Set carbs on rd 250 e - 1978 Yamaha RD 250

Either the float is set to high, you have trash in the lines, or the more likely scenario is the atmospheric vent line is pinched or plugged.

check the cables have freeplay and the carb slides move freely and havent been installed incorrectly.
intake manifold leaks can also cause high reving

Remove the cylinder heads and de-carbon the heads and top of the pistons. Hot spots of heated carbon buildup are igniting the fuel after the key is off. Install new spark plugs > NGK B8HS. This will fix the continued running problem.

The out of control revs is an air leak problem. Un-carbureted air is making the fuel/air mixure lean. The hose clamp at the front of the carbs may be loose and/or the gaskets from the reeds to the cylinder are no longer keeping a good seal. The carb joints and reed gaskets should be replaced. The gaskets are cheap. The carb joints are expensive. Considering this, you may want to put some gasket sealer on the carb joint mating surfaces and see if they will seal up okay. If the carb joints are cracked, you pretty much have to replace them. Please rate my answer, thanks.

yes change the motor, it is a direct bolt on

first off what country are you in ???? the 1979 rd 350 was an air cooled engine, same as 250 . the 1989 engine was water cooled with yamahas ypvs exhaust valve both very differnt in design although some frame and body parts cross over.the manual for the air cooled is: isbn 0 85696 505 7 . i dont have the water cooled number but could find it you require. the rd was exported under various different names ie: rd , rz , ypvs and so on. you can contact me @ [email protected]. hope this helps.

HI. YOU MAY BE GETTING GAS TO CARBS BUT IS THE GAS GETTING TO THE PISTON. IF IT WAS ME I WOULD PUT A LITTLE GAS IN THE END OF THE CARB, AND IF IT STARTS OR EVEN KICKS A FEW TIMES YOU HAVE FOUND YOUR PROBLEM. JIMBO

check the neddle valve seats under the float bowls,may find that theseats are not sealing,to test,take the carbs off the bike,remove the bowls ,compress the floats untill they are all the way up(simulates full bowl of fuel)then blow through the fuel inlet pipe,you should not be able to hear air passing throgh the valve if you can replace the valve seat and the needle valve,sorry cant remember point settings,long time ago since i worked on one of these

no - the are close - but allow more air flow and less back pressure (very important)