I apologize if this is not the right section. This is my first time posting. I'm helping the neighbor with his 49 Cad. The gaskets on the carburetor (Carter WCD) were dried out, so the carburetor was seeping gas at the seems, so he bought a rebuild kit for it and I offered to clean and rebuild it for him. I dis***embled the sections, and soaked them in a heated sonic cleaner that was filled with Berryman parts cleaner. After re-***embly and installation back on the car he said it ran great for awhile but then started hesitating. I checked the timing on the car and retarted it a little, since he also mentioned it was hard to start when it was warmer. Car idles great and has good throttle response. He said he put a Protronics ignition system on it, so it no longer uses points. The plugs only have a few hundred miles on them. I sprayed brake clean around the carburetor and the car did not idle up. Idle mixture screws were out about 1.5 turns. I turned them to 2 turns out to see if a little fatter helped the problem described below. I have not checked valve clearance, but the motor is not noisy. We drove the car together and what is happening is that the car will hold a gear a little longer than it probably should and then the motor starts breaking up and misfiring. I think the holding of gear could be the kick down being misadjusted, but I'm not sure where to start with the breaking up, since the car runs well under all the other conditions.
Does it happen every time the up shift is delayed, and only when the up shift is delayed? If this is the only time you have the misfire, correct the up shift issue and retest, that may be the only problem. Not familiar with 49 Cady ignition, is there a spark advance system that may be not advancing, or maybe hanging in the advanced condition? How old is the gas? Current gas starts to deteriorate in 3-4 months time, these days. What RPM range is the misfire happening? Is the motor fully at operating temp when the misfire condition happens? There have been a lot of problems with the aftermarket ignition systems lately. The old systems are failing due to age, the new ones are failing due to poor quality.
Gas is new. I didn't look at the tac to see when it was breaking up, but I would say probably above 2500-3k. Motor is warmed up. I unhooked the advance when I checked the timing, but I didn't check that it was working. I should probably do that. I agree on newer products. I see so many items bad right out of the box. Yes, it happens, most times, when the shift is delayed, so I think I'll start there.
I think it could be that the engine issue is affecting the gearbox rather than the other way round. I’d rule out any timing/ignition/vac advance issues first.
This is an issue that could have a hundred different causes. Go through a full inspection of mechanical, fuel and ignition to confirm proper operation of all the components. Then check trans too. If you've been to a drag strip a few times, you probably seen a car that runs fine but breaks up at high RPM and load. There is no single answer to this, each system/component is operating at it's peak operating point.
Yesterday I texted him and advised him to take about a 1/4" out of the kickdown and then drive it to see how it effected it. He did and texted back that the car was running perfect and shifting much earlier.
Good to hear the fix! I remember that my old stuff didn't like running high RPMs that are more common now. That said, he should still check things over to ensure this isn't something starting to go and will get worse over time.
ya, I'd def like to put his timing back to more advanced. Its been a long time since I've owned a car with a distributor, but when I did, I would always run it a few degrees more than spec
The fuels of today are not what they were, either (understatement!). I'd run a fuel system cleaner like seafoam or techron, since the flathead has a greater surface area prone to deposits. Bump the timing to where it's happy and doesn't ping. ensure it has timing advance. Make sure the road draft system is clear. Enjoy!
Adjusting the throttle rod on the transmission may be a band aid fix of the real problem. Late shifts and breaking up just before the shift point to an engine problem, probably ignition, but that's a SWAG. I'm guessing that if you really get on it you will find it still breaks up at higher rpm. Years ago I bought a 54 New Yorker that had been driven exclusively in town for at least 10 years. I was planning to drive frequent 100 mile trips with the car and needed to make sure it was up to the task. After going through every thing on the car, I took it for a ride on the interstate. When I jumped on it, the engine would buck, miss and sometimes backfire with black smoke rolling out the exhaust. Let off the throttle and it would run fine. The problem was that it was badly carboned up. Accelerating easy it would run fine, full throttle acceleration and it would break up. Frequent full throttle runs from about 50 to 80 finally broke all the carbon loose. After that it ran fine. That might be the problem on the old Caddy.
I checked today that the timing was advancing under throttle and it was. My neighbor said he gaped the plugs at .40 which was what he read to do with the new ignition and flame thrower coil. As I'm writing this, I guess that seems a little wide for an older car. I think .35 has always been the standard for systems that weren't coil on plug. I drove the car today and observed that it's only breaking up when you're asking more than 1/2 throttle or say like a slight load like trying to accelerate up a slight hill or really doing anything other than driving like a grandma. It was occuring over 2k but usually closer to 2500. Would anyone concur that it could be possibly valve related, like the valves aren't sealing well? I'd imagine valve float is really only an issue when we're talking 5-6k right?
Breaking up / misfiring under load can be a symptom of a basic ignition condition issue. Stuff like Old plugs, bad wires, conductive oily deposits on the coil nose, carbon tracks on the ignition rotor or the distributor cap. Spritzing with water mist and watching the engine at night can reveal errant sparkage. If the points' gap is dirty or has excessive resistance it can chop the coil spark output. Maximum of 0.3 volts volyagr drop across closed points comes to mind. A fat blue spark across a test spark plug with the gap pried open to .1" or so suggests the points and condenser are in decent shape. Similarly A tester like this answer a lot of questions about ignition system condition. https://cal-vantools.com/products/adjustable-spark-plug-tester/ Once or twice a fuel filter has been restricted just to the point of limiting HP to 18 or 20. Just enough to cruise at 45 mph on level ground, but slightly more throttle and the engine would fall flat. A standard fuel pressure and volume test at the carb could help answer questions about fuel system issues.
With the problem seeming to be related to above 1/2 throttle, I believe I would check the fuel pump for the correct pressure, and for delivering the correct volume. I am ***uming you have already checked the condition of the fuel lines, and have already replaced any fuel line hoses with new hoses rated for the current fuel. The problem still could be a carb issue. The carb looks like the old 4bbl, maybe there is an issue when the secondaries open that create a rich, or lean condition, when they open. I believe I would also pull the plugs and see if they are showing a run lean or even a run rich condition, or maybe at the higher rpm, its pulling oil into the combustion chamber. While there, it wouldn't hurt to do a compression test on the motor and evaluate its condition. We are now chasing a high rpm miss, that changes our approach. The condition of the motor and all of it components need to operate correctly.
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