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BJ8 Vacuum Advance - disconnected -RIGHT - when setting total advance??


Senior Member
I just need to get expert clarification. The vacuum advance for a BJ8 (64 PH II) is to be disconnected and plugged when setting the maximum advance of around 35 degrees at >3000RPM and 15 degrees at 600-700 RPM at idle, tickover or whatever it is called.



So follow up question with vacuum advance connected and working properly what advance should one see at idle and at >3000RPM??

Jim 58 BN6

Jedi Trainee
Well, expert is a relative term, but in general, here's what I would do:

1. Vacuum line removed from the distributor, and the line plugged: Set the timing at idle, then check the distributor's mechanical advance at >3000RPM.
2. Reattach the vacuum line: Check the TOTAL advance at >3000RPM, which is the sum of the idle setting, mechanical advance and vacuum advance.

I hope someone can chime in with a Healey specific answer to your second question, but I think the total distributor advance at >3000RPM is about 20 degrees, and that's in addition to the idle setting of 15 degrees, so 35 degrees total. If the vacuum advance line is connected when you check the timing at idle, then it might give you an incorrect, slightly higher reading. GL, Jim


Senior Member
Follow up,

Got a cheap Harbor Freight Advance timing light for $29.99 less the 20% and free flashlight, to double check my 40 year old Craftsman light. The HF light work very well (at least for now).

I have 15 deg at 650 RPM vacuum disconnected, and around 35 deg at over 3000 rpm vacuum disconnected and plugged.

With vacuum advance back in service, I still have around 15 deg at idle, and now just over 40 at over 3000 rpm.

Do these numbers make sense for a freshly rebuilt 64 BJ8.


Jim 58 BN6

Jedi Trainee
I think they're close to the specifications. At this point, drive it, and see if you experience any pinging when the engine is under load. If it pings, retard the timing a couple of degrees at a time until the pinging stops. The timing shouldn't require much readjustment at your current setting. If you can only get low-octane gas, then you may need to run it with the timing a bit retarded anyway. This technique is simple, and has always worked for me. Jim


Country flag
...With vacuum advance back in service, I still have around 15 deg at idle, and now just over 40 at over 3000 rpm.

The factory manual: General Data pg 12 says "Maximum Advance.....35 deg (Crankshaft) B.T.D.C" -- therefore I think you should retard your distributor slightly to 35 degrees with the vacuum connected.

Assuming since they didn't say disconnected vacuum at the maximum advance - that it should be connected as per normal driving.

The stock pulley is 6.25" D. Therefore 35 degrees is 1-7/8" BTDC; 32 deg is 1-3/4 BTDC. I trust my old Sears non-adjustable timing light more than the HF adjustable which had a floppy knob on it.


Senior Member
I rechecked everything and both the HF light and the old Sears match.

The final numbers are

Dwell 33 deg point gap .016 engine totally fresh with less than 200 mi since rebuilt.

Vacuum disconnected and plugged Idle (650rpm) 15 deg BTDC >3000rpm 31-32 deg
Vacuum connected Idle between 15-16 deg >3000 rpm 35-36 deg

Dizzy is a 25D

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