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On 29 Jan 99, at 20:03, whizby wrote: > Backfiring on over run means that the carbs are running too lean, at > least at that moment. It is also well known that the better > breathing promoted by a better exhaust will require you to jet your > car slightly richer. So all the evidence is consistent. > hey Jim, care to elaborate on that. how do you do it? specialty drill bits? > little files? do you have a measurement in mind based on engine displacement > or just experiment till the plugs look right? > i have been trying to get this question answered for about three weeks now. > i know my engine's running lean, but i don't want to destroy anything. You replace the jets with larger ones. In general you don't want to drill them out for 2 reasons: You probably cannot do a very good (or consistent) job, which is VERY important if you're working on dual carbs, and then the experiment becomes irreversible. There's actually a good third reason and that is that the jets have a size stamped on them and once you start changing them you have no way of identifying what they actually are. As to how to change them, every brand is different, there's a long learning curve, there are several jets, as well as different kinds of jets, in each carb, and the parts are becoming hard to find. You should start by shopping for a good book on your brand and studying it carefully. Then, perhaps, rebuild one slowly so you become familiar with all the parts and passages in each. Once you understand how they work and what part each piece plays, then you may start to get a feel for what you need to change to get where you want to be. If this sounds daunting, consider going to the junk yard and buying a carb from any other car just to take apart and become familiar with. Shoot for a CARB that is the same make as yours. I would look at the spark plugs and watch the gas mileage to get an idea of where you stand at any given moment. Jim - ******************************* Jim Adney, jadney@vwtype3.org Madison, Wisconsin, USA ******************************* ------------------------------------------------------------------- Search old messages on the Web! Visit http://www.vwtype3.org/list/