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-   -   911T tune up (http://forums.pelicanparts.com/porsche-911-technical-forum/90881-911t-tune-up.html)

Carolyn's 911 12-14-2002 03:01 PM

911T tune up
 
I just acquired a 1970 911T. The car has a bad backfiring problem. Can anybody help me with tune up specs. Need to know ignition timing, dwell angle, points gap, plug gap and idle rpm. I want to do a tune up to see where I am. Any info/tips would be appreciated

tmctguer 12-14-2002 04:30 PM

here are the specs from a chilton book from the early '70's:

'70 911T:

spark plugs: W250P21
gap: .024 inches
point dwell: 38 +/-3 (bosch) ; 40 +/-3 (marelli)
point gap: .016 inches
timing: 0 degrees, 35 BTDC @ 3,500 RPM
idle speed: 850 - 950 RPM

john walker's workshop 12-14-2002 05:09 PM

the plug heat ranges in the old manuals can't cope with today's fuels on carbed and MFI cars. they run too black and foul easily. NGK BP6ES works well these days. see how they look after a 1000 miles and go hotter if needed. NGK numbers go down for hotter, as opposed to bosch which goes up. BP5ES would be hotter.

mskala 12-14-2002 06:37 PM

Quote:

timing: 0 degrees, 35 BTDC @ 3,500 RPM
Hey, if this is like the '69T, which I think it is,
you need 35 degrees at 6000RPM, not
3500.
Mark S.
'70 914-6

Carolyn's 911 12-14-2002 06:50 PM

I think you're right about the high end timing (6000 rpm). What is the timing at idle?

john walker's workshop 12-14-2002 07:03 PM

when you set the timing at full advance, which is the rpm where the timing quits advancing anymore, whatever it idles at, timing wise, is what it idles at. in other words, it doesn't matter. yours may well get to the full advance point well before 6000rpm. try it and see. use the last mark on the pulley (farthest to the right) if you don't have an adjustable advance timing light. raise the rpm until you don't see any more timing advance as you shine the light on the pulley. the idea is to get the full advance mark to line up with the fan housing mark at that point. turn the distributor to accomplish that. the idle speed may have to be turned down a bit when you're done.

911pcars 12-14-2002 07:33 PM

On a 69T, the timing at idle should be 5º ATDC, but make sure it meets spec on the top end (35º BTDC) and let it be whatever it is at idle.

Sherwood Lee
http://members.rennlist.org/911pcars

PS: The timing at idle could also be 0º (TDC) depending on whether you have a "smogged" engine or not.

tmctguer 12-14-2002 08:56 PM

my mistake on the high RPM timing.........

it should read 35 degrees BTDC at 6,000 RPM.

Superman 12-14-2002 10:38 PM

Follow John's advice.

tryan 12-15-2002 08:06 AM

backfire out the tail pipe is an overrich condition or exhaust leak.

check your float levels/seats and exhaust durring your tune up.

john , did you see the van in this month vw trends? pretty sharp.


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