Confirm my suspicion: sticking vac advance

[boyo]

I've been trying to figure out what the minor tuneup problem with my '72 911T 2.4L MFI engine could be. Just wanted to get an expert opinion before diving in - but experts cost too much so I thought I'd ask here! Jes' kiddin'...


The car starts pretty quickly, but requires some gas pedal pumping and takes about 30 seconds to warm up and idle smoothly. After that it idles and runs almost perfectly.

When driving at 3K-4Krpm, a light pressure on the gas pedal causes stumbling, hesitation, and sometimes pops. However - full throttle responds immediately with good power.


Sound like vacuum advance, or a distributor which needs cleaning? Saw the previous post on this topic, sounds like a good idea.

How about points? And why do new coils cost $125 for my car?

I have not done a full tune up, which would get the timing, spark plug gap, and points gap set correctly. Awaiting all the books and manuals I asked for to arrive on the 25th...


The PO mentioned something about $25/ea spark plugs that he later found out were "too hot" for the car, according to the local Porsche mechanic - born in Germany and factory trained back in the 60's, so chances are he knows what he's talking about.

'm considering changing those out and making trophies out of them. New spark plug recommendations? Thanks,

-Boyo

[tobluforu]

The #1 thing to do FIRST on a MFI car is tune it up. Do not try and do anything else until you get new plugs, points, cap, rotor, adj timing, dwell, make sure all wires are working properly-new ones maybe, new air filter if needed, adj valves and don't forget the fuel filter. Then you can mess with the distributor or the mfi and all the rods, etc.
I use bosch super plugs. 3 electrodes, about 4.50 each.

[jkeyzer]

My car (same as yours) has been known to do the same thing under light throttle. I think that maladjustments with the MFI microswitch, linkages, and bleed screws (as well as wear in the throttle bodies) show themselves the most when you are barely on the throttle.

After doing all the adjustments outlined in Rice's MFI article and the check/measure/adjust booklet it feels like the problem is much less severe than it used to be.

If you are interested in the opinion of someone who is not an expert by any means but has been tweaking his ignition and MFI for 4 months now, I am actually visiting family across town in Fair Oaks for the next three weeks. I can take a look at your MFI setup and see if there is anything obviously out of whack.

PS As far as the coil goes the price is because it is a special model of coil that goes with your CD system. I avoided spending the money on a new coil by instead upgrading to an MSD ignition. I think the plugs I am using now are NGK BP6E's. My mechanic in SD pushed them on me and they have worked fine for a couple months now.

[tmctguer]

my friend...........been there, done that, got the shirt! please review my long post entitled

"post tune up problem"

you will see the things i did to work my problem from start to finish.

you may be at the point where you need to jump into learning about your MFI system. i recommend downloading and studying "check, measure, adjust" from the pelican technical site.

also, check out the threads from Early S Man about distributor maintenance. this may or not be part of the problem, but if you're going to go through the ABC's, you should include distributor maintenance in your recovery plan.

[Matt Smith]

Forget those $25 buck plugs. Use the NGK BP6ES: Lots of us here use them and everyone has good things to say.
I had the same hesitation at 3k rpm when I fist bought my car. Could be LOTS of things. I suggest just going through all the factory set up info available here on Pelican. I really think you need to understand that the MFI engine is rather dependent on EVERYTHING working in synch- electricals, normal tune up stuff, valves etc etc etc.
If you plan to own this car for any length of time you will need to know how to do all these things properly anyhow, so just start learning the system thoroughly now.
Probably wouldn't do any harm to clean and check the dizzy first though. It's not too difficult and is quite rewarding.

Good luck! Lots of experience on this board if you get lost, so just ask!

[boyo]

Good advice...starting with all the simple stuff first. I do plan to own this car a while, but wanted to ease into ownership and not attack the MFI injection system just yet... Runs well enough!

I think I've seen the microswitch - from what I can tell the adjusting screw is backed out so far it will never engage the switch. I didn't think that looked right, but didn't mess with it either.

Can't wait to get them books!

-Boyo

[Matt Smith]

Almost ALL the info you will ever need is here under the Pelican Technical section, including the whole "Check, Measure , Adjust" factory 'blue book'.
Start reading now...

[jkeyzer]

The microswitch cuts off fuel when you're coasting at high rpm. (avoiding backfires, although I never had any while mine was broken) You can test if the microswitch, RPM transducer, solenoid, and associated wiring is actually working by revving the engine to 2-3k rpm, and then manually pressing the switch while keeping the throttle constant with your other hand. The engine RPMs should dip way down and then surge back up again in a regular pattern. If this doesn't happen, adjusting the screw isn't going to help. Lots of info on this on the BBS.

Good luck!

[boyo]

Got the "Check, Measure, and Adjust"...thanks!

-Boyo

[my72911t/rs]

Dont spend all the money on a regular coil get one from NOLOGY.com . I got wires coil and silver core sparkplugs very very hot spark....Matt