To get in the ballpark, adjust the mixture screws on both carbs--keeping the
everything
else the same--until you get maximum RPM. Then use the method Eric describes to
fine tune (you'll be pretty close already). Be sure the airflow is the same on
both carbs
using a Unisyn or other flowmeter, or by ear if you wish.
If the carbs are set up properly both should take (close to) the same number of
turns on
throttle, idle valve and mixture screws. If there's a big difference between
carbs on any
of these there is something amiss.
bs
********************************************
Bob Spidell San Jose, CA bspidell@pacbell.net
'67 Austin-Healey 3000 '56 Austin-Healey 100M
********************************************
> Barry, my BT7 is equipped with HD8 carburettors as well and I have the same
>problem with the idle adjusting screw.
> Though the screw is fully turned in and the throttle is fully closed, the
>engine idles at around 800rpm (but fairly
> smooth).
>
> To control the setting of the mixture it is important to lift the piston
>around 1/32 to 1/16" maximum. I did a basic
> adjustment (2 turns down after jet was flush with bridge) and after that fine
>adjusted with the piston lifting method
> until I had the engine speed increasing momentarily and then dropping back.
>When I had done some miles I recognized
> the bumper getting black in the surrounding of the exhaust pipe showing me
>the engine ran slightly rich. So I turned
> the adjusting screws out a quarter turn. The engine now runs like never
>before, very smooth, even when it's cold.
>
> My assumption for your engine running rough when lifting the piston is you
>lifted it too high. This way you get a
> mixture which is too rich. I used two hollow ali rods inserted into the
>hollow piston rods with two wires bent at
> right angles with the rod pointing at each other. That way there's no problem
>adjusting the carbs and lifting the
> pistons not too far. These rods and wires are for sale here in Germany and I
>guess they are for sale in the US as
> well. They sell for about 25$, but it's worthwhile.
>
> Regards
>
> Eric BT7
> Heinsberg/Germany
>
>
>
>
> When the mixture is adjusted and the piston is lifted, how long should
> the idle increase before dropping off. Mine currently idles the same or
> just slightly increases for a second at most and then runs rough until I
> release the "lift button". Should I increase the mixture until it gets
> too rich and then back it off? I also don't get much effect from the
> idle screw adjust (the larger screw) over a fairly large adjustment
> range. It definitely will run rough when turned all the way down but not
> much effect from 2 to 3 turns out. Barry Pate BJ8
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