1974 Valiant Scamp, timing retarding when revved

And if it persists or if the timing lite shows dropped sparks, swap the clamp over to #6. If same going on here then I would reverse the polarity on the pick-up coil. I have seen that a few times.
I made my boss $1500 on a motorbike once, that was doing this.It seems several other techs had worked on this bike and had changed about everything electrical that could be changed to no success. Well unbeknownst to me, the customer and my boss haggled out a deal for $1500 if I could fix it. It was doing the same thing as your car, but I didn't know it yet. It would only rev to about 3500rpm and then it hit a wall, running progressively worse as it got there, kindof like it was running out of fuel. When I sawed on the throttle sometimes the Rs would take off like normal. Well if you know anything about motorcycle CV carbs this is almost a sure sign that there is something wrong with the carbs.So I went and asked my boss "Anybody have the carbs apart?"to which he replied yes a couple of other techs had had them apart and couldn't find anything wrong. So I pushed it into a corner (this was winter work), and carried on with other things and let my brain mull it over.Did you know that the brain can figure out stuff even at times when you are not in charge of it? Well, mine does anyway.
Well a couple of weeks go by, and the idea comes to me to put a timing lite on it and low and behold, the timing is going backwards, and forwards, and dropping sparks, and just generally misbehaving. So I go ask my boss, "anybody been working on the electrical?" to which he replied yes. In fact the entire wiring harness had been changed and every sensor on it.And the EFI computer too.Ok I said and pushed it back in the corner, and continued with other projects.
Well a few more weeks go by, and one day a memory comes to me. A couple of years earlier I had a pick-up coil fail on me in my FormulaS. After I replaced it with a good used one (from the glovebox where I used to carry spare electrical stuff), I fired it up and set the idle timing, and like a good little boyscout I went to check the power-timing and there it was; all this misbehaving.Well after a lil headscratching I got the idea to reverse the polarity of that pick-up coil and presto, back in action. I had forgotten this little nugget. But my brain had obviously filed it somewhere.
So this God given miracle of creation,brain of mine,hauls out this memory and parks it a lil closer to where I can see it. Well I said stranger things have happened.
So I ask my boss," has this here sensor been changed", to which he replied that he'd have to call and find out. So I push it back in the corner, and go back to other projects; winter work in a small community is like that. In order to not have to lay me off for lack of work, my boss used to bring in winter work at a much discounted rate. It was my idea actually but that's another story.
So a few weeks go by, and the answer comes back; yes all the sensors were changed and this particular one more than once. Ok I said, and return to my work area.So now it's getting close to spring, and my boss still has not told me about the deal.
So now I got nothing to lose. That memory is prodding me. So I pull that mean machine out from it's resting place, blow off the dust, and pull up a chair and a wire stripper. A few minutes later, I hit the key, and it springs to life same as usual.So I let it idle to warm up and carry on my business, I got other projects on the go, don't you know.
Well after a while I come back to it and roll into the throttle a bit, not knowing exactly what to expect. But Huh, it takes the throttle, so I twist it a bit more and Huh,it takes that too. So I put the light on it and sure enough the computer is advancing it exactly as it is supposed to! Nice work!
So I get to sawing on the throttle, cuz I know the boss is around and he's getting anxious to see this thing out the door,and he knows the sound of this old girl.But he knows how I work, so he's being patient(we have by this time, about 20 years of time spent together). So all of a sudden he comes bursting into the shop, to see what the heck I'm doing, and finds me sawing on the throttle and the engine is responding as if nothing had ever been wrong with it.
Well that guy is beaming.
Now he tells me the backstory.
I finish the repair with solder and shrink tube,polish up the bike and finalize my time spent. He gives me a pat on the back.
Life is good.Spring is here.