Reese Neis

So we were trying to diagnose what was causing my 350 to miss we’ve already done plugs plug wire cap rotor timing adjusted the air fuel mixture and firing order is correct and it’s still missing yesterday while we were messing with it we pulled a plug wire while it was running and it didn’t run any worse we did this a few times on different cylinders and still didn’t run any worse so would it be something ignition related causing it to miss

olds 307 and 403

Make sure the ground strap was installed with the new cap and rotor. Hopefully a quality brass cap and rotor was used. Pulling a plug wire should make it run crappy. What spark plug gap did you use? Where exactly is the miss? It basically leaves the coil and ignition module.

Reese Neis

plug gap was 0.35

Vintage Chief

Does it miss primarily @ idle or does it miss through all RPMs? Curious if the miss is any different driving than idling etc. while working on the car or if the miss changes on the road under load. Is there any backfire when de-accelerating on the road?

Reese Neis

Through all rpms but no backfiring at all

Reese Neis

so I put a different coil in that I had in another distributor and it helped a lot but it’s still missing just ever so slightly so should I just get a whole new coil tomorrow or could it still be something else

olds 307 and 403

It shows it is ignition related, I like the Accel HEI Supercoil. All of them are Chinese these days. Try increasing your plug gap to .045" to .055", .035" is pretty tight for HEI.

7314haywood

Broken or weak valve springs? Just changed mine with new cam and 7 of the old ones had 40lb. Seat pressure and were about a 1/4 shorter then the others. Did not drive car previous but I'm sure it would of mis fired and no power

Tedd Thompson

Is this a point set up or HEI? if HEI I missed that post but if points it could be the condenser breaking down..... Tedd

olds 307 and 403

What did you set the base timing to?

cjsdad

I have posted this several times, but I once bought a Chebby pickup from a friend that had a miss. Did a complete tune up with plugs, wires, cap, rotor, points, and condenser. Adjusted the carb and timing. Still had a miss. Checked compression and all looked decent. Not great, but decent. Changed to HEI and adjusted appropriately. Still had a miss. Changed to an Accell HEI. Still had a miss. Long story short, I eventually replaced the heads, intake, carb and valve train. Still had a miss! So there I was, 5 days before driving over to California to help my Mom clean out the house after Dad passed, sitting in my living room floor muttering to myself about my antichrist of a truck. My darling Wife asks me if I changed the plugs? "First thing I did", I reply. "Change them again", she says, "they're cheap, right?" I went to Auto Zone and bought new Accell Rapid Fire plugs and the engine magically ran beautiful! I had swapped my "new" plugs from the old heads to the new ones and apparently they were bad outa-the-box. Three months I had been banging my head against the wall trying to figure out why a SBC had a miss after a full top-end rebuild. Get good quality plugs when you change them out!

70W-32

Besides plugs being made in China for the major manufacturers, there's also the issue of counterfeit plugs sold on Ebay and Amazon. Always check where the plugs are made, and where they're being shipped from, if applicable

ByronF

Like cjsdad I had a similar problem on my 77 Toronado. Drove me crazy for months. New pugs, wires ,cap, rotor, and coil plus 2 carb rebuilds and a new distributor replacing the old MISAR system. Managed to tone it down but still there sporadically. Finally in desperation had a local shop that has experience in these old beasts check it out and they determined the problem was a bad plug. Replaced all the plugs and voila! no more problem and running just fine for 2 years now. So try replacing the plugs, its cheap enough!