2 stroke tuning (plug tuning) Let me explain...
So, I just want to share a few thoughts I've learned over the last 40yrs of racing full size 2 stroke shifter karts, dirt bikes, 125cc Honda road race GP bikes, and on road 1/5 scale gas rc while tuning 2 stoke gas for my sons and I. Not saying that I am an expert by any means however, we were very successful in most of the mentioned classes. I learned very quickly, especially in 2 stroke Kart racing that "plug tuning" really gives you a sense of engine limits and more importantly the "sweet spot" based on plug burn and color.
Plug tuning: Obviously we like to run our initial brake in with these small bore 2 strokes a bit on the rich side. However once you decide to really dive into getting the most out of your engine you really need to check the plug immediately after every hot lap or full out run. What we have always looked for is a very uniform
"golden brown" burn on the ceramic insulator of the plug. With larger bore 2 strokes we have much more control of jetting options to achieve the perfect burn based on fuel, and air temps. Colder days are what we call "Fat Air". This means we need to add more fuel to the additional oxygen levels to achieve the perfect mixture/burn which is done through jetting options. With these smaller bore engines/carbs we typically have to achieve the perfect burn with the two needle jet tuning screws. Hi end and low end screws. Plug tuning is based around the hi end needle when running flat out at top RPM.
So, after a long top end run, kill the engine and pull the plug. Check the burn color. If dark and oily, you are on the rich side and loosing top end (however not a threat of damage) . If on the white side with some dark spots you are on the limit of detonation (not good). The sweet spot should be a uniform
golden brown burn on the ceramic. This is optimal burn and will yield the best results for performance and longevity of your engine with regular maintenance. Always toss in a new plug to confirm your settings at top end run.
-The below pic of my Taylor 35cc reed engine shows some golden brown however also some darker areas meaning still a bit rich on the top end. My break in fuel started with Klotz 32:1 with 91 octane pump gas for 1 full tank then once the 2nd tank was half full I added 40:1 Amsoil Dom with 91 oct. I will eventually switch to at least a 93 or higher at some point with a 50:1 ratio of Ams Dom. Once fully broken in, I will be looking for a more uniform golden brown burn all around the ceramic insulator. That's the sweet and spot. Changing to new plugs to establish a clean slate is advised while working out your tune/plug burn.
