1972 911 T runs rough when warms up

[Drew Rollins]

After a 3 year slumber it started right up.It took about 15 or 20 min. to clear the old oil out of the jugs.I have set the valves,changed the oil,gas lines, fuel filter.When it gets warm it starts to cough at idle.Could it be the preheater for the MFI ?The bottom flap never opens when it warms up.What should be idle RPM?Does anyone rebuild the preheaters?It is comming along thanks to your help...... Sure would look good silver....

[1972_911T]

I would think it most likely the pre-heater as you say not leaning the engine out as it warms up, make sure the left heat exchanger is in good condition and the thin pre-hetaer hose that goes to the pre heat assebly on front of the MFI pump. The pre heat assembly itself is fairly simple to strip and clean incase it bunged up just make sure you keep all the disks/washers in the right order.

I belive supertec do a manual cable operated overide to replace the pre-heater assembly may be worth looking into.

Steve

[Grady Clay]

Drew,

Welcome to the Forum.
You will find a lot of help here.

Your T looks like a great project. Keep at it.

Our 911s don’t take kindly to resting quietly. They like regular
driving. Your 911T obviously it isn’t easily drivable in current
condition but you might get a temporary permit and take it out
to get a load on the engine and fully warmed up. Another
possibility is ”Oil Change After Winter Storage?“.
Wil’s high rev solution might work for you IF your cold running
thermostat turns off and you get 180F oil temperature for
15 minutes or so.

I would not adjust your MFI until the 911 has been up and run
for quite some time. That is unless it absolutely isn’t running
correctly. In the interim you need to make sure the thermostat
turns off each time it is started. You can generally tell by the
temperature of the thermostat housing. Anything above about
170F is usually OK assuming it functions correctly. The good
news is the running condition you describe is usually lean.
Does the exhaust smell rich?

Pay attention that your oil doesn’t start to smell like gasoline
or starts to gain in level – a sign of oil dilution.

You might add some cleaner (Tectron?) to the gas.

How long until you will have your 911 back on the road? Tell
us more.

Someone is sure to chime in about using the Pelican search
function. There is an amazing amount of stuff about MFI
and everything else archived there. Try a search using “MFI”
and “thermostat” and see what you find.

Clearly you figured out how to post images. Here are some
hints: ” How to post images (pictures) on Pelican“.


Your engine looks great – and original. A little attention and
some decals will make it close to perfect.




What is this little fuel filter (red arrow) for?
What is this (green arrow)?
Your MFI fuel filter (blue arrow) is there.
Is the 415 Sepia Brown original?
Do I see some 114 Signal Yellow?

Looks like a great 911, ready to come back to life.

Best,
Grady