Large diesels are not popular because:<div>

1. fuel is $12-$14 a quart in the US plus shipping
2. conversion heads are over half the cost of the engine
3. none of the large hobby sites like Tower carry diesel engines or the heads
4. lack of advertising
5. gasoline engines are becoming smaller and cheaper
6. electric motors and batteries are cheap
7. smell
8. most hobby shops do not carry model diesel fuel in the US
9. oil mess

<div>But all in all the main reason is the fuel cost. I mean why would anyone want to buy or convert an engine to burn expensive fuel when they can get a DLE 20cc or that new NGH 9cc and burn regular unleaded? Even glow engines can be cheap to run if one can get methanol locally by the gallon and mix it with some castor. One can get a whole gallon of castor from FOX for $20. Methanol is only like $4.00 a gallon.</div></div><div></div><div>just my .02</div>