RE: Tapered-Bore Engine Break-in - Upgraded
BW,
Maybe the part of Bob Brassell's post that you should look at again is this:
"When Dub mentions "rich" in the break-in instructions, he has instructed that you have set needle valve initially at a very rich setting .... this to avoid any possibility of starting the engine lean. A Jett engine simply will not run blubbering rich (some other engines will) even with the glow plug driver on. It has to come up to a decent temperature and have a smooth mixture just to run stable. So by rich, he is stating that the engine is running, stable, with the glow driver on, clearly 'wet' sounding and clearly not peaked. This is, in most cases, a rich 2 cycle or just on a 4 cycle break."
Even they do not actually recommend you should four-cycle your two-stroke engine...
Le Fou,
Looking into this document; stage 4 of the procedure only tells you to run the engine at half-throttle for about a minute (apparently to prevent a heat-soak/spike), after which stage 5 tells you to go to full-power...
It is the later part of that stage which I cannot agree with... "Very rich" defines absolutely nothing!
It can be a rich two-cycle, or rich enough to four-cycle - there's no way to know what is meant by that term.
It seems this procedure, along with the 'sequel', in-flight continuation, which is very reminiscent of a ringed engine break-in procedure...
...Too reminiscent of this!
This procedure begins on page 3, with an explanation of the tapered-bore principle...
...But this is not carried on in the procedure itself; continuing, as if this engine is a ringed-piston model...
Also, please note the "Important" remark, at the top-right side of page 4...
A 30% RPM gain from 'unloading'??? Can you imagine propping your engine for 12K on the ground; only to have it spinning 15,600 RPM in flight?
Air entering the carburettor with higher force at speed???
Is someone suggesting Mach 0.7+ compressibility sets in at 100-200 kph flight speed???
The person who wrote this part of the manual, apparently had some 4-5 drinks too many, on an empty stomach; before taking on the task...
This is the reason I always suggest reading the manual and checking that it does not defy logic, before 'automatically' following it...
If in doubt; the procedure detailed in the beginning this thread, for ABC/AAC/ABN/Plasma Ceramic P+L engines, is as logically explained, as the character portrayed by Mr Leonard Nimoy in Star Trek possibly could.
I earlier gave the OS manual example; stating your should set your engine to four-cycle... and later directly contradicted by [link=http://osengines.com/faq/product-faq.html#q2]their Q&A[/link]...
The Magnum XL .91ARNV manual, in its break-in procedure; says many things, but actually says nothing...
I suggest following the info in this thread instead.
"Live long and prosper."