Tuning at 1/4 throttle is not going to do it. It needs to be under load, full run of the throttle. . Mixing at 100 to 1 is not going to do anything to a O2, its the 20 to 1 I am talking about. Does your WB record? If not, then its more of a toy. I have lots of experience at tuning with WB/computers. Turbos to be more exact. That is an art on carbs. EFI is nothing. Either way good luck i hope it is working out. Some info is better than none. Some people just read the spark plug too.

Great news folks! I absolutely recommend anyone interested to go ahead and get this setup! I cannot believe how fast and easily I was able to finalize the tune on my FL400 today. Although I got real close with plug reads/chops/butt dyno, I was still a bit ways off!

Before final carb adjustments:
Throttle positions
1/4: 12.3:1
1/2: 13.4:1
3/4: 12.2:1
WOT (Wide Open Throttle): 11.0:1 @ 7300 RPM peak

After literally a few hundred feet I immediately read my 1/2 throttle was too lean for my liking; even though the Engine sounded absolutely perfect. To make an impression, I dropped the clip on the needle 2 positions and came out as follows:
1/4: 11.8:1
1/2: 11.2:1
3/4: 11.2:1
WOT (Wide Open Throttle): 11.0:1 @7300 RPM peak

Making progress, I raised the needle clip back one position and the results:
1/4: 11.8:1
1/2: 12.0:1
3/4: 11.8:1
WOT (Wide Open Throttle): 11.0:1 @7300 RPM peak

Much happier me and Engine at this point. Then it was on to adjust the main jet. Starting was with a 175. I dropped the main to a 170 and here is where I left it:
1/4: 11.8:1
1/2: 12.2:1
3/4: 12.2:1
WOT (Wide Open Throttle): 12.3:1 @7800 RPM peak

So you can see I gained about 500 RPM just by leaning up the main jet slightly. The 175 main was choking it like a rev limiter and the 170 let the Engine breath more with freedom

Now for the best freaking part of this - the part that separates the boys from the men so to speak. See, I had planned on spending hours finalizing the tune on my pilot - hoping to make it perfect for the coming months riding season. I had planned on tuning in the morning, and then calling it good enough and just have fun riding in the afternoon. No need here. It literally only took me 45 minutes today TOTAL to get this machine dialed in. New Plug chop looks perfect right at 2MM smoke ring, and the insulator is coming out nice and dark brown. Engine doesn't skip one beat what-so-ever!

So that makes two for three machines tuned in less than an hour with this WB O2 sensor. Next time I'll tune my FL350r.

GET ONE of these!

Wow. It’s really that easy. Might have to look into this.
What do you consider to lean.

Anything leaner than about 12.5:1 at any of the 1/4 positions is too lean. My FL400r really likes lower 12s all the time.

so what are you egt's.

are these just regular O2 sensors

you should make a video for us to see lol

EGT for my FL400 is running right under 1200F between 1/4 and 3/4 throttle. Full throttle is running 1050F.

No. This is not a regular O2 sensor. Not one bit in fact. This is called a Wide Band O2 sensor which reads between 10:1 and 20:1 AF. Regular 1,2, and 3 wire O2 sensors are not nearly the same. This one is like a 5-wire sensor. Hence, the cost is a lot higher - though these devices have come down in price over the many years. 20 years ago a sensor like this would have cost $2k, but now they are commonplace is modern vehicles and are much more affordable at about $200.

I'll mount my go-pro to my FL350r when I tune, but its going to be a minute before I get that machine out to a suited area. Am in search of a grassy field area close by for tuning it.

Picture of throttle markings.

OK this picture is of my FL350.

The BLUE mark to the right is ZERO throttle, but with the throttle cable taught but not lifting the throttle slide.
The RED mark to the left is FULL throttle with the throttle fully pressed and the slide lifted all the way.

The BLACK mark right in the middle is where I marked directly 50/50 in between the other two marks. This is 1/2 throttle.

For 1/4 and 3/4, I just line up in-between for the run desired.


