Vacuum Advance Question - 1979 FJ40 Stock 2F Engine

Joined
Oct 24, 2015
Messages
208
Location
Clarksville, TN 37043
I’m not an engine guy so please bear with me.

I’m in the final stage (I hope) of restoration of my stock 79 FJ40. It has NOT been desmogded. It is still running a stock carb & distributor.

For the last two days I have been reinstalling new vacuum and emissions hoses. Trying to carefully check the service manuals against the photos I took during tear down and vice versa as the work progressed.

If I’m reading the schematic correctly then, based on my preteardown photos, it appears the two lines on the vacuum advanced got flipped, at the vacuum advance, sometime in the past.

I only drove the FJ40 for about 50 miles in the city before starting the restoration. The engine seemed to run fine.

Shouldn’t there have been some performance issues with the hoses flipped at the vacuum advance?


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Dizzy

SILVER Star
Joined
Feb 5, 2018
Messages
541
Location
Santa Fe, New Mexico
Those are the advance and retard functions of the vacuum spark timing on the distributor. I would not be surprised if there was no noticeable performance problem, but spark timing is important for efficiency and engine longevity.
 

1911

chupacabra
 
Joined
Aug 11, 2006
Messages
5,292
Location
Parker County, Texas
On your distributor, the inner vacuum line and diaphragm (closest to the distributor) is the main advance, and the outer one is for the High Altitude Compensation system. The outer HAC one adds an additional 6 degrees of ignition advance (on top of whatever the main diaphragm has already added), when you are driving above 3,930' elevation. The inner vacuum line should go to the advancer port on the carb, and the outer vacuum line should go to a T which in turn one side goes to a one-way check valve and thence to the intake manifold, and the other side goes to the big round plastic HAC valve. All this is well documented in the "2F Engine Emission Control Repair Manual". You can download the manual for free, here on Mud. If you can't find it, PM me with your email address and I will send you a copy.

Your engine will run with the vacuum lines reversed, but it will run a little better with them routed correctly (assuming that the vacuum diaphragms and the HAC system are all in good repair).
 
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