random miss fire on #1

[stingger68]

hi, I am stumped. I have a 1973 SE with the 318 auto, Holley 2 barrel. the day I got it I noticed that is had a random miss fire. I have replaced the plus and wires, still has the miss. I installed a new HEI distributor for the small block 318 and 360's and it is still there. not so much at ideal but while driving. I put the timing light back on it and rechecked everything again. I have also turned the crank by hand with somebody looking to see if the rotory turns, and it turns like it should with lil to no slack. checked for vacuum leaks with carb cleaner and no was found. any idea what am I not checking or missing? thank

[flyinlow]

Plug a code reader in and see what it says... 


OK,  seriously now a couple ideas.

With an assistant, fill a spray bottle with water, start the engine and let it warm up. In a shaded area or at dusk look for arcing wires ,coil or cap. Put the car in drive and put a slight load on it. Spray a mist of water on the wires if necessary to help show trouble spots.

An EGR valve not seating can cause missing. Unplug and try. Remove the valve and put a piece of shim stock between the valve and the intake ,blocking the ports.

[stingger68]

checked EGR and checked wires still same.  I replaced the 2 barrel Holley with a 4 barrel Holley 600 and it runs better but still has a mis.

[charger1972]

Do a compression check . Could be mechanical , chipped or burnt valve ........

[flyinlow]

A compression check would be a good idea at this time.

Also a vacuum reading at idle and cruise would help.

I assume when you went from a 2bbl to a 4bbl you changed intakes and all the gaskets are new and seal well. You also adjusted the idle mixture for best vacuum and rpm.

Plug every vacuum line one at a time to see if that changes thing. This would include the power brake booster and charcoal vapor canister if still installed.

Are you running vacuum advance with ported vacuum, not manifold vacuum. Try disconnecting the vacuum advance and see if that helps.

Is the ignition timing set correctly and does the engine make good power at wide open throttle?

[stingger68]

For now I'm just using a 2 to 4 carb adapter. I'll check all the rest again this week and get back to yaw on it thanks

[charger1972]

I doubt it`s the cause of your problem , but a 2 to 4 bbl adapter is a bad idea performance wise .

[stingger68]

I had this issue before I put the adapter. I put it to rule out the 2 barrel carb being the issue.

[moparnation74]

Many simple tests to do.

Determine spark at all cylinders.  Check gap in your HEI distributor.  Test your coil.

Then move to your vacuum tests. Compression check etc.

Make a checklist and post it here.  There are some very knowledgeable guys here but they will need more info.

[68 RT]

Burnt valve? Worn cam lobe?

[stingger68]

I'll make a list. May be a few days got stitches in my hand and rain is here for the week

[stingger68]

I had time today to play under the hood and recheck everything, then it hit me  I never adjusted the 4 barrels air/fuel mix  its running like a champ now. thanks so much for you guys help on this. I thought I did that the day I replaced it buy guess I missed it.