Today I got my AT1 fired up and running with the new carb. I have noticed an occasional spot of oil coming from the bottom of the motor. I have ignored this recently since I didn't have a battery to ride it. 

Today I took it around the block and noticed quite a bit of oil coming from the side cover on the engine. I opened this up and saw a lot of oil in the pump area. I cleaned all of this up and watched the operation with the bike running. I did put some oil in the gas just to be safe. While running I noticed the line that goes the cylinder block would get empty and almost pulse. I shut the bike off and manually primed the oil pump again. It would fill the oil line without an issue and hold it there. As soon as I start the motorcycle it would start pulsing and it appeared the oil was gone. I also took the banjo bolt off the cylinder and let the bike run to see if oil was coming out, and it was. 

Is this behavior of the oil pump line to the cylinder normal? I would think that it would stay full and primed, but maybe that isn't how it works on these older bikes? My RZ350 has oil lines that run the carbs and always stay full and don't pulsate like this AT1 did today. 

1971 Yamaha AT1c with a CT2 Top End.

The curse of the clear oil lines. tis a worry though now you've seen it. First thought is--does the union where the line cones off have the miniature ball & fine spring. Stop them gravity feeding over time into the motor. But i now wonder without that if it would do something like you show.
Or does the pulsing of the inlet blow/& suck to a point.
If yours is reed inlet [AT2 or AT3 use AT1 prefix] & it feed the oil on the motor side of the reed, does that have more affect on pulsing being the reeds are shut--albeit blown shut if not quite touching--when fuel mix it being sent up the transfers & rear boost port. So would 'that' pulse have more affect than a piston port AT1.
Sorry i'm over-complicating it & bamboozling myself.
Ok, pump blead out the screw. Good flow from the oil tank.
Hows it react if you push the cable cam plate back so it gets full stroke, no matter the revs.
I guess the pumps original?. There was something strange on a post once where someone fitted a pump off a reverse motor like an IT175 when those motors swapped sides with everything on the left & chain drive on the right, then things revolved the other way.
Sorry that might've been a tachometer story not pump, ignore that woffle.

I forgot you mentioned oil leak so can the pump seal behind the plastic wheel leak enough to have that sort of affect.
Or gasket at the case where pump mounts--unlikely.
Or what would happen if the case seal into the motor was Bad--or drive cross pin missing so engine plastic gear isn't turning & is 'just doing it's own thing' sort of.
Would something way out of line like that account for it priming on the plastic wheel.
Sorry--too much time on my hands, day of of silly answers.
I'll go mow the lawns lol.
ps, great video by the way, & can slow it right down on youtube too.

One more--has the pump been apart. Are the two drive pins with springs in there the the big gear uses to turn the internals. Ok i guess if they were missing the plastic wheel wouldn't turn by running motor.
If the big internal gear was flipped--Na guess not as teeth would be cut to match the worm drive from the motor.
Ok back in the corner--i'm out of here till later.
But wait there's one more. Is the feed line way oversize ID. Original is pretty small & needs expanding onto the fitting & maybe is matched to the minimum pulses at minimum stroke. I can see your minimum stroke is visible so has 'some' & doesn't need much at idle & slightly above until the revs/& stroke increase.
I guess a lot & we didn't have pump troubles when i was working in the shop in those fun days of late "60's & later. Had me stuffed when pumps came out with No Plastic Wheel--nothing to play with lol.
I think DEET? is the pump man?. Hope he comes in & 'sorts me out' & sorts your problem all in the same breath.

My opinion is you're using way too large a hose. It could also be the source of your leak.

Let me give some more background on this motorcycle. It has been in my family since new. Mom was the original owner. I used to ride this when I was 15. About 6 years ago I did a full nut and bolt restoration. NOS Wiring harness, complete motor rebuild, oil pump was rebuilt using a kit. Motor is a Frankenstein. Started life as a AT1-c with piston port, kept the same bottom end, but bolted on a CT2 top end with a sleeper pipe. The original carb cracked and was not repairable. I just purchased a Mikuni VM26 to replace the stock VM24.

The oil pump when removed for the restoration still worked without an issue. At this time I wanted to rebuild it to ensure no issues in the future. I vaguely remember putting that ball and spring in the oil pump to prevent bleed back. It does seem that the oil is being "sucked" into the port on the cylinder. As I mentioned when the oil line was unhooked from the cylinder it pumped oil no issue. The other Yamaha 2 strokes I have don't inject oil into the cylinder. They do this at the carb. So it just pushed it into the throat of the carb vs. at a high vacuum point in the cylinder.

I may start with replacing the oil line going to the cylinder.

Do these copper crush washers ever go bad? Can I get these locally somewhere or yamaha only type of part?

Why do you think the hose it too large? If the inside diameter fits the nipple for the barb fitting then it should be good. It could have expanded in the last 7 years and need to be replaced. I will try to replace that today and see if this stops the leak. 

imgur.com/a/zxqvnRA
I took a few pictures. Link above. It appears the oil line was leaking a bit. I'm assuming this was causing it to pull in air when the engine was running. I put a new line on and it is not pulsating anymore. I'm going to let it sit a day and see if it leaks any oil before trying to ride it again. 

This harder tygon line is great, but eventually gets swollen from oil or gas over time. The metal band clamps cannot keep it tight against the barb fitting. Typically, I use zipties to keep it from swelling on my jetskis. I elected to not do this on the AT1. I will report back with my findings. If it still leaks then pump might need another rebuild or at least new seals. 

Keep'em smoking folks!
 

Yamaha still sells the correct delivery line and clamps. I've gone down the "clear line" rabbit hole and there is just no benefit to using hose after the pump other than the stuff Yamaha supplies for the purpose. And there's a lot of potential for problems with different line and clamps.

I 100% agree with MarkT Yamaha had this figured out over 50 years ago it worked then and it works now they used that hose and clamps for a reason