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Posted By Discussion Topic: '40 Deluxe coupe runs rough warm -- page: 1 2 3     Goofyfixer 03-16-2021 @ 7:01 AM reply profile send p.m. Member Posts: 9 Joined: Feb 2021 I have recently purchased a '40 deluxe coupe that is in very good condition. It has never been modified (with a few minor exceptions) and is just a good old driver. When I purchased it, it wasn't running due to weak spark. I bought a coil which solved the problem and now it starts quickly and runs well, good power and smooth until it warms up. After that it starts running rougher and has less power and stumbles when accelerating. The idle, however is still smooth but starts hard if stalled or shut off. Any ideas? 40s 4ever Greg 1931 Flamingo 03-16-2021 @ 7:13 AM reply profile send p.m. Member Posts: 383 Joined: Nov 2019 Welcome ! ! Others will probably "chime" in but you might change the condenser also. JMO Paul in CT TomO 03-16-2021 @ 8:00 AM reply profile send p.m. Senior Posts: 7244 Joined: Oct 2009 That is a nice looking coupe. Here it is right side up. To isolate your problem with rough running, perform a cylinder balance test. This is done by increasing the rpm until the engine runs rough, by pulling out the throttle. Then short out each plug one at a time and write down the ones that do not reduce the rpm. If you can isolate it to a few cylinders, pull all of the plugs and compare them to this plug chart: http://www.verrill.com/moto/sellingguide/sparkplugs/plugcolorchart.htm If you can determine the source of the problem by the plug chart, repair and then recheck. If you did not determine the source of the problem, perform a dry and wet compression check. I suspect that driving the car with a weak spark fouled some plugs. Tom kubes40 03-16-2021 @ 8:06 AM reply profile send p.m. Senior Posts: 3374 Joined: Oct 2009 I'll take second chair to TomO. I'd suggest you get a coil rebuilt by George Haney. You state you bought a "new" coil. What exactly do you mean by "new"? A reproduction? Oh oh. A NOS? Oh oh. A different one? Oh oh. If your car was in my shop, I'd swap out the coil with one I have a lot of confidence in. I keep a number of Haney coils on the shelf. If that cures the issue, we're done here. If not, I'd then replace the condenser. You need to be careful in condenser selection. I buy mine from Joe's Magnetos, 30mfd's. On "show cars" I hide them within an authentic (Ford script) condenser "sh*ll". Remember to change ONE thing at a time. My gut tells me you have an ignition issue. Mike "Kube" Kubarth Goofyfixer 03-16-2021 @ 12:14 PM reply profile send p.m. Member Posts: 9 Joined: Feb 2021 The coil came from Mac's and was stated as being "NEW" which it appears to be. I was thinking that the spark was getting weaker as the engine got warm and wondered about the condenser(s). I actually have 2. There is one mounted to the coil and grounded with one of the distributor mounting bolts and one attached with one of the coil mounting screws with a wire going to the coil voltage wire. Which one should I replace? 40s 4ever Greg kubes40 03-16-2021 @ 5:00 PM reply profile send p.m. Senior Posts: 3374 Joined: Oct 2009 I'd start by replacing the coil with a FORD coil that was rebuilt by George Haney. This may seem to go against logic but rest assured the repop coils are "hit or miss". You get a good one or you don't. You need to have a KNOWN commodity. I'd really suggest you do that first. The condenser that is connected to the top terminal is a static reducer for the radio. At this time, I'd remove that completely. I'd bet heavily the issue is either coil and / or condenser. Remember, one thing at a time. If you don't have a Ford coil to rebuild, call George as he no doubt does. You want this car to be dependable obviously... go to a little extra effort now and enjoy with confidence later. Mike "Kube" Kubarth alanwoodieman 03-16-2021 @ 6:41 PM reply profile send p.m. Senior Posts: 864 Joined: Oct 2009 Skip Haney coil-yes-yes keep a couple in the drawer all the times for my friends who buy DC coils from whomever, some of these work great others last a few minutes. the one condenser I use one from napa but I don't have the number handy. other problem can be the rotor "button" shorting out on the shaft-cure this with a couple of layers of shrink tubing on shaft JayChicago 03-17-2021 @ 8:50 AM reply profile send p.m. Member Posts: 474 Joined: Jan 2016 Good spark on start-up but then weak spark after warm up is typical of either bad coil or bad condenser. Yes, they both can show the same symptom, so is difficult to know which is the culprit. And there is no practical way for the average guy to bench test these things under real load conditions, so we are forced to be “parts changers” with these two electrical components. Here’s another thing they have in common that can drive you nuts: some new ones will be bad right out of the box. This message was edited by JayChicago on 3-17-21 @ 9:28 AM Goofyfixer 03-17-2021 @ 10:38 AM reply profile send p.m. Member Posts: 9 Joined: Feb 2021 Had a nice talk with George "Skip" this morning. Got a lot of good info on other things to check. Also turns out that the 2 coils I got with the car, both with weak spark, had been rebuilt by him in the past. I sent both to him after talking with him. I will continue to report on this thread as I progress with his suggestions and his rebuilt coil. 40s 4ever Greg Oh, and yes, being a semi-retired career auto mechanic, I know too well about how much hair you can pull out with bad new parts. This message was edited by Goofyfixer on 3-17-21 @ 10:40 AM kubes40 03-17-2021 @ 10:48 AM reply profile send p.m. Senior Posts: 3374 Joined: Oct 2009 Hey Goofy, Most likely the coils are not the issue if George had rebuilt them. I suppose even his coils do not last forever. Plus, what none of us know is if anyone in the past had left the ignition on for an expended period. That's a coil killer for certain. I think you are 100% correct in having George check these coils. You MUST be confident in their condition. In the meantime, perhaps you might want to source a condenser with a known (current) good reputation. I really like the ones I'd mentioned previously for Joe Hunt's Magneto's. I had shipped a freshly restored vehicle to the owner just two years ago. And, although I'd placed a tag on the ignition switch "LEVER MUST BE OFF", well, the transport guy left it on and fried a fresh Haney coil. Mike "Kube" Kubarth

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