruise speed. Most noticeable at a steady 30-40 mph. Feels like a spark miss, but the engine pulls well under acceleration which is where I would expect an ignition miss to be most obvious. So I'm thinking possibly a spark advance issue, tried various settings on the advance brake from two turns in to four turns in, no change to the symptoms. From inside the distributor I can easily move the advance brake plunger, so not stuck in the bore. Of course I could be going down the wrong path, could be carburetor/mixture problem. (but the miss is so sharp and intermitent, it feels like spark to me) I did spray the engine looking for vacuum leaks, disconnected and capped the windshield wiper tube. It has a rebuilt carb, done 10 years and maybe a 100 miles ago. I have gone thru a couple tanks of fresh gas, and a bottle of Techron to try to clean out varnish. Any other trouble shooting steps I could try?

2. With car parked, engine runs a little rough with steady throttle just off idle. Idles smooth, and at higher RPMs seems to smooth out, but is noticeably rough at part throttle just off idle. This feels like a fuel/air issue to me, but I guess it could also be timing/spark advance. And with my lack of experience, maybe this is "normal" for a 76 year old engine and carburetor. Again, any trouble shooting tips would be appreciated.

Jay

This message was edited by JayChicago on 8-4-16 @ 12:41 PM

carcrazy

08-04-2016 @ 12:43 PM

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Does your car have the 85 HP engine? To find out count the head nuts/studs on each head, 17 = 60 HP engine, 24 = 85 HP engine. One old rule of thumb for diagnosing engine running problems on a spark ignition engine is that 90% of the time the ignition will be the cause of the problem. If it is a hard miss, it is probably ignition, soft misses are usually fuel related. Have you checked all of the ignition primary circuit connections to see that they are tight?

ken ct.

08-04-2016 @ 12:45 PM

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That's a long time for a carb to sit unused Could be a dried up accel pump ,could be a old style fuel pump diaphragm coming apart. Vacume brake should be almost completely out maybe 1-2 turns in from there. Try some Marvel Mystry oil in the gas and crankcase and run it hard for some miles could be a stuck valve. Common on FH's ken ct.

JayChicago

08-04-2016 @ 4:57 PM

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Yes, its the 85 HP engine.

Oh, yea, it had all the classic ignition problems! Got a half mile from seller's home and it started failing. We pulled plug wires and obviously a no-spark condition. Called for a flatbed truck to get the car home.

As a novice V8 owner I was surprised at the lack of a decent shop manual for these early cars. (I do have the green book now, which is some help.) I had to turn to the internet, and this forum, to get educated on the flathead.

Trouble-shooting, I found 1.7 volts at the coil.(should be 3 volts or better) I assumed a bad ignition resistor, but resistor and wiring tested good. I did find a 1.2 volt drop across the ignition switch, which is just a simple switch, should have near-zero resistance/voltage drop. Replaced the switch and finally got good voltage to the coil.

But then things would be fine on start-up, but again no-spark when engine got warm. As I learned, this is the classic early Ford V8 coil issue. Those coils are inherently weak and break down over time, and then they work cold but fail when hot. I read that that the replacement new coils on the market are also unreliable. So I bought a coil from the guy in Virginia who advertises his innovative vacuum process to remove moisture from used coils......that coil was no better, also immediately failed when hot. Sent one of the bad coils to be rebuilt by Skip Haney. Problem solved! Been running with that coil for a few weeks, no problems when hot. (I sent my other bad coil to be rebuilt by Skip Haney, so I can keep a spare in the trunk.)

I also bought two condensers advertised by Bubba's in Speedway Indiana, because I read how you cannot trust any of the new or NOS condensers from the usual sources to be any good. I also cleaned/sanded the contacts/rotor in the distributor best I could. I am trusting that the points and calibration of the distributor are good because it is a rebuilt unit with practically no miles on it.

So I think I solved the ignition problems, but perhaps not completely, cuz I still have that intermittent miss under cruise driving condition. Still need to find out whats causing that; would like to hear any ideas on that.

Jay

This message was edited by JayChicago on 8-4-16 @ 5:07 PM

JayChicago

08-04-2016 @ 5:03 PM

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Ken

Thanks for that advice. I will try some Marvel Mystery oil. And thanks for all your previous postings on this forum. Reading your many writings is a great help to a new guy.

Could a sticky valve be an intermittent thing? Would I be likely to notice it more under light load and maybe not detect it under acceleration?

Jay

This message was edited by JayChicago on 8-4-16 @ 5:17 PM

ken ct.

08-04-2016 @ 5:26 PM

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Well thank you for the good words , it means a lot to me. I'm retireing from rebuilding and trying to get rid of all my rebuilt stock and cores. Super prices. I will be at the Gettysburg ford meet and Hershey ,pa meet as my last show. I will probably still post and help where I can on here and over the phone. Do carbs,fuel pumps and distributors for the last 25 yrs (only fords). ken ct. 1-203-260-5945 cell.

40 Coupe

08-05-2016 @ 5:09 AM

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You may want to consider a Carb. rebuild. Dayton in Fla sells a good rebuild kit. or Just take the carb apart and clean. If the acceleration and the hot re-start after running is good it appears most of the carb is in good shape. What Carb is on the car? Is it marked 94 with 91-99 ? What is the condition of the spark plugs are they burning with a slight tan color, black wet, soot?

carcrazy

08-05-2016 @ 7:25 AM

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The region of operation where the problem occurs, just off idle, is the transition area of the carburetor between the idle circuit and the main circuit. Something is delaying the main system from delivering fuel at the correct time. The fuel level maybe too low, the screws holding the fuel nozzle bar in place may be loose allowing excess air into the system, or the main system air bleeds may be too large.

ken ct.

08-05-2016 @ 11:53 AM

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You have your PM section disabled , that makes it hard to discuss problems you may have. Reinstall it. Call me @ 1-203-260-5945 cell if you have free LD calling or I can call you . Daytona does have the best kit BUT !!! I hate to type,lol. Easier to explain things person to person. ken ct. my email is IGADORE@SBCGLOBAL.NET

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