Ignition Arc Big Time

This is one I have never seen and am at a loss. I have a Manta Kit car. It has a HiPo 350 Chevy with 4 IDE Webers for induction. It also has a Mallory Electronic Ignition with a model 29150 coil.

Investigating what was thought to be ill-synchronized Webers I discovered 50% of the aggressive "pops" were not backfires through the Webers but rather rather electrical arcs across the manifold. Some upwards to 6" in length centered near or around the water inlet at the front of the manifold.

Any thoughts?

I'm not familiar at all with your setup, but how are your grounds?

It's all pretty standard stuff. Battery grounds to the block. It is a fiberglass body so many components are grounded near their location on the tube frame.

I see. Yeah usually when I see arcing on newer model cars poor grounds are to blame, that's why I asked.

Thanks, Someone else built the car, thinking I will go through and check and re-ground all.

Thanks

Are you saying that the secondary ignition wires are arcing to the manifolds?
Engine is mis-firing then too?

Most good wires can lay right onto metal and not jump thru.

Uncertain of what wire exactly. What I saw was; with a point of view looking straight down over the intake manifold. There was 1 - 6" arc and 1 - 3" arc emanating from the thermostat housing connecting to the two nearest manifold risers for the IDF Webers.

There was a subsequent backfire from the exhaust.

My guess is that even though the block is grounded, it isn't the path of least resistance, that appearing to be through the coolant system instead.

Arcing from carbs can be a bad situation (gasoline present), so redo the block grounds to be as short as possible and using large gauge cable to provide the least resistance. Same with the battery straight to the frame.

Hope this helps!

Bad situation indeed. Here is what I have done thus far. Checked coil, (Mallory) for cracks, checked wires, (Accel) both are in good, clean and relatively new condition. Checked, cleaned and reset distributor ground, battery to block ground and added a clean battery to frame ground. Ground to bare metal, threaded a 5/16" for a stainless bolt to hold the 12" 4 Ga. to battery terminal.

While futsen with coil, the coil wire that mounts through a plate on the coil, low and behold falls off in my hand. "This has to be it", I think to myself. I disassemble, snip the wire for a clean contact and reassemble.

With confidence light her up. Sounds strong sounds clean. Let it warm up and let the Webers settle down back it out of the garage for a test and . . . there it is that painfully familiar orange tentacles from again thermostat housing. :banghead:

Are the carbs grounded as well?
If they are sitting on risers they maybe insulated from the block, but picking up a charge somehow.

They are not grounded per say, e.g. there is no ground wire attached to them. Though the arc from thermostat housing goes more after the towers, which are 3" tall themselves. Though I can certainly try that.