Wilsons Sandbox

Toby wrote in response to my suggestion about carb icing as the cause of the intermittent sputter some folx have experienced during rainy rides:

> > Tom, > > Very interesting. The air through the carb really is

hauling ass a.fwy

> > speeds huh?You may just have something here. This would

account for those

> > 'smooth' or even' power losses I think. Wouldn't it? Maybe

even some

> > 'sputtery' ones usually typical of water in 'spark system'

sort of

> > failures.If this turns out to be 'IT', I hope somehow,

someone knows how

> > to loo under wierd problem #2' in the archives. >> > > So recycling warm air, or some sort of carb warming

device would sort

> > this possiblity eh? > > > > Slide

And Bogdan added

> Warming device eh what? Kris Cichon (Mariola's squeeze,

remember her?) is

> convinced missing is caused by HOT air from the radiator

hitting the fuel

> line. He wants to install a COOLING device. Tom, if I recall

correctly,

> lives near Atlanta, no heat there. Kris lives in the middle of

Chicago,

> known for its mild winters. Wonder if location is influencing

anyone. Course

> they both could be right. Bogdan

As counter-intuitive as it may seem, icing is possible under conditions as high as 60 degrees F - I've seen it first-person back when cars were carbureted (practically ancient history now). Maybe that physics professor lurking out there can explain the dynamics of the Venturi effect? My KLR exhibited the symptoms not in Atlanta, but in the White Mountains of New Hampshire last week, where it was raining and in the 40's F. Can I prove it? No, it's a transient condition and as soon as one slows heat rising from the engine quickly warms the carb body enough to make it go away. Mine only did it for about a mile during the coldest part of that ride, and when I slowed for a motor home chugging up a long climb it disappeared. FWIW, heat-related problems usually cause fuel in the carb or supply line to vaporize leading to hot-restart problems. I suppose if it were hot enough around the carb to boil the fuel - and that's increasingly likely with oxygenated fuels - one would experience a symptom more or less like that of running off "Main" and onto "Reserve", a rapid and complete loss of power. It's also possible that the problem we're talking about is being caused by roadwater intrusion into an electrical connector during a rain. My bet would be the modular plug that connects the coil to the wire harness. Whatever is being splashed up off the pavement by the front wheel contains tire dust, which contains carbon black - the stuff that makes natural rubber black instead of that weird brown color - and enough of it in a connector and there could be some "new" electrical pathways that would lead to no spark. Complicated, ain't it?? What puzzles me about that scenario, tho, is that it wouldn't be transient, so I kinda doubt the likelihood of the roadwater intrusion explanation. Sorry for being so wordy. Tom Bowman Atlanta P.S.: Say, Bogdan - you're not Dave Swider's evil twin brother, are you?? If you are, hope Tina's doing well....

At 12:43 AM 6/21/00 +0000, Steve Anderson wrote:

> > > > As counter-intuitive as it may seem, icing is possible under > > conditions as high as 60 degrees F - I've seen it first-person > > back when cars were carbureted (practically ancient history now). > > Maybe that physics professor lurking out there can explain the > > dynamics of the Venturi effect > > >I ain't any kind of professor let alone a physics professor unless >all my professing makes me a professor;-], but carb icing is pretty >straightforward, at least that's what they drilled into me during >aircraft pilot training. The venturi effect lowers the pressure, >which pretty much proportionally lowers the temperature. >Additionally, if not more important, is that the fuel vaporizing >(boiling) also cools the air appreciably. If the walls of the >venturi, where all this cooling is occuring gets below freezing, than >the moisture in the air can condense and freeze. It generally will >happen in a narrow range of temperature/humidity/throttle/power >settings. Some carbs are completely immune. > >I'm not comfortable speculating on whether this is causing any of >these *wierd problems* however.

I aint no smarty either. SmartAss yes.. Professor no... I've heard of this happening on carbs as well. But the venturi effect only provides the pressure differential and the Thompson effect cools based on the differential. How that is gonna fix the problem or how that is actually relevant to the cost of pork bellies this morning... I don't know.... What I do know is that one of my B-day presents (12er of Sam Adams) is going down awfully easy and PUI is no way to gain respect among peers in the physics community. Have a great night.... I'm off to the garage.... LaterZ Dash