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TM Racing 300 + Lectron + Wideband O2

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I want to share my experience with a Lectron Carb in my 2015 TM Racing EN300 2 stroke.

I have been using a Lectron carb for at least 6 month. Always felt like the engine was too hot, no matter how much I tried to richen it with the metering rod but the bike runs reasonably good.

After doing a top end rebuild I welded an o2 sensor socket to the pipe… in the bottom part looking backwards. This way I could run a wideband afr meter but when using the cap it is almost invisible.

Today I did some pulls and found some interesting things:

1. Low rev AFR was lean from Lectron, half turn to rich side and got 13.5 afr from idle to half throttle.

2. Hi rev was ok but either way I gave half turn out (making it richer) to get 12.5 afr at full throttle (I’ll try 12 for safety).

3. THIS IS THE INTERESTING PART, well at least for me. If you start accelerating progressively the engine will be ok and go smooth from 13.5 to 12.5 as revs goes up but if you are riding hi gear and low revs cruising (light load) and hit full throttle (same gear), the carb will allow too much air to go into the engine but power jet doesn’t react that fast… critical lean condition (16 and more) gets there for too much time.

I will do more testing but in the meantime my advise is DOWNSHIFT everytime you want to switch from light load to high load, that way the engine suction ramp up very fast and the power jet blasts enough fuel to keep afr in the right side.




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I've seen this on a dyno with a smart carb ,the general thing you notice is they run lean in spots ,it's a reason why they save fuel 


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