Bizzare tach / starter short?

[Glen Getchell]

I am working on my Race Car (356 SC). Ran a race / test this past weekend and it failed miserably. Breaking up at higher RPM's. (which has me in a bind as I am scheduled to run a Hill Climb in NC in two weeks) I have replaced every ignition part in mass no affect. I have pulled the carbs apart, in fact one cylinder compression is not up to what it was prior to the race so I pulled the engine and jug to make sure I hadn't broke a ring. Nope, it all looks pristine (deposit on valve?). Anyway hoping for a magic fix I put it all back together and put the engine in the car. Deciding to take advantage of the A/C in the garage I did a compression test bone cold. Ya, no magic fix, but I know that the compression issue is not causing the engine to break up. Now you have the back story,

While testing the compression the starter acts like it is binding on occasion. Now this is not a new problem and over the years I have tried every thing to correct it (replacing starters, bushings, etc...). Usually it just means letting off of the starter switch (which is separate from the ignition switch) and hitting it again and all is fine. Well I noticed today when it acted like it binded the tach swung up. Now riddle me this. With the ignition off (The starter is direct wired to the starter switch). No, zero, nada power is going to any part of the car except the starter. So now riddle me this. Why would an electric tach jump when it has no electricity? And is this my breaking up problem?

Glen
64Cx2

[Mike Wilson]

I can't explain or surmise why an electric tach would jump w/o electricity. It must be getting current somehow. As far as the breaking up, my 356 had such a problem caused by a badly spliced tach wire intermittently grounding out. I discovered the wire when I removed all my wiring prior to a bare metal restoration. I had the same problem on a truck I once had. The previous owner had installed a tach and the truck would cut out now and then. Turns out the insulation on the wire from coil to tach had worn off and would ground out against the intake manifold.

Mike

[Doug McDonnell]

I would also double check the transmission to body ground. Your starter is grounded there.

[Glen Getchell]

What are your thoughts that might be wrong with the ground? Thanks!
Glen
64Cx2

[Mike Wilson]

Basically it could be a bad ground between the chassis and transaxle. Especially clean the area on the chassis to bare metal.

Mike

[Glen Getchell]

I'll take a look at it before it goes in the Hauler for the Chase the Dragon hill climb this weekend. (Oh please Porsche & GMC Gods, don't let the hauler break down with my wife & elderly dog on board! Please!!)

Pretty much narrowed the breaking up to carb problems. Must be crap in there some where. They looked clean, but the ole take apart blow it out and put it together magically fixed most of the problem (that is how I fix most things). Rotor seems to be getting 3% of the problem as well. (Have a new one on the way. That is kind of B.S. because it only has a couple races on it. Bosch is not what it used to be!) I would say that it is running at 97-98%, and that is going to have to do.

I swapped the starter out, and replacement does exactly what it has been doing for years. And when it sounds like it binds (which is on rare occasions), the tach swings up. I'm not sure but I would guess that it has been doing it for years. I never focused on the tach before as I was always trying to figure out why the starter does this (no its not the bushing). I just never actually thought about it till now. It makes no sense.

Glen
64cx2