I have a head scratcher type puzzle. On climb out my 350i occasionally has an unscheduled power drop of around a hundred rpm. Not every time, just occasionally. In static tests on the ground it is a brief drop then climbs back up. Like in flight, not every time. Static rpm is around 2600 to 2650 at current prop pitch.

Ideas on how to troubleshoot? Checked gasolators, they were clean. Small leak on hose fitting, turned out to be on a return line, not likely source of air in lines. Fuel pressure is around 48+-.5 psi at full throttle. Pumps run either or, pump 1 or pump 2 runs, never both at same time. Might happen only with pump 1, or it could be coincidental. Seems to be more of an issue on first take-off of the day. Or it might be that I just quit flying when the engine is not running to expectations.

Something temperature related? If so, what?

Engine has been flying for 300 hours since I last did any significant changes/work on it. 650 hours over all. Burning a small amount of oil, leaking a very small amount onto engine mount and fire wall from mystery source.

Ideas? Suggestion’s on how to troubleshoot? Ray did not have an immediate answer. Not something he has come across.


N750RP Cruzer 

Views: 863

Reply to This

Replies to This Discussion

Glad you solved the issue...good info for UL owners Ralph.  Did you happen to notice "before" and "after" fuel pressures values.  You should be able to upload the .cvs files from the Dynon user data log into Savvy Analysis online and review the values.

As to solving the issue…maybe. With a couple of hours of good performance I was feeling positive until I Aborted a takeoff the other night due to slight power bump. Have not had much time to work on it since. The one static test I ran elicited one 70 rpm power drop and slight fuel psi drop from 49.5 to 48 and back-up again. I have already purchased another fuel filter. It will be interesting to see if changing filter again gives me another reprieve. I will install the new software driver so that I can download the data from the Dynon, somehow. 


How’d you make out with this Ralph? 


Scary as it sounds, I played with wires, reviewed data downloads, small stuff basically. Has been running like a champ, with nothing I can attribute to fixing the issue. On the thin possibility that it was air in the line I now flip between both fuel pumps prior to flight and do an engine run-up to 2300 rpm’s and hold it for 15 seconds on first flight of the day.

Nothing is as soothing as a problem that just goes away on its own!

Now I have a different issue, oil temp and oil pressure numbers flicker up and down on my Dynon D120 at cruise. At idle the numbers are solid. Searching for possible loose wire or grounding issue, so far no joy. Added new ground wire from battery to block. Will review Dynon ground connections wire by ground wire next. Owning an airplane is so relaxing!


I know what you mean. I’m fighting with a chronic leak on the copper washer between the fuel pump housing and check valve fitting. Changed washers 4 times and just today striped the housing female threads of the pump. Yayyyyy! I really don’t light the design of these.

I too swap out my pumps during the ground run up and use both on take off. Haven’t had a power drop yet, knock on wood. 
All very “stress free”.

Cured the oil temp flutter issue. Took the lead off from the front sending unit, used Emory cloth on the contacts, and tightened it down. Works much better. Oil pressure still bounces more than I like, will continue to chase loose or dirty connections.



New from Zenith:

Zenith Planes For Sale 

Classified listing for buying or selling your Zenith building or flying related stuff...

Custom Instrument Panels
for your Zenith

Custom instrument panels are now available directly from Zenith Aircraft Company exclusively for Zenith builders and owners. Pre-cut panel, Dynon and Garmin avionics, and more.

Zenith Homecoming Tee:

Zenair Floats

Flying On Your Own Wings:
A Complete Guide to Understanding Light Airplane Design, by Chris Heintz

Builder & Pilot Supplies:

Aircraft Insurance:


West Coast USA:

Pro Builder Assistance:


Transition training:

Lavion Aero

K&S Aviation Services

Aircraft Spruce & Specialty for all your building and pilot supplies!

How to videos from

Developed specifically for Zenith builders (by a builder) these videos on DVD are a great help in building your own kit plane by providing practical hands-on construction information. Visit for the latest DVD titles.

© 2024   Created by Zenith.Aero.   Powered by

Badges  |  Report an Issue  |  Terms of Service