According to the 1980 Cessna 172 manual priming with one to two full strokes should be sufficient to crank most engines that are cold, in normal conditions. This should apply well to all KR engines where the manual primer is properly matched to the engine. In winter up to 6 strokes may be necessary. Also, priming during starting IS permitted, however a notation is made to insure that the primer knob is secured prior to beginning flight operations due to the possibility of drawing fuel through the primer, which is unregulated, and unmeasured. This is what I meant about unknown amount. Unless you take one apart, and then measure the injected amount, you have no idea how much fuel you are putting in, same as the solenoid. Too much causes cylinder wash which greatly increases the amount of wear on the engine. MOST low hour pilots over richen their engines, or fail to lean properly, or at all. The reason we teach not to use while cranking is the increased fire hazard due to causing a backfire, and the fact that it could be left unsecured, causing an over rich condition in cruise. This makes for two problems: 1) Lack of fuel economy expected, which could result in an emergency landing (number one reason for emergency landings overall, running out of fuel); 2) fuel fouling plugs causing carbon buildup and excessive engine wear, low power, and possible engine failure/shutoff in flight.
Just because one gets away with doing what is not recommended does not mean it is correct, or good to do. If the manufacturer does not endorse it, and they are the "expert" of that setup, then don't do it no matter who recommends it. There is ALWAYS too much other information missing that allows that person to use the unusual procedure that doesn't make it on to the page when talking. Just my 2 cents worth... Colin Rainey [email protected] EarthLink Revolves Around You.
