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DT 175 mysteries

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Hi forum 

I did try to get to the bottom of an issue I had a while back but never really got there so hoping this time I can get to the bottom of it 

76 DT175

Bike runs ok (although air screw pretty much full in),  can start easily with No choke, pulls well..for a while 

After 10 15 mins it  suddenly loses power and lots of blue smoke seems to be worse if forced to idle, say in traffic 

Put a new carb on it 

Burnt out exhaust with heat gun

Running with  air filter 

Running on oil pump

Would crank seals cause this?

Weak spark from primary coil breaking up when hot?

Any suggestions or knowledge most welcome before I just start throwing parts at it

Thanks in adv






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Define 'new carb'.

New as in quality replacement mikuni, new as in good second hand or new as in cheap and horrible Chinese crappy copy. Did you check the size of the jets, if their clear?

It starts with no choke and the air screw is fully in so something is up in the carb, no matter how you spin the bottle its rich and sounds like its choking out once its warm.

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check the gearbox oil level, if its low ,it will be R/H crank seal   [sucking oil]  = smoke,  and  the pilot is too small if you can screw it fully home without stalling the engine, [at idle] ,,,  plug colour ?   tells a lot,

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