lean or rich? confused

[Nitroistop]

Just a little poser for you all, I have been running my buggy in cold weather recently, when I say cold I mean 32f or freezing point. It is about 4 months old and hd about 1.5 gallon through it. I had to lean it to as little as 1/2 turn out on hsn to get good performance and also had to lean the lsn in these temperatures. Now the weather is warmer (12c - 52f) I have had to richen it to one turn out on hsn to get it to even start and run without struggling for fuel.
Everywhere I have read online says richen in cold weather and lean in warmer conditions, yet what I have experienced with my buggy says the opposite! Whats the truth on this?

 

[cptvkirk]

cold air equals denser air can use more fuel in combustion vs hotter, thinner air at same carb setting. Don't get wrapped around the axle on it though, each first run is going to be it's own fine tune to get set just right. Lean or fatten based on engine response and, if you have a gun or temp probe, the head temp.

Other things effect air density besides temp. on your colder day, you may have had a lot of moisture in the air. water displaces air molecules and therefore requiring leaner settings. Your warmer day may have been much drier air actually resulting in more air available resulting in a richer setting. Atmospheric pressures also vary from day to day. There is just too much to consider in weather to use atmospheric conditions to estimate tune for the average RC technition. Just tune to performance using temp, performance and good ol' fashioned trial and error. You'll get the hang of it and it quickly starts making sense vs a lot of guess work.

 

[Cyclop3000]

Gotta love nitro hehe...

 

[Suicide]

also if you don't wrap the head of your motor in something. it will wanna run in the 200 to 220 range, but all motors are different

 

[XxVASSAGOxX]

i had my XL out today and i had to wrap the head and lean is out to hit 240 yet its 40 degrees out and most say you will have to richen it, but it runs better lean.

 

[Crunkvilletx]

Runs better when lean but it's worse for it in the long run. A little rich is always better

 

[cptvkirk]

there is a peak tuning curve at the top of which is the absolute perfect tune and peak performance with most effective combustion and power output. From that peak, performance will fall on either side of that tune, rich or lean with a differnent rate of change for either side. You can wind up with the same power output slightly leaner than perfect as you would from slightly richer than perfect. If you are not at perfect tune, it's better to be on the richer side. When peak tuning with traxxas' published method, you continue to lean out till you hit that peak performance plateau, as in you no longer see an increase in performance. From there you back off the hsn just a bit. That allows you to be still running at peak performance but increased fuel and oil keep down temps and wear. Possibly just as important as tune is the fuel you use. Pay attention to the oil content. Unless your racing, you'll want 16-18% oil by volume. Yes, more oil means less fuel and less power but much better lubrication and protection for your mill. It also protects better against a not so great tune job. Racing fuel uses around 12% oil by volume. Less oil in the cylinder means more fuel, and better combustion and more power but less fuel in the cylinder also means less oil getting to those critical rotating parts in the crank case and cylinder walls, thus faster wear. Not a big deal for sponsor backed budgets to replace or overhaul prior to every race weekend but the average basher typically cares about being able to run a mill for at least a summer if not more.

i had my XL out today and i had to wrap the head and lean is out to hit 240 yet its 40 degrees out and most say you will have to richen it, but it runs better lean.

many hobbyists don't fully understand the importance of wrapping the head in cold temps. On cold days, you go out and tune up for the conditions that day don't wrap your head, sure your car will run ok...in fact it might even seem to run great. Keep in mind metal expansion and what temps do to your piston fit. Not allowing the head to come up to normal operating temps results in the piston expanding normally and then squeezing against the not so up to temp and expanded cylinder. For instance, it's why full sized cars have thermostats that cut coolant circulation until optimum temp is reached. Many people make the mistake of simply tuning leaner to bring temp up but it often will wind up with a leaner than safe setting and the increased temps are a combination of combustion as well as friction and wear from the increased internal temps breaking down the oil and not lubricating as well. Just remember richer is recoverable. Start with a covered head. If you find that when reaching your operating temp that is sluggish, lean it out a little and then gradually expose more of the cooling head until right tune and temp are reached.

Now a question for the big brains: Is it best to start exposing head from the base of cooling head or uncover the top first? I can't find anything on it so far so maybe it doesn't matter much based on cooling head design but hopefully we'll get an opinion or two to weigh in.