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Engine revs slow to drop

Posted: Mon Jun 24, 2024 3:21 pm
by Huds71j
Hi all - I have just completed a rebuilt of my 71 2.2T and am struggling to get it running smoothly.
Engine is stock with Zenith 40TIN carbs but I have 123 dizzy and MSD 6AL ignition.
I had the carbs overhauled and they removed the enrichment system as they apparently don't need them for uk driving but the revs are very slow to drop when I lift off the throttle.
The vac ports are blanked apart from one that goes to the dizzy. The solenoid near no6 cylinder is still connected but it doesn't work.
Any pointers or suggestions of things to check would be much appreciated.
Thanks

Re: Engine revs slow to drop

Posted: Mon Jun 24, 2024 4:22 pm
by Nine One One
My 2.2 has no vacuum advance on the distributor, so have you got the right 123 one?

Re: Engine revs slow to drop

Posted: Mon Jun 24, 2024 5:13 pm
by Lightweight_911
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Have you checked your throttle linkages to see if one or more are binding ?

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Re: Engine revs slow to drop

Posted: Mon Jun 24, 2024 5:51 pm
by Huds71j
Checked throttle linkage and pedal has now got an additional return spring but still too slow to drop.
The 123 dizzy was what I was advised to get but it was too late to return it when I realized my stock one didn't have vac advance.
I took a vac feed off the carb but I can't imagine it would make much difference

Re: Engine revs slow to drop

Posted: Mon Jun 24, 2024 8:34 pm
by jwhillracer
Huds71j wrote: Mon Jun 24, 2024 5:51 pm Checked throttle linkage and pedal has now got an additional return spring but still too slow to drop.
The 123 dizzy was what I was advised to get but it was too late to return it when I realized my stock one didn't have vac advance.
I took a vac feed off the carb but I can't imagine it would make much difference
Did you blank off the vacuum feed nipple on the carb? That would keep the revs up by bleeding air in

JW

Re: Engine revs slow to drop

Posted: Mon Jun 24, 2024 8:54 pm
by Nine One One
Did you actually disconnect the throttle linkage to the carbs to see if one bank is actually feeding more fuel at tick over, than the other?

If the 123 is the wrong type of distributor have you checked the timing at tick over to see what the advance actually is? Do you know what model it is, and what the advance curve is on it?

Re: my non-Porsche picture of the day

Posted: Mon Jun 24, 2024 9:41 pm
by RobFrost
Try the throttle in the engine bay at the carbs and make sure visually no throttles are sticking there. Then you can 100% rule that out.

Then try the same again with your thumb over any open vacuum leak.

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