Exaust pipe get cherry red after a feew minutes of running time and backfires out carb and exhaust.

I have changed or checked the following:

- changed exhaust pipe donut
- changed intake o-ring on carb side
- changed intake o-ring on cylinder side
- changed fuel diaphram in carb
- checked valve gap
- checked spark plug and gap

Please send information if you have any suggestions. This problem is costing me riding time!
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Sounds like you're running lean. Have you tried increasing your main jet size?

 

if your valves are adjusted too tight it will run hot. this happened on my XR250

 

I have checked the valves and they are adjusted right. This thing must be sucking in air from somewhere making the thing extreemly lean. I am close to wits end with this thing. It sat up for about a year?