Hey guys, had some engine issues his weekend while competing in the Biltwell 100. The first 27 mile lap the bike ran great (besides laying it down twice) but about a third of the way through lap 2 I started having some ignition trouble. Pulled the sparkplug out on the course and it was hotter than hell and seemed like it was running lean so I swapped the plug and messed with the idle/air control screw to try to make it run a little richer. Made it a few more miles and it died again. Pulled the plug, it definitely didn't look as bad but still was extremely hot. Threw a third plug in but could not get it to kick over. Waited about an hour on the side of the course and tried to kick it again to no avail. It still had compression but probably about 50% of what I started the day with. Have not pulled the top end apart yet and I'm sure it needs to be rebuilt but I'm wondering what I could possibly do to keep the engine cooler on longer desert races. Thanks!

do you have a picture of the plugs?
how do you know your overheating?

If its down on compression then you'll soon know what caused it to overheat as lack of comp will have it trying harder to perform & create more heat. But hell they get hot anyway--so what is the limit of 'hot'. I guess melting thins like piston & plug. When its all back together i guess run it as rich as practical on the needle & main jet but don't want it annoyingly blubbery. & run a cold plug like a NGK B9ES. Reading your story again, i think maybe there was something going on heading into lap 2 & whatever it was it just nibbled away until rings got stuck in the grooves & compression dropped off. & now the comp is too low to start. So possibly all was well at the start but a less than perfect piston/rings & cylinder just called it a day from getting a hard time. Look forward to what's happened when you go looking.

I don't think overheating in itself was the issue, more of a symptom of the problem.  Could be lean jetting or too much timing.  If it was pinging then I would expect piston scuffing and perhaps some degree of seizure.  May have stuck a ring.

You could try different needles with a more aggressive taper.  Keep the 1/8 throttle range clean and give it more fuel in the 1/4 to 3/4 range.  Jetting is challenging on these big air cooled singles.

On a normal engine plug is way too hot to touch after running so not a great way to judge overheating... 

You might consider getting a Trail Tech CHT gauge...  washer goes under spark plug and then you'll have a better idea of temp. 

two strokes tend to act too lean when they overheat. I will second the trail tech cht as well and I have one on my 1978 dt175, I used it when I was tuning the bike and I use it to monitor my engine temp. I need to put it one on 3 other bikes I have as they run a little warm.

are you using oil injection.  if you are your pump has either quit working,,   came dislodged for the end of crankshaft drive,,,or it has an air lock.  This is exactly what happened to me when the oil pump mount screws came out and the pump ended up laying inside the cover.  It is sur acting like a lack of lubrication.  Mine 4 corner seized and after I got some oil in the mix  it works fine but the compression is a little lower
Doug

Are you running Bitwell this year? I’m in SoCal and thinking of racing one of my DT’s.