dodgefred écrit:
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C'est ce que j'avais fait mais ce fut une véritable catastrophe!!! c'est à cause de ça que j'ai touché au calage de mon allumeur .....;) plusieurs fois j'ai eu des hesitations retour au carbu toussotements( richesse trop pauvre) malgré un nettoyage total du carburateur (bain acetone joints neufs, soufflette!!!) ET un re- reglage des vis de richesses... quand le sieur PETER a branché son mano à depression sur la sortie de gauche on a tous de suite entendu la difference... maintenant ça marche;) :whistle:
Il se trouve que quand tu te branches "à droite" (manifold vacuum) il y a déjà de la dépression au ralenti donc si tu règles l'avance avec la dépression capsule bouchée quand tu rebranches la durite tu rajoutes cette avance.
Si tu te branches sur la "ported vacuum" tu peux aller jusqu'à avoir du retard !
La capsule de l'allumeur est bonne ? Car généralement sur 2 voitures sur 3 elle est H/S (même avec des allumeurs neufs montés il y a quelques années, vive la fabrication mondiale)
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At idle, the engine needs additional spark advance in order to fire that lean, diluted mixture earlier in order to develop maximum cylinder pressure at the proper point, so the vacuum advance can (connected to manifold vacuum, not "ported" vacuum - more on that aberration later) is activated by the high manifold vacuum, and adds about 15 degrees of spark advance, on top of the initial static timing setting (i.e., if your static timing is at 10 degrees, at idle it's actually around 25 degrees with the vacuum advance connected). The same thing occurs at steady-state highway cruise; the mixture is lean, takes longer to burn, the load on the engine is low, the manifold vacuum is high, so the vacuum advance is again deployed, and if you had a timing light set up so you could see the balancer as you were going down the highway, you'd see about 50 degrees advance (10 degrees initial, 20-25 degrees from the centrifugal advance, and 15 degrees from the vacuum advance) at steady-state cruise (it only takes about 40 horsepower to cruise at 50mph).
et à propos de la "ported vacuum advance" :
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Now, to the widely-misunderstood manifold-vs.-ported vacuum aberration. After 30-40 years of controlling vacuum advance with full manifold vacuum, along came emissions requirements, years before catalytic converter technology had been developed, and all manner of crude band-aid systems were developed to try and reduce hydrocarbons and oxides of nitrogen in the exhaust stream. One of these band-aids was "ported spark", which moved the vacuum pickup orifice in the carburetor venturi from below the throttle plate (where it was exposed to full manifold vacuum at idle) to above the throttle plate, where it saw no manifold vacuum at all at idle. This meant the vacuum advance was inoperative at idle (retarding spark timing from its optimum value), and these applications also had VERY low initial static timing (usually 4 degrees or less, and some actually were set at 2 degrees AFTER TDC). This was done in order to increase exhaust gas temperature (due to "lighting the fire late") to improve the effectiveness of the "afterburning" of hydrocarbons by the air injected into the exhaust manifolds by the A.I.R. system; as a result, these engines ran like crap, and an enormous amount of wasted heat energy was transferred through the exhaust port walls into the coolant, causing them to run hot at idle - cylinder pressure fell off, engine temperatures went up, combustion efficiency went down the drain, and fuel economy went down with it.
Bref, à mois d'avoir une voiture avec tout le système anti pollution de l'époque en état c'est une catastrophe: conso en hausse, voiture qui chauffe plus, moteur qui tourne mal ...
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