MFI, 1972 warm-up issues (combined)

[304065]

The Pertronix wouldn't. Something about your points install was incorrect, either the part number, the gap, the dwell, oil on the contacts, or something wrong with the wiring.

The old points only carry 420mA of current so it's not like they wear appreciably. Porsche deleted the condenser in 1969 for this very reason.

The trouble with Pertronix is you can't see it working, so when it malfunctions you need an oscilloscope or logic probe. Points can be fixed at the side of the road.

But if it works for you, drive on!

[Early_S_Man]

After having my points close up for the 3rd time this year and having no luck getting my Crane ignition to work, I broke down and ordered the Pertronix.
__________________
wahoofan

As John said, there was something about the installation of those new points that wasn't correct! Either no Bosch grease on the rubbing block and cam, or a stripped thread allowing the points to work loose, improper fit, or SOMETHING not right ... NO WAY should a new set of points close up three times in one year!!! My guess is that the points weren't even pitted significantly, yet, right?

[304065]

And you can thank Warren for the 420 mA number! He's the one who went to the trouble of determining the resistance value for the points circuit, 33 Ohms. E= I R so 14V= 420mA * 33 Ohms. Or thereabouts.

[wahoofan]

You guys could certainly be right in that maybe I didn't have them installed correctly, since this is the first set of points I've ever seen!
And yes, Warren is right, no pitting at all of the points. At any rate, now that the car runs this much better with the pertronix, there's no way I'm going back to points. Now maybe I can finally spend some effort on CMA, which I have been putting off until I got the ignition part of the equation squared away.

[donstevens]

My car has Petronix ignition as well as installed by the previous owner and it does run as good as any early car I have driven.

I went through a rough running period for a year though. I ditched the old rusted out heat exchangers for straight headers. Big Mistake. The car didn't run worth a damn. Intalled newer heat exchangers a few months ago with the proper hose to the MFI thermostat and it runs like a champ. The point is, I learned how importanat a correct exhaust is to an MFI street car.

Don

[domtoni]

Couple of points:
- the pertronix unit uses a hall sensor, and give you a timed spark at full juice every time.
- the problem with headers (I learned the hard way as well) is with the cold start thermostat. If you delete the thermostat, the car will run.
Supertec make a manual actuator, and others have shown how you can make a screw actuated unit.

Not good if you want the car to work automatically.

I agree, I like my SSIs !!!

Best Regards
Dom

[wm711]

my 73E runs great when cold, then stumbles when warm. Full throttle, no problem. I re gapped the points, made no diff. Changed the fuel filter, better, it seemed. The engine is a fresh rebuild, and the car sat for quite some time(3 years) after the rebuild. I have only had the car about a month. What would make a car run rough when warm, cold start not shutting off? TIA-Bill

[domtoni]

WM711,

Grady can give you better advise, but from my experience I suggest:
- make sure the fuel system is clean, run a cleaner though it (if your gas has lots of detergent, then that is probably OK)
- make sure the thermostat washers are clean and working You should be able to look into them (through the hose port) and see what they look like

Aside from that, not sure.

Best
Dom

[svandamme]

Originally posted by domtoni

- the problem with headers (I learned the hard way as well) is with the cold start thermostat. If you delete the thermostat, the car will run.
Supertec make a manual actuator, and others have shown how you can make a screw actuated unit.

Not good if you want the car to work automatically.

I agree, I like my SSIs !!!

Best Regards
Dom

warm up is not the only problem with headers, my Bursch headers ran like **** down low, even when fully warmed up
great at WOT , just rubbish at anything else...

as soon as i went to SSI's it ran better, even without the hose to the thermostat... adding the hose , just gave me automated warmup...

also , with Bursch, dunno about other headers, they were to close from the lower valve covers, not even enough room for heet sheets... those Bursch headers are utter crap , they basically cook your lower valve covers , might as well put a blow torch on them...you'll have similar results.

i don't see how these things would be a good solution for any 911 engine for that reason alone... PelicanParts should take these headers out of the catalogue..

[wahoofan]

Well, two weeks and a fair amount of miles later and the pertronix remains a big hit! Starts right up, even in chilly/damp weather, idles at 1200rpm(haven't reset timing yet), and definitely delivering more power than before. Still running rich, especially when cold, but that will be a job for this winter. Thanks again to all who have added advice and comments to this thread - I think it has helped several people to better understand these great old engines!

[wm711]

this is the best thread ive ever seen-