I heard the thicker formula was so the gasoline didn’t evaporate so readily from the bowl (and the fuel line, etc), to provide quicker starts and less cranking. Nowadays, if a carbureted car has been sitting, you take your squirt bottle and fill up the bowl, then turn her over. But I heard that second-hand and didn’t know there were “seasonal blends”. I suspect you are also correct.
This weather hurts my engine's performance!
- Thread starter Minimichael
- Start date
Down here in eastern North Carolina, we rarely go below freezing for two weeks at a time, so I'm not sure they change our gas formula for seasonal weather, but @Minimichael is in the frozen midwest, so he might get a seasonal change of gas blend.
I like the idea that the hot, humid air might be too saturated to allow fuel to evaporate. I plan to research that theory.
I like the idea that the hot, humid air might be too saturated to allow fuel to evaporate. I plan to research that theory.
Yes, gasoline vaporizes better and more efficiently in less humid air. [1, 2]
Humid air contains more water vapor, which displaces oxygen molecules. This leaves less room for the oxygen your engine needs for complete combustion, reducing power output and creating an overly rich air-fuel mixture. Conversely, drier air contains more oxygen, resulting in a cleaner, more efficient burn. [1, 2, 3]
From AI quoting a study by Sunoco race fuels
Humid air contains more water vapor, which displaces oxygen molecules. This leaves less room for the oxygen your engine needs for complete combustion, reducing power output and creating an overly rich air-fuel mixture. Conversely, drier air contains more oxygen, resulting in a cleaner, more efficient burn. [1, 2, 3]
From AI quoting a study by Sunoco race fuels
And so in our brand of humidity around these parts my air-fuel mix is overly air-rich and thus water rich – with reduced fuel concentration (either by droplet size or other measurement like evaporative non-solid volume ratio). And if the carb body's refrigerating effect on the bowl fuel is to keep it feeding nice and chilled gasoline ...
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Yeah, there's that, too. Thanks, @sparkwizard .
So, in regard to that then, possible tweaks might include:
1) Opening the air screw seems one way I might rebalance a fuel-rich slow jet. Reducing that jet size might be another.
2) Raising the slide's idle position from throttle body floor could allow more overall air flow, and dropping the needle itself a notch could also compensate here and/or further tweak by delaying fuel flow volume allowed by the needle taper profile.
3) Decreasing the main jet size will reduce maximum fuel flow.
Welp... One thing at a time, I guess.
So, in regard to that then, possible tweaks might include:
1) Opening the air screw seems one way I might rebalance a fuel-rich slow jet. Reducing that jet size might be another.
2) Raising the slide's idle position from throttle body floor could allow more overall air flow, and dropping the needle itself a notch could also compensate here and/or further tweak by delaying fuel flow volume allowed by the needle taper profile.
3) Decreasing the main jet size will reduce maximum fuel flow.
Welp... One thing at a time, I guess.
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...
And I plan to test just that, in cooler temps but very high humidity the next two late nights, and see if it's still struggling to start/run. (this thread's original issue involved high temps as well as humidity.) If it won't start, I'll clean and look for corrosion on them jets and try again. If that solves things, I'll have no choice but to shelve all this science once again. But if not, I can look at the condition differently, because after y'all's input, and @sparkwizard's superb research, I'll approach the engine as if it's flooding — keeping in mind it may be flooded because very humid air flow lacks the usual amount of oxygen. And we'll go from there...(Keeping in mind another factor could be poor evaporation of gasoline into the flowing mixture, and the fact we can't say it's flooded if it's also not getting enough gas. Fascinating stuff, I know.)
Ok now after five days of just sitting in the garage, it started normally. But then again it's 72° and 55 percent humidity. Vastly different from when it didn't want to start —in 95° and 85% humidity. Nevertheless, I haven't opened the bowl or made any changes yet, so I'm still calling this a controlled experiment. And while tonight's weather offers to get downright balmy in low 60s with humidity in the high 80s, I won't be up that late. I mean I'm curious but I'm not crazy, right? Who is up revving a minibike at 5am on a Tuesday morning?