I thought about the Fox 35. 

I am a new Grand Dad this week.  Sometimes I know when "Not" to leave town for a contest.

Have fun.

I am a new Grand Dad this week.  Sometimes I know when "Not" to leave town for a contest.

Have fun.

Congrats PAPAWWWWWWW I'd try more castoroil. Mama used to give me a tablespoon per week whether I needed it or not!

Congrats PAPAWWWWWWW I'd try more castoroil. Mama used to give me a tablespoon per week whether I needed it or not!

 Regularity aside,  I don't think so. I have had all sort of funny run problems with excessive castor. Even Powermaster GMA, and Howard's home-brew of similar content, had enough castor to start loading the engine up at the bottoms of inside loops. That's how David and I ended up mixing fuel on the l-pad and test flying after dark at the 2007 TT - David switched engines and I needed to mix some 10/18.

     Obviously I don't know for sure, but I would guess you had a lean run that varnished up the liner with the hot run and now it's binding up at times. I would run with either Powermaster RO-Jett fuel or SIG Syn-power for a while to devarnish it. Then, keep running it forever. Alternately, I would crock-pot the engine to clean the liner. That's very much a second choice because I would prefer not to disassemble the engine, even to take the head off.

     Brett

I've had one lean run on the engine and have primarily run the 10/18 all synthetic since some of the first flights with the engine. 

   What kind of 10/18 all-synthetic do you have?

    Brett

     I run all of my engines on Wildcat 10/18.  The oil content is 80% synthetic and 20% castor by volume. Check out their website, if not available locally they will ship.
     It so happens that I'm running that same set up in my Chizler, RoJett .40 BSRE, muffler and a 10.75 x 4.25 three blade Bolly.  Runs are consistent and it holds the needle through the whole flight.  A few of us around these parts are using this fuel with good results. NO added castor!  My new model doesn't use any castor, only electrons

Mike Haverly

I think it has something to do with that PINK paint !!! That engine was not designed for a sissy colored plane.

I'm not a engine expert but I did say at a Holiday Inn Express once.

I don't have any shoes that match your plane.

I appreciate the help very much.  I'll post the results whenever I get to fly again.

What is wrong with pink? I have had several pink airplanes.  My 64 Fairlaine was pink(Salmon) color that turned a pretty lavender under street lights.   

No harm Doc,
I have just been busting Zuriels balls over it. Kind of a running joke between friends.

Dang it Doc !!!! Now see what you did !!!

He is going to order more PINK paint !!!!

 

Hi Zuriel, I suggest thar you open the vent tube and plug the over flow tube. And make sure that the tube ends has a piecxe of tubing tnhat points into the slip stream of airt!

Phil Spillman

Just went back and reread the original post.  If it only burps on the first inside loop of the horizontal and continues running, quit worrying about it.   Relax and ignore the engine run if it runs the same time after time.  While in school in Texas a guy asked me to try some of his fuel.  I was running Omega fuel at the time.  At the top of the circle I could swear the engine was dead.  I mean if was silence.  But, then would kick in until at the top of the circle again.  After three flights I went back to my Omega fuel.   

This engine shouldn't need to be on muffler pressure, a little hard to set up anyway; header muffler has no tap.  I would try a little hotter plug, mine runs on a Thunderbolt RC idlebar.  Also, it might be the tank height.  For sure cut back on the castor oil so it will run a little warmer.

Mike Haverly

Try a few degrees leaner needle setting. Just a tad. Even tho the tank is uniflo could be that the extra fuel head at the very beginning of the flight causes a slightly rich mixture. As the fuel head is reduced the engine might be running a bit leaner. The change may be enough to eliminate the burp. Wait. Wait. The inside loops precede the inside loop on the horizontal eight. Perhaps you turn the inside of the eight slightly tighter than the  other insides in the pattern. Maybe a smidgen richer would work. I've had plane/engine combinations that worked well when the loops were 45 degrees but did not like 35 degrees. Recently I had a well used FP40 powered plane that did that. Swapped out the engine, replaced it with a $4 Tower 40 swap meet mutt, an engine that needed cleaning and unlocking before it would run. Plane and that engine are a sweet running combo. The Ro-Jett is, of course, a different class of power. Big bucks is big bucks. Doubt that you would want to simply swap that engine out and replace.

I thought synthetic lube didn't burn and leave varnish like castor. Would a lean run leave a residue anyway? Lean runs on AAC, ABC or ABN (how can I learn the alphabet this way) usually don't ruin p/l fit. The liner expanding faster than the piston until power falls off. At least that was what I thought happened. After the engine sits and cools down, clearances come back to normal, no damaging liner/piston gouges. Also no warped rings.

Is it possible that the back plate or cylinder head loosened up? This seems to happen to some of my engines. Dunno why. Especially when newly cleaned and assembled. An over lean run might also stretch those bolts or... whatever happens. I've been surprised a number of times by engines that need retorqueing now and then.

Zuriel...I'd check with your fuel guy and see if he's using Klotz "Techniplate" or "Super Techniplate". The Super has 20% castor in it (check this at Tower's website, if you wish), which might be ignored when the oil content is being described.

That said, it sounds much more like a lump of solder in the tank, or some similar sort of problem, or a filter problem. I am not a fan of tiny filters. Big filters are good! But possibly, it's just installed backwards? It matters...  Steve

 

My two cents,
I'd check the tanks for leaks, but also I might suspect the uniflow line has a crack in it about half way down its length.  About the middle of the tank, the uniflo uncovers, due to the crack, and the tank momentarily drops off rich. 

I finally had the chance to get into the shop today.  I removed the engine first and when I put my hand on the fuel tank, with a little pressure it moved at the front inboard corner.  Not good.  I removed the tank and performed a pressure test, no leaks.  I reinstalled the tank with new shims and a tighter fit.  Put it all together and headed to the field.

I used the same amount of fuel and the same launch RPM's and the odd cuttout is now gone. 

I want to thank everyone who made suggestions and comments.  I hope my cure may help someone else sometime.

Zuriel