I'm Stumped ! what else could it be ?

[87BlazeLS]

If it was an internal vacuum leak how would that be detected ? If I cannot get close to what the problem is I may have to take it to a specialist for higher end diagnostic eval....

Don't want to. but man this is a bit$ch to figure out.

 

[tetomas]

Plugs are new AC Delco and they look fine. burn wise.

What would cause arcing ? Every component in the electrical to the motor is new. New battery wires, All wires from fuse box
to motor, ect. Only does this at just above idle not all the time.

If you hold the rpm at around 1500 to 1800 you can see the motor shake as the miss occurs.
Above that RPM it acts fine. Good power no miss or hesitations.

Have you thought about having it put on a scope to see what the primary and secondary ignition are actually doing.
That would also help narrowing down what, If any cylinder might be the problem with a Cylinder balance test.
It could be something as simple as a defective plug or as serious as a broken valve spring.

+1 The scope could be your friend. The scope could isolate an ignition vs a vacuum problem. You said you installed a new dist. what about the coil? Again the scope could show the coil voltage when it is stumbling. I had a cracked spark plug act like this, it was brand new and took me around the block for a while before I found it on the scope. Cant explain why it would miss at part throttle, and run like a striped ape at WOT.

 

[87BlazeLS]

Felpro gasket set KS 2600 was used for the motor. I used the intake gaskets in this kit for the mounting of the RPM intake.

Problem with that ?

I am on the verge of getting a manifold leak eval done. I think if anything could be wrong other than electrical
it would be the manifold or gaskets. I do get just a slight weep of oil around the middle bolts.

Leak? Carb spray does not pick it up. Internal manifold leak. We may have something .

 

[hereiam]

I havent been following this, so please excuse the question
What motor is it and what distributor are you using

 

[87BlazeLS]

My tag line at the end of every post shows the current setup in this car . I could not be more specific then that ...

jake

 

[chevy2480]

Sounds like you need a bushing and spring kit for distributer. Sounds like the springs are to light and it letting the timing come in a little to soon. Might want to install heavier spring and install a bushing to limit the amount of advance. Even with vacumn unhooked the distributer will still advance the vacuum hooked up advances timing beyond the built in adv. hope this helps

 

[Ringers]

You need to get your car on a chassis dyno with wide band O2 sensors to find out what is going on. All the driveway tune and guessing is eliminated this way.

 

[87BlazeLS]

How much would a test like this cost If I could find a place to do it ?

I do have a shop up the street from me that is pretty good. I can see what he can offer based on his equipment.
They do a bunch of street rods and muscle cars. I'm sure he could get me some kind of test that will show whats
happening in there.

thanks to all for the suggestions...

87BlazeLS

 

[Ringers]

We are $175/hr on the dyno. It sounds expensive, but you need to realize, we can and do run cars through all phases of drive cycles, from idle, acceleration, part load, hills and of course, WOT. We are able to run your car at top speed, while data logging all parameters. Air/Fuel, EGTs, Vacuum (or Boost!) vehicle speed, shift points, torque, HP. All of this done in the safety of a shop and not chancing a ticket or planting your baby in the ditch or against a pole. We are not the only shop with a dyno in the country. Find a reputable tuner in your area. Contact them and start a relationship with them. Dynos are expensive and it is in the best interest of the operator to form and nuture relationships with enthusiasts like us. Once you see and feel the results, you will be a repeat customer. Stop beating your head against a wall and being aggravated with your drivability issues.
Oh, and have fun with your car!
Cheers, MFR
White Flag Racing

 

[hereiam]

SORRY I never read that part of the post.
Put a digital timing light on the motor, start it, rev it to where it starts to bog or miss and read the degrees. Then rev it farther until it cleans up and read those numbers. I would be interested in that info