Like I said it will rev up on it's own with no choke.when you try to give it throttle it just bogs down. I thought the leak down test would show something but it didn't

I know this is a dumb question but are you sure your flipping the lever off choke and not on? i recently figured out that i been running mine on choke this whole time lol normally you flip the lever up to choke it but on these old enduros you push it down to choke it. Im sure someone else will jump in to confirm it. Your air mixture screw should be turned out 1.5 turns and i believe the needle should be in the 3rd position.

Maybe try raising the Jet Needle a clip position down on the jet needle and see if that helps with the bogging, this is a good and cost free test to do. it is part 17 and 18 on the parts illustration posted here and in the link.
www.partzilla.com/catalog/yamaha/motorcycle/1972/rt2/carburetor
going down a clip raises the needle and makes it a little richer there.

I would take a close look at the Jet Setter O-ring. this connects the main jet in the float bowl to the needle jet and jet needle on the throttle slide together.

the Jet setter O-ring is #7 in this pic and costs 3.28 at Partzilla.


with it passing the leak down test you eliminated a possible cause.
the plugged up pipe is a very sneaky and well hidden problem too. I would burn out the pipe with a torch and clean the silencer, if nothing else, if the pipe has some two stroke goo in it, it will run better and make more power if there is problems there.

Just to clear something up no need to explain parts I have been working on bikes for 30yrs but I'm stumped on this one. I moved the clip on needle already and I put new oring on main jet. Today I will clean exhaust see if that helps

No great guesses, but it's always the carb in one way or another. Got another carb to put on it?

Ya something I'm missing. I think it might be the carb. I might be able to borrow one off of 250 if it will fit I'll put the 360 jets in it and try it out

For what it's worth.....my DT360 is running with a carb off a DT250. I realize your bikes are older than my DTs, but mine runs OK with the smaller carb, although it falls short on top end performance.

Carbs are fairly straight forward if you follow where everything leads to. [I'm sure you know that with 30 years experience]. so reversing my theory on exhaust based on running away at idle & bogging on open throttle it now sounds super lean. Bogging as in 'it'll stop if you held it open' in which case 'Lean or blocked main jet. Main is in the side fitting in the bowl & sucks in reverse--like the fuel enters the holder then flows through the jet from behind. Now, i've seen bits of something plasticy in that area so when you open the throttle it sucks the 'crap' up against the back of the jet hence gasping/bogging on open throttle. So remove the jet out of the holder & look behind & give it a poke. Sorry if i'm telling you what you already know. I've had close to 60 years working on carbs mostly in a yamaha shop--well not for 20 years --but!! still working on mine at home. I'm sure crank seals have been covered to death--well it holds the pressure test so forget that. Choke's been mentioned--lever 'up' for closed. Has someone used a slide needle from something else & too fat. Try it without the needle, that'll prove a point & should just drown out. Cheers.

You've already got a lot of good advice... I'll throw my first thoughts in after reading through...

Key sheared again. Someone mentioned this (probably RT325) and I will say I've seen it happen more than once. The taper fit provides almost all the "hold" to keep the flywheel from slipping. Taper fit is usually damaged when key shears and depending on how bad, key could shear again immediately. (Key is mostly an "assembly aid", not required at all to keep flywheel from slipping on the crank)

Vacuum leak. The first Enduro I bought in recent years was cheap because it had a "runaway" problem. Previous owner spent $$$$ at a Yamaha shop and couldn't get it fixed. They even replaced the carb. He had receipts showing they pressure checked it. I figured it was an air leak and they just "said they did". I was bummed when it held 5 psi OVERNIGHT... was still at like 4.99 psi in the morning. Then I tried to vacuum check. I could not pump the Mityvac fast enough to pull any vacuum to speak of... it leaked immediately. Had to be a seal so I packed thick grease around the ignition-side seal. Held vacuum perfectly. Replaced the seal and bike ran perfectly.

I know this type of thing isn't common... but original RT seals are hard to get and several ebay sellers are substituting generic "single lip" seals designed to hold pressure for the original "dual lip" SW seals designed to hold vacuum and pressure.



Just some thoughts... I know how frustrating things like this can be... hope you find the culprit soon (and let us know what it was when you do!)

It's probably nothing this simple, and your years ahead of me on experience, but you haven't replaced any of the carb brassware with stuff from the rebuild kits have you?