Vacuum Advance Question

gearheadgreg · gearheadgreg's Garage

I've got 1973 911T that I bought recently. Hasn't been running in several years (due to body/chassis issue, not engine). In doing a once-over getting ready to try and start the engine, I found several vacuum caps that were cracked, etc. but I also saw that the vacuum advance cannister on the distributor was hooked up to a hose that ran to the manifold below the carburetor.

I thought that the vacuum advance should be connected to the carburetor vacuum fitting, that usually runs to a port just above the butterfly when shut, right?

My thinking is that the engine doesn't need any additional advance at idle, but under part-throttle load, which is what the carb-vacuum port should do.

Sorry to bother - if I had a manual I would have just looked, but haven't found one yet.

Thanks for the help!

moneymanager · 07-06-2009, 11:13 AM

Someone will correct me if I'm wrong, but I seem to remember this is a vacuum retard in 73, not advance. All the advance is I believe mechanical and controlled by the weights. The vacuum retard serves only to bring the idle down quickly to save gas and emissions.

gearheadgreg · gearheadgreg's Garage

AH. That would make more sense. Silly me. Thanks for the help.

RoninLB · 07-06-2009, 02:23 PM

early_s_man/Warren said only the factory carbed engines had vac advance

gearheadgreg · gearheadgreg's Garage

Yep - mine was CIS converted, so that is probably right. Glad I asked before trying to start her up.

unclebilly · unclebilly's Garage

at idle you have max vacuum. Under full throttle you have little vacuum. Placement of the line above the buttelfly makes no sense.