Haha yeah that guy is interesting. Glad we have sweepers in here to keep the place clean. Anyways...
Lean versus rich conditions are things it seems a lot of folks don't really get. Surprisingly a lot of people that you think should know better. One of the things that throws people off is it's not linear behavior on each side of the scale. What I mean is that a 10% rich behavior tends to exhibit a greater degree of out-of-tune than a 10% lean mixture. It seems like it's more like 10% versus 100% exhibit similar degrees of behavior. I remember going over this is boiler combustion at the academy for the scientific answer but you'll excuse me if I share anecdotal evidence instead of digging out the textbooks. It's been awhile. Some examples of behavior:
-On power boilers it will take about 10-20% rich to absolutely black out the stacks. Conversely you don't see a "white out" until your 200-300% too much air (lean). Because of EPA and CARB guys are so scared of getting fined for blackouts they run super lean all the time.
-At the track running two strokes (I ran a Honda RS125 for a bit) you couldn't convince folks to jet down. Everybody was jetting "safe". What they didn't get is that at one jet too lean you made less power, at two and three sized lean you'll do the same and detonate a little, and at four or even FIVE jet sizes too lean a risk of seizure. Seriously. Five jet sizes to kill it. Now two jet sizes rich and it would run like shit and make no power. So you see not linear. Never could ride that bike as well as I could jet it.
-Here in our world of motorbikes even experienced folks think backfiring is caused by a rich condition and nine times out of ten it's a lean one. People think the unburnt gas is exploding in the pipe. Now in trailing throttle conditions this can be true, but in closed throtlle decel likely not (race bikes at high rev exception here that's another story). The question you have to ask yourself is this: is the pipe hot enough to cause ignition? If the bike is truly rich aren't all those unburnt hydrocarbons actually carrying excess heat out the pipe and COOLING the exhaust? More often than not this is the case. So while jetting and trying to "get on the paper", so to speak, keep this in mind. If you suspect too rich go one size lean; if you suspect too lean go two or three richer. I found this especially useful on jetting FCR pumper carbs.
-I've spent the last decade or so working on gaseous fueled generators for a living (natural gas and propane) and made some observations. First of all machines running lean is endemic. Lots of them out there are lean and people never know it. Why? Because it shows up slowly and over time. Remember what I was saying about having to be really, really lean and running hot? They cook themselves over time. Half a dozen or ten year old machine with low hours all cracked and brittle from the heat. How is it that folks never know this? Simple: they never run them to full power. Takes a load bank to find out. Most units are over sized to be on the safe side so folks never find out unless it's really bad. I mean like half delivery at full load, say 5 or 6" WC on an LP unit. When folks call me to work on their stuff I'm always looking at the gas system. You guys wouldn't believe how often I find it out of spec.
-A month ago I decided self employment was driving me crazy and took an offer to go take care of the boilers, generators and compressors at the 51 buildings that comprise Cisco Systems. I have something like 108 overgrown hot water heaters in the 2M BTU range to care for (I won't call them "boilers" because they don't make steam you see). Our concern with the AFR and lean/rich over there once again is cooking millions of dollars of equipment over time. That gets, very, very expensive. Also we have regulatory agencies all up in our business. Too rich and the HC count sets off flags, too lean and the NOx gets out of hand. Once again a little too rich to cause trouble with the HC count and a lot too lean to do the same with the NOx. I'm trying to convince the bean counters I need a portable 4 gas EGA to save them money but so far I get a lot of blank stares and dumb looks (read: we don't believe you). We shall see my boss the Chief gets it.
-Seems like we have a lack of good classes on basic combustion theory. Guys that get this backwards have engineering degrees and are pretty smart folks. All I can figure is there was a gap in their education. Mine came from an instructor we called "Boiler Bob" at CMA ages ago. Combustion theory isn't exactly hard and there are basic rules. We have been doing this for awhile it shouldn't be rocket science. Contrary to popular belief you do not need a dyno to tune your bike within a size or so of optimum. Some "seat of the pants jetting", an IR thermometer, common sense and a day on a back road can get you there.
That's what I have FWIW. I find it easier to tell a story and provide experiential evidence than to tell people "this is how it is". Experience is the best teacher and if you see one then teach one. Also it's pretty tough to whip out a textbook and give a class on a forum.
I don't typically expound at length such as this simply to avoid the engagement of said idiots that are on vacation from this place. So once again I appreciate the cleaning crew.
But that's not the case. The mixture is quite a bit richer with the choke/enrichener activated
