Great explanation Mnt Track!
GREAT POST!!!!!Mtn-Track said:OK, so I'm an engineer and pilot. This is how it works in the realm of an aspirated aircraft engine and how it relates to the coolant heating of the Yamaha carbs;
The majority of normally aspirated (carb) aircraft engines are updraft with the carb below the engine, out in front. Like I said in my earlier post, carb icing is an issue whenever the temp and dewpoint spread are within 10 degrees, not as likely at 50 degrees F as 20 degrees F, but still a possibility! An aircraft carb has a diverter valve on the front of the carb that can be switched over to draw air from around an exhaust manifold. This heated air is also what is used for cabin heat. When you do this, however, you loose some engine RPM and ‘power' since you are now drawing warm (less dense) air into the carb and also losing the ram-air effect in front of the carb. Does it change the air/fuel mixture? You bet it does and the result is power loss. You DO NOT want to spend much time with the carb heat on in an airplane as it's only intended to be temporary, and only long enough to clear out the carb ice. This is due to the richer fuel mix that can fowl the plugs and the natural thing to do is lean out the mixture (which you can do in a carb'd plane) to compensate for it. But, if you shut the carb heat off in that condition the engine immediately goes lean and will either stall or seize the engine, or both! Air cooled aircraft engines are also REALLY sensitive to thermal shock.
Now the Yami set-up. Can you imagine the warranty disaster they would have on their hands if they produced a sled with a rider-controlled carb AIR heater valve? It would also adds lots of extra weight to have the additional set-up of the exhaust heat exchanger, plumbing, and valving. So the easiest and safest method? Just run heated engine coolant through the carbs, and stipulate that it either be on below 32F or off above 32F. Though not anywhere near as effective as aircraft carb-heat, it will help to reduce carb icing and minimize rich/lean issues with the air/fuel ratio. Since a sled engine rarely stays at a constant high-rev state, the heated carbs will have a chance to clear out any ice that may be building up when you let off the throttle and reduce the mass flow of air into the carbs. Unless you're on the ragged edge of being lean, the temperature difference between having the carb heat on vs. off should be almost insignificant, especially at higher RPM's. The air does not have the residency time in the carb to significantly alter it's temp, thus density.
In short: If the dewpoint is between -10C to +30C, and the temp is between -20C to +30C, carb ice can be an issue.
There. That's the story as I know it and I'm sticking to it!
Oh, and my carb heat valve is always OFF! The air way up high is usually far too dry to be an issue. You lowlanders may need it though...
staggs65
Moderator
i'd say that covers it, and it's in english 