I have a YS91 with a TME Simple Smoke Pump. It puts out the most amazing smoke you ever want to see. And there's no pre-heating.

It took me about a year of messing with it before I got it right, but believe me... I got it RIGHT!

There are a few things that you need to get good smoke. It's like when you want to make fire, you need heat, fuel, and oxygen. To make smoke, you just need heat and fuel, BUT... they need to be the right amount of BOTH!

First of all, I would be very hesitant to use a system that works off of muffler pressure. Even the TME system leaves something to be desired as there are times when it will stop working, (usually if it has been off for a minute or two) and I have to fly at idle for a while before it kicks in again. The B&B system is the best, but it only works on BIG engines.

So, you want a good pump to be sure that you are delivering a good, constant flow of oil to the muffler.

Next, you need heat. I don't pre-heat the oil, but I did wrap my muffler with a few layers of fiberglass cloth, wrapped that with aluminum tape, and then wrapped it with some thin copper wire to keep the tape from vibrating off.

My next consideration was fuel. I'm a cheapskate, so I looked into home-brews. But everyone had a different recipe, and most of them used things like fuel oil, diesel fuel, kerosene, etc. All these petroleum products will leave a residue on your plane that can attack the coverings adhesive. I didn't want that, plus several people mentioned how those mixtures stink up your car, and workshop, etc. So, after doing some extensive on-line searching, I found Ultrasmoke. Now there may be others, but this is what i use and it is fabulous! It's not a petroleum product, so it won't attack your covering, and you can use ANY kind of fuel line. It also doesn't stink, in fact I can't smell anything. it costs $10 a gallon from these guys:

http://www.aircapitalhobbies.com/

10 buck is a lot of money, but for the smoke I get, it's worth it!

The next (and one of the most important) thing is a flow control device. Too much oil is as bad as too little heat. There's a picture of the one I made. It's very simple to make. you just run the oil line through the hole and pinch it with the screw. With the engine running at full throttle, and the pump on, you just tighten the screw until the muffler is getting the right amount of oil. You'll know when that happens, because your neighborhood will disappear in a cloud of smoke.

One of these days, when I have nothing to do, I'm going to try it out on a 40 (and maybe even a 25) engine. I think it might work, although you would still have the weight problem to deal with.