I need help from the 2 stroke gurus!!!!

pushing

My husband (Dirt) negleted to mention that after you do a plug chop... you're gonna have to push the bike back to your pit. He knew he'd never get me to do it, so we got the SpeedTune...

 

I am finally racing my TZ250/CR500 hybrid. Did a search and this thread came up.

The motor has a wide ratio transmission. I avoided long pulls at top RPM. Short shifted down the straights.

Some quick questions:

1) Ideal water temp? Looks like Ray is recommending 65 deg C. Why 65? Why not 70? 80?

2) Why A747? I was using Super Techni Plate this past weekend. I know a MX'er who likes it so I tried it. I was running 32:1.

3) Any advice on exhaust gas temps? What should I be looking for in EGT?

The water temp started at over 100 deg C! at the beginning of the weekend. As soon as I saw I was going over 100 I pulled in, so I didn't run it long at that temp. Some fiddling with the cooling system and I got it down to 80 deg C (top temp in a race was 81 deg C).

I did not build the bike or the motor. Previous owner says the carb has the largest main he could find. The motor responds well and I have no ridability issues. My biggest concern is heat. If I add more premix, will that richen things up a bit and get the temps down? What about a different heat range plug? Didn't do a plug chop, yet.

Any advice will be appreciated.

Oh, and another thing, yes it is a lot of fun!

 

The plug itself won't raise/lower the engine temp.

A colder plug will retain less heat in the tip, and less chance of melting holes in your pistons.

Always ran B10ES NGK's in my RZ, just to be safe...

Richer jetting should burn cooler.

 

I've heard 1250-1300F as max EGT temps. Don't use this anymore, as I prefer the 02 sensor as a measure of how rich or lean I'm jetted.

80C seems very high to me to operate the bike. On my TZ125, I'd shut the bike down if it ever went above 75C.

 

81 degrees this time of year will have you in trouble in a few months. Time for a bigger radiator. I run a radiator that is too efficient and just tape some of it off when needed. At Barber this past weekend I needed two strips of duct tape for practice when the outside temp was in the low 60's F. At Jennings two years ago when it was 98 F in the shade my bike still ran below 78 C. I like to run my bike at a temp between 65 C and 75 C. I run Maxima 927 at 32:1 ratio for the past 4 years with great results. I also use Sunoco 110 fuel. It works good and only costs $4.20/gallon at a local station.

 

Dirt,
Make sure you keep those Hondas around 50-55,after that you will be just throwing HP's out the window.

Steve

 

Phil Schilling / Cycle magazine raced a Rotax tandem twin in 83 and did a lot of testing on Kerker's WATERBRAKE dyno. To document the effect of temp they started one set of runs at 50c and a second set at 70c. The difference was minus 1.4hp at the low end of the powerband up to minus 2.6hp at the power peak.