oldtimer

OK thats probably a stupid question , but when I got my 911 (2.4S) the vacuum advance pipe was disconnected and stoppered.

I got the garage to reconnect and do a 'tune-up'.

The engine works fine BUt it will not pick up smoothly from 2000- 2500 RPM , and if caught in this rev range when you push the throttle it lurches - sort of stop-go and the harder you push the worse it gets. Makes it awkward in traffic - OK on a circuit though where you keep the revs up. Plenty of power on dyno.

Soooo I'm thinking maybe was a reason to disconnect the vac line ?

race911

There are sooooooooooo many places to start here.

What's the mechanical advance though the rev range? Where's it set static? Does this engine still have points?

And we're not even getting into the mechanical fuel injection (which is where I'll guess the solution lies)................

oldtimer

Hi Ken , I dont have the answers to your questions unfortunately. I'm in the hands of the garage men if it needs diagnostic equipment. The last proper tune up was some 300 miles / 6 months back on a rolling road by a respected UK man knowledgeable on MFI engines. He reset all the linkages and balanced the airflows and set the fuel a bit leaner using exhaust analysis. The symptoms I'm describing were there before and after this work.

Bill Verburg

There are 2 types of vacuum sources
vac w/ closed throttle as at idle
vac w/ open or partially open throttle

on a 2.4T, E, or S the vacuum is the first kind, it is max at idle and drops as the throttle is opened.

The vacuum pulls on the movable distributor plate causing timing to retard. Since this only affects idle and low speed operation it doesn't realy hurt performance.

W/ the vacuum connected idle timing should be set to 5*ATDC, if you pull the vacuum the idle timing will advance by ~5* to ~ 0* or TDC.

the critical timing is up near 6k rpm. You can check it by disconneting the dist. vac and revving to 6K where the timing should be ~30*BTDC