G'day all

I recently bought a LEO 46 pretty cheaply on a certain auction site. I bought it as a challenge and to later convert to diesel as an experiment but in the mean time I have put it in a friend's plane to give a a bit of running. I am running a commercial fuel with 10% nitro, 5% castor, 15% synthetic and methanol. I think the plug is an OS A3 because I had several I got by accident. The prop is a Bolly "clubman" 11 x 5.

It started easily from new but it seems to have high compression and is easiest started by hand. The carby seems to me to be be very insensitive - large changes to the HS needle make very little difference and the LS needle is also a blunt instrument.

It flies the plane well but as the plane is overpowered (it is a Sig kit built LT25) it flies best on about half throttle. On full power, everything sounds fine, idle is reasonably stable for a new engine (has had about 20 minutes running now) but at mid range I suspect it is pre-igniting. Lots of crackily popping noises on top of the normal two stroke exhaust note.

I am considering adding an extra head washer and perhaps trying some lower nitro fuel but none is available where I am so I am open to other ideas, hints etc. And could the A3 be too hot and so causing pre-ignition?

Thanks in advance.

Mike

.....yep, add the shim and fit a cooler plug. It should be OK. [sm=teeth_smile.gif]

FBD.

Thanks for the info Dave. I waited to see if anyone would answer as well but it seems that they all think that you got it right in one. I am going to try some FAI (0%nitro) fuel tomorrow and I have an OS8 plug to try too. If that helps, I will also get a shim and try that as well with 10% fuel. I like to have just one type of fuel for simplicity. Thanks again. Mike

....the engine is likely detonating, not suffering from pre-ignition. The first
remedy is to lower the nitro, or the compression. Then go with a cooler plug,
and if necessary a ligher load....smaller prop.

[sm=teeth_smile.gif]

Good advise all. Personally I change one thing at a time until I get the performance I am looking for. Usually the easiest thing like the plug or the fuel. If it will run on FAI fuel heck why not. If you don't want to have to change the fuel screw in a colder plug. I am having the opposte problem in regards to propeller size with the SIG Aviastar .46 I just got. When I try to run a small prop it will detonate, must be something to do with the cylinder filling dynamics. It will turn a 12X5 prop to 11,600 on the same setup without a hit of detonation but a 9X6 is crackly.

Thanks everyone. I went out today but was unable to do any testing. We had a working bee that went on all day and by the time I could have a fly, I was just too tired. So next weekend (or perhaps before) I will give the changes recommended a go. I have not yet managed to find a suitable head spacer. The bore is 22mm. Any one know if any common OS head gasket would fit this? I can easily get OS parts but Leo - I would not know where to start.

After we finished painting, digging, cementing, cleaning and carpeting today (our pits are carpeted!!) a friend was flying an unusual aircraft. He is using it as a trainer for his 15 year old son. It is a fibre glass fuse from a 40 size Extra fitted with a non standard parallel sided wing. A sort of home grown Something Extra (but more of a Something Less). It is towed around by an elderly Enya SS40. Flies really well and the Enya sounded amazing puttering around at about half throttle. Hope I managed to get the Leo to sound so good.

If you can remove your old one and give us a measurement I am sure we can find something that will fit. I am not certain who makes the Leo. I am going to make a guess and say Megatech .46 is the same engine. http://www.megatech.com/product_deta...es.php?ID=4709

if you can buy some thin copper shim you can make your own head spacer.

Mike,


The OS A3 is probably the hottest plug in current production.

Hot plugs go with little engines, low nitro and low compression...

In their larger engines, OS [link=http://www.os-engines.co.jp/english/line_up/plug/pluindex.htm]recommends[/link] this plug only for break-in...

The only larger engines that run very well on this hot plug (without resorting to too rich a mixture setting), are Evolution engines, as detailed by Barry Williams (blw) in other threads.

Greetings all.

Well I finally did some real testing and everything worked out very nicely indeed. Today I flew the Leo 46 in its Kadet LT25 for the second time. It is rather more than the Kadet needs but its weight is just right and I was able to remove the lead I had added to the front to balance the previously fitted ASP 30 four stroke. The engine is fitted with an OS "PBOX" muffler as the Leo did not come with one. Just bolts straight up and keeps the din down well.

The changes -

1. I fitted a rather second hand OS No 8 plug.

2. A friend mixed me up some FAI fuel. (20% oil, 80% methanol).

3. I re-adjusted the high speed needle quite a bit leaner but still running slightly rich.

The result -

1. No more pinging.

2. Easier to start with the electric starter. Was always easy to hand start and still is.

3. Will idle forever and the transition is fine.

4. Unbelievable economy. We have now made about six 5 to 10 minute flights and have only managed to use about 300mm of fuel. We are running mostly at about half power but the bloke that owns the trainer is mightily impressed by the frugal nature of this engine/plane combination. It is about as good as the 30 FS was.

Nitro? Who needs it!

I am running the same Bolly 11 1/2 x 5 prop which gives tons of performance at what sounds like sensible revs.

I suspect that this engine was made for the European market where nitro has alway been expensive and used sparingly. I have routinely used 10% in all my engines (mostly Saitos) but this engine simply does not need it and positively thrives without it. It may not be the most powerful 46 around but it is very easy to use and produces more than enough power for most sport models and trainers. My mate is so impressed, he wants to buy it from me.

Thanks to all who provided advice.