DT250 missing at high revs

[Catbird]

Hey guys. I'm trying to troubleshoot a problem that popped up not long ago. Going into the heat here, I switched my gas tank out to a newer tank, because the petcock on the older one leaked and I didn't have a spare tap lying around to mount.

Here's the symptoms.
THe engine starts to break-up at high revs, but can be "recovered" enough to run stable at up to 70MPH, just shy of the bike's top speed, by backing off the throttle at about 45 and slowly easing back into it.
In my thinking it's either a fuel delivery problem from the tank or petcock, contamination in the carb, or the engine is running way too rich at the top end due to the fact that I tuned it during the cold last fall, and have been running it in 85-degree weather.
Here's the confusing part.
When I read the plug, it's a nice toasty golden brown, which tells me that I'm either wrong about the rich mixture or that I'm not testing it right.

I've got a new fuel tap now, because I needed one to replace the leak in the older tank anyway. So I'm going to start by checking that solution.
Is there a possibility that my problem is elsewhere? Ignition, perhaps?

 

[Spoonz]

Sounds like a points issue, They maybe floating at high rpms.

 

[Catbird]

That makes some sense. What would be the correct way to fix this then, if that turns out to be the case? Just re-adjust them and burnish them, or buy a new set?

 

[Catbird]

For anyone who digs this thread out of archive for reference, the points *were* floating, yes, a situation aggravated by a little bit of power loss due to a heat wave. Replacing the points caused 99% of the trouble to go away and the bike now runs straight up to redline no trouble at all.

 

[xb33bsa]

good to hear
just for future reference the hotter weather will make it run richer not leaner

 

[Catbird]

This I know! As air temperature increases, so does the kinetic energy in each molecule in the mix, thus increasing the physical volume each takes up, ergo, less particles per unit volume of oxygen. I'd rather run rich than lean though. so I haven't tuned it back, I just carry a spare plug. THat way I don't have to richen it out again to ride it in the fall.