Flathead Crab distributor with pertronix and correct coil. No ballast resistor. Vacuum brake hooked up to manifold vacuum. Edelbrock slingshot intake with dual 97's. Edelbrock heads... 6 volt pos ground. Runs good, maybe a bit rich but knocks under load/hard acceleration. New to all this. What should I be looking for or try?
Running too much total advance can cause it.Low octane fuel can cause it.The flathead can have a problem all its own....on some heads the plug doesn't thread deep enough.This leaves the last couple turns of thread in the head exposed as a sharp edge.That edge builds carbon,and becomes a hot spot.You would have to pull a head to check this.Aluminum heads are prone to this.One cure is machining a "pocket" around the plug tip to open a flame path to the chamber.It also removes the unused last turn of thread.If you don't have a couple books on flatties buy them.I just got one by Frank Otto,and he has pictures of what this looks like.One last thought...do you get it out on the highway,and open it up to blow out carbon deposits which can cause hot spots? Cruising around town at 25 mph a lot can cause carbon.
Definitely not saying this is your problem. But This past year I’ve notice slight pinging on my 8ba. Haven’t had this issue for the 15 yrs it’s been installed I used Marathon gas. Had a friend complain about issues on his car and decided to try another type. It stopped immediately. Regular gas
Just getting it on the road. It was a used engine that had been freshened up by previous owners mech. (He ended up putting a OHV eng in instead when street rodded) I added intake, carbs, and dist. There is no timing mark on crank. With pertronix is the vacuum brake supposed to be used or not?
1st I think you need to find TDC ( top dead center ) & check your timing. Mark the damper. Does your fuel have any alcohol in it - helps bump up octane to avoid ping especially if u think running rich. How did u set timing? Try retard spark to avoid ping.
Excellent advice. Depending on the severity of the pinging, I might just try higher octane fuel first. Not likely to be hot spots since it only happens under heavier load. Compression is unknown of course, but not really likely to be an issue on a flattie unless it was increased a lot. Advance and octane are the only variables here.
Try screwing the vac advance bolt in a half turn and give it a go. Then try another. Report back to us.
Been over 50 years since I touched a flathead, and the ones I had were either 8ba's or had the old 3 bolt "diving bell" dist. The 8ba's weren't the "crab" design, but gear driven and angled up to the front and were more conventional in that you could rotate them to adjust timing. And I don't remember any of the front mounted, whether crab or diving bell type being rotatable to adjust timing. But as I said, it's been a long time! I do remember, as Alchemy said screwing in on the adjusting screw on the vacuum brake pushed on a spring, and the more you pushed on that spring, the more vacuum it took to pull back that piston to allow the weights to swing out and allow the dist. to advance further. And I don't remember the pre '49 models having any timing marks on the front pulley, as there was no need for them with a dist. that was non adjustable by rotation.
Been 50 years for me also. Owner added distrib, how he set initial timing & what is start up & advance timing now? I would want to use timing light to check. Is engine rich or burning oil under load? I remember getting engine hot, up revs & pour little water down carb to “steam clean” cylinders blow out carbon. May be old wife’s tale but did it on old 6. Anyone else? Believe new products sold with same claims. Maybe not for modern engines
Take it out at night , run it up to 90 and drop back into second gear and let up on gas . when you see sparks flying out of exhaust it either carbon or piston rings !
Vacuum advance is adjustable , by shims or screw adjustment , daily it in and your problems will be a memory
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