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Trouble starting


josjonkers

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I had my carbs overhauled about 6 weeks ago and afterwards the engine is starting more difficult and yesterday I could not get it started at all.

 

I know that the choke works and the procedure I follow is Full choke, throttle forward about 0.5 inches and crank. After 5 seconds stop and crank again.

 

After about 5 times I stopped and re charged the battery overnight and I am going to try it again today. I did not deplete the battery, the plane is in a hangar at 65F and outside temp around 25 F.

 

Does anyone have any feedback as to what else I should try.

 

Before the carb overhaul it started very quickly mostly on the first crank but then failing the first try always on the second attempt.

 

Comments appreciated.

 

Regards,

 

Jos

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I would re-open the carbs after I checked the engine start speed.. This is the only thing that changed and now you have an issue. If it isn't a low battery then my money says something was not done quite right in one or both carbs. The choke could have been put in wrong, the diaphragm or float arms adjusted wrong? It could be anything. There is no way to tell unless you pull them off and go back through them. Personally I would not waste anymore time on everything else and use that time to work the carbs. When you put re-built carbs back on it should crank right up. The only other thing it could be is the battery was a tad weak and the engine could not reach enough rpm to fire. You would not be able to tell with the human eye or ear unless it was really slow. This could be taken out of the equation by using a known good battery to try a start. If that doesn't work then pull the carbs, something in there is wrong if it isn't a slow turning prop on start.

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Thanks Roger.

 

I went out today and the battery was on charger all night.

When I did my normal start procedure it cranked over and caught right away at the first try.

 

This makes me suspicious that my 4 year old battery needs replacement.

 

I will order one soon.

 

Cheers,

 

Jos

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I know that the choke works and the procedure I follow is Full choke, throttle forward about 0.5 inches and crank. After 5 seconds stop and crank again.

 

 

Jos,

 

For the choke to work the throttle should be fully closed. Also, if your idle is set too high the choke will not work.

 

Once the engine starts, slightly advance the throttle, then turn the choke off.

 

John

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For the choke to work the throttle should be fully closed...Once the engine starts, slightly advance the throttle, then turn the choke off.

 

I concur.

 

It took about 4 attempts to get my Sky Arrow started yesterday, at about 28ºF. This is with the Soft Start Module installed, and the first starup after my Annual Condition Inspection.

 

The problem is that she does, in fact, start best with full "choke" and throttle closed, but will not continue to run there. But advancing the throttle often results in the engine dying again. It's hard to find just the right balance of partial throttle and full or partial "choke" to keep her running after the initial "light up".

 

Much less drama with the Soft Start Module, but that's probably not an option on SLSA planes.

 

 

Note: I put the word "choke" in quotes because Bing carbs do not really have a choke. More properly called a "starting circuit" that enriches the mixture by adding fuel, not "choking" air flow. Again, designed to work best with the throttle closed, not necessarily the case with a traditional choke.

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Hi Ed,

 

Try less choke and not full choke on start up. For some cracking the throttle just a tad and I mean a tad does help some because they usually have their idle set too low. In cold areas reducing the spark plug gap down to .024 will help, too.

 

Thanks Roger,

 

I'll try those things. We took the plugs down to .24" when we just gapped them. And my idle is a bit on the low side, as I recall, so the throttle open a tad might get it back to the :normal" zone.

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Thanks Roger,

 

I'll try those things. We took the plugs down to .24" when we just gapped them. And my idle is a bit on the low side, as I recall, so the throttle open a tad might get it back to the :normal" zone.

 

I use two different Rotax-certified mechanics to service my plane and am very satisfied with both. The main reason for two is that I sometimes have service done by the dealer and sometimes have service done locally. The mechanics do not agree on the idle. One likes it around 2000rpm the other 1800rpm. Makes a minor bit of difference on whether I add a bit of throttle on starting. Is there a universal recommendation regardless of aircraft for the 912 ULS?

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My CTSW would not start well when I first got it. I soon found out that full choke enrichens mixture too much (unless it is extremely cold) and my engine will not start at full choke. You can find the 'sweet spot' for your choke by starting the engine, then immediately moving the choke around to find where the engine runs best. This should be the right choke setting for the next time you start. I put a little dab of torque check paint next to the choke lever at this spot. As others have indictated, my CT will not start if I have any throttle opening with choke. Must be at idle to start with choke.

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This makes me suspicious that my 4 year old battery needs replacement.

 

I guess!

 

I don't know what kind of battery the CT takes, but I just replaced a one-year-old Odyssey PC680. The old one was just fine, but I have a BMW K1200RS and its battery was getting marginal, so it inherited the old Sky Arrow battery. I actually have a second bike that takes the same battery, so I may continue this hand-me-down procedure next year as well.

