Got a miss

[64von]

Good morning
I have a 1964 with a miss. Rebuilt carburetors , brand new electronic ignition and each cylinder has 100-120 psi You don’t notice it at idle but when you rev it up you can hear it. Thanks in advance


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[66vairguy]

Based on your statement there is NO misfire at idle. If you have dual exhaust you can identify which side of the engine. If you can do that then a carburetor side to side swap will tell you if it is a fuel issue.

One thing NOT to do is pull each plug wire to isolate a misfiring cylinder at low RPM. This is an old diagnostic process and is fine with points, but it tends to damage electronic ignitions unless you ground the spark plug wire.

Sometimes electronic ignition failure results in intermittent spark plug firing. Depending on the type of ignition putting a set of points back in will tell you if it's the electronic unit.

If the misfire only happens under load, then an examination of the spark plugs would be in order.

[64von]

Thanks for the info vairguy. I only have single exhaust. May check with a heat gun


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[terribleted]

If you are talking about a spit or pop when holding the rpm's up above idle it could indeed be a basic misfire from a bad spark plug wire, or plug, or timing, or a valve or valves sticking or a little tight, or carb issue. If the car has dual exhausts you can usually isolate such a symptom further to one side of the engine or the other. You can usually feel a misfire as pulses in that tailpipe. If with duals it only does it on one side you eliminated the other other side of the engine and the distributor and timing settings as possible issues. If it is missing on both sides then it is likely not a spark plug wire or plug issue. If it is a single exhaust of course not much to be learned this way.

Your compression is on the low side. Not likely to cause a miss but under 120 usually indicates a worn engine. Around 100 all over the engine or multiple cylinders usually indicates time for rebuild or at least head job and re-ring.

[64von]

Has new wires and plugs and a brand new electronic distributor. Yes if you hold it a little above an idle is when you get the sputter.


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[terribleted]

Only a little above idle? It goes away when you accelerate the engine a little more? May just be the point where the vacuum advance is becoming active, or becoming inactive as the rpm increases. When you do this watch the vacuum advance arm. see if the sputter coincides with the vacuum advance either advancing or with the vacuum advance going up and then coming back down (vacuum advance is active just off idle and becomes inactive again as the rpm increases). Does it doe this noticeably when driving the car? If it is not noticeable while driving (engine under load) it may be a non issue. Is the distributor the correct number for the application? How about the vacuum advance number does it match the application? All distributor and vacuum advances are not the same.

[66vairguy]

Has new wires and plugs and a brand new electronic distributor. Yes if you hold it a little above an idle is when you get the sputter.


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Do you mean a NEW stinger HEI type distributor? If not what type of electronic ignition is installed.

[bbodie52]

A carbon track or hairline crack inside the distributor cap can also be the cause of a misfire. A burned rotor contact can also be the source of a misfire.

[64von]

This is the distributor. The miss was there before I put in the new hei distributor the same as it is now


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[masonjones5711]

Good morning! Since you still have a miss when you rev it up, I would suggest checking the spark plugs and wires, as well as the distributor cap and rotor. Sometimes, even with new ignition components, there can be issues with connections or quality that cause a miss under load.