Q I operate petrol-engined vans equipped
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with constant-vacuum carburetters and when running in dense traffic in high ambient temperatures, the engines tend to stall. Can you suggest the cause and a cure?
Acting on the assumption that the lower density of the hot intake air results in a weakened mixture, I have tried enriching the mixture slightly, but this makes matters worse.
AIn the case of a fixed-jet carburetter, an
increase in the temperature of the intake air tends to reduce the mixture strength. but the linear-flow characteristics of the needle jet of a constant-vacuum carburetter are such that heated air provides a richer mixture and this may cause fouling of the plugs if the engine continues to run at slow speed for a long period.
Adjusting the mixture strength to the minimum compatible with even running in normal temperatures should obviate the stalling tendency. It might also be advisable to increase the tick-over speed.