All I did was - from a complete stop - I moved the throttle precisely where I wanted to run/tune. I simply line the mark straight with my eyesight as best as I can and held it perfectly still for the ride. Then while the machine gets up to speed I look closely at the AF gauge to be sure its at least RICH or on target. The moment it runs too lean - LET OFF and change jetting.

After making initial changes, I ran down the track while varying the throttle from 1/4 to full and back to 1/4, watching the AF gauge to be sure it was on target (And it was). I also performed some quick throttle stabs starting from 1/4 and 1/2 throttle to be sure a quick pump wouldn't make the mixture run lean (And it didn't).

Easy does it!

so I my egt I usually try to stay around 1220. 1250 and higher I am letting off although I have seen it in the 1300's. so I am curious why you have everything around 1200, then go super fat and drop to 1050

My first pull where the A/F shows mid 13:1 actually pulled a 1250F. Once I fattened it to 12.2:1 the machine gained mid-throttle power and then dropped to 1200F. Its possible a cooler machine can perform better in this area. Then at full throttle, I was only hitting 950F when the machine was too rich at 11.2:1.

My full throttle is now running 12.3:1 at 1050F EGT. Its possible my EGT placement is wrong, or maybe the mixture may still be just a hairline to rich (Maybe go from a 170 to a 168 main?). Rich is safe. The machine absolutely screams now. I'd be afraid to run leaner until I have a few more sessions to go by.

I personally don't think EGT is all that accurate. Its slow and depends on placement and where the wet line is. Plug reading is very accurate, but having this gauge in what little experience I have thus far - has become highly valuable for me personally. The only thing an EGT defiantly has going for it is lifespan over the WB sensor. You would NOT want to keep this WB installed. It cant take the mud/water nor the hard 2-stroke environment for long.


End of the day tuning in regards to EGT, WB gauge, head temps, water temps, and plug chops and reads it's all taken into account. This thread is just a new method but not a replacement.

yeah rich is safe for sure..and if it runs better than ever and its fat on the top end, I would just leave it. but you could drop one jet size just to see what happens lol
am running a39mm pwk. 190 main jet and I don't hold my Oddy wide open very long, egt start climbing. so I am lean on the top end but good down below. I don't have any jets bigger than that, need to order some
I would really like to try this and see how close or off I am

Understood. I can tell you this - the WB gauge is basically instantaneous compared to EGT. So, if you think you are running lean - its going to show it in a number on a gauge much quicker than an EGT probe gains heat. It may take 15 seconds for your probe to climb, whereas I saw my 1/2 throttle running lean within 1 second (aka right away) and only noticed 1250F on the EGT at the very end of the 1/2 throttle run - maybe 10 seconds later.

this is something I might invest in. my egt has a quick response probe, but how quick who knows.

If you are running air cooled then the over-all heat in general tends to rise, along with EGT. Its just part of the embodied FL350r's originally designed spirit.

That being said I'm glad I tested two water cooled machines before testing my FL350. Started with a 4-stroke dirt bike, then my FL400, and will soon do my FL350.

my 350 is water cooled as well.

ok I saw your other thread on this one. I'd say (based on my 1 hour of experience with this gauge) you are probably running 13.5:1 or maybe even 13.8:1 AFR, which IMO and from what I read online about AFRs and 2-strokes - is too lean. If it were mine I would jump up to a 200 main jet.

Great thread. Well done.
Good info for any future tuners. I like also how you compare the EGT and the wide band. This is important as I also feel that the EGT is just a waste of money. It didn't help me years ago when I was trying to diagnose why my engines were blowing up. It's just to slow. Just my opinion.

Now I'm wondering on how to adapt my o2 sensor? doesn't your sensor probe obstruct the exhaust outlet?
I would now do a comparison of the EGT with the probe out to see if it makes any difference.

On EGTs, from my understanding it is critical on where exactly the probe sits in the pipe, I would also imagine that different pipes, port jobs, RPMs all play a part in the ideal placement, use the SGT more as an indicator from when you have your Engine tuned the way you want either by plug chops or dyno or o2 sensors, when things change, altitude, temperature, humidity ect. you can get close to your optimum tune using the EGT baseline.

