turrican64

1974 Yamaha GT80A

Go to yamahaenduro.com and PM a guy by the name of DEET there...he is a mod. He does FANTASTIC work...makes them look better than new and is very reasonable with pricing.

You're going to need a slotted screwdriver to get it out. That pilot would be the best thing to check.

They are different. The air screw is usually near the air filter side of the carb, and the idle adjust closer to the middle of the carb.

When you clean a carb out, make sure to use a good carb cleaner, dismantle the whole carb and soak all the little bits in the cleaner for at least a few hours. Go through all the jets and passages with a fine wire and an air compressor. As soon as that's done, set your air screw at 1 1/2 turns out, and the idle screw (should be able to turn it by hand) at 3-4 turns out for a start. Pop in a new B8ES plug and you should be off to the races.

What's the bore size? Maybe you could get away with using a piston from another bike...like a GT80 or similar.

hvc cycle

I had a hell of a time with "cheese" head screws on my RD400s baffle. What I do is soak it in penetrating fluid and let it sit for an hour. I then take my best screwdriver and mallet and whack the crap out of it a few times, then try turning it. If it doesn't budge, whack it again. They eventually come loose that way, but you really need to make sure that the screwdriver is engaged with the screw absolutely perfectly.

Find yourself a wiring diagram and trace all wiring before you do anything else, lest you burn your bike up. It's a PITA, but you need to do it.

You need to get a better air filter or oil yours more if it's a foam unit.

First thing you should do is get fresh gas and fresh two stroke oil. Premix it at 32:1 for now. Disassemble and clean the carb out thoroughly with a good carb cleaner (keep that stuff away from the rubber parts). Poke a soft wire through all jet orifices and be very thorough. Ensure the throttle is not stuck, slide is in the right way, float height is correct and needle is in the right way. If the problem still continues, ensure that the autolube line on the carb or mainfold is connected to the autolube pump and make sure you clean out the oil tank and renew the oil. Worst case scenario: purchase 1mm gasket paper, replace the bottom end and manifold gaskets, anneal the copper head gasket and replace the magneto side crank seal. That should rule out an air leak. Good luck. I had two of these and they're neat little bikes.

RD's are awesome bikes for the age. I have two RD400s myself and love them.

Post a picture of the inside of the carb if you can get around to it.

Have you checked the float height? Floats/needle the right way around?

Did it do this before the float level change? If not... 1. Any aftermarket filters will require a jetting change. 2. A rough estimate would be 1 1/2 turns out on the air screw. 3. Clip could go down the needle...better making it too rich than too lean IMO. If that helps, you need to fatten your jetting up. So go ahead and try it if the above don't work If this doesn't fix it up...maybe an air leak?