Hot Rods High RPM miss/mess

I don't claim to be a 'tuner' these days and helping folks on a phone call or you tube video is stretching my old brain so I'll ask you guys for opinions on the high speed 'flutter' seen in this short video starting at about 0:57 .
The engine is essentially stock with a small cam regrind. I'll pass along any/all suggestions to the owner.



.

 

what happens when you disconnect the vacuum advance?

 

Sounded like ignition timing or something in the secondary system.
It does sound like the mixture may be a little rich, but ignition problem can do that.

 

Point "bounce" or a broken valve spring, maybe???

 

Run it on an oscilliscope and see if the pattern changes as RPM is increased. Also, if it has dual points, try inserting piece of match book in one set of points then the other. It should run on only one set. I've seen many of these distributors that had widely varying dwell from one cylinder to another. If so, replace dist. And as above, disconnect vac. to dist.
Eddie

 

Totally agreed with Squirrel , possible that one of the the wires flexing on the advance plate have been moved to many times.
Sounds to me at when high vacuum the plate moves to full advance causing the wire to lose conductivity then when vacuum goes down ( no spark) as the plate returns back the wire reconnects causing miss.
It also is not wanting to run at idle when vacuum is high, no spark at high vacuum again.

When the vacuum is disconnected the plate won't move wire won't flex

 

I had a real "head scratcher" once like that.
Come to find out the BATTERY wasn't fully charged. Replaced weak battery and all was well. I checked wires/plugs/carb/timing/fuel sys...........almost everything but the battery.
6sally6

 

check the spring on the points. I had a customer do his own tune up and had the same trouble. I checked the points and he never put the little strap spring on.

 

I'd also look the cap over closely while I had it apart.
Pete

 

Long shot but easy to check see if the coil bolted down tight. I had and engine that sounded a lot like that the coil was loose tightened the mount fixed. According to Motors manual points tension should be at least 17 oz.

 

I've had a broken valve spring act that way but in had an inner damper so it kept running.

 

Some very good thoughts here, I'll pass them along. ...and I'll take more.
If I get a 'all-clear' from the owner I'll pass along the cure.

Thanks