I have read previous threads regarding the use of a cylinder head temp sensor on a LO206. What the argument seems to boil down to is that you can’t cut the compression washer off the spark plug per Briggs rules. Because of this, running a CHT sensor with the compression washer in place will effectively lift the plug up out of the cylinder head which is not desirable for performance (though the real world impact of this seems a bit questionable).
However, I have been reading a few LO206 carb tuning guides and they do mention using CHT as an indicator of whether the engine is running too rich or too lean. The normal operating range for the LO206 seems to be 375F - 400F. If you are running a CHT sensor and see that the engine is running below that, it would be running too rich and above that range, too lean.
As a newer driver/mechanic, this seems like a very handy quantifiable metric to have in my pocket for tuning. However, I do understand the concern about lifting the plug out of the head slightly when running a CHT sensor. To solve this, I have seen it recommended to simply run a Mychron CHT sensor during practice sessions, use it to tune and then remove it for qualifying and races. However, I would think that tuning the engine while the plug is higher up than it will be during the race wouldn’t be ideal. So then I was thinking, could I have two spark plugs? One with the compression washer in place that I use for qualy and races and another one with the washer removed for use with the CHT sensor during practice?
One downside I can think of with this idea is potential variations between the two plugs. However, with the newer Autolite spec plugs, there is no electrode gap which could otherwise easily cause variations between two normal plugs. So, I am thinking that two Autolite plugs would be consistent enough to use in this tuning method. Thoughts on this?
Another alternative in the interest of keeping things simple, is to get a IR temp gun and take a reading off the head after each practice session. Would this be accurate or reliable enough to use to make tuning adjustments?
I use one on practice days, and haven’t noticed any difference in power.
I don’t use it as a carb tuning tool yet use it to determine if the kart is bound up on exit and bogging the engine down. If the engine is under a larger load the temp is significantly higher.
On the hottest daysof the here in Kansas City I’ve ran around 385* when it grips up and I don’t chase the adjustment I’ve ran in the 415* range.
I run my engine on the rich side. .870 float, 3 OR 4 on the needle
Interesting, could you not view the bogging via the RPM trace during the session? When you say you don’t, “chase the adjustment” are you saying you don’t change anything unless you are in the 415F range?
I am only really trying to zero in on a carb tuning methodology. But, if the kart binding up can significantly impact CHT, then perhaps using CHT for carb tuning wouldnt be accurate?
Are you racing in relatively consistent conditions where air/fuel mix variations are not influencing to your CHT readings which you attribute to the kart binding?
I’ve raced in cool temps with great air quality and I’ve raced on hot temps with high humidity. I have been on the lean side before with a bound up chassis and I’ve seen the temp stay above 400 all race/test session Free or bound up. On the rich side of things if the chassis is bound up the temp will generally fall below 400 one I change my driving to compensate the condition
My float and needle setting rarely change. I tune the air bleed based off idle RPM.
It’s a 4 stroke. Keep it on the rich side, work on setup and driving. As my engine builder/prep would say it’s not a 2 stroke so “kiss” …keep it simple stupid.
I’ve ran the same carb settings for four years at every temperature, weather condition, and elevation I’ve been to. Don’t worry about it. Pull the rope and just drive your dick off.
While your approach sounds nice, it does not seem to mesh with all of the information I have been able to find regarding tuning a LO206. Even Briggs recommends adjusting carb settings when conditions change. From what I can tell, adjusting your carb settings per the conditions each day is standard practice.
I commend your wanting the best and also your wanting to learn. However, there is really nothing to be gained by carb tuning on head temp. It is not reliable enough to give you accurate data on engine performance. It also does not tell you what to change.
Everything you suggested in your first post is 100% possible and may be a good learning exercise for you when it comes to gathering data and acting on it. However, there is about 0.1 seconds in engine performance from carb tuning between a cool spring day and the hottest summer day.
You do what works for you to learn and get better, but believe it or not, 90% of 206s that win have whatever carb setting it left the builder/tuner with.
