johnr Posted March 8, 2015 Report Share Posted March 8, 2015 238 Hi All, My CTsw 2006 was down a little on power on takeoff, running well at 5000rpm. Checked the plugs & they are a llittle sooty. The fuel burn has increased by 1 / 2 litres an hour of late. There is a slight fuel stain on the drip trays each side. Total hours on engine is 540. Is there a reccomended time on carb rebuilds & is it normal or reccomended best practise to replace needles & jets at 500 hrs. In my experience with motorcycles , it was normal to replace needles & jets. John austwa Link to comment Share on other sites More sharing options...
FredG Posted March 8, 2015 Report Share Posted March 8, 2015 Others will have to comment on what is normal or best. The Rotax Line Maintenance Manual (Ed 3 Rev 0, 05-20-00, page 15, 2012) states, "Removal/assembly of the two carburetors for carburetor inspection" every 200 hours and references the Heavy MM, 73-00-00, Sec 3. Also, elsewhere, the Line MM notes that the carb diaphragm must be replace every five years. The Line Maintenance Manual has a section for troubleshooting a rough running engine. If my 2006 CTsw was doing what your airplane is doing, I would remove and disassemble the carbs, inspect and clean everything, and replace all rubber parts and any other part showing wear or incorrect function (I have a US registration E-LSA and such maintenance is permissible for this registration). I would check the floats and the adjustment of the float arm. I have no formal Rotax or FD training. My comments are for your information only and are not intended to replace owner review of Rotax documentation nor are they an endorsement of any specific repair or maintenance procedures. Link to comment Share on other sites More sharing options...
Roger Lee Posted March 8, 2015 Report Share Posted March 8, 2015 Hi John, I rebuild lots of carbs each year. Some have been way over due and some done early. Rotax has nothing in writing about when to rebuild a carb. Since you brought up plugs what is the gap? Fuel usage can be affected some by a poor carb sync, dirty carbs (they only need to be cleaned), incorrect plug gaps, prop pitch (a big influence, what is your wide open throttle rpm at your average altitude), dirty air filter. Before you do your rebuild make sure all these are ruled out if you want to solve your small problem. 540 hrs. isn't that long on a carb, but you now have 9 years on them and "O" rings can crack and split. Total usage hours on carbs isn't the only factor to look at when making your rebuild decision. Time in existence should also play a factor. The fuel in the drip tray may be from a leaky bowl gasket. If you want to do a rebuild at this time then no problem. It can never hurt. The carb rebuild kit is about $270 and that is for both carbs. No new floats, but unless they are sinking you don't need them. The new carb kit will replace all "O" rings, diaphragm, needle valve, main jet and needle, both gaskets. Make sure to check the float armature height while doing this. It should be 10.5mm. Link to comment Share on other sites More sharing options...
Rich Posted March 8, 2015 Report Share Posted March 8, 2015 Roger, Could you explain "float armature height at 10.5mm" Thank you Link to comment Share on other sites More sharing options...
johnr Posted March 8, 2015 Author Report Share Posted March 8, 2015 248 Thanks for the prompt reply & advice Roger & Fred. I replaced the diaphrams at the 5 year rubber replacement. I have the plugs gapped to .7mm. Prop pitch was set to WOT 5600rpm at my approx normal cruise. I did a carb sync about 3 months ago & was very happy with what I believed was a smoother engine at all rpm. I had the bowls off before the sync & they were remakably clean. Only about 30 hrs since the reusable filter was washed & lightly oiled with Casrol filter oil. I use 95 octane mogas that has no ethanol . (Our octane rating in Australia is rated differently & 95 would be similar to a US 92 if there was such amix.) I am very careful to keep the fuel fresh & if it gets more than 3 weeks old I would drain it (& put it in my wifes car) It has been a hot summer here & although it was start of autumn on 1st March we are still having mid 30s (celcious) every day. I have flown on much hotter summer days & not seen this recent degrade in performance. I thought that maybe the float seats were not sealing well allowing the occasional overflow & staining the drip trays. Would a slightly temporary over rich mixture reduce my take off performance? From what you are saying it would seem that a thorough clean & an overhaul kit would be the way to go. Seems strange that there is not an overhaul date on the carbs. Thanks again for the advice. John austwa Link to comment Share on other sites More sharing options...
IrishAl Posted March 8, 2015 Report Share Posted March 8, 2015 Hi John. From my own motorcycle days, sooty plugs always pointed to an over-rich mixture. First two places I'd check would be the air filter and then that the choke mechanism is functioning properly. Issues in either of these areas will soot up the plugs, and will also increase fuel consumption. Link to comment Share on other sites More sharing options...
Roger Lee Posted March 8, 2015 Report Share Posted March 8, 2015 Your 1-2 liters difference could also be a mis-calculation with your instruments. Even a weather change if it went from hot to cold could make a difference of 1`-2 liters. They may need adjustment (the "K" factor if you have a fuel flow transducer). You would have to confirm the extra fuel use manually which is difficult at best since you can't be exact on any two flights and we are only talking 1-2 liters. It may also just be a difference in your flying. For the 1-2 liters I don't think I would worry. All the things above in my last post can affect the fuel and 1-2 liters is nothing. You can measure the float arm height in two ways. First you can buy a little tool from Rotax for about $35 that can help measure this. Not worth the money to me. The easiest way is to take a mm ruler, turn the carb upside down (it has to be this way), stand the mm ruler straight up on the edge of the carb lip or edge. Slide the ruler over to the float arm so you can see the numbers on the ruler up against the float arm. The edge of the ruler is still in contact with the carb edge. The float arm should be 10.5mm high. If it is not you bend the tab ever so slightly where the needle valve hooks on to. Check both sides of the float arm for each carb to make sure the float arm isn't twisted and one side isn't the same as the other. My money on fuel in the drip tray is a leaky bowl gasket. That's what it is 90% of the time unless your vent tube also empties into the drip tray, but a CT doesn't. Link to comment Share on other sites More sharing options...
Rich Posted March 8, 2015 Report Share Posted March 8, 2015 Jacques, Thanks for the information. I am subscribed to the Rotax Owners Group and I re-watched the video a few minutes ago. The 10.5mm must be the level position to the carb body. The measurement just wasn't mentioned in the video. Thanks again Link to comment Share on other sites More sharing options...
Roger Lee Posted March 8, 2015 Report Share Posted March 8, 2015 They use a special tool to measure. The measurement is in the Bing carb manual. $10-$15 Link to comment Share on other sites More sharing options...
Anticept Posted March 8, 2015 Report Share Posted March 8, 2015 Be aware that the tool for the carbs has not been in stock for some time at leasing edge, and it is a special order item. Took 6 weeks. Might be different for other distributors. Roger, what bing carb manual? Link to comment Share on other sites More sharing options...
Roger Lee Posted March 8, 2015 Report Share Posted March 8, 2015 You can order a Bing 64 manual right from Bing. I did this about 10 years ago and it was $10. Link to comment Share on other sites More sharing options...
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