Re: Distributor advances too much

Karl wrote: 
"P.J. Berg"  wrote

 Seems like your mechanic in charge is not fully into aircooleds..

 J.

Or even into understanding basic vacuum advance, aircooled or not.

Under a load, i.e. driving down the road, vacuum advance GOES away.

Vacuum advance only comes in when you accelerate or rev the engine in neutral.

Cruising down the highway, you just have centrifugal advance.

Your mechanic needs to go to City College and retake Auto Mechanics 101. Problem is, all they teach now is computerized crap and how to replace parts.

Cruising at steady speed and very small throttle openings gives you strong vacuum at the throttle plate, where the vacuum signal for the distributor is taken. I.e. max advance.

Accelerating: At first, when you touch the pedal, you get6 a sudden rush of gasoline from the accelerator jet, to accomodate the even bigger rush of air going in. On top of that you get a strong vacuum signal just as you step on the gas pedal. Helps kick things in motion. After that, the more throttle you give, the LESS vacuum there is.

Vacuum is strong ONLY at very small throttle openings. Load or no load. It's a strict effect of air being sucked through a narrow gap between throttle plate and carburator body. Small gap, huge suction, FAST airspeed at the vacuum port. Open the throttle wide open, and the overall volume of air going in grows, but the SPEED at the vacuum port actually drops.

At cruising speeds you have very little load, and small throttle openings, so it's safe to have more ignition advance.

Jan
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