My observation is that you are not likely to gather meaningful or actionable data from 206 CHT except in situations where something is quite a bit out of range. Even thence the CHT may but even help you.
There are lots of variables acting on the CHT reading and your jetting is just one.
If you feel you’re lacking power I wound pursue things like gearing, chassis bind and overall engine health (leak down/compression test). Include carb under engine health from the perspective of the internals being clean, no air leaks and the float height is correct for stock settings.
Also keep in mind many racers will do things simply because they see others do it, or they feel they need to even in the absolute lack of objective evidence that it helps.
Well then the only thing I can suggest to you is go put the time in at your track to find what works and what doesn’t. Start at .870 and clip 3, and then go to .880, .890 and so on. I’ve spent days, and thousands of laps to find out what works and what doesn’t. I know exactly when I need to go to clip 3 or 4, or when I need to adjust the air bleed.
23 years of karting under my belt. You asked a question, I gave you an answer for what CHT could be used for. Go buy an extra header and put an egt or lambda sensor in it and learn.
Okay, thanks for the information everyone! Sounds like I am just trying to over complicate things. I am a very analytical, data obsessed type person (accountant lmao) and liked the idea of a quantifiable measure I could use in the absence of experience. But, I hear you guys and will focus my energy elsewhere.
Spencer, hopefully you don’t take anything to heart regarding some of the answers. Like you, I am extremely analytical to a fault at times and like to understand as much as possible regarding everything from what ingredients are in my cereal to the complex workings of a 4 rotor rotary pushing 1500hp on 60+ lbs of boost. I’ve recently gotten back into karting as an owner, having always previously rented whenever I went. The Briggs 206 is a very simple engine with very limited tuning due to the spec class they designed it for. What I’ve learned quickly from the experience of others that have been running them since they were first introduced is that chasing a tenth of a hp wouldn’t make a real world difference on track. 8.8hp vs 9hp wouldn’t translate into much time improvement on track. It’s all about chassis setup, momentum and driver skills. I’ve dropped my lap times over 5 seconds in the couple of months since I got my kart merely by getting seat time, some chassis adjustments and just learning how to be smoother with my inputs, entry and exit lines and applying throttle before mid apex. I set the valve lash when I first got my kart just to make sure it was correct as well as the float height. Since then I haven’t revisited either and I’ve pretty much only changed the air bleed in or out a turn at most depending on the temperature from morning to mid day here in central Florida since it’s finally starting to cool down just to prevent it from stalling from the time I start it in the paddock until I get into the seat and head out on track. The engine hasn’t run any different in any of my sessions that I could tell from my minor bleed adjustments once on track. I’m actually loving the simplicity and what Briggs has accomplished with the 206 class. Minimal maintenance like oil changes, get in it and go turn laps and have fun. In the end that’s what it’s all about. Putting a smile on my face and relieving stress from my hectic work week. Now get out there and give it hell and have some fun
Data and analytics can be really fun (I’m a big data guy when it comes to karting coaching) but also can certainly make you a victim of overthinking.
In 206, it really is more about jumping in and driving your best as @CrocIndy said. In a faster, more technical class you will see bigger advantages when using data and tuning metrics. But 206 is designed to be easy and foolproof so your energy is best spent learning proper driving and chassis setup.
No harm in wanting to analyze that stuff, but it probably isn’t correct to prioritize it yet at this point.
I’m just learning how to use Racestudio and hot damn, I’m a great driver once a lap, in a particular sector at a time. The next lap I butcher the same section but improve somewhere else. My theoretical best lap makes me look like a national championship contender. My herky jerky actual complete laps humble me to a back of the pack crackerjack
Tee beauty of the Briggs is you don’t have to worry about any of this. CHT is not important. We’ve raced them at the highest level in the US and had lots of others under the tent with us that were running up front or winning at events like the CKNA Grands, and nobody touches the carb. Grip it and rip it.
Thanks for the input everyone! I’m definitely focusing on building up my driving skills primarily. I am just naturally drawn to optimizing as much as I can in every hobby I pursue. I enjoy the learning process and having such a helpful community to bounce ideas off and absorb knowledge from has been great!
