Don't understand timing marks on pulley

rs911t · 01-10-2003, 04:42 PM

The timing specs for the '72 are 5 ATDC at idle 32-38 BTDC at 6000 rpm. But the marks on the pulley don't seem to help with these settings. Looks like below - what does "FE" mean?

dean · 01-10-2003, 06:01 PM

I don't know what the FE means. Are you having trouble timing your car?

rs911t · 01-10-2003, 06:20 PM

Not right now - I'm fixing carbs. I'll need to determine 5 ATDC when I set the timing. My light has advance - not sure how to go the other way.

pwd72s · 01-10-2003, 06:24 PM

Greg, I brought this thread to Ron's attention...I hope he weighs in later. Just a little tip here tho...think backwards. When you are looking at the timing marks on a P car, think backwards from looking at them on a Detroit V-8...even though you are standing behind the rear of the car, you are looking at the front of the engine in a 911.

skinnerd · skinnerd's Garage

Greg:

The FE is the mark for timing your MFI pump; I won't go into any more details than that. It's used to insure your MFI pump is timed correctly with the rest of the engine. If you need to get the MFI pump synched with your timing, be sure to read the instructions very carefully or you can easily be 180 degrees out of whack. I know because I'm been there before and the engine doesn't run too well (or at all).

The Z1 I believe is top dead center, with the 30 and 35 being the BTDC (before top dead center) timing marks.

Hope this helps.

RoninLB · 01-10-2003, 07:56 PM

Quote:

Originally posted by rs911t
Not right now - I'm fixing carbs. I'll need to determine 5 ATDC when I set the timing. My light has advance - not sure how to go the other way.

the carbs are for the 911.. so what dizzy are you using? a MFI dizzy? Pelican has a 2.7 RS dizzy that's great for carbs, cost about $260 brand new.. and I'd forget about timing it for smog w/carbs...............Ron

82SC · 01-10-2003, 07:58 PM

what does the 5 mean on my SC pulley

MJ

rs911t · 01-11-2003, 05:41 AM

MJ, I'd guess the it's the 5 BTDC timing mark.

Ron, I don't know what dizzy I have. My initial guess would be the stock MFI dizzy, but I'll figure it out today.

Here's a theory. The pulley timing marks are consistent with the timing for a 70/71 engine, according to the Haynes manual. When the engine was built circa 1975 (replacing MFI w/ carbs) they removed the 72 pulley marked for the 5 ATDC / 32-38 BTDC specs with the earlier one marked for TDC / 30-35 BTDC. Why? Dunno. Maybe that's how they wanted it timed...?

I guess my question is - how do I set timing?

(a) 5 ATDC at idle, 32-38 BTDC at 6000 rpm per the 72 spec, requiring me to place my own 5 ATDC mark.

(b) TDC at idle, 30-35 BTDC at 6000 rpm per the pulley.

RoninLB · 01-11-2003, 06:07 AM

Quote:

Originally posted by rs911t
I guess my question is - how do I set timing?

well rs, Warren is the expert around here on dizzys.. but I would disconnect the vac line and time to a total of about 32-33deg and see what happens.. should be fine.. the idle will probably fall to about Z1.. I like starting on the low end for total to avoid preignition while getting everything sorted out.. leave the vac line plugged and run without it.. bump timing up latter and listen for pinging... I would check the side to side play in dizzy shaft. it should have only an itty bitty bit of play.. a rebuild might cost some bucks for parts.. compare the cost to a new RS dizzy. PMO used to recommend them..............Ron

rs911t · 06:04 PM

All the carb leaks are fixed and all the adjustments are now effective. New plugs, valves adjusted, plug wires now plugged into the correct plugs (i.e. how to make your 911 backfire

).

But, the timing is erratic. Idling around 900-1000 the best I can get is TDC stable for a few revs then advances and falls back. As rpms increase, it becomes more erratic - I was expecting a smooth advance, yes?

My dizzy is a BOSCH 0-236-169-005. I have a Crane XR700 optical unit and an MSD 6AL. Where to begin ... ?

RoninLB · 01-12-2003, 06:48 PM

Quote:

Originally posted by rs911t
But, the timing is erratic. Idling around 900-1000 the best I can get is TDC stable for a few revs then advances and falls back. As rpms increase, it becomes more erratic - I was expecting a smooth advance, yes?

My dizzy is a BOSCH 0-236-169-005. I have a Crane XR700 optical unit and an MSD 6AL. Where to begin ... ?

man, I'm no pro. Warren may be around and JW jumps in to clear things up.. but the optical may be greasy or screwed up, the timing advanced may be stuck.. and the Beru connectors may be bad.. I'm assuming the routine stuff, like the cap isn't cracked and fuel/carbs is ok, full MSD hook up OK.. when you say "erratic", that means you can see the strobe bouncing between different timing.. whatever it is it's gotta be simple to fix.. what I like about carbs is that an erratic engine can be reduced to fuel or ignition easily by reving it and knowing what's breaking it up, then going after the details...........Ron