[quote=“urodacus”]um, minor positions of a mm or two in the float height do not affect the flow through the main jet much at all.[/quote]That’s correct. You run into problems when gravity from the gas tank fills the bowl. From there, it keeps being fed into the carb via the main jet with just gravity all the while the carb is sucking on it which accelerates the flow. Within no time, ignition fails because the carb can’t provide enough air for all that fuel. The bike dies out like a candle in a sealed container.
[quote]more major differences in fuel height will, yes, affect the pressure difference pushing fuel through the idle passgeway and through the jet, but there it is still dominated by the idle mixture settings and thus the diameter of the pilot jet or the idle jet or whatever you want to call it.[/quote] That’s correct. The diameter of the jet is directly dictating how much fuel gets through under normal circumstances when the vacuum is functioning without interferences. The thing is, the vacuum sucks far less gas into the throat of the carb than a gravity feed from the gas tank does. And that’s what happens when the bowl is full. The gas has to go somewhere, and gravity pushes it right through the main jet and it smothers the spark right out.
[quote] but the principle of all carburettors is that they are most sensitive to the difference in pressure between the inside of the bowl and the carb throat, and that is how they deliver the fuel.[/quote]And that is also true. But when the throat is filling up with fuel and delivering it right to the combustion chamber, it’s just too much fuel altogether. The bike is not designed to operate in such conditions. [quote] (and if there is crap in the lines or in the jet, then you have difficulties). the actual level does not really matter terribly much, unless it’s WAY too high (in which case you may get overflowing of fuel out the standpipe of the bowl, or flooding, or both,[/quote]Also true. And that plays against my personal tentative diagnosis. Loretta did not report smelling or seeing gas.
[quote] or unless it’s way too LOW, in which case you get fuel starvation and lean running, intermittently, especially under load and full throttle.[/quote]Under load and full throttle being the key words because that isn’t Loretta’s problem, either. [quote]the only point of the bowl float is to stop the fuel from running in when the bowl is vaguely three quarters full.[/quote]Yes, and that point is somewhat defeated when the float sticks, the bowl fills up and floods the carb’s throat.
[quote]the fuel level in your carbs IS NOT stable when you are riding, in case you need more evidence of this. [/quote]It’s not stable, but it’s not flooding the carb’s throat, either. And that’s my point.
[quote]I also had a GS650G at one point. it was a heavy piece of crap and didn’t steer well, but was fairly comfortable and had the advantage of not chewing chains.[/quote]Mine had a drive shaft-no chain. Also heavy and the handling was also crap. I think it was a 1981 SUZUKI GS650ES. We called her Suzie, and the bitch had only 5 gears. To make up for it, it had a green display to show you what gear you were in placed between the odometer and the RPM gauges.
[quote]i also seem to remember carb problems on that beast, magnified by having four of them. almost always traceable to diaphragm leaks or spring stickiness in the CV system.[/quote]Mine ran very well, but it did have a very, very, very slight delay when slowing down and accelerating again. I had the carbs looked at and calibrated, but that didn’t help. I figured it was the diaphragms leaking. It was an older bike that had been stored for quite some time. I rode it like that and I ended up trading it for a Honda Civic 4x4 station wagon a few years down the line. Did me well.