ORIGINAL: downunder
I'm puzzled...you said most Jett's won't 4 stroke because they're high performance...now you're saying I can get mine to 4 stroke because they're high performance? In other threads you've called the Rossi a high quality sports engine (no argument there BTW). Which way does the wiggle factor go? Believe me, there's no trick to it even with the zero nitro fuel I was using which you always say is hard to tune.
Your comment about the tuned pipe was something of a diversion too because I'd said I'd lengthened it so it wouldn't come into play. In fact it was 21 1/2" from plug to first baffle so it would have been tuned for around 8000 revs. This was done to make sure it'd have no affect on whatever rev gain the engine made when leaned out from initial 2 stroking.
You're on the right track with the higher than normal BMEP but I'll leave you to think some more on it. I have no idea what you meant about the Diesel forum though.
Brian,
You connect between unrelated things that I write.
Normal Rossi engines and OS VF engines are high performance engines, but not even close to most Jett and Nelson engines (and Profi and other state-of-the-art racing engines). So they can be made to run at a steady four-cycle, but their behavior, RPM gain over the step and other traits, are very different from 'sport' engines, despite the fact that they are able to four-cycle.
I have never actually seen a Jett. The fact that they cannot be made to four-cycle, is from what Bob Brassell wrote to me, 6-8 months ago, when I disputed the very rich 60 seconds, in Jett's break-in instructions, as four-cycling.
When a tune-pipe is adjusted too long, the engine to which it is connected is said to be 'always on the pipe' (Copyright Macs). It will get very little RPM boost, if any at all, as a result.
An RC engine with a pipe, should be adjusted so leaning the mixture very little, beyond the two-cycle/four-cycle step, will get the engine on-the-pipe, with the whole RPM gain that results and one should not lean it any further.
The RPM gain from leaning a piped engine, will be much greater, in most cases, than 500 RPM.
But without a pipe, on a sport engine, you should not expect to see much more.
The 'harder to tune zero nitro' issue is, as I already addressed previously, from what a magazine engine guru wrote. I personally have zero experience running zero nitro, despite my 25 year experience with model engines.
I just never had a chance to do it.
As to the Diesel issue, please read post #9 in [link=http://www.rcuniverse.com/forum/Too_much_ether%3F/m_2650652/tm.htm]this thread[/link].