787 Oil Injection Cable Throw Length Too Short?

[msk186]

Hi, I'm installing the oil injection cable on a 787 engine ('96 XP) and the throw length seems to be too short. The throw length is 4.375" and overall cable length is 37" which I believe are correct for the OEM part. However, when I connect the ends to the oil pump and PTO carb lever assemblies, I am not able to open the PTO carb butterfly valve more than 3/4 of the way. It's as if the 4.375" of throw length is not enough for the carb and oil pump to have the required range of motion. I've checked the end connections multiple times and even removed the carbs so I could clearly see what was going on. I've compared my installation to the parts diagrams, reviewed the shop manual, and looked at photos and videos of the carbs and oil pump and I can't find a discrepancy to my situation. What could I be missing?

When I bought the ski the oil injection was deleted and I'm adding it back in.

Thanks!

 

[etemplet]

I've never measured "throw" length. I just did (2) 787s perhaps you don't have everything connected properly. Pictures would help. This is off a RFI so for reference only.

I just looked up the one I bought last week. You measurements are correct so you have the correct cable you may have the mount upside down. That's doable.

 

[msk186]

Here are photos of the cable connections at the pump and the PTO carb. I removed the carbs from the ski for better visibility. In the carb picture, I have the lever assembly rotated clockwise as far as the cable throw will allow.

 

[etemplet]

If we are not physically present solutions are difficult to recommend. That end looks correct. I assume you've checked full motion of the pump and carb without the cable connected. Sometimes that oil pump throttle gets bent and contacts the housing, or the spring prevents full motion. Good Luck !

 

[msk186]

etemplet, thank you for responding/engaging. I agree it can be difficult to troubleshoot some issues remotely. You made a good point about the range of motion at each end of the cable. I connected the cable to the oil pump and PTO carb individually (the other end free) and took some pictures. Would you mind having a look and providing your thoughts? Thank you!

Because the oil pump was not on the ski when I purchased it, I'm not familiar with how much it should rotate. The picture below is the oil pump rotated counterclockwise as far as it will go. Should it advance beyond that point? If so that would be the reason my cable seems "short".


At the PTO carb, I connected the cable, rotated the lever assembly all the way clockwise until the butterfly was fully opened, and made sure there was no slack in the cable. At the top of this picture, you can see how much "extra" cable I would have for connection to the oil pump. There isn't much which makes me think my oil pump needs to be rotating more. What do you think?

 

[etemplet]

Do you see on the oil pump how the cable is not feed straight into the cable guide at the connection? That is one problem. I just checked one of my oil pumps and the pump itself can move past 12 o'clock toward the cable entrance, your position being 3 o'clock in the picture. I'd look more closely at the oil pump. Good Luck.

 

[msk186]

Thank you! After continuing to search for reference photos and videos, and based on how much your oil pump rotates, I think my oil pump range of motion is restricted. Because the ski came with the oil pump deleted and I sourced a used oil pump I wasn't sure what normal operation is. I appreciate your guidance; I was at a loss after several hours of trying to figure out what was going on.

 

[etemplet]

It shouldn't be the oil pump internals. I'd check the throttle plate on the pump.

 

[msk186]

Following up to close out this thread and share my resolution. I ended up sourcing another oil pump. The throttle plate on the new pump rotated counterclockwise much farther than the original pump I was working with. I believe the root cause was the spring on the original pump I was using was installed incorrectly and therefore limiting the range of motion. Because the ski came without an oil pump, I wasn't familiar with how they should operate. With the new pump installed I was able to properly connect the oil cable linkage to the carburetor throttle plate and have full range of motion and the alignment marks on the pump are properly set.

Hope this helps someone in the future if they find themselves in a similar situation looking for help,

Thank you etemplet for pointing me in the right direction to solve my problem.

 

[etemplet]

Thanks for the follow up. It is very helpful for others experiencing problems. Glad it worked out.