I was looking at part numbers for oil pumps and the AT1, CT1, DT1 have the same part number, begins with 214 number. In the tech library they show a spec on min and max oil delivery at idle and full throttle. At idle the AT1 and CT1 deliver less oil than the DT1, At full throttle they are the same delivery rates. How if the pumps are the same does the 250 pump deliver more oil at idle. I started questioning my pump after noticing there is no smoke coming from the exhaust. I have a spare 125 pump but not sure now it will pump enough oil at idle, It does show the reduction drive is different from 125 175 and 250's, is that the plastic drive gear that drives the oil pump worm gear that makes the difference?

If you spin the plastic "starter" wheel.. you'll see the actual pump shaft goes up and down.. There is some shimming that can be done... 
Due to the way my RT2 pump sits in the cavity, I turned the starter with my thumb, counting the strokes with the out put tube in a syringe.. That way I could verify how much oil was coming out... one with it at an idle position.. another wide open position

I spun the starter wheel and watch oil come out up by the cylinder, need to do the volume test I guess. The procedure says 200 turns of the wheel, bet that takes some time. I was thinking of adding a shim also to increase flow.

Could run the motor & count 200 by marking the pump wheel. Then ya loose ya count--start again. Motor idling or up a bit will still be minimum stroke. Bit of premix or a squirt of an oil can into a breather of the carb so goes into the fuel bowl, she'll last that long.

Much easier to count the pump plunger moving up and down than revolutions of the wheel in my opinion 

good point haha, but small movements i'd likely miss one. why don't they pic an easy number like 99.

You could just use math if you don’t want to spin the wheel 200 times. Divide the output by 200 and that will tell you the amount one revolution will produce. 
If 200 revolutions produced 200ml, then 1 revolution will produce 1ml. 

But the idea is to reduce the margin of error by using a larger volume. 
The margin of error would be even less if you did 400 revolutions. 


Just my opinion. 
 

To address the real issue, a 125 pump won’t work for a 250. 
The plunger, pulley, ring gear and worm gear have to match. 
You can’t shim a pump to make it work for a different application. 



Once again, just my opinion. 

Why do they have the same part number then?

I can’t tell you why Yamaha didn’t assign a unique part number to the pumps. 

There were dealer bulletins issued explaining the color code system they used to tell the pumps apart. 

The assumption that the part number would indicate that they are the same is false. 


Just my opinion…. I’m not an expert on anything.