1954 Blue Flame 6 missing under load


Hi There,
I am having trouble with my 1954 Chevy Belair Blue Flame 6 missing, at high RPM, when I accelerate. I have the original 6 Volt electrical system with the Petronix point system. I am running with AC Delco R43 plugs gapped at 35 thou. I have cleaned and checked the plugs, checked the condition of the spark plug wires and changed the coil, but still have the same problem. I have also checked the timing, and falls into the normal spec. There is no engine miss under light acceleration or normal driving speed 55-60 MPH.
Are there any thoughts out there?
Thank you in Advance


@kimlynnsharpe - Could be a fuel issue. You were smart to start with ignition though.

If the jetting is off and the truck runs too lean or too rich at high rpm it could indeed cause a misfire. Sufficient fuel flow at lower rpm and idle would explain why it only appears under high rpm situations.


I have that engine but not familiar with the Petronix system. Does the Petronix system just eliminate the centrifugal advance but still use the vacuum advance? If it does, then it sounds just like an issue I had some years ago when my vacuum advance went bad. Otherwise check fuel delivery or something really worn on the distributor itself. And I’m not sure how they set gap on the Petronix…seems like that could cause similar symptoms.


@Jim-R - Pertronix shouldn’t require gapping. I believe the Pertronix can be either a hall effect sensor or a lobe sensor, neither of which are gap dependent like points. One of my initial thoughts was worn distributor bushings, something that rarely gets checked but can wreak havoc since the problems can be intermittent and hard to replicate sometimes. might be worth removing the distributor cap and seeing if the rotor has any side to side motion.

Low voltage can also cause problems at higher rpm. Grabbing a multi-meter and checking voltage while running and making sure it is within spec is an easy check too.


Does it still use the vacuum advance for higher rpm like OEM?


@Jim-R - With little research to confirm my hunch, I found Pertronix is simply points replacement in most cases. Meaning if the engine is set up with vacuum advance it is best to continue to run it (assume the Pertronix is the only change.)

Of course, you can always block off the vacuum advance, Typically only a good fit for performance situations though, not needed for a street engine.


Hi Kyle,
Never thought of trying to block off the vacuum advance. Maybe will try that and see if it is any better.


If that doesn’t help you might want to keep it. As I recall that is for high rpm. The diaphragm, or the line might be bad. But it’s an easy and relatively cheap fix.