FastEddieB Posted September 17, 2013 Report Share Posted September 17, 2013 I flew on Saturday and the ROTAX 912 in my Sky Arrow performed perfectly. But when I taxied in, I thought the engine was just a tiny bit rougher at idle than normal. When I switched off the #1 ignition, it got quite rough. When I switched off the #2, it was much smoother. I then ran it up to about 3,000 rpm and checked each and there was very little drop and no roughness. Back at idle, running on #2 (#1 off) was still rough. I just happened to have my GoPro running: Kind of hard to see what I'm talking about - the tach is just to the left of the Garmin. I'm supposed to fly to Indiana on Friday, weather permitting. My tentative plan is to run over to the airport and maybe start out by looking at, cleaning and gapping the plugs. Then, if that doesn't work, maybe take the SoftStart module out of the loop and see if that makes a difference. (note: the SoftStart retards the spark on #2 when it senses starter solenoid voltage and is supposed to revert to normal timing a few seconds after that voltage is lost) Any thought? Am I just zeroing in on ignition when it might be something else? Would appreciate any advice. Thanks! Link to comment Share on other sites More sharing options...
FlyingMonkey Posted September 17, 2013 Report Share Posted September 17, 2013 Maybe pull and inspect some plugs? The fact that it's only rough at low RPM would make me think it might be marginally fouled plugs. Link to comment Share on other sites More sharing options...
FastEddieB Posted September 17, 2013 Author Report Share Posted September 17, 2013 I said that was Plan A this afternoon when I head over to the airport. Decowling the Sky Arrow is kind of a pain, but I haven't done it in a while and I can take a closer look at a lot of things with it off. And the plugs will be first! It's also feeling a little fall-like in the mountains, so it might be a good time to tighten up the plug gaps a air to their winter settings. Link to comment Share on other sites More sharing options...
FlyingMonkey Posted September 17, 2013 Report Share Posted September 17, 2013 Whoops sorry...got distracted by your video and didn't see the rest of the post. Link to comment Share on other sites More sharing options...
Doug G. Posted September 17, 2013 Report Share Posted September 17, 2013 Squirrel! (Have you seen the movie UP! ?) lol Link to comment Share on other sites More sharing options...
Roger Lee Posted September 17, 2013 Report Share Posted September 17, 2013 Hi Eddie, You won't be able to rule out carbs unless you throw a set of sync gauges on. It isn't a plug or you would have seen it on the mag drop at idle or 3000. Even one poor plug or bad connection usually tags you fro 200-300 rpm. This surely sounds carb related. The idle jet is so small it can get clogged easy. I just had one in my hangar two days ago for this vary thing. Put the gauges on, an electronic won't work because you can't diagnose with them. Find which carb is the offender, pull it off, strip it and flush cleaner through every orifice and then follow up by high pressure air. Every orifice. To clean the idle jet I take an 16 gauge wire and strip it then pull out one strand of wire to fit down the the extra small hole in the center of the idle jet. Down at idle you use mostly the idle jet, but at the higher rpms the carb is running more on the main jet and so it isn't obstructed any more. If you have any question just give me a call. Link to comment Share on other sites More sharing options...
C ICEY Posted September 17, 2013 Report Share Posted September 17, 2013 I just went through an ignition troubleshoot. I used EGT to determine the cylinder that was misfiring, and learned to make just one change at a time. I initially ruled out carbs with a mag test with choke pulled out part way, maybe Roger can detail that one..... My initial problem was one bad (loose) spark plug boot, which I replaced, but at the same time I put in another plug, which turned out to be a bad plug for whatever reason. I swapped one problem with an identical one. my penance for not doing this was to do a complicated swap of leads from the coils and stators, and to send my ignition units out to get tested. they all tested normal, which brought me back to the cable and plug boot, and a swap back to the original plug. good luck with the troubleshoot. Link to comment Share on other sites More sharing options...
