skippydiesel

True for the ball bearing sealing but my understanding was/is that the epoxy coating covers a much wider surface area, possibly all - something to do with casting porosity concerns

What concerns me, is the advice, from Rotax Owner Forum, that the carby's have an epoxy sea that may be damaged by a chemical cleaner. I have often been accused and suffered from the application of excess zeal, when it comes to cleaning engine parts - old & doddery now, I hope I have learnt some moderation. The temptation to use magical bottle/can/packaged repairs/enhancements/cleaners, etc can be very strong - best to resist and do the job the hard way - dismantle & use a tried/recommended solvent, lint free cloth, soft wood and air to do the cleaning.

My apologies - I thought we/you were talking service interval/content.

The rubber replacement isn't cheap , is conservative at 5 years & does not usually include the floats. My last 912ULS was a 2000 build - the floats supplied at that time would seem to have had an indefinite life span. Younger variants had fuel absorption/reduced floatation problems. The latest is hopefully back in the indefinite lifespan. The test is simple, dry & weigh- From Rotax Maintenance Manual Line: 12-20-00, Page 36, CHECK THE WEIGHT OF FLOATS "Step Procedure 1 Let the floats dry for 1-2 minutes, then weigh the floats. Only weigh dry floats. 2 Check the weight of all affected floats using a calibrated scale. Measuring tolerance of the scale: max. 0.1 grams. 3 The results of the measurement must be documented in the maintenance records. The max. allowable weight (of both floats together) is 7 grams. ATTENTION Replace all floats which exceed the max. weight" It does.

Word of caution: I just found out (on the Rotax Owners Forum) that the carby's have an epoxy coating(looks a bit like varnish) - this should not be removed

Rotax recommend a "rubber" replacement every 5 years - little to be gained by doing this at 2-3 years, other than a lighter wallet. Be careful of "kits" that supply parts that you don't need - weigh your floats (the expensive bit) befog commiting to new ones. Rotax have the weighing procedure & max weight, in their maintenance manual. Jewellers scales (for weighing floats) are not very expensive.

Not that I am aware of.

Rotax specifically warn against using ultrasonic cleaners on the carburettors; From Rotax Owners Forum: https://www.rotax-owner.com/en/912-914-technical-questions/10074-why-is-there-glue-on-my-caburetors

This may help - From Rotax Owners Forum; https://www.rotax-owner.com/en/912-914-technical-questions/10049-rough-running-around-5000-rpm In the above case it seems likely the cause is a warn dog clutch

I inherited , with an almost complete homebuilt, a forward oil cooler and an aft radiator. The radiator was beautifully installed, so that there would be no air leaks. The cowling also had few air leaks. Result - On Ground, high coolant/head temperatures, fair oil. In Air, good coolant, high oil temps. After trying all sorts of fixes - realised that the radiator itself, being the only exit for the air, does not allow for sufficient air to pass through cowling/heads/oil cooler ie pressurising cowl to the point of restricting adequate air flow through oil cooler. . Have returned aircraft to workshop - Radiator relocated from aft position, leaving large exit hole, to position under crankcase (fwd). Oil cooler, now the Rotax Extra Large (formally Large), relocated to aft position but not blocking exit air. Sounds a little odd I know but this follows (sort of) my last aircrafts successful cooling lay out. One of the original, partially successful, fixes, was the installation of a pilot controlled cowl flap. I am hoping to use this to control exit air - that is to encourage more flow on the ground/during TO & CO and reduce flow (higher velocity) in cruise.

Hi Glen, I have zero experience with ULP in what would normally be an AvGas engine however I pass on the following; I have a friend who flies a 100 hp RR (Continental?). He switched over to ULP (STC). Engine ran fine until it got valve problems (not sure what - stems / seats?). Got it all fixed up - same story repeated $$$$$$. He has gone back to 100% AvGas and not a problem since.

Thanks Mark, By accident, my scoop is much like what you describe as a "pressure recovery chamber" having a relativly small opening, that widens into a lager chamber, with the radiator being the only (I hope) exit for the air .

Your a true gentleman Geoff - I think my Son has some "fine" stuff. Its more like a soft fabric, than a fiberglass woven matt. If its not "the goods" I will be in touch. Thanks again.

Thanks Mark, First attempt was to use polystyrene solid tube draft excluder, wrapped in "cling film" to prevent melting - might have worked but for the next comment. Found out, the hard way , about the glassing of small radius. Starting again, only three day lost this time - getting used to the frustration. Pressure recovery chamber? - do you mean NACA duct? In my limited experience - space is always an issue. I assume the LCH J200 with radiator is Rotax powered?

True! But its all about doing the best that you can with resources available eg two 90 degree fittings one high flow, one not.

Thanks for that OT. I have gone to considerable trouble & expense to try and make all my unions/bends high flow. Most of my fuel line fittings have come from Aeroflow Performance . https://aeroflowperformance.com/pub/media/external/downloads/cataloguev13.pdf

I take your point about fuel line losses due to constriction & friction. To a large extent this has been addressed by enabling the Boost pump to draw from the Header tanks. In practice this will mean using the Header (rather than Wing tanks) for TO/CO. The Header is right behind & slightly higher than the engine, so has the combined benefit of a shorter delivery line and a bit of gravity, to assist in fuel flow. I have never seen any where near 27L/hr on my two Rotax 912ULS engines. Yes that's what Rotax specifications say for max power ,however I think a real world figure might be more like 24 L/Hr

I don't think I disagreed with the idea that the aircraft should be able to fly without a Boost pump - just that mine gave every indication that it might not. I never tried a TO/CO without Boost pump, so I can't say what might have happened, however with mechanical + Boost pump, my fuel pressure dropped below 2 psi (the Rotax min). Engine never lost power/hesitated but my heart did. As mentioned , several fixes were tried, with limited success. Aircraft returned to workshop for a range of improvements (including fuel system) - yet to be tried/flown. One of the fuel mods, was the installation of a Boost pump fuel bypass (as per Rotax recommendation) - this will remove any tendency for the boost pump itself, to restrict fuel supply (one of the possible in-line restrictions to good flow). When its back in the air, I will try a full power climb, at altitude, without Boost pump , just to see what happens - let you know.

