No vacuum to distributer

[htbetz]

My 74' 2.7 911 has developed a lag during acceleration. Idles fine although a little low and revs strong. I checked everything that you all told me to check without no luck. The symptom is like the timing advance is not advancing as the engine revs. Messing around with the dist. discovered that there doesn't appear to be any vacuum getting to the vacuum diaphragm. I pulled off the hose at the dist. and revved the engine with no vacuum. The diaphragm does work when I suck on the hose. Shouldn't that vacuum as the engine revs advance the timing?
What could cause no vacuum?

Thanks
Harry

[cgarr]

The vac is only there at idle to retard the timing, as soon as you hit the throttle the vac goes away and the timing jumps advanced. At idle when you pull the hose off it should speed up. Make sure the mechanical advance weights are move free inside the dizzy

[don gilbert]

harry, on your 74 i dont think there is a retard mechinism as stated above, how many ports on your dist? should be just one, which will have vacuume when accelerating, which advances your timing. I'm pretty sure that is correct,

[stlrj]

Originally Posted by cgarr

The vac is only there at idle to retard the timing, as soon as you hit the throttle the vac goes away and the timing jumps advanced. At idle when you pull the hose off it should speed up. Make sure the mechanical advance weights are move free inside the dizzy

That's how my 74 worked.

[don gilbert]

went out and tested my neighbors 75 w/2.7, craig is correct, looses vac on accel. to advance

[RoninLB]

early_s_man/Warren once posted that only stock carbed 911s had vacuum advance.

all others are retard

[Paulporsche]

If indeed it is vacuum related, check all the CIS components, hoses, airbox and the injector seals. I found a hole in the metal pipe way around behind the airbox recently.

OPften ignition problems are mistaken for FI issues. Make sure your points, plugs, rotor, cap and wires are all OK.

How about compression and leakdown? Others may want to comment on this: could pulled head studs cause this?

[cgarr]

If the mech advance is working then check the timing with a light and see what the full advance is at around 3500 its not as easy to static time these because of the retard.

[htbetz]

Thanks everyone for your help! From all your information I should have vacuum to the distributer that pulls on the diaphram at idle - wich I don't. Any ideas?

Thanks
Harry

[stlrj]

Maybe your throttle plate is out of ajustment. It must be fully closed to provide the vacuum at idle.


Joe