Hello,

I have a 1974 Yamaha DT125E and havening issues. I have it so it kicks over and idles ok, runs until you get to 20-25 mph and it bogs out. Every time I open it up it runs boggy.

I have cleaned out the carburettor and checked the fuel runs freely, I have fited a 150 main jet as that was recommended by Yamaha for the bike (although I have tried a 250, 190 and 115) none of which make a difference?

I have fitted a standard air filter also as suggested by Yamaha to insure the correct amount of air is getting through.

Now I am stuck, any help or ideas would be very very appreciated.

Hi

Are you still running the auto-lube system or using pre-mix?

This could be a problem with oil delivery weakening the spark, or there is a problem with the carb which only shows up under load.

When you had the carb out did you check for wear in the needle valve etc?

Or you could have an ignition fault - badly pitted points or faulty condenser - check all of these things, especially standard settings before ruling anything out.

Good luck.

Hi, thanks for the help,

Im pre-mixing and diconected the pre mix just to be sure i have the right mix, im using 2%.

when you say needle valve it that the needle jet or throttle valve??, sorry for my ignorance but im new at this and working from the termanology in the manual. I have got a new main jet so know thats standared, i am trying to locate a new needle jet but yamaha has discontinued them? any ideas? ??

You need to clean the whole fuel system, it could be fuel starvation. It could also be running very weak due to air leakage into the intake track. Check that the petcock is not partially blocked.