55AX mid throttle issues, fixed I think
 

Hey Bax

Brand new 55AX broken in per manual, maidened in a new airplane, first 3 or 4 flights fine with no incidents. Engine suddenly starts dying at mid throttle, right where I like to fly. Here's some background:

Mounted in Goldwing SBach at 270 degrees, muffler down and needle valve straight up inside a cowl with appropriate cooling cut-outs.
All brand new fuel system using O.S. bubbleless clunk
Wildcat 15% nitro, 18% castor/synth blend (brand new jug)
12X6 MAS Prop
300' above sea level, 90ish degrees, moderate humidity

Can easily duplicate on the ground. Cowl removed to observe fuel line and absolutely no air bubbles or disruption of fuel when engine quits. Engine does not hesitate or sputter, dies like a light switch turned it off. Good idle at around 2800/3000 RPM. Perfect transition to full throttle with no hesitation, Perfect full throttle flight at around 9000/9500 rpm adjusted slightly rich from max rpm. Tried pretty much everything: tuned needles, changed glow plugs numerous times and they looked perfect (OS #8), re-built entire fuel system. Removed and cleaned carb, nothing found.Raised tank to get it in-line with needle valve. Flown with cowl off and engine is definitely not overheating. Same exact problem. Still dies at half throttle...

Here's the kicker: Changed to an OS F plug and problem instantly solved. Put her back together, cowl installed and 10+ perfect flights later with absolutely no mid throttle problems anymore. Do you have any ideas why the F plug would have made such a difference??

Also, after reading your previous posts concerning RPM, I dropped down to an 11X6 and running at 12,750 rpmsslightly rich with a perfect light smoke trail at full throttle. She's much happier at the higher rpm and is pulling around that SBach like nothing!

One more question: OS 75AX, already broken in. I think I'm over propped with a 14X6 at 9000/9500 rpms. Going to drop down to a 13X6. Can you recommend a good rpm range for the 75AX. No worries about noise here. Thank you very much.

Randy

RE: 55AX mid throttle issues, fixed I think
 

If you run the .75 AX so that its peak RPM on the ground when properly leaned is in the 11,000's, you'll be doing well. However, the 10K-plus range will work......and then whatever prop turns that RPM and flies the airplane well is the one to use.

We'll even turn the .91 at just under 12K for best performance.

O.S. selects props that give the best noise profile coupled with respectable throttle handling. The high "paractical" RPM range, though, tells us that you can really use a higher RPM as a baseline if you're willing or able to handle the increased noise output.

RE: 55AX mid throttle issues, fixed I think
 

Yep . . Mine and others I know of do exactly the same thing. For what it's worth . . i have ALWAYS run an 'F' from my pre EP Pattern days. It's no good for slope soaring balast . . any other ideas ????

JB

RE: 55AX mid throttle issues, fixed I think
 

just so you know i to have been having the same problem went thru 22 dead stick landings but its in a saratoga and always gets back to the field tried everything you did even the f plug suggested by a old timer but still died i cant believe how good she runs for three minutes then just shuts off like a kill switch i did fix the problem though after replacing all fuel lines and clunks and filters and finally a new tank complete from hangar 9 i had bought two engines from tower so i finally switched engines and guess what 33 full flights and not one problem im sending the 55 back as this is being writen hope they can find the problem
                                                                                                                                        
                                                                                                rick nunes