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Rotax 503 won't stop running
I have a 503 DCDI mounted inverted in a J3 Kitten. I am using an Ivo
in flight adjustable prop and the engine plain just runs great. The problem is that I can't turn the engine off if it is running in the "smooth" range, the mag 1 mag 2 switches will only cut it off if it is at a lower rpm and running roughly. The manual says this can be from the engine "being hot" but I actually have a problem in that the engine is running too cold. I took the fan and belts off and chiseled off the fan housing (weight) and added a forced fan shroud that directs incoming prop wash through the cyls towards the carbs. At full throttle with the IVO set at max pitch for max rpm I get 975F to 1,050F for EGT and 190F to 230F for Cyls (which seems too low). I am using a Smart Single EMS 503 gauge (I tested the probes for cyl and egt and they are accurate). The cyls run so cold they don't even have a bar appearance on the EMS 503 guage. These readings come from an engine that does not have the cowling on it yet (still making it from fiberglass) so I figure once the cowl is on the cyl temps will go up a little and I can always add a louver to control/reduce the flow of air into the cyls if I need to "heat them up" a little to get them into the 350 F range (so the engine will run at the correct heat range and not too cold). But this mag thing is throwing me, when I first start it up, I can do a mag check, but if I increase RPM to 3,000 the mags won't check and I can't kill the engine, I can't believe that this is because the engine is "hot" as it has only been running for a minute or two. Also, I would imagine that an inverted engine would have the opposite problem and would suffer from fouling and not from "run-on" since the cyl heads are basically flooding with fuel all the time. Today I changed to a new type of NGK plug with a slightly longer electrode because I read somewhere that inverted rotaxes need this plug so the plugs don't foul. No change in how the plane runs or whether I can cut it off or the temps. One other thing I was concerned about with regards to these new plugs, they got me resistor plugs but that's not what I wanted. I read that you are not supposed to use resistor plugs if you have resistor caps, how do I tell if I have resistor caps ? (this resistor issue is not the cause of the won't stop problem, happens with either type of plug). I have run 20 gallons of fuel through this engine with the plane tied down and this mysterious malfunctioning kill switch issue is my only problem so far. If I turn the mags off at 6,000 rpm, and then start backing off the throttle, the engine will not cutoff until it gets to something under 3000 rpm. This is the SMOOTHEST, QUIETEST, LIGHTEST and MOST POWERFUL rotax I have ever had, it's perfect, how do I cut it off : ) Thanks |
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