LO206 engine temps on a cold day

Hi Guys,
At our last club race this season, my brother and son (LO206 Senior and Cadet) found that the engine temps were quite a bit higher than the previous race. The last event we raced in prior was in Sept. and the outdoor temp was around 65-70F. Both engines maintained in the upper 250-280F throughout the day. Our last event was Oct. 19th and the outdoor temps ranged from 40-55F. On this day both motors ran over 300F. My brothers ran around 400F toward the end of the Prefinal and Final. Not sure if there was some kind of adjustment we should be looking at? Any ideas, we are done for the year as here in the Northeast as it is getting a bit chilly!

You might find that with the drop in temp the engine is running leaner due to the increased density of the air. This is assuming there are no other variables.

To compensate you can raise the needle (drop the clip) and/or adjust the float height to allow more fuel to flow.

It was running leaner, I noticed last winter when we had a chance to get out to the track in the 40s I would get to the low 400s if i stayed out for 18-20 laps.

Ok, I wondered if it was due to air density. Not knowing enough about the adjustments we monitored it. Never went above 410F so we kept running it. If it jumped too much more we were going to park it.

Good to know about the needle, that is likely the easiest adjustment.

Your easiest option is to change the needle position as the jets are fixed per the rules, but the shop that setup my 206 said not to touch the carb unless I go to a track with a different altitude. Hes got it set on the second richest setting which might be part of the reason he said not to mess with it.

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@Shaun_Dobbins I had the same trouble with mine during the same LO206 Senior race. I made a needle adjustment before the final, but it didn’t work. It was fine for the first few laps, but then fell on it’s face. Did all the research that was pointed out above. I got a lot to learn about tuning the carb for the day.

My head temps were running 360-380F most of the day, and that’s where it normally runs during the season also.

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As I understand it needle position affects mid range mixture.
At full throttle, main jet and float fuel level control the mixture.
As you can’t change the main jet you are left with fuel level in the float chamber.
Raising the float raises the fuel level and richens the mixture.
Unless specified main jets vary in flow…

I think I need to start messing with the float height. I’ve never adjusted one before, but I think it’s time to play with one over the winter.

Does anyone have tips for tuning for cold or other weather conditions at the shop? I don’t have a dyno, so anything that can be done with the engine on the kart or bench would be great.

I too would like to know if there are any tips. Racing in the Northeast means we start in April/May when it is wet and the temps are cool, go right through the hot summer (80s-90s), and finish in October when the temps in the morning sessions are 40F.

Thanks for the info so far!

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If you’re adjusting the float level now, what indicators are you using to determine how much to adjust it? As the air density increases/decreases, how much do you have to adjust the float.

The needle does affect full throttle to an extent by how far it protrudes into the nozzle. But yes, float level is the primary adjustment for full throttle.

Main jet is fixed on the Briggs 206 at this time and has been since inception around ten years ago.
I’ve done a little cleanup on the topic here to avoid confusion.

The possibility of mapping air density to float height is an interesting one though…

It might vary with the fuel being used based on composition and specific gravity. Something to ponder.

:shushing_face: I thought something was missing.

3 posts were split to a new topic: Briggs 206 Jetting rules

I tried messin with float heights engine can b rich lean just get float some wer between 860 875 thousands forget playin with carb top racers don’t play with floats that much ther eng builder sets it then they tune the kart not carb

I have never understood why all the car racing around the world. Won’t let you change fuels when you run in different altitude, or temperature, or moisture difference. Because only in dragracing are you allowed to do this as long as the engines don’t change. You should be able to change jets. Because it’s a fact that fuels can help keep temp down. Also can help with rings and bearings. Therefore they should let you change fuels if need be. Like I say I have never understood this why they won’t let you. The only thing I have ever been told was it’s a rule. All I can say is it’s a money making rule. That’s puts money in the engine builders pocket. I understand everyone wants to be on the same page in LO206. But things like, fuel, plugs, and jets. I think that’s a little nitpicking.

Karts can adjust jetting. On the carb there are dials/posts you can open and close, high and low. These get messed with when you have atmospheric changes which I guess are pressure changes. A more mechanically inclined person can explain better, if this is new to you (jetting ).

I did not know that. When it comes it big block mountain motors. I know about. I know you got to pare the plug for the CC’s of the cylinder, and fuel type you using. Then match the wires to run the plug. Because each plug has a number that tells you how hot or cold it’s burns. All this has got to match up. To each other. That why you can’t run to big of a wire to you plug. You might burn the fuel to fast. In my engine I need the fuel to burn all the way through the stroke. So I don’t run that high of a burn rating.

In this case, I am incorrect. Apparently not on LO. But on 2 stroke that I am familiar with, you can fiddle with jets.

I I understand 2 stroke engines are cooled by the fuel and air right. Some air cooled with water right.