 

I have a very long cable run from the battery to the starter, and $125/yr. seems like relatively cheap insurance to always have a reliable starting source.

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Hi Dave,

 

It is taught in class that 1800 is good, but so is 2000. With 2000 some say it is harder to land because of the rpm increase and idling back to 1800 is easier. Both are right so you make up your mind and tell them where you want it, your paying them. You could be in the 1750 range to, but it isn't a good idea to idle there or lower for long periods. If you have to just sit on the runway and wait your turn to take off, idle around 2000 -2200 to help the gearbox smooth out because the 10.5-1 compression will beat it up at low idle rpms. I try to set my clients up[ at 1750.

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Mine is set at 1500 RPM. This gives me about 1900 on a 55K final with throttle closed. On the ground I manually keep it at 2000 RPM. One year I set it at 2000 and on my first approach I thought I was going to land in the next county!! Alot of float. Sure, I could have modified my approaches to fit the higher RPM but I didn't want to do that.

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1,500rpm is what the current CTLS AOI specifies. It actually says "approximately 1500" because it is almost impossible to get it perfict. We usually see a 100rpm increase on the idle when the cowl is installed.

 

There is a yellow arc on the tach from 1400-1800 so the pilot knows to bump up the idle when stationary on the ground.

 

If the idle is set above 1800 it will be hard for the "choke" to work properly.

 

John

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Hi Jos,

 

At 4 years on the battery I think you got a good service life out of it. It just doesn't have enough zip to get the engine up to a starting rpm any more and keep it there. Sounds like a new Christmas battery is in your future.

Damn Rotax, this is all their fault. The Odyssey has a 10yr+ service life if properly cared for. Here's why they don't last: Rotax uses un under-rated regulator on their alternator, a Ducati POS with a nominal 13.8V output but which drops with temperature to about 13.4V for most CT's with lots of e- load since the thing overheats even in normal usage. the charge voltage should drop with battery temperature but the regulator only can go off its own temp and that is about 40°C higher than ambient (alot) with ~100W load. Charge voltage ought to be 14.3V for the battery as a decent semi-float level (the Odyssey Technical manuals call for 13.8V float and 14.7V normal cyclic charge voltage and in between is ideal for a vehicle system). So at 13.4 the battery never gets anywhere near a decent charge and sulphates up. That and you won't get much panel life if the alternator ever dies and you are prone to low voltage warnings at engine idle, especially if you add a big load like a landing light, can't start if you sit the plane for a month in the cold, etc.

 

http://contrails.free.fr/elec_ducati_en.php

 

There is a handy fix if you're interrested and it costs all of 4¢

If you look in section 74, 3.7) of the ROTAX 912 heavy maintenance manual you'll see the wiring setup for the Ducati. Normally there is a small wire loop connection between +B (positive battery output) and C (Control voltage input) on the orange regulator wiring plug. If you remove that wire and replace it with a 1N4001 diode with the cathode (silver band) aimed at the C terminal, then you have added a 0.7V drop to the circuit. The regulator compensates by driving an extra 0.7V on the charging output to yield the same voltage on the C terminal and voila, you end up with 14.2V out which is ideal.

 

It would be nice if ROTAX would just change their wiring installation like this to compensate for this crappy thing or better yet, qualify in a regulator that doesn't regularly burn itself up while slowly ruining these nice and expensive AGM batteries.

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  • 6 months later...

Roger, i have 14.2volts at battery while running and battery is newer 2 years old. it always starts great and voltage always reads 13.4 to 13.8 while flying. when i idle at say 2000rpm voltage will drop tp 12.8 or so. but i never idle there only to see what voltage does. i mostly idle and taxi at 2300-2400rpm for gear reduction drive.BUT almost always when i land and drop rpm below say 2500 my alternator light will come on even thou voltage can still read 13.4-13.5. i think that red light might not be correct? Any Thoughts? Thanks Bill

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Mine is set at 1500 RPM. This gives me about 1900 on a 55K final with throttle closed. On the ground I manually keep it at 2000 RPM. One year I set it at 2000 and on my first approach I thought I was going to land in the next county!! Alot of float. Sure, I could have modified my approaches to fit the higher RPM but I didn't want to do that.

 

I set all the CT's at 1550 RPM with all the cowlings on and an indicated CHT of at least 180F. Any other airframe I set at 1800 unless the mx manual says different. I also never set the idle with the carb sync gauges hooked up.

 

I do a carb sync, then I set my idle around 1600 RPM. Then I cowl it up, do all my post runs (this gets the temps up as well) and then observe the idle. It will always be around 1650-1750. Then I shut down and open the trhottle to file down the center consoul and close the throttle. Keep taking small amounts out until 1550 RPM at 180F is achieved. Oh, also remember to back off the Bing throttle stops or they may hit and throw everything out until you figure out what happen.

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