77 GTB Carb car ignition specs

I have a 7 carb car that is not revving well beyond 4500 RPM. I am trying to find the ignition specs for this car and I don't have the GT4 WSM anymore.

Is this correct?

1,000 RPM: 5 degrees BTDC
5,000 RPM: 35 degrees BTDC

 

Another question, who is selling high quality distribution caps now? (2 caps, 4 terminals each). I had four from one vendor that did not work well. Terminal 3 did not make continuity with the wire.

 

Those timing numbers aren't crazy for a 1977 using R1 points only, but maybe:

1000 engine RPM = 7 deg BTDC
5000 engine RPM = 35 deg BTDC

You can get a copy of the 308GT4 WSM here:

https://www.dropbox.com/scl/fi/g1eldf93xydo27acwn2jv/308GT4_workshop.pdf?rlkey=5bxdrp2drax9hp61yrlfv2kza&st=b6v8zp5l&dl=0

(but use the ignition system information in Section O for an S159B dist advance curve US version (not section L for a euro version with the S159A dist advance curve).

Have you updated to the much wider tip 308QV distributor rotors 124288?

 

Well, it does not have any points. It does have Pertronix pick ups (2) inside the 1 distributor, and the two pairs of wires coming out to the two coils. There is a second distributor to act as a spark delivery vehicle for bank 2.

 

That's still an "R1 only" set-up (i.e., only one thing firing each coil).

 

Alright @Steve Magnusson

Here are the updates, for your comments:

1. The car is now set up for 5 degrees BTDC at 1000 rpm, and 30 degrees BTDC at 5,000 RPM. It will not advance more than that. Leads me to believe the distributor either is bad or needs calibration with a Sonex machine nobody has anymore.
2. The car will rev past 5,000 RPM at higher speed (50 mph or more).
a) once past 5,000 it will pop out of the exhaust on acceleration side, but will not pop on deceleration side. Leads me to believe the carbs are running rich with the main jets / emulsion tubes
b) sometimes on shut down, there will be slight to medium back fire out the exhaust. Leads me to the same conclusion as above.

There may still be some ignition issues. The old ignition wires were just replaced, new rotors (with wider blades) replaced, but I am unable to find any good distributor caps. My usual go to source of reproduction caps crapped out with one of the four ignition contacts. So I am still using the old caps with some of the plastic encapsulating the contacts breaking off.

What do you think is causing the pops at >5,000 rpm ?

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1. 30 deg total at 5000 engine RPM is pretty wimpy. Is the advance mechanism in the other distributor any better? I'd swear that there were several recent threads mentioning places that could deal with checking/correcting the mechanical advance distributors (but that's your homework to find ).
2. What do you mean by "at higher speed"? Are you saying that it won't rev beyond 5K RPM just stationary in neutral?

 

No, it revs just fine beyond 5,000 rpm in the garage. That is how I checked the advance at 5,000 RpM.

 

A question for you.

If I set up the engine to run at 10 degrees BTDC at 1,000 RPM (By messing with the idle screws), will the dizzy get to 35 degrees at 5,000 RPM?

 

Yes, it should -- the advance change from 1000 RPM to 5000 RPM should be the same regardless of where the 1000 RPM idle timing is set (but you seem to have some more general runability issue).

 

https://www.marellidistributorservice.com/

 

I think I might need some new main jets .... Maybe one size smaller.

 

If you can't get to 10 deg. Adv. with the distributor you need to move it 1 spline on the drive.

 

Sorry...BTDC not Adv.

 

I have the same pertronix in my 308. When I set timing I set it to 34-35 degrees at 5000 rpm. As these were US distributors with an advance curve around running the two points system, I found this leaves me at 9-10 degrees at 1000 rpm. Mine revs clean all the way up. The only thing I find is that it takes a tad longer to start than when it was on its original points with less timing at idle but no big deal. I would try advancing your timing. I set it at 5k and just verified it at 1k as the timing on the high end is more critical. Btw if you haven’t done it, take apart your distributor and clean and lube the advance mechanism. Mine was really gummed up but after a nice clean, the advance is clean all the way up when checked with the timing light and there was no need to send it out to have the advance curve calibrated.


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Would the lack of timing advance at 5000 rpm cause the popping in the exhaust symptom?

 

Retarded timing can. I’m not sure if 5 degrees is enough to cause this but it’s possible


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Update:

I advanced the car at idle to 10 BTDC and now the engine will advance to 35 degrees BTDC at 5,000 RPM.

The popping still happens at above 5,000 RPM on the acceleration side (foot on pedal), but not on the deceleration side (foot off throttle). I think at this time, I will have to experiment with main jets.... I think the ignition issue is resolved.

 

Info starting at post #277, may or may not be of help...

https://www.ferrarichat.com/forum/posts/136295538/

 

It does now rev past 5,000 RPM with the advance at 35 degrees so I don't think it is ignition anymore.

At this point, since leaning on the gas at 5,000 RPM causes the popping and letting off the gas the popping goes away at 5,000 RPM, I am looking into lean running due to fueling issues. I am changing the fuel pump to a proper fuel pump (Ricambi) and will look at the carb's bowel level next. If that does not work, I will experiment with main jets when I can get my hand on a set of new jets.

 

So now you get to 35 degrees adv. at 5,000 rpm on both distributors? You still have coils, don't you? How old are they?