Hello

not sure where to start really,here goes.

I have just put my 1977 DT 100 back on the road after 31 years. This has been a great project for me and my 20 year old son. We have replaced a few oil seals,battery tyres, air filter (original foam type).Cleaned the carb half a dozen times and it now runs fine on idle and revs. My problem is that it will not pull up the rev range,it is flat out at 30 mph (ish) and you can feel it holding back. I have tried to clean out the exhaust (by heating with propane gas torch) as I thought that might be the cause. Not sure if it could still have a carbon build up. Also the fuel tap will only work on reserve, could it be running out of fuel under load? Any advice would be great.Thanks Richard & Matt.

I would be thinking the same as you about the exhaust...including the silencer!

is it of a type that the baffle can be removed for cleaning?

I would be thinking the same as you about the exhaust...including the silencer!

is it of a type that the baffle can be removed for cleaning?

Hi no it is a sealed unit, it splits as a whole unit. More heat might do it.........

I once read of a 'test' and can see the sense in what they were saying.

Using a cylinder type vacuum cleaner note the noise of the motor when running...then seal the end of the exhaust pipe and silencer (each in turn) to the suction tube. a blocked pipe would cause the motor speed to increase as can be witnessed by the higher pitched sound of the cleaner

it is a test i have never needed to do.

I once read of a 'test' and can see the sense in what they were saying.

Using a cylinder type vacuum cleaner note the noise of the motor when running...then seal the end of the exhaust pipe and silencer (each in turn) to the suction tube. a blocked pipe would cause the motor speed to increase as can be witnessed by the higher pitched sound of the cleaner

it is a test i have never needed to do.

Yes I can see the logic. I have also been told to look again at the carb, could a jet be blocked even though it runs evenly, but only shows as a problem under load?

thanks

I just have a gut feeling exhaust, after all you cleaned the carb to within an inch of it's life

Any way you could have just a quick razz with the silencer removed...yes I know i'll be noisy but for all I know you could live miles from nowhere.

Just re-read your opening post

The fuel tap is worth further investigation it could be starving for fuel. There is no doubt a filter screen within the bowl of the tap...take care unscrewing (10mm hexagon?) the matal is very soft and easy to round off...i would use a 6 sided socket such as the 1/4" drive ones

Hi

Can anyone tell me how to set the air screw on my carb please? not sure how many turns out it should be.

Diagram of my carb at http://www.cmsnl.com/yamaha-dt100d-1977_model8610/partslist/B-02.html

Thanks.

1 1/2 turns out is the norm.