I did a search for BBTU and Brett Buck but did not find anything to answer my question. Google was no help either.
There has never been a topic covered in more detail and at more extreme length in the history of CL Stunt internet forums. There's a 30+ page document on what you should do.
The chap that I was referring to was flying an OS .25 with a Hayes 3 oz. tank and lethal looking plastic 9-4 prop in an OTS plane. He was getting a great engine run!
I had a feeling that Mr. Buck was exhibiting a bit of tongue in cheek humor. Lol
Mr. Buck did not invent the term BBTU, and he's a notorious pain in the ass with no discernible sense of humor.
I think Doug Moon (or possibly Steve, also a notorious wise-guy with admirable skills, although he has failed to attain even a Top 10 on the Larry Fernandez "Biggest Smart-Ass list") coined the term, but Dirty Dan Rutherford elevated it to high art .
The joke is that there is *no* tune-up. The magic trick to the 20FP is to *run all the parts that come in the box without drilling, grinding, modifying, ANYTHING*. That means
STOCK OS 20FP-S ABC or OS 20FP-S RN ABC, engine, completely unmodified.
STOCK venturi exactly as it comes from OS.
STOCK spraybar exactly as it comes from OS. This includes the "nozzle" in rear-needle arrangement. or conventional spraybar for the front-needle setup.
STOCK E-2030 muffler with nothing drilled out, ground off, "removed for better flow"
STOCK APC 9-4 Propellor. You can satisfy the insaitable need to modify something by sanding the flash off the TE, to the point you can flip it forward without cutting your finger.
STOCK glow plug that comes with the engine, or, discarded Thunderbolts or other quality hot plug, scrape taters off the element with an exacto knife if there are any.
Any tank that is offset less than 1.5" outboard from the mounting lugs (profile) or centerline of the engine (upright or inverted). Inboard is OK, but not necessary. I use a Sullivan SS-4 clunk tank (about $3.95, no modifications) with the wide part up against the fuselage. If it is a suction tank, hook up a pressure line from the muffler to the vent. If it is a uniflow tank, use it normally with an open vent.
Any normal Hobby Shop fuel from 10% on up.
Despite the perfectly clear and absurdly simple directions (since they tell you to open the box and bolt it to the airplane), extensive painful experience has demanded a long list of DO NOTs that I feel compelled to add:
DO NOT disassemble, adjust, disassemble/clean/lube the engine. DO NOT replace the screws with "better" ones, and the engine comes with a perfectly good Allen wrench, so use that. There aren't any "chips" or "swarf" in the engine. In fact, of someone comes around you and uses the word "swarf" with respect to modern production stunt engines, move carefully but quickly away from them and don't let them near your 20FP or another other engine you might have.
DO NOT, repeat DO NOT, replace the spraybar and venturi with the "better ST needle" and/or a venturi from the "How I came in 4th at the 1956 East Podunk Stunt Exhibition and Chili Cook-off" venturi chart.
If you have an RC version that you want to convert, get the STOCK, repeat STOCK, OS replacement CL parts which are still available from Tower. I would suggest the rear-needle system, only because the 20FP version is much less prone to damage from inverted crashes than the front needle, or the 25LA plastic backplate mount (which is otherwise perfectly fine and does not need to be replaced or modified).
DO NOT "add head shims" or modify the head in any way, or even take it off or loosen the screws. DO NOT buy or make "replacement" head shims, because all that will do is induce some genius to start stacking them in there.
DO NOT substitute an "equivalent" propellor.
Break-in should ideally consist of one ground run of the 4-ounce Sullivan tank, in the airplane, at a wettest-possible 2-stroke. Then fly it, Set it on the ground by peaking it out in a 2-stroke, then backing off the needle until you get a distinct reduction in the RPM, 6-8 clicks of the needle (which you have not foolishly replaced with a ST or other "better" version). Be very aware that the engine, particularly the plain-bearing section, will loosen up dramatically over the first few flights, to the point that it will go very rich by the end of the flight. Reset between flights as indicated. The venturi and front end will usually be BLISTERING hot after the first few runs. The fuel consumption will be astronomical, you may only get through the round 8s on 4 ounces on the first flight. It may want to quit, particularly on inside maneuvers near the end of the flight. The needle will have to go in (using the same methodology, peak out lean, then back off until you get a distinct drop) after every flight, which indicates that the engine is loosening up. This effect will get smaller and smaller over successive flights, and if you keep putting in 4 ounces of fuel, all of a sudden, it will run 12+ minutes. That means you should reduce the fuel carried, it will get down to around 2 ounces for a complete stunt pattern.
The airplane should fly around 4.5 sec/lap or slightly slower. This should provide abundant line tension for any appropriate airplane (basically, profile trainers designed in the miserable dark ages to use a Fox 35), and will *not* seem fast in the maneuvers. Use .015 lines from around 58 to around 62'. 58 will tend to screw you into the ground. It should run in a medium 2-stroke in level flight and pick up slightly to a lean, near-peak 2 in the maneuvers.
In case you (and everyone else) has not gotten the point, this engine has a better stunt run quality than any other engine you have or will every likely have, using it STRAIGHT OUT THE BOX WILL ALL THE PARTS EXACTLY AS IT LEFT THE FACTORY. I have long since lost track of the number of times I have had people come to me and say that the engine doesn't work like I said, and it has no power, or it "runs away",. In every single case, someone has decided to "improve" or "substitute" "better" parts, took it apart to clean out the "swarf", etc. In every one of those cases, the "improvement" caused their problem they were complaining about. In many cases, I took my ~20-year old engine with hundreds of flights and maybe run on gasoline/Wesson oil* or an a brand new, never-run, stock engine straight out of the plastic bag, and a stock APC 9-4 straight out of the package, bolted it to the airplane, started it, and all their problems were immediately solved.
You DO NOT know how to improve it, and neither does anyone else. That in particular includes the legion of people who proclaim themselves "engine experts", in fact, most "engine experts" will almost IMMEDIATELY screw it up with the very first thing they do, and almost none of them know what you actually need from a stunt engine to optimize overall performance.
Note also that more-or-less the same thing applies to the "new" 25LA, except that it seems to have substantially more power, that needs to be LEFT ALONE WITH NO MODIFICATIONS as well.
Brett
Topic: What is BBTU? (Read 3731 times)