Perhaps this won't be new to many but it did cure a problem that I was having with one particular 46. No matter what I did it still would not settle down and give me the run that a 46 was expected to do. I was using a 12.25X3.75 APC prop, powermaster 5/22 or 10/22 depending on conditions. OS25 venturi, Randy NVA, an extra head gasket.and a thunderbolt plug. Tank was a Sullivan plumbed for uniflow. With all of this I couldn't get the engine to settle down. It was running more like the problimatical LA40's.
Went flying yesterday,Saturday, with some fairly  knowledgable guys and as it ran badly. I said that after all of the changes it had to be something simple that was being overlooked.
Skipping all of the debate on causes and condition the plug came into consideration and it was pointed out to me that the plug OS recommended was an A/3. This got the conversation to the length of the plug and a quick comparison of 2 specimen plugs. The difference is about one thread turn on the length of the plug and makes it I guess a medium thread. So we installed a RO/Jett plug and fired up and flew. The engine behaved perfectly with consistant 5.4 second laps and a clean quit each time. While I was aware of plug heat ranges I apparently forgot that length will also advance the timing as surely as the heat range.
This just might be the solution for all of those badly running LA 40's that we keep hearing about and it only cost a few bucks to find out. as for me I'm going to get a few more of these to put in the box as another trimming tool.
dennis

Thanks for sharing your findings guys.  I'm using the Thunderbolt plugs so I have not noticed that problem so far.

Many years ago we got an OS .46VF from Tower in the "Scratch and Dent section, almost new and for well less than 1/2 price. (gotta figure how "Cheap" I am! LOL!!) but it didn't run worth a hoot.  I pulled it down and found the cylinder was installed wrong from the factory.  Orientating it properly fixed the problem!  Turned out to be a great piped engine.  Later, PaPa Dave Hemstraught gave us one of Randy's AAC sleeve/piston set ups and we used the engine for a long time.

It wasn't the first engine that I had seen with parts improperly installed from the factory.......

Big Bear

I run my OS 46LA on a APC 12*4 with an Enya 3 plug. Due to pinging noises I put an extra head gasket in. Now it runs perfect, on 5% nitro and 20% castor oil.

When we started using the piped OS .40VFs, the Enya #3 was the "HOT" set up.  Only thing I disliked was that once you used your glow plug lighter on one, it wouldn't fit anything else! LOL!!

Big Bear

I run my OS 46LA on a APC 12*4 with an Enya 3 plug. Due to pinging noises I put an extra head gasket in. Now it runs perfect, on 5% nitro and 20% castor oil.

Finally, I had all my OS 46LA heads modified. The squish band has been halved and the combustion chamber is more of a hemi head. Now the engines run in a perfect strong 4-2-4 mode.

I now use a wooden 11x5 prop, 5% nitro and 20% castor oil, and a Enya 3 plug.
Lap times on 65 ft lines is about 5 sec.  All my problems are solved.

My brother had a run problem with his, tryed differents things, it was the back plate. Put on a new one from Randy and this thing run's great.

Most LA 40 problems are due, I think, to using too much prop and not enough rpm on too big an airplane.  I bolted one in place of a Brodak 40 for nose weight in my Smoothie.  With the everything stock including the muffler, except for putting an OS needle valve up front, it turns a 10/4 prop at about 11,500 in the air in a full 4 cycle.  Slight break at the top of maneuvers.  It uses an A6(formerly A3) plug, 10% nitro, 11/11 oil.  The Smoothie now weighs 39oz. and has gobs of power.

Hello Chris,
I was under the impression that only the early 40s had a boost port? Later production was without the boost port? I stand to be corrected on this, as I have never owned a 40 or indeed pulled one down, so I may well be misinformed or just a senior moment!

Regards,

Andrew

I have always run my la 46 with a Thunderbolt RC long pplug and have never seen a reason to use anything else. I can usually get a full flying season out of one plug. I also use them on my Stalker and Super Tigre engine and I like them because they tell you when they are getting toward their live span by loosing RPM when you take the glow starter off. I also use them on my Fox engines which are verty good at blowing plugs unanounced. Ask me how I know that one.