So...I have an La 46 on a Cardinal that has run flawlessly for months. Set up is stock LA 46 with ST needle, FP metal back plate, 2 head shims, thunder bolt RC long plug/sullivan 6 oz on uniflow (hidden behind the back plate cuz it works) Always lunch at 9300 rpm and it just does it's thing. This weekend all of a sudden it goes lean on launch. Of course I replaced all of the tubing...outside...and tightend all screws...backplate, head, the little one on front of the plastic sullivan tank, needle valve...everyhting I think of that might be sucking air. I have not replaced the inside tubing on the tank, might just replace the entire tank set up. Here is what I did change...fuel! I went from 5 to 10% (GMA 10/22). I have changed like this many times when it gets hot here in texas and noticed minor changes in engine runs but this went from a fast 4/wet 2  to a solid 2. Launch RPM is 9300 with a XOAR 12-4 balanced prop. Before it would unload and settle to a 5 second lap time on 60' lines. Now it goes lean and does a 4.75 lap time. Doesn't really sag in maneuvers but 4.75 makes everyhting happen a little fast for me...line tension is GREAT though! So now it's doing a dead 2 stroke which I kinda like where before it was actually breaking a little. Goes rich the last couple of laps which was normal cuz of the uniflow i suppose.
 My question is: would changing form 5 to 10 cause this or should I continue to look for air leaks? I even thought about leaving it running the way it is and going to 63-64 foot line which should put me back close to 5 sec lap times......

yeah...forgot to say I tried that...launched at 8600!! FAT city...and it still jumped lean after launch, exactly the same as launching at 9300 ...or 92 or 91. It's not screaming lean...jsut not like it was. I screwed the pooch when I bought 2 gallons of 10% for the summer I guess. Don't have any 5% but I guess I will pick some up...or scrounge a tankfull from a buddy. Wil also try a new plug...old one does have a lot of time on it, but it doesn't sag after removal, not that that means its still good...or bad.... Oh well...so many htings to try. Just want toget back to practicing the pattern...not jackin' with motor runs ya know...

It could just be that you have some crap in the NVA or the fuel filter (if you use one) is getting blocked. Maybe you don't have an air leak but a partial fuel blockage, this would give similar symptoms?

Regards,

Andrew

I put a squirt of armor all in the fuel and have a pad under the tank to prevent foaming but...yeah it could be foaming fuel...i've had that before. AND...I have a brand new LA broke in and ready to go if the liner is taking a crap on me already. The engine on there now has about 120 flights on it, but that's only about 12 hrs if I did the math right...

Shot in the dark here but a flying buddy had the same thing happen to his high time LA-46. Did all the previously mentioned things, no help. Ran a few tankfulls of synthetic fuel through it and it fixed itself. Was castor-ated. The synthetic fuel cleaned things up and it went back to running the way he was used to. Might be worth a try.

All is well again in LA46 land...went flying last nite and one of the things i did worked cuz it ran really well again. I think it was probably the screw on the front of the plastic tank...the one that holds the cap on. Like Randy said above it was probably something inside the tank cuz it would needle just fine...everything was the same until it took off and the fuel got pushed away from the front of the tank and allowed air in.It was a little loose...not really loose but maybe enough to suck a little air in. Now I can set off at 9300 and do 5.1 or 5.2 laps in a really strong 4.
NOW...it breaks a little hard for me...like comes on at 10 o'clock and stays on through all of the round stuff. everybody says these don't do a 2-4 that well but this one sure does want to. I've got 2 head shims in...what else can I do to soften the break?....I KNOW...I'll go read Randy's engine run tips again...I bet it's in there!

using a XOAR 12-4. I've tried LOTS of props and this one seems to give the best overall performance...especially in the overheads. An APC 11-4 did OK too but really loaded the engine. I don't have the ground clearance for the 12.25 x 3.75...barely have it wiht the XOAR12-4. By the way...the XOAR props are really nice...I've had 4 or 5  and all were balanced right out of the box..nice finish too. I might try cutting a 12.25 x 3.75 down...I know it's just 1/8" off of each tip to get to 12 but I already have the gear pigeon toed to raise the nose up as much as possible and the Xoar gets nicked on the tips all the time. Maybe a 11.5-4 apc. I don't know why but i just dont like the APC props. I know some swear by them but i like WOOD!!!

Chris,

I have on a couple of occasions, had the same "run away" syndrome with "proven" LA46's.  On one more memorable occasion, the run away went on for several weeks while I tried everything I could think of.  I even took the head off and scraped the piston top.  It was about that time, although I would not want to say it was necessarily related to that scraping of the piston, that the problem simply went away.  I liked Balsa Butcher's comment about the synthetic to clean the engine.  I will certainly add that "fix" to any problems I encounter in the future.

I log my engine hours and my oldest LA has an estimated 280 flights.  (I estimate engine run hours by multiplying each flight by an arbitrary 6.5 minutes.)

As for the Xoar props, I have almost exclusively moved to Xoar for the reasons you note.  In my humble opinion, they load the engine as I like and I almost always get good engine runs.  I have a scratch "Green Box" Nobler that comes in at 53 oz and I run an LA46 with a Xoar 12 x 4.  I have tried the APC 12.25 x 3.75 on other planes with LA 46's but they just seemed soft in a lot of the overhead maneuvers.  I have converted all of my LA46's to either ST51 or Randy Smith NVA's.  In so doing I found I had to drill out the venturi to about .287" to get the power to adequately turn the 12 x 4.  That did cause an increase in fuel consumption so I added an extra head shim and am still testing that set up.  I did improve the fuel use over the single head shim but am still testing for any power changes.  (A 7.3mm drill bit gets the .287" size.)

Hi Chris,

I'm glad you got the run back.  As to the Bolly props, they have been out of production for a few years.  They are tough to come by.  There are a few guys who are making CF props, some are kinda copies of Bollys.

BIG Bear
RNMM/AMM