Symptom's of rotary valve seal leak.

[Mekanix]

On a 787 what symptoms would you attribute to a rotary valve shaft seal leak that would only leak while running.

I have a head scratcher here. Plugs are black, Idle is rough, Running on the main jet ie 5k and up is great and smooth but everything on the low speed circuit seems overly rich.

Tried tuning, even had the low speed's turned off entirely and had proper pop off and even went with smaller pilot jets. Still same symptom's lol
Tried another set of carbs, same thing.

Pressure and suction test on the engine when it was rebuilt showed the rotary cavity to be tight. Haven't checked that again yet though.

 

[jjsinaz]

Did you ever figure out what was causing this?

 

[Mekanix]

Nope.
Replaced carbs with new and it helped a bit but still same thing.
I think I have to jet even smaller on the pilot circuit. As in down to 62.5 from 70 as 65's didn't make much of a difference and neither did 67.5's.

I dont think it was the RV shaft seal because I did after all change it and no effect to the problem.

 

[jjsinaz]

Thanks Stephen. I'm having a similar issue except my idle is fairly smooth. It's a newly rebuilt engine and I wasn't having this issue before. I've been through the carbs a couple of times now and can't find anything glaringly wrong (I have another thread going on this that has all the details)

Thanks again for your reply

 

[esahlin]

I had something similar on a 96 787 GTX that anything at light part throttle seemed excessively rich or lean. Everything at 3/4 to full throttle was fine. I went higher and also lower on the jets in the pilot circuit with little change. Turned out it was the exhaust water control valve. The retaining clip had rusted out and the diaphragm had a hole in it. Fixed this and my part throttle improved dramatically.