1974 DT125 Running rich (Tech Question)

[cameronflynn]

I've narrowed the problem down a bit:

The bike runs great when the air boot between the carburetor and filter box is disconnected, but runs like crap past 3,000rpm when the boot is connected- with or without the foam air filter inside. It starts cutting out, smoking, and will not accelerate- and will stall at WOT.

I'm not really sure what the deal is. I've soaked the carb in carb cleaner, blasted out all the fuel circuits and air passages with compressed air, adjusted the mixture screw, the floats, timing, etc. It is something to do with the air filter box. Anyone have any ideas why it is behaving like this? I've spent hours and hours trying to figure out what was wrong until I narrowed it down to the air filter box. It looks relatively clean, and I did blast some air in it. Maybe it is clogged up in a passage I can't see? Maybe I'm way off the mark.

[Airhead]

It should run lean without the filter so two things spring to mind

1: There is some debris blocking the filter box inlet somewhere

or

2: You have a rich carb issue that you are compensating by removing the filter

Check your float heights, give the float a shake...is it punctured?

[Cynic]

It should run lean without the filter so two things spring to mind

1: There is some debris blocking the filter box inlet somewhere

or

2: You have a rich carb issue that you are compensating by removing the filter

Check your float heights, give the float a shake...is it punctured?

I'd agree with Paul, i had something similar that was doing my box in. Turned out to be the floats had perished and were allowing fuel in and spoiling the settings.