365 GTC/4 Ignition issues

Distributor cap(s), points and rotor(s). Sounds like she has the single distributor if you only have one of each. My old Daytona had two distributors and it was a 5 minute job to pull a distributor. A bit tougher with them (it) buried under the dash on the GTC/4.

Ignition advance weights could be sticking, too.

 

You would have to check the gap of the plug, take the proper heat-range (taking into account that the origonal champions ref is way to cold except for redline).

On my 400i my mechanic installed bosh plugs with regular tip but three ground straps. These do work quite well, even when running overly rich. Thin tips plugs were not as userfriendly when idling (once flooded they have to be replaced)

 

These types of problems are usually caused by lack of fuel or lack of spark. For your fuel system, did they replace all the filters? Check the fuel pump pressure? Set the float levels in the carbs? Clean all the screens in the carbs? For the ignition system, it's wise to overhaul the distributors and check the advance on a distributor machine. This is a process of elimination. You need to evaluate each component in the fuel system and the ignition system. A less likely problem could be a valve that is not completely closing. You can check this with a compression test of each cylinder.

 

Do you have the system with:

1 distributor (and 1 dist cap) and (4 sets of) points

or

2 distributors (each with 2 sets of points), a throttle microswitch (and "anti-hop device"), and 2 Dinoplex ECUs? (There's plenty to go wrong in this system ).

 

There's plenty to go wrong with each of those systems. A step by step analysis of the distributor(s) and setup on a distributor machine, will find and likely correct the problems.

 

Most fuel system problems are in the distributors.

Vintage 12 and early V8 distributors almost universally suffer from neglect.

Had a Daytona here wanted a carb adjustment. Dwell meter hardly read anything. I told him as soon as we adjusted valves and serviced distributors we can look into the carbs.
He took it to someone who would adjust his carbs.

 

Throttle switch input swaps to secondary retarded points when throttle closed.

Brief explanation from the dino section:

There is more information on function and adjustments for GTC4 in the factory manual "365 GTC4 Additional Instructions for the USA Version"

Anti hope device = Silenziatore antisaltellamenti microinterruttore p/n 350335

 

That should make things more simple to figure out. If the throttle microswitch is gone, you might want to physically disconnect the R2 points (although with no microswitch they should never activate unless something really strange happens like a chafed/loose wire shorts to ground or something gets physically broken). When you reported a shift in RPM that comes and goes, my initial thought was the R2 point function coming and going for some reason. One simple initial diagnostic step would be to measure the R1 point dwells at idle as Brian suggested just to see if they are quasi-reasonable or crazy (and crazy = needs repair/adjustment). You may have something else electrical going on since Dinoplex is involved .

I don't have the publication that Adam mentioned, but the anti-hop device is also shown on page 24 of your 63/72 OM. But as Adam noted, it's just shown as a "black box" and there's no text description of its operation at all. On later F models, with a throttle switch controlling the R2 function, they added a motion damper to physically slow the throttle plates from closing when near idle (so no such electrical anti-hop device present), but the description he gives makes a lot of sense to me for a throttle mechanism that can close to the idle position quickly when shifting. It's also shown on this US 365GTC/4 SPC page (item 15):

https://www.ferrariparts.co.uk/diagram/ferrari/365-gtc4/051-usa-electronic-ignition-air-pollution-system-oct-1972

 

Sorry, here is a link to a pdf version of the US supplement
http://365gtc4.com/library/#USAdditional

 

No.

 

It's normal for an old Ferrari with deferred maintenance.
Fix ignition problems first.
Carbs might need work as well, but you won't get anywhere fiddling with them with wonky distributors.

 

Check that coil to distributor wires are in spec. Check that connections between ballast resistor and ignition coil are tight. Mine were loose, which resulted in poor idle, spitting back through the carbs, and backfiring on decel. Once corrected, ran like a different car.
This, after carb rebuild and valve adjustment