Roger Lee Posted September 17, 2013 Report Share Posted September 17, 2013 Always do the most common and free things first because most problems are easy fixes. (not all of course) Knowing each aircraft system (i.e. fuel, oil, coolant, electrical) and how to navigate each system from A-B-C-D usually saves time and money. Knowing the system many times may tell you the problem couldn't be A or B, but would have to be C or D which makes life a tad easier. Link to comment Share on other sites More sharing options...
FastEddieB Posted September 17, 2013 Author Report Share Posted September 17, 2013 Update: The plane started instantly. As soon as it smoothed out, at about idle killed one ignition and then the other and the drops were identical. Tried various rpm up to 3,000 with the same result. Flew the plane for about 10 minutes. After taxiing in, did it again and now ignition two was again a tiny bit rougher, but not that much. Decided not to futz with anything right now. But I'm unclear - how could one carb having an iffy idle circuit cause differing rpm drop with different ignitions? Whichever ignition is chosen, each cylinder on each side still has a firing plug. Sure seems to me that would cause about the same drop with either ignition selected. Right? Link to comment Share on other sites More sharing options...
Roger Lee Posted September 17, 2013 Report Share Posted September 17, 2013 Because you have something floating in the carb bowl and you have had a hose change. I would pull both carb bowls and look. floaters many times can be intermittent as well as a permanent obstruction. The other day you were bouncing around and the floater was moving up off the bottom. Today you pushed out and it stayed on the bottom and the run up wouldn't have an issue. If it were me I would pull both bowls. If it is a floater it may not show up on a carb sync either. If it were me I would pull both bowls and look. That way if nothing is there no harm no foul, but if something is there you may have just prevented an off field landing later. Look at the video that was posted to remove the carb bowls the easy way. Link to comment Share on other sites More sharing options...
FastEddieB Posted September 17, 2013 Author Report Share Posted September 17, 2013 My bowls are easy. I'll look tomorrow. But take an iffy idle jet on one side (cyls 1 & 3, let's say). With ignition one firing, it would fire an upper plug in one and a lower plug in the other. Switch to ignition two, and the opposite plug in each cylinder would fire, lower in one and upper in the other. That is how it works, I assume. It's not like ignition one fires one side and ignition two fires the other - then it would make perfect sense that when you switched to the side with the bad idle jet it would drop more. So, why would one ignition have a larger drop than the other? Link to comment Share on other sites More sharing options...
FredG Posted September 18, 2013 Report Share Posted September 18, 2013 "But I'm unclear - how could one carb having an iffy idle circuit cause differing rpm drop with different ignitions? Whichever ignition is chosen, each cylinder on each side still has a firing plug. Sure seems to me that would cause about the same drop with either ignition selected." Eddie asked a very good question. The carbs don't change when you switch ignition circuits. How can it be a carb problem affecting rpm and running smoothness when the problem occurs when changing from one ignition to the other? Link to comment Share on other sites More sharing options...
FlyingMonkey Posted September 18, 2013 Report Share Posted September 18, 2013 Squirrel! (Have you seen the movie UP! ?) lol Actually my wife says that exact thing ("squirrel") all the time...I am...um...distractable. Link to comment Share on other sites More sharing options...
Roger Lee Posted September 18, 2013 Report Share Posted September 18, 2013 It wasn't the ignition firing causing the drop and roughness it was a poor fuel flow on one side. They will both cause drops and roughness at low rpms. Was the mag drop at 3500 about equal? If it was it is fuel caused. You said when you advanced the throttle it went away. If it was electrical it wouldn't have gone away, but the fuel is on the idle jet at low rpms and more on the main at your higher rpm so it smoothed out because you got better fuel flow at the higher rpms so it points towards fuel because the next day it wasn't there. Check them then you can rule out one cause. Some diagnoses are done by ruling things out as much as ruling them in. Link to comment Share on other sites More sharing options...
FlyingMonkey Posted September 18, 2013 Report Share Posted September 18, 2013 Are mere mortals allowed to pull carb bowls, or just mechanics and ELSA owners? Link to comment Share on other sites More sharing options...