I’m sure it might a little but honestly I saw no difference in egt nor felt a performance difference. The aperatus is designed well so I guess it doesn’t cause a restriction. Exhaust flows through it so it’s not really an obstruction.

Is anyone buying a similar setup?


Actually I was thinking maybe I could rent this out to folks when I am done tuning my FL350r as I feel most folks only have a machine or so.

I have a dyno jet wide band with lcd screen. Can monitor rpms and afr,saved the data to a SD card where u can view it on the computer. Will also monitor throttle position on vehicles with a throttle position sensor. It has been used very little I used it on my street bike for about 6 months and it didn't fit into my drakart set up. Works great and the sensor is like new. It's the lcd 200 not the new display they now offer. 200$ shipped. If anyone is interested message me.

that's not a bad deal. If I didn't already buy this AEM I would have gotten that one from you. That WB can provide a lot of information - moreso for tuning EFI I believe.

For carb tuning, 2-stroke carbs work around active throttle position than much of anything else. Sure it would be nice to see some RPM and other figures and also data-log entirety - like for EFI tuning, you want to see throttle, rpm, boost pressure, AFR, intake temp, EGT, ignition timing, knock sensor values, etc - and then you can tune specific points across a line.. etc.

Our machine's engines are very basic when it comes to those things; much simpler and we can really only check on a few things like EGT, water temp, head temp, RPM. I don't think we can observe timing too easily and we cant really tap into the CDI (Capacitor Discharge Ignition)... 2-stroke carbs are quite simple. They only have about 3x~5x different circuits from bottom to top which really only operate at specific throttle positions. Sure the circuits do over-lap a bit but as I found its not too overlapped.


I don't really think RPM is needed for tuning except to find and know your obvious maximum RPM capability. EGT is nice, and timing cannot be gathered. Head temp and water temp are nice but way too slow to make any tuning adjustments.

I started tuning my FL350r a bit today until I developed a coolant leak.

pilot: 40
Main air jet: None
Needle Jet: 166 series, Q6
Jet Needle: 6F5 on the #1 clip (Leanest)
Main jet: 450.

So, EGT at WOT (Wide Open Throttle) lands on 1200F, and then slowly crept to 1250. A/F was measuring 12.5:1 at WOT (Wide Open Throttle) which is on the edge of lean for my liking. Will test again with a 460 main.

The rest of the RPM range was running about 12:1 or richer. With low throttle and still a lumpy idle, I'm going to try a different/leaner needle and get a 35 pilot jet for next time.


This was all observed with 10 minutes of running about!!!

So does the sensor need to be heated. Some of the reading I was doing they kept saying the sensor has to be heated and in the expansion chamber. Do you think your reading would be any different if you had it in the expansion chamber instead of sniffing at the end of the muffler

This AEM sensor IS heated. It takes about 10~15 seconds for the sensor to warm up before it will read.

The thing I've found is I cant get a good reading below about 1/8 throttle - it shows nothing on the gauge. I think the gauge may be picking up a bit of atmosphere mixture or just not enough exhaust gasses at very low throttle at the exhaust exit. I bet if I put it in the chamber I'd get more accurate down low. I wonder if this has to do with exhaust scavenging affect of a 2-stroke, where some exhaust heads back award the Engine. I can only imagine trace fresh air may also be pulled in at the exhaust exit?

However, once moving at 1/4 throttle and greater I feel the accuracy is right on at exhaust exit. If anything it may actually be measuring leaner than what the Engine is seeing. I've been shooting for 12.3:1 AF all around. Its possible the combustion chamber is actually seeing richer than that.

I'm not about to mess with drilling and welding my chamber. I still stress the use of all your tuning techniques but this is by far the best active tool I've come across in years of tuning 2-strokes.

My riding is mostly likely done for the year. Might try for one last ride before the -40 hits us. But I am interested in getting one of these. And see just how close or far off I am.