Thread: Small miss in 350 SBC

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Have a 76 Camaro with 350. I am assuming it's a 70's motor also.
It has been garaged about a year but started up monthly. Last Fall
was running just fine, but now will not idle at 800 RPM. It's stock.
Changed plugs, dist cap and rotor button. Has HEI dist. Changed carbs, checked for vacuum leaks but no change. Will idle about
1200 RPM, but has that small miss. Checked compression and
110 on all cyls.
Have not changed plug wires or coil in HEI, but plan to change wires
this week. What am I missing here. Buffaloed

Have you checked the fuel filter? Sitting idle leads to phase separation in ethanol blend fuel, which makes the fuel extremely aggressive to rubber, and by absorbing moisture from the air can rust up your tank, too. Thinking it might possibly be a lean miss as opposed to a spark miss? Just a WAG, actually.

Forgot to mention did put on new fuel filter.

have you inspected the vacuum hoses?

I have sprayed carb cleaner around all vacuum connections and carb
base as well as intake with no change in engine sound.

When your checking vacume issues on these series cars, don't forget to check modulator lines at transmission---------

It's a Muncie 4 spd manual.

When you say it "...won't idle at 800rpm... " but that "...it will idle about 1200rpm" does it falter and die below 1200, or how does it perform? Seem like it's running out of fuel, or is it like turning off the key? Manual fuel pump or electric? Did you verify fuel level in the float bowls?

Sorry for multiple questions, but it's a head scratcher....

Will not idle under 1200 RPM but falters and dies. It's still got the miss
at 1200 rpm. Manual fuel pump. Carbs have been completely changed
with no difference, so I'm leaning toward something beside carbs. It does
have a 6al MSD box on it. Would that give any reason for sporatic miss?
As mentioned in original post, this just started within the last 30 days.

Did it do this before you changed plugs, dist cap/rotor, carb???????


If it has only done it since you changed plugs, cap/rotor--------check out the order of the plug wires--not only at the cap, but in the proper order and location-It is not unusual for a novice to mix up some or all of the wires-can be just a couple switched, all put on cap starting wrong place, wrong rotation. Chev common to have # 1 & 2 mixed-also at plugs easy to cross wires as each pair on a small block are equal

Originally Posted by jerry clayton

....It is not unusual for a novice to mix up some or all of the wires-can be just a couple switched, all put on cap starting wrong place, wrong rotation. Chev common to have # 1 & 2 mixed-also at plugs easy to cross wires as each pair on a small block are equal

Another way to say that is that it's not unusual for an experienced mechanic to mix up the wires, either on the cap or at the plugs..... It never hurts to check for the easy things.

Another thought, what brand plugs did you put in? Many today are made in China sweat shops, and it's not uncommon to get a bad one (or more) in a set. AC is one that used to be top quality, but have seen problems in recent years. I use NGK's now. Same on the new cap? Accel is one that has seen more than it's share of crappy parts, to the point that many won't trust anything with their name on it any longer. Again, just a thought, just trying to help.

Thanks for help. The miss took place before I changed out anything. Plugs
are AC Delco. Engine is timed and wired properly. Will let you know the problem
when and if I find it.

Originally Posted by rdobbs

Thanks for help. The miss took place before I changed out anything. Plugs
are AC Delco. Engine is timed and wired properly. Will let you know the problem
when and if I find it.

Rdobbs, I'd seriously consider buying another set of plugs to replace the AC Delco's. I could post the YouTube video of the Chinese sweat shop where they have a bunch of people assembling plugs and throwing them into huge bins when "done", but suffice it to say that AC Delco's QA/QC process on spark plugs is not what it used to be. It's not at all unusual to get a bad plug in a set these days.

Do you have one of these, link below, that you can point at the exhaust manifolds and try to pin point better which cylinder(s) are missing? That'll help you determine which plug could be bad. Shoot, a friendly mouse could have made a nest in there and be blocking intake passages not allowing gas and air to get to the cylinder. Those stupid things can get a lot of places a person wouldn't think they can.

http://www.amazon.com/HDE-Non-Contac.../dp/B002YE3FS4

Ditto on what Roger said. I like - Autolite 24 - .460 reach, 14mm tapered seat for most every 350 with stock heads. Run them and pull one out and look at the tip - should be a nice ivory to caramel color. If it’s dark, go to a 25. If it’s real white or pitted, go to a 23.