Hi, I have replaced my old oil pump on my DT 175, 1974, with an oil pump from a slightly newer DT 125, the pump looks the same as the old one. I have taken out the inside (gear) and the old pulley 364 from the old pump and put it in the 125 pump, which I thought would work. The problem is that at idle I get the right amount of oil out approx. 1.20 cc at 200 strokes, but at full throttle it only delivers 5.2 cc at 200 strokes, it should be around 9 cc according to the manual. I think this seems fishy, ​​the only difference I can see besides the gear that I changed between the pumps is that the old pump has a slightly thicker piston that pumps the oil and that in that case it would pump more oil, but then it should not deliver the right amount at idle I think. Anyone have an idea??
Regards

With the exception of fittings, externally the pumps all "look the same" from 1964 on.  Even when they dropped the primer wheel in about 1976-77, the actual pump body and appearance looked the same with the same number cast into the body. 

At minimum stroke, the oil amount is controlled and adjusted by pump shims. The output is about the same at idle across most models.  

The problem with the "output at 200 strokes" is even if your 125 pump had the same full throttle output at 200 strokes, oil amount could be WAY off because of the gearing of the pump. 

The "200 stroke" spec is meant to be used with the proper pump for the engine... 

On the later 125/175 models, the "200 stroke" output was about the 5 cc's you've mentioned.  BUT, those models also had a different primary gear ratio (gear on crank was bigger).

Think of it this way...  your early bike at full throttle at 5,000 RPM might achieve 200 strokes of the pump in one minute due to the pump gear ratios.  That would be 9 cc's a minute. 

Say the later pump has different gearing so maybe at full throttle 5,000 RPM it hits 200 strokes in only 30 seconds...  but remember it puts out only ~5 cc's per 200 strokes!   So because of the pump gearing difference it actually delivers MORE oil... 10 cc's per minute under the same RPM and throttle conditions.

Pump gearing is critical.

If you know what year/model the pump you installed is from we might be able to determine the gearing differences.  But best practice would be to find the right pump or have DEET rebuild your original.

Ok, that might explain some things, I hadn't thought along those lines. Unfortunately, I probably can't repair the original pump as it is in too poor condition. The pump I'm using now is for a 125 DTMX 2A8 from 1977 - 1979, maybe this one could work if I know the gear ratio? Would another alternative be to look for a 125 pump from 1974-75?? I have a feeling I read that these are the same as for the 175 cc. Thank you very much for clarifying my thoughts.