Technical missing, now what?

Hi All,
I finally have got around to looking at my 'new' 47 coupe. It seemed to start first time and run fairly well. However, on closer inspection, the plugs were really rusty and the leads were very corroded. I changed all the spark plugs, fired up the car and all of a sudden it was missing. Sounded like it was running on 7 cylinders. So, by process of elimination, found it was no.8 that was not firing. So, suspecting a dud 'new' spark plug, I put on of the old ones back in - same thing - missed.
So, decided I'd change the leads - just as well as they were all corroded at the distributor end - so much so, three would not even come out! Decided to put new rotor button, new distributor cap and new 8mm silicone leads along with a new coil lead on. Fired the car up and it is still missing on no.8 - but NOT as badly as before. only seems to be under load when I rev the car, with a back firing of sorts from the right exhaust bank. Given that it was running fine before i changed anything - is it just a coincidence that this has happened? Maybe a sticking valve now? Firing order is definitely correct. Has anyone had this happen before? Really don't want to start pulling off heads and manifold if I can get away with not doing so. I've only ever driven the car about one mile.

 

Number 8 is now firing, that’s why your getting the back fire. Before there was NO spark at the plug, now there is. Drive it at moderate speeds, trying not to back fire, maybe the valve will loosen up, if it’s sticking. Or just run it in on the drive way at moderate throttle and see if it clears up.

Bones

 

How about you check the carb mounting bolts. Maybe you have a vacuum leak.

Sent from my SM-G955U using The H.A.M.B. mobile app

 

My 40' had a miss in it like that when I first got it. Turns out it was a valve stuck in the guide,no big deal to fix. I run some Marvel mystery oil in the gas now. Do you have any valve train noise?, or do a compression test yet?.

 

thanks guys, I'll check for vacuum leaks and around carby and no valve train noise that I can hear. I'm here in OZ (australia) so no Marvel Mystery Oil supplier out here, but we probably have some equivalent product (I've also heard ATF does the same thing?). Haven't had a flathead for about thirty years, so racking the memory bank on the little issues that they have. Sure is good to have one again though! BTW, the motor has what is supposed to be original 67,000 miles on it. Sure it would have had stuff done to it over the last 80 years, but no idea what. I'll try to get some photos and even a video uploaded.

 

Whoa! It's not 2027 yet!! The years go by fast enough when you're my age.

 

so, found it! The three way plastic piece on the vacuum line was split - must have been when I was changing the leads over - it is quite brittle. hard to find - but yay me!

 

Glad you found it. And came back and told us before 19 pages of guesses.

 

The record is 127 pages and usually the OP croaks of old age before it gets solved.

 

as 56 and Bob said good on you for reporting back with the cure.I wish there was a way to track those that never report back after people go out of their way to help.next time they seek help it would be nice to have the power to burn their fingers when they try to type next problem

 

As 3WLarry would say...patiently waiting for pics.

 

no pic problem solved