Hey Guys,

I've been struggling with this bike off and on for years to be honest and have hardly ridden it. This winter I thought I finally solved my problems but it turns out I'm still a miserable failure...

It starts easily runs very well at idle and pulls well at all throttle positions up until about half RPM and then effectively refuses to pull any longer. It really wont even rev out if you hold it WOT.

So far I've done the following:

• carb rebuild and replaced jets to stock (220)
• gone as high as 240 and as low as 190
• Rebuilt/repaired decompression mechanism
• New crank seals
• Timing adjustment
• Reed valves look as new
• Baffle is clean and clear 

Anyway, any ideas?

Cheers,

Wes

Pic of the old girl:  photos.app.goo.gl/JVqJseXLzcjzuZmy6
 

Try running it with the air filter off. Do you know what the compression is? i too am having trouble with mine and been fighting it for like 2 years now so dont feel bad lol

Piston in backwards?

Sounds like a classic case of No7 Oring not sealing, so wide open throttle gets drowned by too much fuel. Either that or exhaust blockage in the spark arrestor deep down in the end which you might need a torch to see or point it at the sun on a good day. Needs a burn out. Now i'll go read the story properly lol as just passing & couldn't stop myself looking in. Its addictive. Welcome also if you're new. Cheers from NZ downunder.
www.partzilla.com/catalog/yamaha/motorcycle/1973/rt3/carburetor

Could be the float height too, i know that O ring #7 can cause some serious flooding issues as RT325 suggested checking out.

I'm curious if it runs "clean" and just doesn't have power. 

Video might be nice.

Thanks for all of the suggestions guys.

Piston:  is there a mark indicating direction?
No 7 o-ring:  I put a new one in and its in good shape.  Will triple check
Float Height:  I've struggled with that as the manual I have is wrong.  I've set it 0.84" I believe, from the gasket flange to the float tabs set at the center of the carb.  I'll post pics
Exhaust:  I'll pull it off and check.  

If none of these provide any insight, I'll get some video.

Thanks guys, I really appreciate the suggestions

Wes