jlw (04/15/83)
>From Gary.Cottrell@rochester.UUCP Thu Apr 14 21:46:24 1983 Via: mhuxv!mhuxi!mhuxj!mhuxt!eagle!harpo!seismo!burl Date: 14 Apr 1983 13:27:15-EST From: seismo!Cottrell@Gary Subject: Holly carbs To: seismo!harpo!eagle!mhuxt!mhuxj!mhuxi!mhuxv!burl!sb1!ll1!otuxa!we13!lime!houti!ariel!jlw What does the 32/36 refer to in a carb description? Also, what does the mechanical vs. vacuum downdraft mean? want to understand my carb better, gary cottrell (allegra or seismo) !rochester!gary (soon to be gary@rochester if your host tables are updated) _____________ >From jlw Fri Apr 15 08:22:59 1983 Subject: Re: Holly carbs The 32/36 designation means that the primary barrel is 32 mm diameter and the secondary is 36 mm. A mechanical linkage links the primary butterfly to the secondary. When the primary is opened a certain pre-determined amount, the secondary starts to open. The secondary is geared to open at a faster rate than the primary and after a little bit more throttle is given both are opened full. In a vacuum operated system the secondary opening is controlled by the total vacuum in the intake manifold. As you can see the mechanical operated unit is deterministic. Whatever the angles and lengths of the various levers do determines the butterfly openings for a given accelerator peddle opening. When the engine is running at low rpms and the throttle is rapidly opened, in theory, the mechanical system experiences a severe drop in intake manifold vacuum. This, since the carb works on the venturi effect, lowers the feed of fuel through the main jets. The vacuum operated carb on the other hand operates the secondary butterfly in response to the amount of vacuum in its operating circuit. This is probably, and here I'm on shaky ground, controlled by the amount of vacuum in the manifold with a bleeder controlled by the throttle position. In other words a low throttle position bleeds a lot of vacuum causing the secondary to remain shut, while the high throttle position stops this bleeding. The amount of vacuum in the actuating mechanism is then proportional to the engine speed. These carbs are prone to getting mucked up and to leaks, and as you can see they are much more complicated than a few levers. Joseph L. Wood, III ABI Holmdel (201) 834-3759 ariel!jlw