I have a 1975 Yamaha DT 125 that runs great when its cold and then after about 5 minutes it gets a bog if when you give it a lot of gas which is really annoying mostly because it can barley make it up the hill in my yard when its warm. I have tried adjusting the air to 1.5 turns out (recommended) but it runs best at 0.5 turns out. The spark plug looks like a cardboard brown and I cleaned the fuel shutoff filter (which was pretty bad, but it didn't help). I'm probably going to clean the carb today and charge the battery (it needs a battery to run, and the alternators broken). Has anybody ever had this problem? Any suggestions would be appreciated.

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rebuild it, its low on compression, if it runs great cold then gets the bog it would most likely be that

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I'll test the compression today. Hopefully that's not what it is, but you might be right.

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Does anyone know what the compression is supposed to be?

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it will run pretty crappy at 110. but it should be up at like 130-140

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Well I finally did a compression test with my gimpy compression tester that you have to hold and I think it went around 115-120psi. So I'm going to try a new spark plug tomorrow.