When I back out my L 72 from the gagarge (from a cold start) and let her idle on the driveway, the rpm speed starts at about 1,000 but as she warms, from 5 to 10 minutes, the idle speed gradually increases and tops out around 2,000 rpm at which time I'll hit the accelerator pedal and its falls back to a steady 1,000 rpm. Is this gradual build-up of RPM speed during warm-up normal or is something not right that needs adjustment? Thanks
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Re: Fast Idle Cam
John, I believe that is close to normal. As the oil warms it provides less resistance to engine rotation, and the engine speed will increase. Also as the intake manifold is warmed by exhaust gasses fuel is better vaporized, and the intake system becomes more efficient. The usual increase may not be quite as much as you have indicated, however.
Modern electronically controlled engines do not act this way, and we have become used to that mode of operation. We then notice the operation of the older engines as quite different than we are used to. All carbureted engines of thirty years ago acted the way you have described.Terry -
Re: Fast Idle Cam
Normal! For my L-76 the fast idle speed is specified at 1750 hot. You adjust the fast idle speed screw on the AFB to achieve 1750 with the fast idle cam properly indexed with the choke fully closed. The cam can be manually placed in this position when the engine is hot and the choke open to make the speed adjustment. The proper index mark position with the choke closed is achieved by bending the fast idle cam control rod if required. When first started cold the speed is about 1500 in mild weather and if you don't bump the throttle during warmup the speed will slowly increase. Your L-72 should have a similar fast idle speed adjustment and "hot" specification.
If you drive right off (at very moderate speed, of course) the fast idle won't reach full hot speed because movement of the throttle will allow the fast idle cam to rotate off the index (high point) as the choke relaxes due to engine warm up.
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