Hi, 1975 yamaha dt175 oil pump, should the priming wheel be able to turn in both directions when bolted to the bike?

No.  If you look at end of wheel it probably has an arrow on it.

There's nothing that stops it from turning backwards. It only pumps oil into the motor when turning the correct direction though. If you try to spin it backwards it simply won't prime.

Pretty sure that if pump is assembled correctly, priming wheel (only present on pumps up until around 1976) can only be rotated in one direction. 

thanks all for your replies,i’m glad i found this site

Testing on the bench with the drive installed demonstrates that the pump will turn backwards less than 360 degrees before hitting a mechanical stop. If it stopped in the right spot it would not turn backwards at all.

I thought--& might be wrong--that it wouldn't turn backwards because the springloaded pins lock against the inside of the gear '& then' ya trying to turn the engine via the drive spiral gear [well ya can try]. Primer wheel turns in the priming direction because the pins ramp out & compress until they click over each lap which you won't feel on the priming wheel as pins are lightly sprung. If you happened to stop the primer wheel just before the pins clicked over then i guess you'd be able to go back 9/10 of a turn until locking again. I don't have a pump in front of me & might be talking rubbish of course haha.

Wasn’t there some folks talking about the bikes getting push started backwards around here? I would think then the pump would be broken? Sneezles61

Good point but 'no' the motor would run the pump in reverse & it would pump as normal--i recon!!. Its just that trying to revolve it backwards with the plastic wheel has 'no chance' & in theory--if you could--the gearing would be ridiculous, like one turn backwards of the plastic wheel would turn the engine 100 times or more--guessing how many times of course but does anyone know the gearing of the pump?, like how many revolutions of the motor to 'one' pump of the pump.
This is becoming interesting. I hope DEET, if he's the oil pump man, will rescue us or 'me' haha before i make 'more' of a fool of myself.

Might have to revise by post--umm--i think the pump gear has almost straight cut teeth meshing with the spiral drive from the motor, so probably not even possible to turn the spiral via the pump gear even on the bench. I give up. But i'll go find a pump & try it anyway.