Fair enough. "Hi Skip, I'm not advocating no boost pump in your aircraft. I'm just suggesting that the fuel system should be able to work comfortably without it." - it does. "As to the Sportstar, I agree it's comforting to have the pump on in those critical phases of flight, but when I was last flying with an instructor in the RH seat, his comment was, "it's unusual, but follow the POH" ie. leave it off. " - There are times in life & POH's, when common sense should prevail, no matter instructions to the contrary. My advice use the Boost pump at all critical stages of flight. It costs nothing and may save your life. An unrelated example; I was taught to use carby heat when required. Many years after obtaining my PPL, I was flying with an instructor in Canada - his advice, use carby heat every time you initiate descent power and leave it on until returning to cruise/full power. I thought about it, made sense, cost nothing and adopted the habit and that's what I do now (when in an aircraft so fitted).

Hi Thruster, See above answer to RossK for responses to most of your observations. I think RossK was leaning towards the Sportstar concept (no Boost Pump) I cant accept that.

Hi RossK, "It seems that your fuel delivery system may have a lot of restriction (lines, connectors, pumps etc), which is limiting pressure and flow." Restrictions - for sure; Long (pipes) all the way to the wing tanks Failure to install a pump bypass as per Rotax installation advice Changes to the fuel system, is to plumb in my (new higher pressure) boost pump & bypass to my 40L header tank. Previously the boost pump would only draw from either wing tank. This change should have two benefits - header tank is pretty much on the same level (head) as the carbs/ engine & very much closer (frictional losses) to the engine. The downside to installing a bypass, etc, is many more joins, additional non return valve & convoluted pipe work. So far only ground check, will be interesting to see what happens on the first TO/CO. "POH actually says the boost pump is on only for start up and emergencies. It's off at all other stages of flight, including take off and landings." Can't agree with any of that. All my training requires; Boost On pre start / check pressure / Off / start engine - This is a check pump function & prime of carb float chamber Run up bay - Boost On / check combined mechanical/boost pressure / TO &/ CO to safe altitude / Off - This is to ensure continuity of engine function through the most critical phase of powered flight Pre landing - Boost On / Off after after landing - Again this is to ensure continuity of engine function, when in close proximity to very hard ground. "The boost pump is actually an optional extra for the Sportstar,... "" I can accept that a high wing/tank may have good fuel flow (engine continue to deliver power) even if mechanical pump fails, however a low wing does not have this inherent safety feature. "...the fuel system will work just fine relying on the Rotax pump alone." Sure - all of use who have forgotten to use the Boost Pump, at one time or the other, know this BUT what happens when the mechanical pump malfunctions????? I suggest it gets a tad quiet, followed by potential nasty noise a little while later. The Boost Pump is a low cost safety feature that all aircraft (in this class) should feature.

Anyone got any thoughts on the likelihood of a pump, with a higher flow & pressure, delivering a worthwhile improvement, in fuel transfer time, given that the piping (aluminium) will remain as is.

Hi BrendAn, In this instance, pressure is used as an indicating of flow. Rotax 9's require a pressure of between 2-7 psi. If flow is reduced (pump unable to maintain sufficient flow), pressure will drop. Its as simple as that.

OK - I now have a low hrs (50) cube boost pump, surplus to requirement, works fine just a bit low on delivery for mys system, see above for estimated performance - intersted?

Thruster - Boost Pump The Rotax advice of max 5 psi is specifically to reduce the chance of pump pressure overwhelming the float chamber valve. Rotax also advise the use of a #35 return flow restrictor, which in my application delivered 7+L/h back to the tank. The combination of fuel burn at max power (TO & CO) plus the return flow, came close to equalling the max flow from both mechanical & boost pump combined, leading to low pressure at this time. After determining that the system was working as expected, I looked for a way to improve the pressure - cheapest/easiest was to put in a smaller aperture return line restrictor reducing return flow to 5L/h this produced a small improvement but not enough. A reference, on Rotax Owner Forum, to RV's advice to RV 12 owners to install a pump with a higher pressure & flow spec grabbed my attention. On reading the RV advice document I quickly saw the parallel with my situation - hence the installation of the higher capacity pump and the reinstallation of the #35 restrictor jet. My Sonex is still undergoing a host of major/minor mods, the boost pump change being just one, so yet to see if there is a beneficial change in TO/CO fuel pressure. Transfer Pump Yes the transfer pump works BUT its so sloooooow! In my limited in flight fuel transfer experience, the longer it takes, the more likely the pilot will be distracted by other tasks/situations leading to venting fuel overboard - not good!. My dilemma is; the 50 US GPH pump (costly special order from The States) will make a transfer time difference BUT by how much?? given the physical restrictions inherent in piped systems. Yes my transfer methodology & rates have all been logged in the POH