This is my hotrod. The side-pipes have muffler inserts but I can still hear the exhaust quite clearly, as you can imagine. Today as I was cruising around town, I started hearing what I can only describe as "chuffing" out the pipes. It sounds like a miss, but it is not coming from any particular cylinder or side. It's random and seems to only happen at idle or very slight throttle. If I get on it it sounds and feels strong with no chuff or miss. I adjusted the timing and that didn't help (16 initial, 34 all in by 2800, no vac advance). I checked all the plugs and they look fine. I checked all the ignition wiring (MSD 6AL, Blaster II coil, billet distro, 8.5mm wires) and that all seems fine. The carbs (Edel 1405s) were set-up for the blower per Edel's recommendations. Fuel pressure is regulated at 5# from a Holley blue pump. The cam is a Comp hydraulic roller, so I don't think I've wiped any lobes. The car has about 1,000 trouble-free miles (except for an issue with the tranny, but that's a different forum . ). The motor has always run very strong with no issues.

Any thoughts on what else I should check? Maybe the MSD box going bad? I've heard they do that occasionally.

BTW: I read the other thread about a mis-firing MSD and checked that stuff too. No joy.

Just a quick thought.
I ran into several bad plugs that only ran a few miles. Looked good.
Random sources, different brands, etc.

I am not around blowers often, but I have had the best service from plain Motorcraft plugs. I've seen some pretty expensive "exotic" plugs that weren't worth diddly.

Don't know anybody that would run a Champion or Split Fire even if they were free.
Split Fires blew out around the insulator with the boost pressure. The porcelin got loose in the steel barrel.

Although I`m not sure X, could it be just exhaust pulses? being the plugs look good and it`s got good power, then it would be my guess. I am also guessing the pipes aren`t connected with a balance tube, sometimes after the exhaust "breaks in" with time and use, it sounds different, and since there not connected there are more pulses that can cause a different exhaust note. As said, this is just a guess. But trying to help.

I will add something that would relate to blowers..how many miles are on the engine?? If the valve springs are getting weak, the blower pressures could be creating some issues with valve seating. Could also be a lifter adjustment/pre-load that needs attention too. I had a Cleveland that would do that after a high rpm pass and it was too long a pushrod( no adjustments) that was creating pump up when it was wound up. After sitting at idle it would correct itself, never happened under normal use...but one pull to high rpm would bring it around as regular as the IRS.

I had a buddy who is a much better engine man than me listen to my motor and he says it's a "lean miss." Now we have to figure out why. Nothing has been changed on the motor recently. Last weekend I drove it on a 140 mile cruise and it ran like a Swiss watch! I'm even running on the same tank of gas. Oh well, that's hotrodding.

E10 seems to make them leaner.
Got real gas?

Fixed... I think. We found that someone had screwed the idle mixture needles all the way in on the secondary carb (the one in front). When I set the idle up I used all four idle screws, so winding in the two on the secondary carb really leaned out the idle and transition. We reset the idle mixture and it seems to be running fine now. This is the second time someone has messed with my car. First time someone pulled off all the caps on the vacuum ports. Fortunately, I noticed they were missing before I tried to drive the car, otherwise it would have been so lean I'm sure I would have burned up the motor.

This is the down-side of having your motor exposed to the world. Any knucklehead can walk up and mess with it. I still want to wire the battery so that all metal parts of the car are charged and the idiot that touches it gets 300 cold-cranking amps... but my lawyer sez I'll prolly go to jail.

Did this for a dog that liked to pee on my wheels.
12 volt electric fence charger with the + hooked to the car and a - wire dropped to the ground = needs to be a big spike nail stuck into the ground for good contact. Got the picture?

Will it percipitate further and worse vandalism?