Hello all,

 I just picked up a 1977 DT250 enduro. She is a bit rough cosmetic wise, but starts first kick. 

  I am looking forward to learning about these fun little bikes. And cleaning her up and making her something to be proud of.

 Someone removed the oil injection system on this thing. Is that something I should look at hooking back up or should I just continue with pre mixing it like the previous owner did? What should I mix at and what type of 2 stroke oil? Synthetic?

 from near Salisbury, UK.

Running with the oil pump, as Yamaha originally intended, is preferable. However, you need to be really careful that you buy a) a working one and b) the correct one. Different models might share the same outer pump body, but have different internals. 

Thanks @Gr8uncleal. So how do I know what the correct pump is? It doesn't have the oil tank either. 

I have been ridding and wrenching on my own bikes for nearly 30 years, but sad to say, this is my first oil injected 2 stroke and only the 2nd 2 stroke I have ever owned.

To answer your premix question. I have several enduros where I have removed the oil pump and added a block off plate. I mix my fuel at 32:1 and use YamaLube 2S. You then need to do something with the oil pump cable. I simply route it under the seat and attach a tension spring to pull on the cable end. I am out of town or I would attach a photo of the simple spring setup.

Edit
Here's a link to the photo showing the oil pump cable rerouted and coming out at the back of the gas tank along the left side of the frame. It is zip tied in place and has an extension spring crimped on to the ball end of the cable. That setup also gives you a nice crisp throttle return.

imgur.com/a/LBDiWt4

Thanks @Schu. Why the Yamalube 2S specifically? 

 I need to rip into it a bit more to see what is there and what isn't. I know there isn't a oil tank or anything coming out of the case. 

 I need to put some new tires on it and ride it for a bit to give it a good shake down. Make a list of what it needs and their priority. Thanks so much for the help guys!

"Thanks @Schu. Why the Yamalube 2S specifically?"

per Google AI

Yamalube 2S is for all-season performance in land-based applications like motorcycles, ATVs, and snowmobiles, as it provides excellent protection and reduces smoke and deposits. 

Thank you kind sir. I really appreciate all the help.

Welcome from NZ. I premix my DT1 & 360 & I guess easier fir you to do that considering your situation. One thing I only just thought of-is-with the pump going down long hills with throttle closed at least the pump is still delivering a minimal amount down the spout. But they servive so I guess not much heat on a closed throttle when not firing.

@RT325 I have heard of this. Thank you so much for the reminder. I have been riding 4 strokes for 30 years and I probably would not have remembered. So I appreciate you speaking up. 

I have a '74 RD200 that I've owned since approximately 1991.  It has the same Yamalube system and I love it.  They tend to be a lot more reliable than people give them credit for and do keep pumping at idle.  That being said, when going down long steep hills.  I do regularly blip the throttle with the clutch in to give it a little extra squirt.