CSI cutting out at top of Rev range 4.5-6K

[ARCSinAK]

Any thoughts on what might be the cause of this condition? I bought a 74 911 with a 2.7 unknown history...she pulls harder than my 80SC and my 70T. Gotta love the 731 pinion..but at the top of the rev range she cuts out. Any knowledge would be appreciated.
My version of a PPI is called a post purchase inspection.

Thanks for your time and knowledge.

Regards-
JS

[timmy2]

Does that model have a rev limiter rotor? What ignition CDI box are you running? How old are the plug wires, cap, points etc.?

[timmy2]

CIS fuel pressures? System pressure? Cold and warm pressure?

[Caledonian]

Rev limiting rotor arm looks like this:


Normal one for engine with CDI looks like this..



I also think they come in various rev limiting ranges e.g. 5000rpm, 6500 rpm etc.


Hope this was of some help.

[redstrosekNic]

How is it cutting out (completely, or just a cylinder or two)?My rev limiting rotor cuts the engine somewhat violently. It scared the crap out of me the first time I hit it!

[al lkosmal]

More info plz. Does it totally cut out, or just start missing? A total ...or somewhat sudden cutout could be your rev limiter. A loss in power or missing could be any number of things, but I have had a bad coil that would go intermittent on me at high revs.

regards,
Al

[Bob Ashlock]

It could be the Bosch CDI unit ... I routinely test and repair these for other members and do see ones that work OK at low rpms, but cut out at the high end. -- Bob@AshlockTech.com

[ARCSinAK]

Thanks for all of the input, here some more info.

It is running a Perma-Tune ignition, strangely enough there are no wires connected to the bottom of the box?

The rotor on the Dizzy is has a Rev limiting arm.

It seems to be intermittent not always occurs, when it happens 4.5 K plus it feels like a stumble, missing with about a 25% loss of power, the motor tries to fight through. Does not always happen. I put some injector cleaner in my last fill up but I'm a dreamer. I think the problems lies somewhere else.

Is it just me or does a 2.7 with a 915 / 7:31 RP quicker than a stock 80 SC. This motor feels so much more responsive and quick. Hoping to solve this CSI issue.

I sure appreciate your time and assistance.

Regards-
JS

[timmy2]

May not be a CIS issue, maybe a CDI issue. Have the permatune tested, they have a history of failure depending on the model and year. I understand they provide very good support.
Take a good look at the rev limiting rotor, they are known to fail where the limiter is mounted on top.

[ARCSinAK]

Thanks Dennis-

Strange that the connections on the bottom of the Perma Tune box are not connected. Are there other plugs in the back of the box?

I also have a wandering tac, unless I am on the throttle.....It will show 4-5 grand and bounces when I'm actually at 3 or less then when I accelerate it lowers to the seat of my ear correct RPM.
She pulls great just need to work out the bugs.

[timmy2]

Tach could be an indicator of alternator problems that could cause your aymptoms as well.
Check your battery voltage is around 13.5 at 2000 rpm and appears to be charging properly. Many posts on that subject. Should be fairly constant when you rev the engine.
I've never physically touched a permatune in my hands, so I can't comment on where or how it is connected to the harness.
Your troubles may just be bad electrical grounds, find all of them and clean them up.
Bad plug wires?
Many, many possibilities, just eliminate them one at a time.

[T77911S]

tach could be ppoints. clean them or replace them.