Misfire help?

[transalpian]

Greetings!

I need troubleshooting help on my 74 series 3, 2.25 petrol, standard points ignition.

Going to start yesterday, starts fine, runs great for 30 seconds, then picks up a miss. It had run fine before, and gets driven regularly.

Change the plugs, check the plug wires for continuity, check the dizzy cap for cracks. Found one plug with no conductivity.

With new plugs, runs great for 30 seconds, then back to same miss. Checked the new plugs and they have conductivity.

Isolated the vacuum line to the brake booster with no difference.

Where to go next?

Thanks

Chuck

[Jeff Aronson]

Is the miss at speed, under acceleration, or in general? It's possible to be a fuel delivery issue, but less likely than an ignition one.

Try these diagnostic steps. Take a small spray bottle and fill it with water. Start the engine and let it idle. Spray each spark plug wire and the coil to distributor wire to see if you can replicate the miss. If so, you should consider a new set of plug wires. Spray your cap, too, to see if you have a tiny crack there.

A miss is sometimes the result of a breakdown in the high tension end of the ignition. Your coil should be warm when the car is running, but not too hot to touch. A coil that's breaking down would create a misfire.

Let this Forum know what you find out.

Jeff

Lastly, do check your points. If they're not gapped correctly, or pitted and blackened at one tip, you'll get a misfire even though the car starts fine.

[transalpian]

Thanks for the help. Despite the burned out plugs ( don't know how it ran...), the problem was a stuck float valve in the carb ( stuck closed ). Somehow, it would get fuel at higher rpms, but not at idle.

Its all about knowing where to hit...

[LaneRover]

Its all about knowing where to hit...

THis is what can take you from $20 an hour to $200 an hour :D