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Porsche 911 SC - Weber 46IDA3C1 - slow at high rpms

Hi everyone,

Thx for an exceptionally great forum.
I've got a problem, where I hope to get a little expert help from all of you out there.

I've recently bought a Porsche 911 SC from 1978 that's converted to Weber 46IDA (3C1) instead of CIS. The car sounds great! (positive), but the problem is that there's good strong acceleration all the way up to approx 3.500-4.000 rpms, but here the acceleration slows down/declines and the car feels slow and boring, which is not what I would expect. :-/
The carbs have been adjusted very recently, just before I bought it, so I assume that's not the problem.

I don't know if the distributor has been recurved, so wondering if that's the problem?

Also the ignition is not replaced to eg MSD 6AL - but would that help the problem?

The exhaust and heat exchangers are just the stock ones - can this be a problem?

Any help or ideas on what could be wrong - it highly appreciated. :-)

BR
Chris


Old 02-09-2020, 03:42 PM
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Stock 3.0 SC engine?

Distributor re-curved?

Need jetting on carbs to be of help:
  • Main venturi size
  • main jet size
  • emulsion tube type
  • main air correction jet size
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Old 02-09-2020, 04:14 PM
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Put a timing light on it and record the advance every 1K rpm. Report back.

+ what Paul says. What cams?

BTW, Weber 46s are junk. I'll take them and I'll give you a CIS setup, I'm not using.
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Old 02-09-2020, 07:00 PM
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Establish a base, jet sizes, venture sizes, float level. 46s are too big a 3.0 street motor. Someone may have jetted it down to be drivable at low rpm, but running out of fuel up top. They can be made to work, but a bit of a work around. Bob
Old 02-10-2020, 12:18 PM
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Stock exhaust is not helping matters much!
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Old 02-10-2020, 03:48 PM
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I agree with r lane. 46's are to big for a 3.0L. "Bigger is not always better". 40's would be better but I suppose you could change the jetting to make it run. Paul Abbott (1QuickS) would know better. Weber's is his 'forte'.
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Old 02-12-2020, 09:58 AM
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Hi all,

THX alot for all your inputs - I really appreciate it.
I'm hoping to go to the garage where my car is parked in the weekend to look more into the problem.
Since I can't adjust the carb myself, I was hoping not to have to disassemble the carbs to find out the info you're asking for: Main venturi size, main jet size, emulsion tube type, main air correction jet size.

But I assume, it will be impossible to figure these out without compromising currently setting of the carbs. Right?

Once again thx for all the helpful inputs.
Old 02-13-2020, 03:21 PM
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You can pull the jets with out touching any adjustments. The biggest problem will be what to do with the gas that drains out of the float bowl when you pull the main jets. Otherwise it is just a matter of removing the air cleaner.

Also, I don't remember if you said the car always ran that way?

Also, can you describe how the car runs. Are you saying you can floor the throttle and it takes off until 3000 RPM, then what? Does it start misfiring? But it will it rev to 6000, but with little power?

Perhaps a fuel flow issue?
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Last edited by Trackrash; 02-13-2020 at 04:11 PM..
Old 02-13-2020, 04:00 PM
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Cams.
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Old 02-13-2020, 04:37 PM
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Fuel Filter Fuel Pressure and check for Full Throttle

regards

Old 02-13-2020, 05:17 PM
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