As a matter of fact, I did get the HEI on the tractor. The centrifugal advance weights "grenaded" and turned the distributor cap into shrapnel at about 4700 rpms. Not to worry, it was the integral coil cap and the associated module pack from the other distributor I bought at the salvage yard. No lasting damage was done to any of your components.
However, I am having loads of problems with the vacuum advance mechanism. I am more than curious at as to why you relocated the advance tab on the magnetic pick up ring. When I hook our engine up to the vacuum advance-it advances way to far and kills the engine outright at an idle. On the other hand, if the initial timing is set to run with the vacuum advance hooked up - it retards so much under acceleration it pops and snaps like crazy being severely retarded.
I also hooked up the advance pot to two different locations to check response. By running a line from each carb (ported vacuum) into a "T" then to the advance, I get no vacuum actuation until the engine reaches about 1200 rpms - then it slams the pot with 20" of vaccum. This sends the distributor into a radical advance all at once causing it to miss and snap. This is an addition to the initial advance plus the minimal mechanical advance. The total vacuum contribution is beyond what my dial can read on the timing light - WAYYYYY too much.
When hooked to the manifold vacuum, it is virtually sucked shut in the advance position right off the start. With the initial timing set at 0 degrees (absent vacuum advance being hooked up) the addition of vacuum advance sends the timing immediately over what my timing dial can read at 500 rpm's - killing the engine outright. The manifold vacuum on this engine at idle is 15".
So, it wasn't a throw it in and off you go situation. I think there is a different way to tailor the vacuum advance range other than relocating the pickup tab. Also, a means of limiting the degree of advance/retard by using movable stops.
It may take some time, a little head scratching, and researching - but I'll get this ironed out one way or another.
I do like the potential here, and I'll share a few of My observations thus far. The electronic adapters attempt to work as the points previously did, however the magnetic field/electronic impulse is limited by the distance the signal can be sent. The old point type distributors rotated the point assembly to effect a change in timing. The electronic devices can't adapt to this very well outside about a 16-18 degree movement.
The HEI distributor on the other hand effects the mechanical change in timing by moving the rotor assembly only, leaving the magnetic pickup alone and using it soley as a location device related to crank position. The vaccum advance is attached to the magnetic pick up assembly and necessarily needs to be limited inside the allowable range of signal from the magnets. A huge range in total advance is possible in these distributors, tailoring the curve and total timing to your specific requirements seems to be the challenge.
In addition, the late model "990" non-computer controlled GM module is about as good as it gets in terms of timing controls. The microprocessor in this chip is able to reliably run a 6 cylinder up to about 7500 rpms from what I have read. The addition of an aftermarket coil can run voltage up to 50,000 volts. The "990" module coupled with a good aftermarket coil shows the maximum benefit in terms of horsepower gains. MSD controllers have nothing to add to this setup in terms of spark energy or the ability to ignite the fuel charge under demanding conditions.
I may not have my exact application lined out yet - but I like the potential.
Hudson
