1979 yamaha dt 125 wont stay running

[bkfranklin22]

i have a 1979 yamaha dt 125 and it wont staying running. The only way to get it running is to put your hand over the carb intake and provide a vacuum, then it will start but it wont stay running unless you feather your hand on and off the intake. Also when it does stay running the rpms go all the way up to 8 or 9 thousand rpms (and of course thats redline) and when you twist the throttle it doesnt effect the rpms its like the needle is staying open. anyone know what my problem is?

 

[ysr89]

Rotted or cracked rubber carb boots will create an air leak. check the boot, and if It's cracked, replace it.

 

[xkevenx]

indeed an air leak, repair your carb boots like ysr89 sayd.

greets sixty.

 

[chevyss_98]

yep air leak, had same thing on a 77 dt115 motor i had on a bike, rebuid carb with new seals and such, makesure airbox is sealed well with carb as well

 

[KTA]

I'll put a forth on the airleak. A good/fun way to test if there is a leak is to:

Put the airbox on.

Start the bike.

Fog the boot area with ether.

If the ether has an effect, you have a leak. Although judging by your symptoms I'm quite sure you do have one. Just get a new boot and pop it on.