Does a 77 C3 have a port to check dwell?

[Bill Jennings]

Hi All,

Saw a post in here identifying a port for checking dwell I think on a SC would my 77 SC have this as well?

Cheers
Bill

[timmy2]

I believe the port you are talking about is for the Jetronic system. You need to check your dwell for your points the old fashioned way.

[Bill Jennings]

Dennis,

I think I may have been having a Crown Royal Moment!

Been looking at all aspects my timing which I cannot adjust to idle timing because the distributor will not move far enough.

Think the PO may have installed the distributor one tooth out.

Cheers
Bill

[Bill Verburg]

Originally Posted by Bill Jennings

Dennis,

I think I may have been having a Crown Royal Moment!

Been looking at all aspects my timing which I cannot adjust to idle timing because the distributor will not move far enough.

Think the PO may have installed the distributor one tooth out.

Cheers
Bill

It's easy enough to install it correctly
1) rotate the engine by hand to TDC compression on #1 cylinder, when the pulley is at the TDC mark, either #1 or #4 will be at TDC, make sure that it's #1 at TDC

2) pull the distributor and reset w/ the rotor pointed to where where the #1 plug wire will be

[Bill Jennings]

Thanks Bill,

As always a concise informative answer.

Will report back.

Cheers
Bill

[Bob Kontak]

Bill V,

I am chatting with Bill J and tirwin regarding distributor timing and vacuum units (SC vs prior)

I remember you clarifying in a thread a few years back that pre 78 vacuum units provided a retard function and not advance. If Bill J's 77 3.0 has a vacuum retard, and it is similar in operation to the SC's retard, his vacuum hose should be "sucking" at idle vs being delayed?

Given the 5 ATDC timing point with hose connected, seems there should be vacuum action at idle. Bill mentions that he can feel no suction on the hose at idle but can move the plates by sucking on the hose.

[Bill Verburg]

Originally Posted by Bob Kontak

Bill V,

I am chatting with Bill J and tirwin regarding distributor timing and vacuum units (SC vs prior)

I remember you clarifying in a thread a few years back that pre 78 vacuum units provided a retard function and not advance. If Bill J's 77 3.0 has a vacuum retard, and it is similar in operation to the SC's retard, his vacuum hose should be "sucking" at idle vs being delayed?

Given the 5 ATDC timing point with hose connected, seems there should be vacuum action at idle. Bill mentions that he can feel no suction on the hose at idle but can move the plates by sucking on the hose.

The '76/77 C3 used a distributor vacuum setup that retards the timing at idle, this vacuum retrd goes away as the throttle is tipped open and at wot there should be no vacuum and thus no retard

When adjusting in the garage the idle timing is set w/ the vacuum connected engine at nominal operating temp and 900 rpm idle, under those conditions 5° ATDC is the timing target, if the vacuum hose is detached timing should advance( I forget by how much)

To check max timing the vacuum is disconnected 32-38° BTDC by 6000rpm

[Bob Kontak]

Outstanding. Thank you.

This helps confirm the one tooth off hypothesis Bill J is thinking may be the case.

FWIW, the SC is set at 5 BTC and then the retard hose pulls mine 10 degrees after hook-up. I have read others say not quite as much but 5 degrees retard minimum.