I have been out of the loop for a while so I may be missing something obvious. I drove the car a few days ago and all was well. I have dual weber 44
Idf's and I changed my main jets last night. Today I started my car, all seemed ok however the air fuel ratio was way too rich so I stopped and changed the main jets back to the old way. Started the car and cylinder 2 wouldn't fire. Stopped again, made sure idle jets were clear and all the main jets were ok. Started again and still cyl 2 wouldn't fire. New spark plugs- still wouldn't fire. Changed spark plug wires- still won't fire. Did compression test- all were 160 +/- 5. Took out spark plugs, let any flooding evaporate- still won't fire.

Any ideas?

Do you have spark at the plug? Use an old plug, or a timing light to see if you have spark....

If you do, it's fuel....so back up slowly...
Dirt in the jet hole...

Idle jets get their fuel supply from the main fuel well where the jet stack sits. Some crud may have come loose while you were in there and plugged the passage. Might try pulling the jets and blowing the passage back.

It's nice to do this with the carb upside-down so the gunk falls out. A long Q-Tip can be used to swab out the fuel well if you leave the carb installed. Just make sure you don't add a bunch of cotton fibers to your problem.

If you have trouble with idle jets clogging in the future, I have had good luck with these. http://www.cbperformance.com/ProductDetail...roductCode=7557

I just got home and worked on the car a bit. Checked for spark and appears to be working normally. Disassembled the carb and made sure all ports and jets we patent. Reassembled and still same problem.

Is it possible that if the valve lash on the misfiring cylinder was off enough- would it cause similar symptoms?

Did you touch the valves before this started?

If not it looks like a plugged idle jet or passage. Did you remove the #2 jet stack, remove #2 idle jet, remove idle mixture screw and blow it out both ways. A rag over the top of carb helps not blow fuel everywhere.

A quick check is to squirt some fuel in #2 cylinder. Does it fire? If so it's a fuel problem.

Gotta back up...what did you do.
Backtrack and verify

Good question- I may be overthinking things but I think that other than yeaterday, I had only driven it twice in the past two months. I vaguely remember the engine seemingly misfiring two months ago. I parked it and made some unrelated changes. I drove the car about 1 mile. I thought it ran fine but I am not certain. Last night when I took the car out, I thought it was running ok however it may not have been cause I stopped and changed to smaller main jets. That is th point that I really noticed the misfire. Every change that I made from that point on doesn't fix the problem.

FYI- I sprayed carb cleaner through the idle and main circuits. They seem to be patent.

My father taught me something important when I was 16 and fighting with a no start on my old Firebird when he said:

"Son, What was the last thing you F*cked with? Because the is going to be your problem."

And you know, he was right.

If it worked fine before you changed the jets, then it is in the carbs and not the ignition or valve lash.

If the spark plug was wet, then you may have a plugged air bleed. Changing jets can stir up crud and get it in places it is not supposed to go. Get some canned air. pull the jets and blow out the passages.

I fixed a clogged carb one time by revving the engine and putting the palm of my hand over the intake for the dead cylinder. That sucked the crud out of the passage and it started to run on that cylinder again. Left a hickey on my hand too. I don't recommend doing it that way.

I like Clay's logic.

Have you tried swapping jets from another known good cylinder to the suspected problem cylinder?


Process of elimination. Good luck!

I would swap carbs (one side to the other) to see if the symptom follows the carb.