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On 31 Aug 2005 at 10:42, gray, douglas wrote: > It's only under acceleration, and it only occurs when the engine is under > load. It doesn't occur when I rev the motor as the car is standing still, > just under load. As others have mentioned, the popping is probably in the exhaust system, not the carbs. This can only happen if unburned gas is getting into the exhaust; 2 things can lead to this. The first is an engine which is too lean, so that it misfires and the gas gets pumped out into the exhaust; the second is if the engine is too rich, and the excess passes on out. Either way, it's a carburation problem. > I do believe you are right about the exhaust leak. I will check this > tonight. I'm not a believer in the exhaust leak theory, but I'm in the extreme minority. > By the way, do you guys get 85 octane gas in Northern Arizona? We have it > all over Colorado, and I've only ever seen it in higher altitude locations. > How does this gas affect our cars as compared to 87 octane at lower > elevations? Higher octane gas is needed to keep the gas from self-igniting just from the heat of undergoing compression. This self ignition occurs when the cylinder gets a full load of fuel/air and then compresses it. At high altitude there is less air to start with, so the peak compression pressures and temperatures are also less, so cars don't need gas with as high an octane rating. Turbocharged cars, however, will still need their full octane rated fuel, because they get the same intake air pressure at 7000 ft as they do at sea level. -- ******************************* Jim Adney, jadney@vwtype3.org Madison, Wisconsin, USA ******************************* ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ List info at http://www.vwtype3.org/list | mailto:gregm@vwtype3.org ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~