DT 115 wont't rev over 4000rpm

[saross]

I have a DT 115, an early 80's model I think. It hadn't been started for about two years. I started it up at home about 10 days ago, it ran a bit roughly and back fired a couple of times but then seemed ok. I took it out today and it started first time and seemed to run smoothly but it doesn't have the same power it used to and won't rev over 4000rpm. Any suggestions as to where to start? The fuel is new and the plugs all look clean.

[Solarman]

Is this a carb'd dt115? Have you been using any fuel cleaner additive? An '80s motor, I'll guess carb'd. It is possible the carbs could have a film of old fuel coating the Jets, restricting the fuel, fractionally, and it is possible the oil mixture may be a little too rich?
The backfiring, may also be an indication that the timing coils, or flywheel, may be breaking down. It had been sitting up for a couple of years, this is not good for motors. If garage stored, out of the weather, there's less possibility that condensation build up should be that bad, but I have seen it happen?

Good luck.