#4 cylinder not firing

[renobdarb]

For some reason my #4 cylinder isn't firing. Not sure what the heck's going on, but I need some help trouble shooting this thing. It started when I put in new plugs. Here's what I've done so far:

- while running, I pulled the plugs from the distributor, one at a time. All have a noticeable effect on how the engine idles except #4.

- There's spark from the distributor cap to the cable, when #4 is pulled

- There's spark from the connector when pulled from the #4 plug

- I tried swapping out the #4 plugs; still won't fire.

- Checked and re-checked the timing.

- Adjusted the valves

- The strange thing is that this cylinder will sometimes fire at first when the bus is first started up, however it cuts out when the engine is revved, and won't start again when the engine returns to idle. I'm pretty sure the cylinder has good compression.

- I checked and cleaned the main jet in the carb. When I dump a little gas down the #4 neck of the carb, it seems to fire for a moment, however won't stay firing.

I just don't get it. I have compression, spark and seem to have fuel, but this thing just won't go. Any ideas?

[Amskeptic]

When I dump a little gas down the #4 neck of the carb, it seems to fire for a moment, however won't stay firing.

I just don't get it. I have compression, spark and seem to have fuel, but this thing just won't go. Any ideas?

A)Classic clogged idle jet.
B) Sometimes spark plug connector. Unscrew from wire and swap with #2's connector. If symptom follows the connector, see if it has excessive resistance.
Colin

[renobdarb]

A)Classic clogged idle jet.

Bingo. After everything I tried, it turned out to be a clogged idle jet. Firing on all four and purrs like a kitten now. Amazing what a little dirt can do. I suppose it's time to clean the engine compartment, eh?

Thanks a million for the help!