I have a 1975 DT250 that I bought cosmetically restored.   I've been working my way through it mechanically.   I noticed the Tach is not working.   I removed the cable from the engine side and did the drill in reverse test and it works.   With the cable disconnected it looks like the tach gear in the engine is not moving.  I have not been inside the engine yet but it runs good.    I am new to this and wondering what my next logical move is.   There is a bolt holding down a metal clip for the drive gear.   Can I remove that and get the gear out without any problems or surprises?      

Thanks in advance.
Dave

There is a worm gear that can be pulled out from the top. If it not a worm gear issue, then you have to pull the right side cover.

Thanks so much! I'll pull that and see what I have.

Cable could be wrong part or assembled wrong.  The cable insert has a stop on it which goes on the bottom engine end.  I've seen insert installed from the top (with stop on the top end) and the cable wouldn't engage the drive.  Removed the insert and installed it from the bottom and tach worked fine.

On my DT400D the plastic tach gear also turned the Autolube pump.

First I'd do is pull the cable from the bottom of the tach, start the bike and see if the cable is turning, if not then go from there but that would be the easiest way to rule out the tach itself.

Thanks for the additional feedback. I haven't had much time to work on it so it went to the back burner.
-I tried to pull the worm gear with no luck. I removed the clip and wasn't sure if it pulled out or turned out.
-Thats interesting on the cable insert stop. The cable on this one is floating. I will check for one. Based on what I've seen thus far, there have been a lot of short cuts.
-So if the autolube pump is working (it is) can I assume the internal gear for the tach is not the problem?
-I am 100% confident the tach is good based on the tests I have done.

Thanks again for all the feedback! It is very much appreciated!!
Dave

..........-So if the autolube pump is working (it is) can I assume the internal gear for the tach is not the problem?.........

Not on your bike.  The 1977-on engine is a different animal than the earlier models.  Your pump is driven directly off the end of the crank and the tach drive is back by the kick starter in the main cases.

In 1977, tach drive was moved forward of the oil pump into the clutch cover similar to the proven 1969-81 125/175 design.

("D" model is the 1977 year model in yama-speak... in the US at least.)

OK, thanks