Mysterious oil pump function

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Hunterb

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I have completed the break in on my rebuilt 1997 GTX and am now going to straight gas in the tank and relying on the oil injection system to function properly to keep the engine alive. I tested it using the reverse drill when the engine was apart and I've tested it using the 'hold it open at idle with engine running' technique and it seems to be working. My question is, how do these pumps work? When I hold the cam wide open I can see the oil 'pulsing' in the lines ever few seconds, kjnd of like a mechanical heartbeat. At idle it barely moves. So, am I right in thinking that the pump just spins away and gradually builds pressure up in the lines until it reaches a 'tipping point' at which time it overcomes a check valve in the little output lines? I did put a vacuum tester on the discharge nipples when I had it apart and they do hold at low vacuum pressure and then release as pressure increases. So the faster the pump spins the faster pressure builds up and the more often the nipples will discharge oil. And some clever Rotax engineer has designed the system to deliver the appropriate oil for the rpm the motor is at, provided you have it lined up correctly.
Have I got this about right? I'm just trying to get more familiar with how this engine works.
 
I have completed the break in on my rebuilt 1997 GTX and am now going to straight gas in the tank and relying on the oil injection system to function properly to keep the engine alive. I tested it using the reverse drill when the engine was apart and I've tested it using the 'hold it open at idle with engine running' technique and it seems to be working. My question is, how do these pumps work? When I hold the cam wide open I can see the oil 'pulsing' in the lines ever few seconds, kjnd of like a mechanical heartbeat. At idle it barely moves. So, am I right in thinking that the pump just spins away and gradually builds pressure up in the lines until it reaches a 'tipping point' at which time it overcomes a check valve in the little output lines? I did put a vacuum tester on the discharge nipples when I had it apart and they do hold at low vacuum pressure and then release as pressure increases. So the faster the pump spins the faster pressure builds up and the more often the nipples will discharge oil. And some clever Rotax engineer has designed the system to deliver the appropriate oil for the rpm the motor is at, provided you have it lined up correctly.
Have I got this about right? I'm just trying to get more familiar with how this engine works.
Since you asked nicely.....here are the pages from my '96 GTX...I can't imagine your particular ski will be that much different....FWIW.....
 

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Since you asked nicely.....here are the pages from my '96 GTX...I can't imagine your particular ski will be that much different....FWIW.....
Thanks for that! This injection system kind of worries me a bit. I gather it is pretty reliable but still makes me nervous.
 
Thanks for that! This injection system kind of worries me a bit. I gather it is pretty reliable but still makes me nervous.
Don't be nervous.....the defacto expert here -> Mikidymac will ALMOST swear by them as very perfectly reliable (BUT they are a mechanical device and certainly can fail).....going pre-mix is not the ideal situation...you can't ever really get your proportions perfectly correct (filling up at a gas dock), so you are always "guessing"....maybe too much oil, maybe too little.....in the end, I believe the conclusion is that you'll spend more on oil than the conversion is worth. The ski was designed with the system to meter oil into the engine as needed....don't mess with it (IMHO), but it does need to be calibrated to work in conjunction with the throttle, etc....so attention to detail is important when putting things back together.
 
I'm not thinking of going to pre-mix. I have a 1984 Cr250 that uses premix and it's a pain. I was really just curious about why the oil 'pulses' through the lines and how such a simple pump system accurately meters oil delivery. I think I understand it now.
Back to the lake!!
 
Your oil injection system appears to be working perfectly, the oil pulses,, and those nipples have one way check valves., and remember that you have engine vacuum to help suck the oil in.
 
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