engine and drivetrain Backfiring through carbs

[TimS]

My rebuilt motor has finally been fired up, and is backfiring through the carbs due to what seems to be retarding timing.

Background-

* Car is a '76 California emmisions, with the vacuum advance/retard distributor, with neither connected

* Timing has been statically set by eye, to slightly advanced

* Advancing the timing decreases the backfiring, but increases the idle speed to 3000 RPM+ with very little advance

* Retarding the timing causes the idle speed to drop, but increases the back firing tremendously

* All four cylinders are back firing

* Fuel is dripping out of the secondary venturis with the backfiring

* All wires, cap, rotor, points, condenser, and plugs are new

* Carbs have no filters or venturi stack installed. These 40's have the retaining screw for the secondary chokes to keep them in place.

* Idle screws are out about 1 turn, adjustment in either direction makes no huge difference

* Korman 300 cam, 9.75:1 compression, 40mm DCOEs jetted to Pierce recommendations for engine set-up

* Spark appears to be weak

Next steps

* Check for vacuum leaks causing the sky-high idle with advanced timing

* Replace distributor with Tii model

* Verify and reset float levels

* Check valve clearances

* Verify firing order

*?

Is the '76 Cali distributor completely incompatible with these carbs etc.?

Thanks.

[c.d.iesel]

SPARK PLUG WIRE / CYLINDER FIRING ORDER recheck.

Recheck,

and

RECHECK

seriously lean idle circuit

more seriously leaking intake valve/seating

valves too tight - no clearance -

[Guest Anonymous]

check the dwell (point gap). That's always been the culprit for me.

[TobyB]

Fuel is dripping out of the secondary venturis with the backfiring

Sure the float level is right?

The venturis may leak air without the trumpets UNLESS it's a bolt-

on style trumpet carb...

But honestly, I think your dizzy's messed up.

No- one ever looks at the mechanical advance...

t

[dapbmw]

floats are not set right, in can be hazardous to you and your car especially if the the car backfires then ignites the fuel in the carbs resulting in an engine fire. replace your dizzy with a mech. advance one as side drafts and a hotter will benefit from it. switch to electronic ignition too.

[TimS]

The problem is partially solved. The issue was the points, which were not properly mounted (the pivot had slipped out of the plate).

The backfire throught the carbs is gone, and so is the fuel gathering at the bottom of the secondary chokes. The fuel gathering I think was from raw fuel droplets being pushed out the carbs and eventually puddling at the bottom of the chokes.

The car still idles horribly, on about 2 cylinders. After further inspection, the coil is an after market unit (no name), that doesn't use a ballast resistor. My car being a '76 has the resistor internal to the wiring loom. That is the cause of the weak spark, and thus rough idle. It's running very rich.

Next step is to find the ballast resistor, and jumper around it.

After that, I'll be upgrading to a mech. advance and aftermarket ignition system for better spark yet.

Thanks.