Richen idle with needle or float?

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are you talking about a bowl type carb? those have a fulcrum arm inside them that opens and closes the inlet needle, you can richen or lean the mixture by changing the height of the fulcrum arm, in my experience, when the fulcrum arm height is set too high, it does richen, but at the expense of the needle not totally closing all the way causing a flooding condition in the carb that cannot be overcome by closing up the needle adjusters...imo better off setting the fulcrum arm height at manufactuers recommendation for engine type and instead working with the adjusting needles to get the engine to idle/accelerate properly...
 
FatOldKartDad said:
Hi Jim - thanks (as always). I do always look through the jet to make sure I can see light and I have gage pins (I bought extras - they are cheap - since I dropped one and could not find again they are so small). Usually the air is not as dense as 100% for us - it's more like 90% in the summer and even today the forecast is for 92% or so. We'll check everything again before we go back to the track. Thanks!
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You mentioned "forecast" for today's air density. Where do you get that "forecast" number from?
The formulas I have for calculating air density use barometric pressure and temperature as operators. For lack of anything better to do, I've been tracking the barometric pressure and temperature here in Austin Texas for over two years. I've seen air density numbers from about 89% to 101%. It never changes that much in one day, that's the amount of change over a year. It does change as much as 5% in one day. I checked it about every 2 to 3 hours each day. Longacre says; a 1% change in air density calls for a 1% change in jetting area. With a Change from .011" to .012" in jet size, that's a 18.947% changing area. (Flow) the area difference between jets gets smaller and smaller as the jets get bigger and bigger. For instance; between a .038" and a .039" jet, the area difference (flow) is about 5%. A .0002" change in hole diameter is real close to 1% change in flow, between those two jets.
I always recommend the Longacre (there are others) air density gauge as an essential tool to have in your pits.
Think about it; you watch your tire pressures very closely, why not the amount air/fuel that's being pushed into your engine?
 
alvin l nunley said:
You mentioned "forecast" for today's air density. Where do you get that "forecast" number from?
The formulas I have for calculating air density use barometric pressure and temperature as operators. For lack of anything better to do, I've been tracking the barometric pressure and temperature here in Austin Texas for over two years. I've seen air density numbers from about 89% to 101%. It never changes that much in one day, that's the amount of change over a year. It does change as much as 5% in one day. I checked it about every 2 to 3 hours each day. Longacre says; a 1% change in air density calls for a 1% change in jetting area. With a Change from .011" to .012" in jet size, that's a 18.947% changing area. (Flow) the area difference between jets gets smaller and smaller as the jets get bigger and bigger. For instance; between a .038" and a .039" jet, the area difference (flow) is about 5%. A .0002" change in hole diameter is real close to 1% change in flow, between those two jets.
I always recommend the Longacre (there are others) air density gauge as an essential tool to have in your pits.
Think about it; you watch your tire pressures very closely, why not the amount air/fuel that's being pushed into your engine?
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Hi Al! I use the website "airdensityonline.com" - it's not the same as having my own gage (I'm working up to that ) but the numbers they have for Austin pretty much match the range you mention. The airdensityonline website does provide a short term forecast of air density which some racers might find helpful.
 
FatOldKartDad said:
Hi Al! I use the website "airdensityonline.com" - it's not the same as having my own gage (I'm working up to that ) but the numbers they have for Austin pretty much match the range you mention. The airdensityonline website does provide a short term forecast of air density which some racers might find helpful.
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It's good that you have a source for air density readings. I have my doubts that your source is giving you "forecasts". I'm pretty sure you're talking about air density readings, like the temperature of the air. Air density is what it is, right now. I've never heard of an air density "forecast". I could be wrong! I know the air density, in any given area, can swing 5 points or more. A change of .001" in jet size will cover, approximately, a 5% change in air density.
I've heard people say they can feel the difference between a 15/60 gear ratio and a 16/64 gear ratio, both 4 to 1. I don't know, but if people can feel the difference in those identical gear ratios, I find it hard to believe they couldn't feel the difference with a 1% chang in jetting.
 
Thanks flattop1, it's been years since I first started looking for this site. Uncorrected barometric pressure, I love it. All the sites I have found only lists the "corrected to sea level" barometric pressure.
 
This is what we were using when we ran shifters. You would normally "check the air" 10 minutes before the start of the race, it would calculate the jet change working off of a base line you established, and off you went. It took the guess work out of it. We still mess with it from time to time for our IAME X30. With the 206's, road racing in those big draft packs, it's hard to tell if small carb adjustments make much difference.
Clark Gaynor Sr.

https://computech.com/products/weather-stations/
 
ClarkSr said:
This is what we were using when we ran shifters. You would normally "check the air" 10 minutes before the start of the race, it would calculate the jet change working off of a base line you established, and off you went. It took the guess work out of it. We still mess with it from time to time for our IAME X30. With the 206's, road racing in those big draft packs, it's hard to tell if small carb adjustments make much difference.
Clark Gaynor Sr.

https://computech.com/products/weather-stations/
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This is where I am with the LO206 - I'm not try to be exactly right with LO206 carb settings - just approximately right ("Good Enough" tuning).
 
Tuning the mixture is not the "whole" secret to going past, but it's a big part of it. I know it's got to be at least as big, if not a whole lot bigger, then changing gear sets of the same ratio.
If you're looking for a 1% increase in lap times, it's not there, but tell me, what was the lap time difference between first and second place qualifying time at your last race?
 
alvin l nunley said:
Tuning the mixture is not the "whole" secret to going past, but it's a big part of it. I know it's got to be at least as big, if not a whole lot bigger, then changing gear sets of the same ratio.
If you're looking for a 1% increase in lap times, it's not there, but tell me, what was the lap time difference between first and second place qualifying time at your last race?
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About 0.5%
 
alvin l nunley said:
Thanks flattop1, it's been years since I first started looking for this site. Uncorrected barometric pressure, I love it. All the sites I have found only lists the "corrected to sea level" barometric pressure.
Click to expand...
Second thoughts; these air density readings are only "predictions". (I didn't even know they were available) As such, they depend on the skill and accuracy of the predictor. Predicting the weather, at best, is an art. Meteorologists, and the accuracy of their predictions, are legend. Not that it's not a big help, but I think I would still favor my Longacre air density gauge.
I have two years of graphs showing the fluctuations of air density, it would be interesting if I could compare those to the predictions.
 
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