I haven't been a very good community member lately. Haven't been on here much. But you've never let me down before so I'll see how we go this time. I have a stock 401 nailhead with stock ignition. I just put an Eelco 6x2 intake on it and I'm running the outer 4 carbs (new big 97s). I've spent the last couple of months on and off getting the carbs running good and I'm pretty close now. Good idle, good coming off idle and pulling well to around 4000. I had been getting the odd backfire out the exhaust that I put down to maybe unburned fuel in the exhaust due to being a bit rich. I wasn't concerned because I was still working my way through the tuning. But today I went out and all of a sudden I had severe backfiring out of the exhaust, mainly under load. It was like I just swapped 2 plug wires or the distributor had spun...or something? I turned for home and after a couple of minutes it came good. I continued past home and out the other side of town and it was running OK, then when I started heading back home it did it again. Then came good again. The fact that it is intermittent is suggesting to me a failing electrical component such as condenser or ballast resistor... but I'm no expert. I'm thinking it is unrelated to my carb set up since when they are good, they are very good. But again, no expert. Thoughts????
I don't have a clue about your problem, but the engine sure is pretty. I think your base diagnosis (electrical component) is the place to start. Good luck.
I had a similar problem with my 322 with three 97s years ago. It would pop through the exhaust while I was cruising and sometimes get worse, then clear up. I installed the Pertronix kit in the dizzy and their recommended Flamethrower coil. All problems cleared right up and ran SO much better! More power, quicker starts and better milage. That was over 8 years ago with no problems at all. Hope that helps and btw... GREAT lookin mill!!!!
Could be a sticky exhaust valve that comes and goes. I had that on my flathead after winter storage. Popped in the exhaust, put some Seafoam in the gas. Was gone after 2 miles of driving.
Looks like your plug wires are realclose to the exhaust. Double check that you haven't burned through one or, that they are not arcing to ground somewhere else.
check the plugs to see if its running evenly on all cylinders. check coil, is it close to heat source, maybe old and breaking down?
I would go with what Nailheadroadster said. I just had similar issues with my Riv. The points they make now are all junk and don't last. The drop in pertronix made a world of difference. Your problem sounds like it's running a little rich and it's getting a little fuel build up in the pipes. When they get hot, it would be less. Try the pertronix. Hope it helps. That's a beautiful motor.
Cracked or carbon track in cap , wires crossed . Probably already checked or not an issue . Just thinkin out loud ! Posted using the Full Custom H.A.M.B. App!
Let me hazard a guess, valve sticking? Do this for yourself, check your oil, I mean really check it, have you run fuel past your rings while you were getting it sorted out? I have heard of gas fouled oil causing all kinds of problems, and gas fouling can be a problem with a nail head just like any other engine. I remember reading an interview with TV Tommy and he said that every time he ran his injected nail head in the T that he had to change the oil because he fouled it. maaan there is a tidbit that I have wanted to share for a long time.
Sounds like a plug fouling and then clearing up. Check the plug type eg: extended tip might be required. I had that problem. Had the correct heat range but the wrong type plug
Plenty of stuff to check here and most of it I have considered but haven't checked yet. Funny there are a few mentions of sticky valves because I did lift the covers off for a visual look yesterday. Early on in my testing this new carb set up I did a highway run and stopped to check plugs. 7 were good and one was fouled. Of course the bad one is on the left and that cover is a bitch to get off because of the linkage. Porknbeaner, I'm sure I ran plenty of fuel down into my oil early on. It was super rich and with all the messing with linkages, I was very aware of that. As soon as I got the car back running OK I did an oil and filter change. I think Pertronix may be an upgrade I should make regardless but I'm going to start with a compression test I think. I reckon that's a theory worth following up. Thanks for all your advice guys. I'll work through all of it and report back. Pete
if it`s running fat enough to dump major fuel vapors into exhaust, you`d know it from the smell and color of the exhaust and plugs. petronics is good thing but change the coil at the same time. I`ve also had exhaust popping from water in the gas. you might try closing the gap on the plugs, if that makes it better then it`s your ignition that`s weak.
I've had several cars [a Pontiac and a buick] that did exactly that when the coil began to go bad. The Pontiac ended up blowing a huge ball of flame out the exhaust and stopped running. The buick ran worse and worse coming home from a trip. Made it back home, backfiring all the way. A new coil fixed both of them.
I did a compression test and had good compression on all cylinders with only 13% between the best and worst. Not too bad for an original engine. I guess if I have an intermittent sticky valve it would only show up if it was stuck at the time of the test so I still can't rule it out. I looked for a seafoam type of product today. Never seen seafoam in Australia. Found a Redex product that seems to be similar and ran a bit through it. Made some smoke but didn't fix it. I also ordered a Pertronix kit today. Tried to buy it locally but the local wholesaler was out of the one I needed. All of their listed dealers (parts stores) had no idea what I was talking about so like usual...get online and buy from the US. It pisses me off that it's so much easier to buy from America than from around the corner. Anyhow, the excitement continues.
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