Misfire at cruise, popping/afterfire at 3000RPM
Here's why its critical to plot the timing from as slow as the engine can be run to rpm it appears to stop advancing.
Let's take a look a the initial timing of 1967 Plymouth 440 Hi-Po and how it works with mechanical advance.
The Dodge FSM says initial should be 12.5* BTC at 650 rpm. Look at this with specs for the mechanical advance.
If we had that distributor and measured the timing with increasing rpm we'ld get a plot like this.
But if we accidentally had been given the distributor intended for the '67 440 with Clean Air Package, we'ld get a plot like this.
That's because the advance in that CAP distributor was set up for an engine with inital of 5* BTC at 650 rpm.
Since your distributor is an unknown, you'll have to measuring the timing from lowest to higherst rpm you are comfortable doing.
Another approach to setting timing is to set it at a moderately high rpm, and then see where the inital ends up. Even with this method, while it will give better driving performance, it still will be really helpful to know the advance curve.
Here's why its critical to plot the timing from as slow as the engine can be run to rpm it appears to stop advancing.
Let's take a look a the initial timing of 1967 Plymouth 440 Hi-Po and how it works with mechanical advance.
The Dodge FSM says initial should be 12.5* BTC at 650 rpm. Look at this with specs for the mechanical advance.
If we had that distributor and measured the timing with increasing rpm we'ld get a plot like this.
But if we accidentally had been given the distributor intended for the '67 440 with Clean Air Package, we'ld get a plot like this.
That's because the advance in that CAP distributor was set up for an engine with inital of 5* BTC at 650 rpm.
Since your distributor is an unknown, you'll have to measuring the timing from lowest to higherst rpm you are comfortable doing.
Another approach to setting timing is to set it at a moderately high rpm, and then see where the inital ends up. Even with this method, while it will give better driving performance, it still will be really helpful to know the advance curve.