missfire assistance please 1970 911T

[twin plugged targa]

Hi guys, I know this takes back to basics, but this car is new to me and so I would appreciate a few simple check I could do to resolve probelm.

Car is a stock 911T with rare but good condition Marelli dist cap and rotor.
Engine has done about 32K miles
Plug leads and HT lead were replaced less than 1,000 miles ago
when new spark plugs were also installed

Car was fine this morning for the 30 mins to work. At lunch time took car for a spin and noticed missfire, possibly on 1 cylinder (maybe 2?).
Checked all plug leads firmly in place, removed dist cap and sprayed with electrical cleaner, left to dry.
No improvement. Car sounds like it is missing on one or two cylinders.

How many cylinders can you lose before performance is really bad?
Car will still run happily up to 70mph+ but sounds rough.
At idle if i blip throttle there is white smoke (unburnt fuel?)
Idle is much lower - down to less than 500rpm.

Any simple routine checks appreciated

Car was running 100% prior to this!

Many thanks
Ben

[berettafan]

Couple things to try (one at a time)
-Pull dizzy cap and check for rubbing. it can be hard to get cap on just right.

-pull plug wires and make sure they are screwed together well

-Check points gap with matchbook (no ****, it really works)

-Check timing


Not all of these things would contribute towards your symptoms but might as well go through them while you're at it.

[twin plugged targa]

Thanks for reply,
what do you mean by check point with matchbook?
Is that for gap or to improve surface with sandpaper type finish?
Do the spark plug fittings usually screw onto the leads then?
Thanks
Ben

[berettafan]

yes, matchbook cover approximates gap very well.

on my plugs the straight part that goes into the 'well' can be screwed on/off of the wire. had an issue with this once and it was a 'missing' type result.

[twin plugged targa]

All beru spark plug leads were old and connectors brittle.
The heads snapped off when I tried to remove them!
Have replaced all and engine running fine.
Thanks to all who responded, to this and other associated threads
regards
Ben

[berettafan]

awesome! go raise some hell on the back roads!

or i guess that would be 'le hell' for you.

[twin plugged targa]

I have discovered the art of holding the throttle around the 'cammy' end of the exhaust note just as I pass between old tall narrow streets in the old town of Cannes - the looks you get are priceless!
The 'wail' and echo of an old flat six is sweet music indeed

[berettafan]

Amen le brother! have some old brick buildings close together in the small town i live in and i LOVE doing that!

[twin plugged targa]

I was based out of Annapolis, MD for 3 summers up until 4 years ago - lovely place!
Unfortunately I was Porscheless as the 'twin plugged targa' was in storage in the UK at that time.
I ran the yacht for the owners of 'Darcars' car dealerships, expect you might have heard of them?
- I now have to 'slum it' on the French Riviera!