Help. 911 st electrical problems.

[m12bug]

Hi.
I started my 2.3 st yesterday.
(Twin spark marelli 121 and 46 IDA's)
First time since August.
August it was running fine.
Now it won't tick over and it's hesitant on acceleration with little power.
The rev counter also appears to be displaying 1/2 the engine revs !!!
Ie engine at tickover 900 rpm rev counter displaying around 400.
Thought it might be fuel but cannot figure out rev counter display.
Exhaust note sounds low. Not the normal rasping crackle.

I have checked the following:
Battery good.
Dizzy cap clean and dry.
Replaced rotor (no difference)
Coils. Both fall within tolerance.
Both CDI make the whining noise.
Swapped HT leads from coil 1 to coil 2. Same issue.
Any ideas?
Could the points gap cause this?
Will put Fresh fuel in tomorrow.

Thanks.
John.

[Mr9146]

Not sure what kind of ignition you're running (points or hall effect), but you might look at that. EDIT: Just noticed the points comment, so I'd start there. Check the gap as well as the contacts themselves. I've had this problem with my Marelli S121 ... the points for one set of plugs would close up partially and the thing would run like dog meat under load. I would readjust the points and the car would run better, but the problem would reoccur not too long after. That was what drove me to have Kurt at Partsklassik rebuild my Marelli and modify it for use with a Pertronix igniter.

Additionally, voltage spikes (i.e. alternator/regulator problems) can wreak havoc on ignition systems ... this has been a recurring theme on my car, too, as I tend to build my personal cars with used parts I have just laying around.

[m12bug]

That sounds about the same as mine.
I will check the gaps in the morning.
As a matter of interest, what gaps and timing are you running on yours?

Could the points gap effect the rev counter?
Cheers.

[Mr9146]

That sounds about the same as mine.
I will check the gaps in the morning.
As a matter of interest, what gaps and timing are you running on yours?

Could the points gap effect the rev counter?
Cheers.

In regard to the tach issues, yes, the points can have an affect on the reading if you're taking the tach signal off the set of points that failed. I take my tach reading off the upper circuit, so when the lower circuit would act up my tach would read just fine. However, when the upper circuit would mess up the tach would react like a Disney clock.

As far as the gaps are concerned I can't give you a measurement, but if you're running a Marelli 121 I can tell you that the dwell should be 19-20* per set of points ... the combined dwell should be 38-40* for each circuit pair.

Check out this thread for more info on my specific situation: RSR Marelli Distributor Rebuild

[chris_seven]

John,

I have 4 x sets of new points that you can try.

Regards

Chris

[m12bug]

Hi guys.
Thanks for the advice.
Engine now running on all 6.
Tacho now also working.

Turned out to be a bad gap and anither bad point.
It had no continuity when closed.
Cleaned up and now working.
Many thanks.