206 rpm/gearing

12jr champ said:
Lo206,asphalt champ kart.YELLOW slide. What would be the optimum target rpm to gear for? Thanks
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This is what I would do to find the ideal gear ratio.

You need a tachometer first off.

Run some laps, observe what peak RPM the engine is turning. Add one tooth to the axle. In the next practice session, if the engine turns 100 RPM more (about) you will be going the "same speed" as before you changed.
Adding another tooth, if 100 more RPM, do it again.
Pretty much the same process if you remove one tooth, except that, if you lose less than 100 RPM, you're going faster. And people say my Excel program "nine sheets" is not useful.

Another benefit; lower air density, add teeth, hire air density, subtract teeth. Of course track condition is also a consideration.
It's called tuning "and tuning is tough" (Al Nunley)
 
I've rarely found a driver (and kart) consistent enough to make a 1 tooth rear gear adjustment on big tracks to be noticeable (repeatable and reliable.)
I always change two teeth at a time and keep going in one direction until the lap times start to fall off, then back up a tooth from there if needed.
If you aren't seeing improvements in lap times (or you are against the rev limiter too long) then go the other way with your gearing - repeat the process above -- changing two teeth at a time until you see the lap times fall off.
Of course, you have to be in the ball park on the driver to begin with, but that's another whole discussion/argument.


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Hello we have a Cadet LO206. We are going to try racing the IKF Grand National in Santa Maria, CA. We are beginners and don't have some goodies like a micron so gearing is trial and error but big swings aren't making a big difference.
We are going from a Green Club Carb restrictor to a blue one. What is the optimum horsepower & torque range with a blue slide.
We've aligned the carb and adjusted the valves but are middle of the pack in first club race (That darned Covid).
Thank-you
 
The link in post #2 has the hp and torque curve for both slides.

Peak hp for both slides appears to happen at roughly 5000 rpm for both slides.
To start, use the same methods for determining proper gearing for either.
The green slide does not drop off from peak hp as much the blue slide does. Over rev will not continue to gain as much as it did with the green.

The challenge for sprint racing is to figure which part of the lap to compromise for lowest lap times. Does this compromise give you an advantage despite being less competitive in another part of the lap?
Being mid pack requires different strategies from starting on front and leading whole race.
The problem may not be all gearing or engine power.
Just a thought.
 
The point I was trying to make is to try to take advantage of the things you and your setup do best.
 
Info at the nationals might be slim .
In that situation if you can ask someone you trust or if you work with a shop that's where I would start .
Stop watch or lap times . Maybe make half a big swing . Counting tenths makes a difference .
 
Mr. SHaw and Flattop, thanks very much... gives us an idea. The track we'll be running is a flat 7/10 mile road course. A couple of long straights with a good amounts of corners... your input helps
 
Is it possible to need a float adjustment based on gearing? I started with 17/66, black slide, C clip in top slot, floats at .860 and 1.05 +/- because that's they way I bought the kart.
It ran great in testing but we race gold slide.
Went to gold slide with 17/68 gearing no carb changes and did ok, we won, but it stumbled a bit and was a bit sluggish coming off of fast left handers and worse off slow left handers. Honestly we kind of lucked into the win.
Tried 16/68 today and the kart is awake with that gearing and really goes initially but won't make two laps without dying especially in slow right hander after a long run of full throttle.
It's obviously turning more revs than previously, are we pulling that much more fuel out of the bowl? Is that possible?
Thanks in advance for any input!
 
Will P said:
Is it possible to need a float adjustment based on gearing? I started with 17/66, black slide, C clip in top slot, floats at .860 and 1.05 +/- because that's they way I bought the kart.
It ran great in testing but we race gold slide.
Went to gold slide with 17/68 gearing no carb changes and did ok, we won, but it stumbled a bit and was a bit sluggish coming off of fast left handers and worse off slow left handers. Honestly we kind of lucked into the win.
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One tooth on the engine is worth right near 4 teeth on the axle. A 17/72 would have accomplished about the same thing. Not very practical.
Have you thought about a 13, 14 or 15 on the engine? Adjust the axle to match. Maybe not as radical as you might think, who knows?
 
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Will P said:
Is it possible to need a float adjustment based on gearing? I started with 17/66, black slide, C clip in top slot, floats at .860 and 1.05 +/- because that's they way I bought the kart.
It ran great in testing but we race gold slide.
Went to gold slide with 17/68 gearing no carb changes and did ok, we won, but it stumbled a bit and was a bit sluggish coming off of fast left handers and worse off slow left handers. Honestly we kind of lucked into the win.
Tried 16/68 today and the kart is awake with that gearing and really goes initially but won't make two laps without dying especially in slow right hander after a long run of full throttle.
It's obviously turning more revs than previously, are we pulling that much more fuel out of the bowl? Is that possible?
Thanks in advance for any input!
Click to expand...

No, you do not need to adjust carb for gearing. Sounds like you have a plugged idle jet or something else causing your issues. Unrelated to gear changes. Clean your carb jets really well, check your float height hasn't changed and give her another shot.
 
In my whole 50 years of experience in karting, I cannot remember a time when my gearing selection ever affected the tune on the engine.
 
I would not expect it to either, other than increased rpms almost the entire track, but the problem showed up after a year change so I started scratching my head on fuel consumption out of the bowl.

I have the pilot jet in hand now the side holes are clear. Should a tip cleaner pass through the jet from bottom to top? If so that’s indeed my problem because it won’t.
 
Hole is too small for my wire torch tip cleaner but I’ve got light passing through it now after blowing it out so it’s clear. I could not see through it before.
thanks guys.
 
Will P said:
Hole is too small for my wire torch tip cleaner but I’ve got light passing through it now after blowing it out so it’s clear. I could not see through it before.
thanks guys.
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Yep. Welcome to the 206. First thing to do when anything weird is going on is to clean that jet. It is so small, it gets clogged with any little thing. I use compressed air or just blow it out with my mouth. Careful sticking anything in it as you could open it up (accidentally) and then fail tech.
 
CarlsonMotorsports said:
^ Good advice, right there.
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Yes thanks again. We ran it yesterday after cleaning that jet and it still ran like crap. Intermittent stumbles and missing. Especially in slow right hander after long full throttle run. Also stumbles on throttle application after corner turn in...slow or fast corners. After we got home my son found a piece of electrical tape in the fuel tank near the outlet. Who knows how it got there??

Things of note that may or may not play into it:
Potentially blocked fuel outlet
2-2.5' air bubble in fuel line between pump and carb-is this normal or is pump going bad?
Carb is positioned as flat as possible, needle set at top clip, idle air bleed is full open, idle screw-I can't recall, floats were tried between .750-.860 and 1.050
Plug was light brown after last race and fouled out yesterday in messing with clip position (tried 2nd from top-no good) and mounting angle.

Going back to test today with unblocked fuel tank, new fuel filter and new plug and carb set as noted above.

Will check kill switch wire and try to see if I can test fuel pressure. Did I read 8psi somewhere?

Thanks again for the feedback. Race is tomorrow!
 
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