Rotax carb submarines

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Posted

My Avid is long gone, but one thing bugged me about my 582.  It was a great little engine, but too frequently my carb floats would waterlog and start to sink.  At first I endeavored to run all the fuel out of the carbs on shutdown, but then realized that I was likely stressing the bejeebies out of the fuel pump diaphragm.  With all the petrol up in the wing, I have lately come to wonder why the damn pump is even needed.  Why not just disconnect and plug the pulse line and do without?  Fuel should go thru the one-way valves in the lifeless fuel pump just fine.  Of course, serious ground testing would be required.  This way, on shutdown, you could run the carbs dry, and the floats might not be so keen to go submarine on you so soon!  Maybe up here in the PNW we are being sold fuel with nasty additives!  Wouldn't it be great if the floats were built the old way, with soldered-together copper or brass sheet metal stampings?  

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Posted


Nice to see you again hows that Sonex treating you?  You getting some hrs on it?

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Posted

I run my Jabiru powered Avid all the time on gravity feed.  I do have an electric pump that I used for takeoffs and full throttle, but I have run at full throttle for a good five minutes at altitude with the pump off, and never noticed any symtoms of it running short of fuel.  The sinking floats issue has been ongoing for quite a while.  The original floats didn't have an issue, but the material the floats were made from was changed and trouble started.  Funny thing, is I have an early type 54 carb in the shop that has a one piece set of floats, they are made from a white material.  My Jabiru type 94 (an enlarger version of the type 64 that's used in the 912s)  has the same style float and has worked fine for many years.  Bing still sells that style of floats, it's on their motorcycle side, for a BMW motorcycle, and they get about $30 for the set.  Verses $50 each for the 4 that would go into 2 stock 582 carbs.   Tempted to give them a try, but currently my floats in the 912s aren't sinking.  They should weigh less then 3.5 grams each.  Lightest one I weighed was 2.8.   One trouble with floats sinking is you will start to get gas flowing out of the overflow tubes, and the last place you want to see a gas fire is in the air.  JImChuk

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Posted


I cant run my Jabiru without the pump electric running It gets off the ground but not by much before coughing. I was going to buy the bigger needle and seat but bought an Rotec TBI and installed that for 2 hrs. Now I'm back to the old Bing.

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Posted

The seat is fairly easy to change.  Used an 8 MM or 10 MM fine thread tap, and put threads on the inside of the jet.  I made a bracket that sat on the carb body, and used a bolt with lots of thread on it and a nut to go through the bracket.  Screw the bolt into the bottom of the jet, and tighten up the nut against the bracket till the jet is pulled out.  Never changed the needle though.   JImChuk

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Posted

On the "new" Sonex, in answer to TJ's inquiry...:

Thanks for asking.  Unfortunately I have not really started to fly the Sonex as yet.  It's in the middle of its annual condition inspection.  Uggh!  After an exciting delivery flight getting it home, I realized that it had more issues than expected, so have been spending time and $$ chasing them down.  In a couple of weeks, the Gorge winds will start winding down for the season, and once the inspection is done, the sky's the limit, so-to-speak.  I owe myself quite a few landings before starting to roam from the old home base.  Will need to upgrade the ELT, though.

It occurred to me that with the new 406 mHz ELTs, since we're trying to communicate with satellites, and not other airplanes, the antenna ought to be more horizontal than vertical, so its toroidal gain pattern points up into the sky, and not just out to the sides.  Wouldn't it be great if somebody made a stick-on antenna for low-winged, canopied airplanes?  Kinda like a decal one would put on the inside top of the canopy.  No additional drag.  And at 406 mHz, a quarter-wave dipole only needs to be about 1 ft long!  Seems like a natural, especially for metal birds.  Has anybody heard of such a thing?  - Turbo  

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