308 breaking down at 4000rpm

When the throttle microswitch on the pedal (or the throttle mechanism if US version) is closed (idle), this connects its base structure of the R2 point assembly to ground, and the ignition won't fire until the R1 point opens and the R2 point opens (which occurs a little after R1 opens if all is adjusted correctly).

When the microswitch is open (anything just above idle, if adjusted correctly), that side of the R2 point is always not ground, so the R2 point is always electrically "open", so the ignition fires whenever the R1 point opens (and it doesn't matter at all what's going on at the R2 point -- it could be open or closed or missing and it wouldn't make any difference).

Since you have the trouble at 4K RPM, your microswitch should already be open, and only the R1 points might be causing your runability problem (i.e., the mechanical adjustment of the R2 point does not affect running at all -- even if wrong -- when the microswitch is open).

If you are unsure of the microswitch adjustment or if it is working properly, just unplug the wires (simulating an always open microswitch which makes the engine run only on the R1 points) -- if that still gives trouble at 4K RPM, it shows you have a more basic ignition problem with R1/coil/cap/rotor/rotor phasing/etc. and need not worry about the R2 stuff yet. Are you running the larger width 308QV dist rotors or the stock dist rotors?

 

Steve- Great description of what the second set of points does on an eight lobe distributor. Retarded the timing for improved emissions, IIRC. Took me a long time to figure that out on my 72 US Dino 246GT with two sets of points and a six lobe distributor. My 78 Euro 308GTS had electronic ignition which was very reliable and low maintenance while I had it. Is it difficult or advisable to swap out this igniton system for older Dinos/308s or is there a better alternative?

Taz
Terry Phillips

 

Before condemning the points themselves, I would look at the entire system. Are the plugs non resistor type? NGK BP6ES are the most common plugs used, just make sure they are not BPR6ES, the "R" means resistor. Do you have the correct black colored extensions? The red ones are for the later Dinoplex cars and have resistance. Test the plug wires for resistance and inspect both wires and extensions for cracks, damage, burns, carbon tracks. Inspect the cap for same damage as well as the carbon brush, and the rotor. Also check carefully the coil wires in the same way as the plug leads, they work 4 times harder than the plug leads and are usually the first to break down. While the leads are off and you have the ohm meter handy, check the resistance in the coil windings primary and secondary circuit as well as good voltage at the coil + terminal. While your in there, most autoparts stores have condensors you can use, any four cylinder points condensor will work. There is a way to test them, but its simpler to just replace them. If you want specifics, the originals are 500v rated .25 mfd. The correct points ignition leads should be solid core wire and should measure approx., 400 ohms per foot.

Points ignitions are very sensitive to increased resistance in the high tension side. Any electronic ignition on the market installed on a sputtering points car will push through poor wires and plugs and make the car run perfectly, the points ignition will see the problem much earlier. High rpm breakup can be caused by anything, you have to inspect all of it to isolate the cause.

 

Taz -- The difficult part is defining "better" (and tastes vary). Certainly, many R1/R2 equipped F get modified to using an R1 only system by either just using the R1 point only or replacing the R1 point with some other "single firing event" system -- which works fine, and gives the advantage of simplicity; but IMO, a working R1/R2 set-up is not a negative in any way. One thing I personally don't like seeing is a lot of (obvious) electrical changes added into the engine bay so if I had a Driver 246/308 I'd lean towards the Permatune (in the cap) system if going to an R1 only non-point based system -- but that's just my thing.

 

Steve- Thanks. I note some of the after market ignition kits come packaged in a pretty good imitation of a Dinoplex unit. I agree with you on keeping it as stock looking as possible.

Taz
Terry Phillips

 

Glad that you got it sorted (and your results just show, again, that the lesser complexity of an R1-only system is easier to deal with), but, if removing the R2 had this beneficial effect, you must have had a basic wiring error rather than just an R2 mis-adjustment. But just a side comment...