ddorso Posted May 29, 2011 Report Share Posted May 29, 2011 Okay, I bought my 2006 CTSW 2 years ago. It was a trainer and currently has 1039 hours tt. It has always been a little cranky about starting. It would intermittently simply refuse to start but once it started, it ran like a top. Lately it has gotten more difficult to the point that it won't start at all. Before you ask, yes it is turning over in excess of 250 RPMs. I recently had the carbs rebuilt by Lockwood and as a precaution replaced the fuel pump. I generally use Mogas but have tried Avgas to verify if the fuel was up to snuff. I also changed the spark plugs and they are wet after attempted starting so, I'm confident that the fuel system is not at fault. I've visually inspected the ignition system but can find no fault there (loose wires, bad grounds, etc.). I am based at KZPH (Zephyrhills, Florida) and there is nobody at my airport either knowledgeable enough or willing to help me. I've taken the Rotax training (service and line maintenance) from Dean at Lockwood and last summer I obtained my LSRM-A rating just so I could do my own maintenance. So...how can I check the ignition system? What is the likelyhood of both modules being bad? How can I check for a spark? Roger, Tad you guys could solve it in a minute but unfortunately you're not here. Short of pulling the wings and trucking it down to Sebring, I'm at a loss. Thanks for any help, David Dorso N40HA Link to comment Share on other sites More sharing options...
chanik Posted May 29, 2011 Report Share Posted May 29, 2011 I would start by ohm-ing out the pickup coils on the back of the engine. Given it runs well after starting, then the trigger cams are likely fine. It sounds like weak spark. Does it run well on either mag once going and have only ~100RPM drop? You should see 0.1 to 0.4ohms across the ignition charging coils primary and 6.5Kohm on the high voltage secondaries out to the ignition modules (see section 74 in the heavy maintenance manual.) Especially if the B ignition sysem were weak, then you would only have the A system effective for starting which fires earlier so makes starting a bit harder Link to comment Share on other sites More sharing options...
N89WD Posted May 29, 2011 Report Share Posted May 29, 2011 Question, is this only hot starts or cold? Link to comment Share on other sites More sharing options...
Roger Lee Posted May 29, 2011 Report Share Posted May 29, 2011 Hi David, What makes you think it still can't be the fuel system? Since the carbs has just been worked on then they are suspect regardless of who re-built them, the fuel pump too. They have been bad right out of the box. Did you try another battery? I doubt that all 4 pick up coils are bad. It could more likely be the two white ground wires that plug into the 6 pin connectors up by the ignition modules or even the red wires. Since this was more a gradual thing that became worse I suspect the fuel or battery delivery. Electrical failures tend to be more acute. I would go back and rule out each individual item within the fuel system. Link to comment Share on other sites More sharing options...
chanik Posted May 29, 2011 Report Share Posted May 29, 2011 Could still be fuel but all the carb work makes me doubt that. Can't be battery for the ignition as the CDI doesn't use the battery. So long as he's turning over 200RPM there should be spark. Link to comment Share on other sites More sharing options...
Roger Lee Posted May 29, 2011 Report Share Posted May 29, 2011 Hi Kurt, I have seen several carbs assembled wrong as there are specific ways to mount the different parts and by opening the fuel system and playing with the hoses and shoving metal ends into them can cause rubber flaking. This may not end up as the problem, but needs to be ruled out. David, You need to take a step back and start at a beginning and move from point A then to B and so on, otherwise you may bounce all around the problem and miss it. I would start with the fuel system as it is easier to rule out. Link to comment Share on other sites More sharing options...
ddorso Posted May 29, 2011 Author Report Share Posted May 29, 2011 Thanks for the responses. Kurt, when it does run, the mag check is fine @ 50 RPM per side. Mike, I only have a problem on cold starts, once it has been started it will start almost immediately. BTW, I did replace the battery a coupe of months ago thinking it may be suspect. Roger, I'll recheck the carbs but I think the problem exists in the ignition and I'll check that also. Wish me luck. Dave N40HA Link to comment Share on other sites More sharing options...
chanik Posted May 29, 2011 Report Share Posted May 29, 2011 So both ignitions seem to run OK once started so the ignition modules must be OK but still could be an anemic spark at the low starting RPM since the system is totally reliant on the inductive energy (proportional to speed) from some relatively slowly moving magnets. I only see two likely possibilities: A bad coil or a as Roger said, a carb problem likely with the 'choke' that is flooding the engine since you said the plugs were wet. The choke idle circuit cuts out as the engine revs up. Do you still see a smooth 1800RPM at idle and reasonable drop as you add choke? Did you ever try to start it without the choke or with it half-way? I don't think I've ever flooded my engine with full choke, BTW It does drop from 1800 to 1600 if I go back and forth on choke once it is running at idle . The choke uses rotary disk valves and doesn't really have any settings to be tweaked but if the disks were inserted incorrectly or something fundamental like that then I would expect you would see weird behavior as you pulled choke with the engine running. Also seems unlikely that both chokes would be messed up. Are the moist plugs just on Cyl 1,3 or 2,4 corresponding to just one carb? Link to comment Share on other sites More sharing options...
