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Every RD that gets an engine rebuild in my shop, ALWAYS get the shafts stripped down...RD's will gall the shafts and gears with run only 400-500 cc down on oil every time...and we all know when RD's are old they leak. Very common problem.
Chuck

This would have been easier Mark...
OEM Yamaha oil pump inline check valve      8CH-1316A-00-00 About $20 each.
I use these on the late model TZR's NSR's and Aprillia's I work on when hard to get oil pump check valves are fussy.
C

RD's will have air issues in clear lines with zipties... I'm a big proponent of testing my pumps before install, then only using Yamaha oem black lines and the stock band clamps. Same for the feed lines from the tank to the pump using the spring clamps.
All still available from Yamaha.   
Aftermarket lines and zipties just don't work for me.
Chuck

Always remember that a non-ethanol fuel will run richer than the std ethanol 93.
My ported 400's I build, all run better with ethanol fuels especially at half throttle in the midrange.
Chuck

I go on the conservative side at 50 ft-lbs, these are old bikes and who know what was done before with over tightening like Lyn said.
Once the seal is out, I spray out with brake clean and glue in the spacer with motoseal against the inner bearing race to prevent seepage through the spacer.
Chuck

I got an email about a rebuilt pump not pumping at idle.
This was my reply to him and wanted to add this bit of info here...

I have found the the rebuild kits all have aftermarket gasket for the 4 bolt housing. They are thicker than the oem gasket. When the gasket is thicker it takes up the idle shimming and takes sometimes a lot of extra shims to get the clearance back.
Most people that rebuild the RD pumps don't know to re-shim after the rebuild.
The other issue can be the cam lobe inside the pump wears out over time and may need to be replaced with another one that may not be worn so much. Remember these bikes are very old now and the pumps had run old school petroleum oil for many years until we started getting synthetic oils that are much better at keeping the pumps from wearing out so much.

I wonder if the modified air filters had anything to do not getting the jetting right?
Unfortunately I've seen a lot of that...if you don't have anyone local to do the job let me know. Boring work is almost 2-3 times a week affair here in the shop. 
Chuck

  
Nice!
Chuck

You should always use new sparkplug caps, the stock ones are over 40 years old....
Why are you setting the timing so high?  3.6mm?
Set it static to 2.0mm then verify with light at idle.
Chuck

RD400's have an adjustable pointer with a screw and pointer is slotted. Use your dial gauge set to 1.9mm and set the pointer to match mark on the rotor, then use a timing light to verify at 3-4k rpms.
Chuck

TM34's baseline on my stg 1 or stg 2 RD400's:
37.5 pilot = 2 turns
310 main
389-QO / no airjet
#1 needle clip most of the time, but you can try #2.
Stock 4.0 slide
YZ85 VF reed cages/ UPP manifolds/ TSR-Barlow boost bottle/ Uni pods

Chuck

Can't wait to hear...
C

I think so. Kinda makes their machined slides appealing, but they specify left side idle, and my 30s are a left and a right. I wonder if something could successfully be done with dirko or hylomar; something that would adhere to the slide but do no damage if it came adrift?

sombody did this to a triple, might have been jim hobbs? said it worked well. I'll never feel comfortable with an epoxy in the intake tract of anything on a street bike ( i know its been done but thats just me), but supposedly worked really well as well.

The aluminum ones that bolt in seem like a better solution to me.

the full slide is a good idea as well.

we'll see as i think we will all have a few versions to compare here soon. 

I did these in Jim Cannons H2 with his 30mm small body snowmobile carbs, mild port, re-milled heads and decks to get a real chamber design and with a few pilots changes worked great! Piston port motor now snaps like a RD reed engine.
I used some in Scott Turner's CB350 racebike and didn't work all that well, was too inconsistent at high rpm throttle snap off and roll on.
I haven't played with with them since...I do cut the slides to 3.0 with them in.
Been using TM34's on my yellow screamer for years and still have the VM34's and a set of ufo's out of Scott's bike if I want to try on them on my RD400...

Chuck

No, you didn't port the stock cases to 400 template! If you were to look at the gasket on your stock cases it won't do jack crap, but take away gasket strength.
Why are you asking the internet when they don't know enough information on it?
You always texted me before...just because of all this covid 19 crap I got slammed out and haven't been able to be on here much. Life took a turn on me!
Chuck

150's mains are way too rich for your stock setup... 130-135 I  would think is would be max.
Chuck