Rich carbs

[AltaKnight]

My 1973 TR6 with twin ZS carbs seems to be running rich.
The car runs great no hesitation or stumbling but seems to smoke at idle (black unburnt gas smoke) and the plugs are sooty all the time even after a good long hard run
I've adjusted the carbs many times with the special tool trying to lean them out by winding them anti clockwise, I think I've likely disengaged the screw inside by now so they won't lean out any more.
When I lift the air piston slightly the RPM still picks up about 100 rpm and stays higher until I let the piston down again. This would indicate too rich.
The car seems to use a fair bit of gas also which might not be uncommon, or at least I seem to be always filling it up, of course maybe I'm driving around too much.
When I wind up the revs on the road over 4K there's plenty of power and plenty grey/black smoke also./ubbthreads/images/graemlins/driving.gif
The motor is in good condition.
Any words of wisdom out there?

 

[SkinnedKnuckles]

The carb float levels are probably too high. It's a PITA, but take them off and raise the float level (upside down) by 2mm, then start over with adjusting. You may have to do this more than once. While things are apart make sure the needles are engaged so turns mean something.

 

[Dugger]

Additionally, if you have the original float valves, these may be leaking, and repalcement with Grose jets valves may save your tweeking of the enrichment needle.

There is a method to check float levels without removing the carbs. Remove the dashpot and using a bright pin light, peer through the jet. The fuel level should be aproximately 1/4" (5-6mm) below the venturi.
Be careful with the removed carb pieces, you really don't want to drop, bend, spindle or mutilate these parts at all!
If the fuel level is closer to the venturi, then you will need to pull the carbs and adjust the float levels, this would be a good time to replace those original valves.

BTW: Many of the local auto parts stores still carry rebuild kits [o-rings, seals, gaskets]for the ZS175's.

 

[vettedog72]

Dugger:
Now, that's whatt I call a helpful note. It is a pain to reset the floats. Your tip will be recorded.
Thanks