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I'm still trying to figure out why my idle mixture is going lean after:
A: Just coming off the highway when the air temp is above 50 deg.
B: Turning off the engine, and then restarting after a ten minute interval
C: Driving at slow speeds in heavy traffic for more than 15 minutes.
My guess is that the fuel (10 percent Ethanol blend in Oregon) is getting too hot, either in the float chambers or the fuel hose. Only the idle mixture is affected, and the car runs fine except for a slow and lumpy idle.
My AFR gauge show the idle mixture going between 16 and 18; the normal idle mixture is around 13.5 to 14 when the car is running normally. If I open the throttles a little and transition away from the idle jet the mixture goes normal for that state, 11.5 to 12
The engine has Mikunis and an electric fan, the belt driven fan has been removed.
Thermostat is working, and the water temperature seems to be well controlled.
The exhaust manifold is ceramic coated, and underhood temperature is lower than that of my other 122 with SU's, which doesn't have any problems as bad as this, aside from the usual hot start in hot weather syndrome.
Any thoughts on how heat can make the idle mixture go lean? If it was an air leak I would think it would be worse with a cold engine, but who knows?
At this point I'm getting ready to adapt a 145 series air box to the car and set up a cold air intake system; I'm also thinking of rigging up some more extensive heat shielding under the bottom of the carbs (where the float chambers are) perhaps this would help...
Bill
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