Backfire:

[Wayne W.]

I"v been experiencing backfire through my exhaust with my 63" 327/360 roadster. This occurs during acceleration in the 3500-4000 rpm range; i.e. between 80- 90 mph. The car seems to "hit the wall" with no futher acceleration. Any ideas as to why this may be occuring??

[Bill Clupper]

Re: Backfire:

Have you checked out the electrical system, dist cap, wires, Plugs, correct length rotor?

[Duke W.]

Re: Backfire:

There's a good chance you ignition is breaking up. The Delco single point was marginal for high reving solid lifter engines. You might be able to fix it with a new set of HD points such as Borg-Warner A112HP, which have higher breaker arm tension than the OEM and replacement points. You should also check all primary and secondary connections and check that the ballast resistor and coil windings are in spec (resistance).

If you're not aware when you distributor was overhauled and if the car has more than 50,000 miles you should probably overhaul it to include checking for bushing wear, regreasing the upper bushing grease well, checking that end play is within spec, and I'd also recommend replacing the vacuum advance with the '65 SHP/FI part. The production '63 advance does not fully pull in until about 15" manifold vacuum, which is less than idle vaccum with the Duntov cam. This will add to idle instability.

Duke

[Duke W.]

One more thing

The vacuum advance constantly moves the breaker plate and eventually it will begin to wear and develop a slight wobble, which can contribute to ignition breakup. The distributor must be removed and disassembled to replace the breaker plate (and vacuum advance). It's a good idea to replace these parts everytime the distributor is overhauled.

Duke

[Patrick T.]

Re: Backfire:

You might want to check the donut gaskets at the exhaust manifold/tailpipe connection. If they are burned up or if you have disassembled them recently, you might be sucking up cold air through the heads, which I know from experience, will cause backfiring. Good Luck.

[motorman]

Re: Backfire:

the first thing i would do is pull all the plugs for a look/see. if any are very dark i would install new plugs to start trouble shooting. carbon fouled plugs will fire under light load but short out under a heavy load.

[Dale Pearman]

Re: Backfire:

Here's some off-the-wall conjecture. Maybe you got burned exhaust valves. That rpm range is in the "resonance" region of the exhaust side. The backfire will kill acceleration. How does it behave at higher RPM? Run a leak-down test and see what shape the engine is in mechanically before fooling with ignition. That's what I'd do, yesiree, that's what I'd do!

Rev. Varooom!