Roger Lee Posted September 18, 2013 Report Share Posted September 18, 2013 Pull them and take a look and fly safe because a mechanic most likely won't be at your side when it needs doing, BUT unless you have a problem or it isn't a scheduled inspection I would not pull them just to do it. Your not changing, altering, adding or removing anything. Your just taking a look. Be careful and make sure you don't pinch the bowl gasket when putting them back on and make sure the carb bowl goes up inside the groove that holds it in place or it will leak quite badly. If I were an owner, which I am, I would buy and keep a set of carb bowl gaskets around in case I found a leak and fuel in my drip trays. This is fairly common. I keep 6-8 gaskets around all the time and I replace quite a few. Link to comment Share on other sites More sharing options...
FastEddieB Posted September 18, 2013 Author Report Share Posted September 18, 2013 If its fuel, why does it consistently drop a bit more when I go to ignition 2, and idle perfectly smoothly with both ignitions on, even at idle? Seems like a clogged idle jet would manifest itself regardless of ignition switch positions. Not arguing - I've had crud in my bowls before, so I'm clear on that concept, and that and the plugs are easy enough to check tomorrow. Just trying to understand. Link to comment Share on other sites More sharing options...
FastEddieB Posted September 18, 2013 Author Report Share Posted September 18, 2013 And Andy - always invited to come up tomorrow and lend a hand! Link to comment Share on other sites More sharing options...
Roger Lee Posted September 18, 2013 Report Share Posted September 18, 2013 'But when I taxied in, I thought the engine was just a tiny bit rougher at idle than normal.When I switched off the #1 ignition, it got quite rough. When I switched off the #2, it was much smoother. I then ran it up to about 3,000 rpm and checked each and there was very little drop and no roughness." This is why I said what I said. If it was electrical it still would have been there. Link to comment Share on other sites More sharing options...
FastEddieB Posted September 18, 2013 Author Report Share Posted September 18, 2013 I'll report what I find tomorrow. Link to comment Share on other sites More sharing options...
FlyingMonkey Posted September 18, 2013 Report Share Posted September 18, 2013 And Andy - always invited to come up tomorrow and lend a hand! I would love to Eddie, but I'm not a retired layabout like you and others on this board, I have to keep working to feed the CT. Let me know when you are back from your trip though, I'd like to get together and compare notes on our babies. Link to comment Share on other sites More sharing options...
Tom Baker Posted September 18, 2013 Report Share Posted September 18, 2013 When you have a border line lean mixture just the difference in the ignition pattern from top or bottom plug firing can cause the results to be different. I was taught years ago when leaning an airplane without an EGT to check the mags, and if it was rough on one or both mags you are too lean. Link to comment Share on other sites More sharing options...
Ed Cesnalis Posted September 18, 2013 Report Share Posted September 18, 2013 When you have a boarder line lean mixture just the difference in the ignition pattern from top or bottom plug firing can cause the results to be different. I was taught years ago when leaning in an airplane without an EGT to check the mags, and if it was rough on one or both mags you are to lean. you are [need] to lean you are to [too] lean Link to comment Share on other sites More sharing options...
Jim Meade Posted September 18, 2013 Report Share Posted September 18, 2013 Well, Charlie, you should have got "boarder" vic "border" while you were at it. I guess Tom's old teacher was assuming the plugs were not placed identically in relationship to the intake valve, otherwise it would seem to me they would act the same. BTW, in one of the references I cited in a recent post, it said that even the plug gap orientation could make as much as 1% difference in power output. To us that is nothing but if you are spending hundreds of thousands of dollars on a racing engine than 1% may be a lot. Link to comment Share on other sites More sharing options...
Tom Baker Posted September 18, 2013 Report Share Posted September 18, 2013 you are [need] to lean you are to [too] lean Send me your phone number. Next time I want to post I will call and dictate my message, so you can type it for me. I fixed it just for you! Link to comment Share on other sites More sharing options...
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