Rossi 91 and Sport Jett 90LX

A quick look at the next round of engines sent for runs from Chris.
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[@don-mcl]

I really appreciate you putting your encyclopedia of knowledge out there for the rest of us.

[@volksfranzl8894]

Very cool engines! The Rossi is a real monster. I don't know the Jett engine but it looks awesome. Looking forward to see them running.

[@mikeeiben3430]

I have a Sport Jett .50, it runs very well but needs a smaller propeller like a 10x6 or 9x7. The transitition is very good with the carburetor. I noticed that the slot that moves the barrel in and out has a flatter pitch between idle and midrange, and then gets steeper from about half throttle to wide open. Mine runs well on low nitro fuel. Wear your earplugs!

[@SomeGuyInSandy]

Jett makes straight up racing engines. Longevity is not their strong suit. The Rossi? Your kids will be running it when you're gone.

[@dmrcflyr2]

That is good information and analogy. Thank you.

[@luisgarza2036]

Those are a really hot engines, specially JETT engines focused on making engines as light and small as possible to increase power to weight ratio.

[@Irvine7214x6apc]

Hi David, never heard of the Sport Jet 90 engine before. Any chance you will be running your magnificent Saito Fa-220 again? My 220 was probably mis-timed by a bloke who undertook a full bearing replacement and it "explodes" on startup, burning the prime and then quitting. This has to be bad timing, if I am not mistaken?

[@dmrcflyr2]

I cannot say for sure what the issue is based on your description. If the engine refuses to run at all then something is really wrong and timing would be the best bet. The operation of the engine is greatly impacted by which direction the timing gear is off. One tooth can result in what you are seeing in, whereas two teeth off have the potential for a valve crash on the piston. I cannot say when I will run my 220 again as there are other engines in que.

[@Irvine7214x6apc]

@@dmrcflyr2 Hi David, just saw your reply now, thank you for the feedback, much appreciated. One other thing I forgot to add is, she primes perfectly well from the carburetor but doesn't suck fuel at all when blocking the exhaust (throttle fully open) - and it should, because that's how I always used to prime it. We will look into the 220 during the weekend and hopefully will find the true cause, most opinions agree it's wrong timing. I know you have quite a queue on engine runs, hopefully it will not be too long until your 220 sings again, so much looking forward to that video, when it comes. Thank you again, regards, Harry

[@Irvine7214x6apc]

@@dmrcflyr2 Hi David, very quickly we looked into the 220 today and indeed the timing gear was one tooth off. Placed it correctly and once again - quite thankfully - I have a very healthy 220 - rpm, response (transition) all perfect.

[@dmrcflyr2]

@@Irvine7214x6apc Very nice! Thank you for the update.

[@larrythomason7422]

I used my ultersonic to clean my ys120 and turned it blue, now what do i do?

[@tempest411]

To what degree are engines like this a pain to operate because of their hotter port timing?

[@dmrcflyr2]

I have been considering your question for a few days. What makes you think that the port timing makes an engine a pain to operate? I’m not following the rationale of the question? Perhaps it depends on your level of experience in operating glow engines? Maybe you can clarify the question.

[@tempest411]

@@dmrcflyr2 I imagine that the hotter port timing would make it difficult to achieve an idle that was as reliable as a more mildly ported engine. I would also think that such engines would be more sensitive to changes in temperature, humidity, and elevation, requiring fine tuning. An engine with more mild timing would, again I"m assuming this, work well across a wider range of conditions. Am I way off on this?

[@dmrcflyr2]

This is a question better asked on an RC Forum than here. Far fewer people watch my videos than frequent forums. I have a little experience with a LOT of engines but not a lot of experience with these type. I also do my best to never operate or live based on assumptions. I believe in first hand experience and facts. This hobby is prevalent in assumptions, opinions, and myth. There are too many variables to draw a conclusion on a question like yours. In the video description I post links to two videos and a Post about assumptions.

[@tempest411]

@@dmrcflyr2 They're not assumptions out of thin air, but rather from my experience with four cycle engines in cars. I just haven't messed with two cycle engines before, so I'm not sure just how relatable the different aspects of their operation are to each other. This whole business of expelling exhaust gasses while at the same time a fresh fuel/air charge enters the cylinder is...pretty weird stuff, really. As for assumptions and myths in this hobby, or anywhere else...about 98% of the time basic common sense works to cut through the nonsense. A lot of people prefer nonsense to the truth.