steve

I bought a Leo 37SF a few weeks ago from Just Engines and am having loads of
problems with it. I've been in touch with Paul at Just Engines and he's been
helpful, so just to be clear I'm not bad mouthing them or Leo but I'm running
out of ideas! I'd like to get some suggestions from you lot before I send it
back to Paul.

Originally the carb had a problem after 20 minutes or so where the spray bar
got stuck to the main jet and rotated with it as you adjusted the mixture.
OK, maybe a one off so got a replacement carb, but it was very hard to set a
consistent mixture. Found the main needle 'O' ring was slightly torn and had
some excess flash around the perimeter so swapped it for one from another Leo
carb. Ran a tank through and everything was fine. I mean idle was smooth
and steady, the transition was clean, WOT was sweet.
Thought I'd fixed it so ran a second tank 1/2 an hour later and had to adjust
the main jet 1/4 turn richer for correct mix at WOT. This inconsistency is
at the root of all the problems I'm having.
If it's going to misbehave you can tell as you open to 1/2 throttle, the note
is different and sounds as if it's going to fluff out (and often will) as if
lean. The note is unsteady as well at any opening when misbehaving.
Adjusting the mixture doesn't really help for long. But when it's right,
it's perfect, so it must be something simple, right?

1. I get the same inconsistent problem whether in the plane or on the
test bench. One tank OK the next isn't. That should eliminate plane tank
positioning, plumbing, clunk problems etc.

2. I've tried three different fuels, from straight, to 5%nitro, to 20%
castor to all synthetic. But I'll get a good run maybe 1 in 6 from any fuel!

3. The engines's had nearly a gallon of fuel through so ought to be
behaving reasonably by now.

4. Tried 5 different plugs, of varying temperature ranges, including a
4-stroke for extra heat.

5. The carb is cleanly seated on the engine and the mating faces look
undamaged.

6. The silencer pressure seems fine and effective.

7. There's no evidence of fuel foaming, and certainly no visible bubbles
in the feed line. The tube fit on the feed/exhaust nipples seems good.

8. I've stripped the carb and blown it through, and poked the spray bar
out with copper wire.

9. The tank holds pressure without any leaks, and in any case symptoms
are the same both in the plane and on the bench with different
tanks/installation.

10 I'm running a 10 x 6 APC prop.

About the only thing I haven't changed is the silencer. Except the engine of
course which otherwise seems fine, good compression and so on.
I'm ready to try one for more day (Sunday) before sending it back to Paul
with a plea for help.

So what else is there?

Thanks anybody
--
Steve

paul mcintosh

Sounds like the engine isn't broken in yet. Even the best engines take
several tanks before they start being consistent. Some Supertigres take a
couple of GALLONS to get to the sweet spot. Give it some more time.

--
Paul McIntosh
Desert Sky Model Aviation
http://fly.mcintoshcentral.com

of

acomm

i have had several leo 37`s and one of them gave the same symptoms you
describe , in it`s case it was the bottom end needle adjusting itself . the
o ring on it just did not grip so it was very easy to turn , a quick fix is
a wrap of plumbers ptfe tape round it and re fit it to the carb and try
again .
i have every confidence in the leo 37 , so much so my son used one for
last and this years bmfa nats in a fun fly.

hope this helps,

trevor

steve

Thanks for the comments so far folks. Keep them coming.

I'm sure the engine is a good model in general, it's just that I have what I
guess is a specific problem.

The inconsistency is so bad that it's *almost* unflyable. On other engines I
hardly ever have to adjust the mixture once setup, and certainly not by a 1/4
turn or more. While I understand the engine isn't yet fully run in, my other
engines were all completely flyable after a few tanks even if needing to be
set on the rich side for safety. When it's good it's perfect across the
range. I should have kept better notes but thinking back I wonder whether
it's usually the first run that's good. Maybe when the dried oil residue
after a day or two does a better job of sealing the needle valve. Then after
that perhaps fresh fuel has thinned it out allowing air to bleed past.
I don't think the idle jet is moving as I'm keeping a note of it's position,
and it's quite tight in any case.

Acomms comment about PTFE tape is a good one. I'm going to the field today
armed with a roll of tape to try extra sealing in turn on the carb body, the
main needle, and the idle jet. I'd really like to isolate the specific
problem before giving up.

Thanks again.
--
Steve

steve

I thought I'd report back in case anyone was interested. I went along to the
field today and started with some PTFE around the main needle thread, and
some fuel tubing over the whole thing in place of the friction lock to make
sure there was no chance of an air leak. Yes, this was a reasonable flight
with good throttle response until a landing abort and flyby resulted in dead
stick after gently opening up.
Managed to land safely downwind since I had too little height to glide around
again in the stiff breeze.

Next tank returned to the original problem, whereby it needed a mixture
change of 1/4 turn for a clean WOT just richened off a few clicks from peak
revs. Then after half a tank it started running unevenly and then died
during level flight. Definitely no movement of the main needle or any
possible air leaks past it.
Again managed to put it down safely on the edge of the strip.

Next step was some PTFE around the carb body where it mates with the
crankcase. No difference, so that's it, I've had enough. Sooner or later
I'm going to be too far away to put it down safely so I'm calling it a day
and sending it back to Paul at Just Engines.

Meantime I'd taken along a new Leo 46 I'd bought at the same time and decided
to mount that and try some gentle running in. Put a 11x6 APC on it, squirted
some fuel in the cyclinder top and started winding it over slowly. My God
but it was tight! It squealed loudly as I turned it. past TDC. A bit more
neat 20% straight castor and a few more turns and the squealing reduced
slightly. So I fueled up, set the needle nice and rich, fitted and connected
the glow and gave it a flick. It clearly was ready to start but just too
tight to keep going. A few flicks later it started and although sounding
like a jack hammer, it ran. I followed Just Engines guidelines and ran about
3 tanks through. It was much freer now and sounded much sweeter. Apart from
when slow idling it never showed the 37s tendency to die and responded well
to the throttle. So I think it's nearly ready to go flying. So it does seem
that whatever the problem is, it's just that particular Leo 37 engine that's
got it.

I still can't really imagine what it might be though so find that pretty
frustrating.

paul mcintosh

Have you pulled out the main needle and flushed the carb with fuel? Sounds
like some swarf in the fuel chamber in the carb. Many times, when using a
new tank you find tiny pieces of tank materials get caught in the carb. I
always rinse out new tanks just because of that.

--
Paul McIntosh
Desert Sky Model Aviation
http://fly.mcintoshcentral.com


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steve

Thanks Paul,

Yes it's possible, although it's a replaced carb, and I have backflushed this
carb assembly, though not today. The symptoms *are* rather like rubbish in
the carb.
I keep telling myself it's got to be a simple problem, and then every time I
think I've cracked it, it rears up and bites me in the backside to prove me
wrong.

Cheers,
--
Steve.