Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10 5/3/83 based; site homxb.UUCP Path: utzoo!watmath!clyde!burl!ulysses!mhuxr!mhuxt!houxm!homxb!delbene From: delbene@homxb.UUCP (K.DELBENE) Newsgroups: net.auto.tech Subject: Re: Re: Proper Needle Sizes for SU HS-4 Carbs. on Detoxed MGB et. al. Message-ID: <898@homxb.UUCP> Date: Tue, 5-Nov-85 09:03:40 EST Article-I.D.: homxb.898 Posted: Tue Nov 5 09:03:40 1985 Date-Received: Thu, 7-Nov-85 04:07:45 EST Organization: AT&T Bell Labs, Holmdel NJ Lines: 32 On the point that one can lift the piston of the HS-4 carb. and check the effect to determine whether or not the mixture is proper, you're right and you're wrong. For background in case anyone else cares, the SU, Stromberg, and Zenith carbs are designed so that the needle is afixed to the end of a damping piston. When the throttle plate is open, the inrushing air causes the piston to rise. Since it is tapered, this in turn increases the amount of fuel that mixes with the air. The piston is dampered with an oil cylinder and piston arrangement, so that the changes in air/fuel ratio are not so erratic. Now, back to the point. The test you do implies that you are starting with the proper needle. I don't think it will tell you if you have the proper needle for the characteristics of your engine. That is the question that I've raised. It really belongs to a more general question: If one changes the characteristics of an engine, how do you find the best carburetion for the new set-up? Other stories I've heard lead me to guess that my suspected problem of overcarburetion is quite common. Another point on setting air/fuel mixtures in general: I've found this and other methods very inexact for setting mixture. About 6 months ago I bought a tool called Colortune and have been very pleased with it. It's really just a see-thru spark plug with instructions on what color of flame you should be seeing. You simply richen out the carb and back up until the flame turns bunsen blue. It works fine on both single and multi-carb set-ups. Kurt D. Del Bene Bell Labs - WB ...!ihnp4!homxb!delbene