So I've had my flathead running in my model A pickup for about 4 years now. No issues whatsoever. Its a 286ci with 3 Holley 94's, Edmunds heads on an Edelbrock intake. The distributor is a Mallory YC dual point with the flat cap. The motor has maybe 15k miles on it. A little back story: Last time I drove it we went on a trip about 200 miles in total. Towards the end of the trip we stopped and ate lunch for a little and I fired up the truck and took off. I noticed it was backfiring out the exhaust mostly under load. I couldn't keep it in 5th so I stayed in 4th and it would do ok, but still kind of running rough. I stopped and checked the points but I was close to home and kept going. What I've done: I've been trying to diagnose this issue since February and can't figure it out. I took the distributor apart. Cleaned the points really well. I set the point gap and dwell. I put in a brand new condenser. I've tried 3 different coils. I put in a Pertronix ignitor II and flame thrower coil (brand new). I took the cap apart and made sure all plug wires were in the cap correctly. I cleaned off the contacts in the cap. Cleaned off the rotor. I bypassed the ignition switch with a jumper wire. I tried a known good battery. I tested resistance on the plug wires (1.4 ohms). I did a compression test and they all came back at 100lbs. I can get it to static time with no issues. With all this done it will not even start at this point. It will pop like it wants to start and then nothing. It coughs through the carb which to me is too advanced so I set the timing again and nothing. Just sounds like it wants to start and then dies right away. I need some help before I swap in a small block Chevy!
WAG's....Good grounds? Good fuel? Dist. installed correctly? Firing order correct? Plugs fouled? Bring number one up on compression (front left when looking at engine), verify rotor position, connect plug wire and ground number one plug, loosen dist., turn on ignition and rotate dist. until plug fires. Start and set timing.
Is fuel getting to the fuel pump? Could be a blockage or restriction in the line, or maybe a bad fuel pump diaphragm. Starting fluid in the carb will confirm if it's a fuel delivery issue. Are you running a condensor? Could be a bad condensor or bad ground. Do you have spark at the plugs? Gotta be air, fuel, or spark related. You'll just have to do a process of elmination to figure out which.
I guess I shouldn't have made a long post haha 1- I static timed the engine and I can get it timed in the correct spot. 2- It ran for 15k miles with the firing order the way it is (checked just incase when I checked resistance on plug wires) 3- I have tried 3 different coils, the current one is new. I have checked the primary and secondary and they are within spec. 4- These engines have no timing chain, it has metal gears (does almost seem as it jumped time. but the compression test would show that, I would think) 5- I did a compression test (all cylinders are at 100) 6- Grounds seem to be ok, I added a couple new ones 7- Has plenty of fuel and its not that old. (Accelerator pump works-lots of fuel down the carb) Thanks for all the replies so far guys!
I should also say that when I had the distributor out I checked the cam gear by rotating the engine over and saw nothing suspicious. It has to be something stupid I'm overlooking.
You said you added a couple oof new grounds try starting there and check to see they are good. I agree it sounds like something simple you are missing.
Checked inside the cap for carbon tracking? I know there are a million of those flat caps out there, but I've never heard of any giving fits like that. But worth a second look. Also, do the run it in the dark test to see if any plug wires are arcing to ground. Maybe something rubbed through?
Running a ballast resistor? If so, when you bypassed the ignition switch, did you jump to the resistor or bypass it and jump to the coil primary? Thinking possible bad (open or intermittent) ballast resistor.
Well, if it's backfiring through the exhaust, unburned fuel is getting into the exhaust. Sounds like one or more cylinders are not firing all the time under load, a classic ignition problem. Could be an arcing plug wire, bad cap or other fault.I'd run it at night and look for arcing or put it on a scope if one is available. I could be completely wrong here, but that's what comes to mind.
When I got my ‘42 running, it would idle great and rev fine, until I got out on the road, then start snorting and popping. Now the wiring in the truck was a mess when I got it. So back to the shop after a week of this stuff and I started pulling the wiring out, well sometime in the past someone ran new wires, once I started pulling the wiring, I found the ignition wire to the coil was wrapped around something under the dash (been awhile) and the insulation had worn through. Looks what was happening in my case that when driving it was getting shorted to the metal every now and then. Kinda like driving and shutting the key off and on I suppose.
My Shoebox decided it didn't want to run very well recently. I ran the gas out of it (Put it in Dec), refilled it and it runs like it has for the past decade. Gas today is junk. BTW...Killer truck!
Yikes! unless there is a bad wire, cracked,etc, in the ignition system I would switch to fuel system - all carbs clean inside, adjusted, clean fuel filter, bad/dirty/water gas pumped when motor started having problem, etc
I'm thinking carbon tracking inside the distributor cap or, maybe now that it won't start at all, the rotor has a carbon track or it is burned through and grounding to the dist. shaft.
Can you confirm why it wint start now? How does the spark look? Pull any plug wire and use a spare spark plug and crank the engine. Observe the spare plug which should be in contact with the head. If it looks strong, and you have confirmed the timing is correct then I'd look at either fuel or valve timing. My absolute first thought when you said it wouldnt pull 5th gear is that you have something weak in the ignition, classic symptom. I'd throw a new cap and rotor on it. Also closely inspect the ignition wire from the coil to the distributor. If any other wires or plugs were bad it would just loose that offending cylinder under load. If it seems like a random misfire then look at what is in common: coil, cap/rotor, distributor (our of time), power to the coil. Personally I never run an external ballast resistor, I use could with internal resistor. Also check static timing with an induction timing light, one which clamp that goes over #1 wire. Then you will confirm lots of things are correct with the ignition in one step.
Nope no ballast resistor with the Pertronix. I've cleaned off the rotor and checked inside the cap. I'll check it again a little better here in a few minutes. Currently it acts like its going to start and then coughs through the carb like its advanced and dies.
Can you confirm the timing with an inductive timing light? One of my favorite ignition diagnostic tools.
Mike did you pull the timing cover sounds like a key might have sheared on the cam or something You have fuel, good compression and you have good spark ? Must be timing
Maybe the key on the crank gear sheared? Wouldn't that show up in the compression test..? That's what I've been thinking but I've hesitated pulling the timing cover off.
Bitchen truck Yes it would but if its just a fraction off it wouldn’t effect it. Also you didn’t say anything about the generator and did you check that out. The reason I say that is I had one short out on me and created a similar problem. I also had a starter short out and was drawing so many amps it wouldn’t start . I tore down the whole motor looking for the issue and was a bad starter. So I would look for a short in either and have both items if you want to swap one of them out and try it..
If you sheared a key, unlikely, you would have no compression. No key on the cam anyway, the one on the crank is 1/4" and the gear is interference fit.
Generator was rebuilt completely when the engine was rebuilt about 4 years ago, so it could have a problem at this point. The starter was rebuilt but as a 6v and I have a 12v system so that does put a lot of stress on the starter.. good ideas thanks man Ill check them out and report back!
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