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Ok start again. Have you been in the clutch side--plates out & back in etc. Try backing off the adjustment on the left in the actuator to give the pushrod clearance. It sounds bad enough that if you put it in gear [not running] it'd roll along like its disengaged or just dragging a little but not enough to turn the motor through compression. Cold be various reasons like burn out fibers [which would stink bad] or incorrectly assembled clutch--new plates but one plate short--& the pressure plate is contacting the center hub before compressing the plates. Been there done all of that in my mix n match similar motors over the years.

This one is the old style with the clutch actuator inside the cover. The 74-76 style and I matched up each part with the diagram and did it right, #17 thrust washer, spacer, than gear that fits over spacer,  than basket. Havent put the kick starter on just the idle gear to see how it lined up. I put a post on thumpertalk and someone said it should be fine. I'm just gonna run it and see what happens

That link shows the early style clutch actuator so is yours electric start & like that as in "74 we had both that shape for electric & later shape for kickstart only, like the "74 175 shape. I guess ya right with the parts pic but just tossing it out there.

Sorry--no help from me--but--I need one too. Think what i'll do is cut it too long then sit the actuator cover up to it with adjuster backed out a bit then measure the cover gap to the case best as i can. Bit of a juggle as cover will want to rock not sit perfect to measure. My motor is dodgy so original perfect Yamaha length probably doesn't apply anymore. Are they "1/4 for silver steel?. 50+ years since i've done one [in my BSA 500 1954] so just heat red the quench in oil? if my long term memory is intact lol. Thanks.

Hi Alan, I'm currently soaking the side cover in my sonic cleaner to see if I can loosen things up, the darn thing was so caked with old grease that when you pulled the clutch then released it the spring would slowly pull it back (f that makes sense).  I am not able to adjust the actuator, seems the nut has welded it self to the bolt, so I have ordered a new nut and bolt.

Thanks for the answer, I will see if I can smell the oil to see if burnt or not.  I have contemplated removing the side cover to see what the clutch looks like but was hoping to not have to do that at this point.  Odometer is only showing about 6,000 miles but then I don't know if it even works since I can't ride it...

Smell the oil & see if it smells like burnt clutch linings. Other than that, not sure. So long as you have clearance on the actuator centre adjuster at rest then it has to drive unless its been assembled incorrectly in the clutch. even that doesn't add up as would still drive. Only other thing-- assuming you don't know what's been played with inside--is, has it had a pressure plate fitted of the splined type which if fitted wrong will sit on the end of the centre rather than slide on the centre-- "call it the hub"--& won't compress the plates. My guess is burnt out plates.

I've been working on getting the modified 400 engine back together.  It was apart when I got it, so there has been some trial and error with shims, shift drum placement, not shifting after assy, etc.  So after about 3 tries and various bench testing, it is together and shifting correctly, ready for complete assembly.  Shifts good, crank spins free, etc.  So I start on the RH side, and get ready to install the clutch - and find the internal actuator rod still on the bench!  Only bike I can remember having apart where the rod doesn't go in through the clutch side -

So it's coming apart again this week, to have the rod installed.  Hopefully for the last time.

Thanks,  Took the cover off again and looks like the ball in the actuator is gone.  
 

Ya thats a good idea on a greas hole I like that. The pic with it apart some was from 5munths ago and the other one is when I brought it home not long before. It's mutch better mecanicly now. I did a similar technique for my pipes. I removed baffles and old packing then used a brush that kinda looked like a smaller toilet scrubber with a long rod and brass bristles and some gun cleaning brushes and coat hanger rods. I had to repair the rear hub. Someone forgot to put the rubers back in it. Had to tig Weld some cracks In that. It's pretty good cosmeticly for the age. But some where down the line it had a less than knowledgeable owner. Probly the guy I got it from. They Unhooked the auto lube and the right side crank seal was rolled from improper instalation I think. I might have a pic of it. Chain was over tight. Carbs wer clogged tanks a little rusty inside but will clean up good no real piting. Had the blue 2stroke oil in the auto lube tank and atf in the Trans. Por kid I got it from had no idea what he was doin lol. I saved it just in time .

So far
New cork clutch disks aftermarket and oem steals 
Rebuilt with good kits carbs and auto lube pump new seals and all
New base and head gaskets cleaned pistons deglazed cylenders, measured, squish and ring gap all in tolerance cross hatch was ok but I used a 3stone floating deglazing hone so It would not fall in the ports long fine stones only cuple passes each with oil I didn't evan have to take  a hole. 001 off just tighten up the hatch and knock the glaze off,
oem rings with oem set ring gap.
all new seals on the cases besides the actuator one.
new tires tubes rim bands
Wheel bearing in rear front feel good
Deglazed the brake shoes front and rear
Kept stock air cleaner set up but wired foam instead of paper with light oil, hoping to not need to rejet. I think it will be ok.
cleaned repacked pipes new cover seals
Lights tack speedo all work idicators too
running good Ole straight 30 non detergent in autolube and a little klotz in the tank and motion mineral oil 10w 30 for Trans and cork clutch disks.

I worked as a motorcycle technician for almost a decade then went to construction management for the money.  I've built a few cool 2 stroke stand up jetskis and I raced mx as a kid. Just always preferred a 2 smoke they have more soal and take more knowledge to do well with. I could slap together a 4 stroke in my sleep but the art of airflow in a 2stroke takes real thought cause it's all fixed.