Roger Lee Posted May 29, 2011 Report Share Posted May 29, 2011 If it runs good after the first start and the mag drop is only 50-60 then you don't have an electrical problem. That should save you some time. So I would go back to the fuel issue and starting rpm issue. You could have a choke put in backwards. That does happen more often than people know from not paying attention during a rebuild of the carb. I would also hook up a nice big battery on the side and try a cold start with a big battery that is charged. If you have a good easy start then replace the battery. If it still persist then you still have a fuel start up fuel delivery issue. The idle rpm should be 1750-1800 after it warms up. You should not be giving it any throttle when the choke is engaged as this will cause hard starting. If you have the idle set too low and then only use the choke it may be hard to start, then you would need about 3/8" of extra throttle. This all sounds like an rpm start up issue or a choke/fuel delivery issue. Link to comment Share on other sites More sharing options...
FastEddieB Posted May 30, 2011 Report Share Posted May 30, 2011 You could have a choke put in backwards. That does happen more often than people know from not paying attention during a rebuild of the carb. Its very easy to do. To avoid it on a rebuild of an airhead BMW Bing carb, I took a picture before proceeding: And so, I've avoided that particular pitfall to date. I assume the "choke" disk on the ROTAX Bing's is the same. Having a digital camera or a camera phone handy while working, and using it a lot, is a great help when putting things back together. Link to comment Share on other sites More sharing options...
chanik Posted May 30, 2011 Report Share Posted May 30, 2011 They should be inserted as mirror images of each other for the L and R carbs so seems like it would be easy to make a mistake Link to comment Share on other sites More sharing options...
Tom Baker Posted May 30, 2011 Report Share Posted May 30, 2011 Remove the clear vent balance tubes and blow into them right before a cold start. If the engine starts right up look to the "choke". Remenber the choke marked with the "L" on the disk goes on the right side and the "R" goes on the left. The dot on the shaft points to the rear. Tom Link to comment Share on other sites More sharing options...
ddorso Posted May 30, 2011 Author Report Share Posted May 30, 2011 Todfay I checked the carb float bowls and they were full of fuel. Used a spark plug tester light and it indicated no power going to the plugs. So, I still think that the problem is in the ignition system. David N40HA Link to comment Share on other sites More sharing options...
chanik Posted May 30, 2011 Report Share Posted May 30, 2011 I like to check the easiest things first, so verifying the choke behavior seemed to be the best first step. You are getting suffient energy at idle but I'm going back to the suggestion to ohm out the ignition charging coils. You see the energy they capture is directly proportional to the time rate of change of the magnetic field. So at 300RPM they will get 6x less energy per spark than running at 1800RPM. Below a certain threshold there just is no spark. Battery powered CDI systems do not have this limitation, but Rotax is direct induction Link to comment Share on other sites More sharing options...
markmn Posted May 31, 2011 Report Share Posted May 31, 2011 This discussion reminds me of the fun of carburetors. Unending maintainance. With the technology of fuel injection today why are we still using an outdated carburetor from the 70s? Why doesnt rotax release the fuel injection we all know they have? Likely related to liability. Nobody wants thier stuff used on an airplane. Is rotax making thier own fuel pump now or? I have had my P2008 carbs synced once now and it is definitely smoother but the idle has somehow gone back down to 1500rpm again and the roughness around 2800-3000 seems to be coming back. I know fuel injection could improve this. Mark Link to comment Share on other sites More sharing options...
Tad Olmsted Posted May 31, 2011 Report Share Posted May 31, 2011 Todfay I checked the carb float bowls and they were full of fuel. Used a spark plug tester light and it indicated no power going to the plugs. So, I still think that the problem is in the ignition system. David N40HA David, I am working at the St. Pete international airport this week until wed. Give me a shout, I am only a few miles from you. Link to comment Share on other sites More sharing options...
Tad Olmsted Posted May 31, 2011 Report Share Posted May 31, 2011 I am fairly confident it is a fuel delivery issue after reading all the posts. HOWEVER,the engine is getting up there in hours and I wonder if the hard starting may be the sprag clutch going out. Does the engine kick back when you try and start it? Tom, you are right on the money with the carb L and R stamping. Not many guys know this and it will cause havoc! Been there, done that. Link to comment Share on other sites More sharing options...
ddorso Posted June 3, 2011 Author Report Share Posted June 3, 2011 ... And the winners are. Roger and Tad for their diagnosis of my carb problem. I brought the plane to Tad in Sebring and he correctly assessed the myriad of minor issues that combined to make a large problem. A poorly adjusted choke, too high an idle and too much tension in the cables in combination with unsynchronized carbs were the problems. Tad did a great job and in no time at all, I was flying back home. Thanks Tad. I'll be seeing you again. You've brought the pleasure back to my flying. David N40HA Link to comment Share on other sites More sharing options...
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