Recentering and Adjusting ZS Carbs

Date: Mon, 19 Oct 1998 16:18:50 -0400
From: (Bud Rolofson)
Subject: Re:Help with getting TR6 started again

Wayne,

I don't know that this will help your situation, it might (if your 73 is stock and has the adjustable needles), it might not, but I thought I'd throw this out for what it's worth for those who have rebuilt or are considering rebuilding their carbs, and for those (like me) who have just messed with their idling mixture until they don't know where they are at and don't know how to get back to square one on both carbs.

I finally discovered what I think can be used as a starting point (square one) or a reference point in adjusting the idling mixture (the one you get to with your special carb adjusting tool by pulling the dampers out) on ZS carbs. It was hidden away in the ZS manual on page 46 #8. It says "draw the needle into the air valve by clockwise rotation of the adjusting screw until the washer (on the needle)is flush with the underside of the air valve". Later on, (page 48 under Idling Mixture adjustment #6) it tells you that you get to turn the adjusting screw "...a maximum of one turn in either direction to set optimum idle quality..".

Now obviously this means that, in order to see if the washer is flush with the bottom of the air valve, you've pulled the top off your ZS carb, pulled the spring out and have pulled the air valve out and have it in your hot little hands with your ZS carb adjusting tool in the adjusting screw. If you hold the air valve upside down with the tool in the adjusting screw you can easily see to get the washer flush with the bottom of the air valve. My guess is that this is a more accurate way to start out than simply turning the adjusting screws in both carbs as far clockwise or counter-clockwise as possible since the threads in the adjusting screws and needles are not calibrated and you could end up with the needles uneven relative to each other. Also the adjusting screws may even sit in the air valve slightly different which would again position the needles unevenly.

Wayne Note: If you turned your adjusting screws counterclockwise as far as they will go (they probably just keep turning forever) then you've backed out the threads of the adjusting screw from the needle and or at least put them at the maximum lean setting (which may be why it is not starting). Turning them clockwise should reengage the threads of the adjusting screw into the needle and you should actual feel a "stop point" when the screw has the needle pulled up (max. richness) as far as it will go. You could use this as a starting point for your idling mixture and turn the adjusting screws equal turns counter-clockwise to a leaner setting. But I gotta believe setting the needle in both air valves at the same position gives you a better chance of finding the correct idling mixture.

I'm sure this isn't new info. to many on the list but it was a bit of information but I hadn't seen talked about on the list and thought it might help others like me that need a specification to return to when we've screwed around too much (don't tell my wife). Hopefully the list can say if this works or not for other carbs (or if there's some better way). I know it helped me to find the optimum idling mixture on my carbs which I believe to be 74-75 carbs (based on the TRF catalog criteria).

Bud 71TR6 CC57365