The tank position in the instructions really only works for a gas motor with their own pump. It is best to have the tank closer to the firewall. This requires a tank floor to be fitted and some material removed from the first former as shown in the pics.

As regards fuel lines and mufflers etc. It all goes back to the plug that you are using (and the fuel of course). All the posted fixes work but it really depends upon what you are fixing!

The OS 1.60 will get hot for many reasons. It will always get hot if there is not enough air to cool it. The CAP cowl is pretty good at cooling the head but you will get better results if you duct some air onto the crankcase as well, by opening up the other side. A large air exit hole is essential to let the hot air leave, especially when hovering etc. The picture below shows the size of exit used. (The second diverter was added after the photo was taken).

In the last picture you can see the crankcase and the 1/16" balsa diverter can be just be made out if your screen resoltion is good.

Back to the plug. We all know that the richer we run this 1.60 the cooler it runs. With an A3 or similar plug you have to run the engine lean to avoid it choking on transition etc. "Lean" means "just right" in this case. When you go vertical it gets a little leaner. Not much but enough to generate unwanted heat. It could be lean because of fuel-draw issues either from tank position or fuel tubing diameter or exhaust pressure.

As regards exhaust-pressure the Slimline did not give enough until one exit was blocked off. It was also quieter and gave an equal vertical climb-rate, BUT sounded less powerfull!!!! The Brison gave enough tank and 2-c back-pressure. If you look closely at one you will see that they have "belled" inwards the exits of each pipe-tube to considerably reduce the exit-area. BTW you can test if you have enough tank pressure by opening up the needle at full throttle. If you can't get the engine to go rich at three plus turns out, you don't have enough tank pressure or fuel supply available.

You can of course fix fuel-flow issues with pumps and cline type regulators. (That's a religious war in its own right). However, the way you set the fuel-mix adjustment is very similar for all set-ups.

Back to the plug again. A plug that is too cold will, on average, not let you set the OS 1.60 rich enough. A warmer plug allows you to set the low-end needle richer without putting the "fire" out. The OS "F" is a good plug for this engne. To set it up to give cool runs with good transition is a pretty straight forward exercise.The target is to set the carb as rich as possible and still get a smooth run. A slight gurgle in the mid-range is acceaptable as long as the engine does not hesitate.

With the engine warmed up with some full throttle runs you can richen the low-end needle and test the transition until it starts to struggle when the throttle is opened up. Then lean out the low-end needle about 1/4 of a turn in. You should get good responses to both slow and rapid applications of throttle. The reset the high end to be a few clicks off maximum rpm. Now find a big guy to hold your GP CAP 232 nose pointing at the sky! It should idle all day in that position and not run lean at full throttle.

Then pull back to 1/4 throttle for about 60 seconds to see if it goes hot. A hot engine makes a metalic pinging sound which is caused by the engine firing too soon due to the excess heat in the combustion chamber. This detonation is the scurge of a 2-c motor. An F-plug and a rich setting will make the OS 1.60 a much happier engine.

There are many other variables in this problem so results at home can differ!

I would close by adding that if you have been experiencing lean runs and the detonation described above, you should change your piston-ring. The hot run detonation can make the ring to go soft or damage the ring seat and cause it to stick. The OS lets you do this ring swap at the field because all you have to do is remove the head and slide out the sleeve to get to the piston ring.

Happy New year to you all,

Eric.