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411 dying at stop signs

Posted: Tue Apr 21, 2020 5:29 am
by Deanaha
I feel like this should be an easy fix, but am getting conflicting advice- so I am asking for input from this group. My 1971 411 was converted from FI to dual carbs ( not my idea, before my purchase). Now although I have been told it is tuned and just needs to be driven- it dies at stop signs unless I put it into Neutral and then into Drive at the green light. To me- it seems to need more fine-tuning. Any advice or suggestions?
Hope everyone is staying safe and well
Thanks for the input

Re: 411 dying at stop signs

Posted: Mon Apr 27, 2020 1:48 pm
by Amskeptic
Yes, it needs more fine-tuning but you are in a bind here. Dual carbs are too much for a little 4 cylinder engine under the load of your automatic transmission. The amount of airflow needed to run the engine is barely a whisper, and the dual carbs cannot mix the fuel half well enough. The factory dual carb VW buses had a centrl idling circuit which made its own high speed air tube to mix the fuel well. Later, they had to add little idle valves to keep the engines running in drive at a stop light, because hot carbureted engines suck at keeping the mixture under control.

You do NOT want to compensate for this stalling by raising the idle speed beyond 1,050-1,100 rpm max, in park or neutral . That would kill your CV joints and engine/trans mounts over time.

First, get idle speed correct at operating temperature.
Next, experiment with the fuel mixture. To record your initial mexture adjustments, turn each mixture screw in until it gently seats. Count to the 1/16 of a turn (ie. a quarter turn is 90*, an eight turn is 45*, a sixteenth is half that. If they are different than each other, leave them be, get the screws back out to exactly where you had them.

Let me know your numbers!