new front sprocket and chain for my DT1E cause this girl was rode really hard and front sprocket was a way hooked
zero degradation of rear sprocket so i mearly buffed it up
14/44 front/rear with 102 links came off and i am trying to put back on
with adjusters all the way out, and then flipped up to see if i couild get a bit more, still a couple of mm short of slipping in master link
I know once this runs under a load for 2 minutes that it will slacken, so before I geek out and make a tool to pull together can one of you dudes who have worked on hundreds of beatiful old Yamahas please share how a skilled Yamaha mechanic back in the day would do this?
thanks!

You won't like my answer.  If front sprocket was bad, rear sprocket is not as perfect as you think.  A new chain will stretch to match the worn sprocket pretty quick.  If you are using the old chain with the new front sprocket, new sprocket will wear quickly as well.

False economy in my experience to not replace both sprockets and chain when one or the other is worn badly.

Standard rear on a DT1 E is 39 T , and chain is 100 links .
The only reason your original chain fitted your sprocket combination ,
was that it was stretched already . If you wish to stay with a 44 rear ,
you need a 102 link chain to do the job . I'd echo Marks sentiments
about fitting a new rear sprocket too .
If you bought a new 42 or 43 tooth sprocket though , your current chain
will do the job .
 

thank you both
somehow I mistakenly thought I had read that rear was 44T, which it is not
so I ordered a 39T so I don't lose top speed and because to ignore  solicited advice is, well, stupid
my new chain is 102 links with 14/44 combo so if i Understood swoop56 this should have fit
i will pick this up next week when the new 39T arrives

on a related topic, could i grind the head off of a rivet and drive out with a punch to shorten the 102 to 100 links?  or do i need to exchange or get a chain breaker?

thanks for the advice

Yes you can grind the head off a rivet and drive it out, best to do it on a couple pieces of wood, driving the pin between the two. Most the time with chain breakers you have to grind the head off a rivet anyways, at least in my experience with budget chain breakers.

I am confused, not a news flash
Spec in Tech Library says 14/44 for sprockets, but experts say 39T and 100 links
also - couldnt get a new 102 link chain around existing 14/44 combo, which Swoop56 I thimk says a 102 link chain should go around, but mine doesnt.
I just want to make sure I get this '71DT1E back to stock so it doesnt top out at a lower speed that gets me run down by a muffy in a range rover
thanks! 
 

I'm not overly familiar with your bike, but have you loosened the chain adjusters such that you have the rear wheel as far forward as needed to make the shorter chain fit? Not trying to shortchange anyone's mental capacity, but sometimes we forget the easiest idea.

I used 14/44 combo on my old street legal  DT1MX.
and Yes , purchaced new front, rear and chain
No problem ever. GFrench loved that bike sooo much, he bought it off me.
 

Stock rear sprocket for the 250 is 44T.

Stock rear sprocket for the 360 is 39T.

I count 102 links on my original unrestored DT1E.

14/44 = 250 from what I see in the original 1971 250 owner's and service manuals. 

(39 tooth rear/15 front was 71 360, online parts lists are not reliable for some parts, this is apparently one of them.)

I always buy a longer chain than I think I'll need...  like 120...  and shorten to fit.