My dad recently installed a vape cdi and his bike finally started since he put it away last year.  It’s a fully restored beautiful bike he’s had for 30 years. 
Now after installing the vape, he’s getting kickback issues, also excess oil in the case is causing it to smoke and eventually foul the plug. He never had a kickback problem before so it’s definitely a timing issue, but when the bike is running it’s sounds like it always did.

Sounds like timing set back before 2.9btdc.
Better go for 2.5 maybe.
But it's likely slipped if not super tight. Just a guess of course.
Motor has likely drained oil from the tank gravity fed through the pump into th crankcase.
If it runs just use a new hot plug to bring it up slowly untill it clears the oil out. Once reving & clear just change plug before beating it around the block. Other thing 'is' the oil will now be soaked into the exhaust packing so you'll be visible for the next 100 miles as it burns off but its not an indication of motor problems--well not yet anyway.

I also have the dt400 with the vape ignition. I had it running once at 2.9 timing. I let the bike sit for a while and cant get it to start back up. Let me know if you have good results going with the 2.5 if you decide to go that route.

In my experience, VAPE will not kick back if accurately timed to stock spec.  ***  That said, I time the 360's and 400's at 0.100" or 2.5 mm BTDC.  They run great there. 


*** Without a key, and especially if flywheel has ever slipped, you need to be super sure the taper in good condition, mating is clean and dry, and the nut is tightened properly or the timing can slip. 

Maybe it slipped during running 1977- & moved too far as you shut it down. Check it again for timing. If its in the ball park then something else. Providing its sparking & not an oiled plug.

Mark, Thanks for the info. My Portugese orange 400 kicks over prettyhard. set @ 2.9.
Second 400, this one Competition yellow set @2.6 starts way easier and runs out very well. 
Going to go change the timing on old Orange boy and see how it goes. 
By the way, even with the Yam air filters both need more air than they can get their hands on. Just what I've found on two consecutive 76 400s.

2.5 is definitely the way to go. I set my first 400 earlier this summer at the recommended 2.9 .
then bought and restored another on same year same everything except this one got 20 over instead of 60 over. 
I set this second 400 at 2.5 and was surprised at the difference between the two. I wondered if it was typical that they weren’t exactly the same. Set the first 400 to 2.5 and it runs much better. It doesn’t fall off in the 6-7 range nearly as bad as 2.9 does. 
Even after I’d figured out these things need a ton of air they were different and the 2.9-2.5 gig made the difference! Wouldn’t even think twice about it, just set it to 2.5. And it kicks over WAY better/easier. Starts better as well. 

Thanks again Mark, 
A couple of days ago I got the second 400 running. Seemed like it had more guts than the first one. I was surprised at how it ran right up to 7000 even though you could feel it weaken a bit between 65-7 it pulled all the way and went through the gears swiftly. 
I just set the first 400 back from 2.9-2.5. What a difference! Right up through the gears with good pull all the way up just like the second 400. Thanks again! You know if one has experience with just one of something it can be easy to feel like “this may be normal” especially with something older like this. Having two of them set to different specs to ride back to back really accentuates the difference. 

On your air filters, try using Twin Air "liquid power" filter oil. (Actually best to get the whole system, cleaner and oil) It's amazing stuff I've been using since the 70's. Filter will flow a lot better.

By the way, I set the orange 400 @ 2.5 BTDC and WOW what a difference! YES it matters and if you've got one of these don't waste another minute bitching about how hard it kicks over or that it doesn't like to start. 2.5, just do it!! LOL!Revs out better, I tried them side by side, one @ 2.9 and the other 2.5. Then changed the 2.9 to 2.5.