I went out to start up the my Sky Arrow today. It was too windy to fly, but the plane had not been started for a while.
It was 40º, but the plane still took 4 or 5 tries to start with a lot of shaking and kick back, in spite of the new Odyssey battery really turning it over.
Here's a ROTAX review of the "Soft Start Module".
http://www.rotax-owner.com/index.php?op ... &Itemid=35
Since my Sky Arrow is Experimental now, I do have this option. Seems like a good investment ($219.95).
Anyone here have any first-hand experience with this module?
Soft Start Module
Moderator: drseti
- FastEddieB
- Posts: 2880
- Joined: Wed Jan 07, 2009 9:33 pm
- Location: Lenoir City, TN/Mineral Bluff, GA
Hard to start
Hi Eddie,
Sounds like too much fuel right at start.
What is your normal idle set at? The more you go over 1800 rpm the harder it starts. As an example if your idle rpm is 2000 then it is harder to start than it would be at 1750 rpm. too much fuel at the higher idle rpms. If your idle is already a little high try less choke next time.
Sounds like too much fuel right at start.
What is your normal idle set at? The more you go over 1800 rpm the harder it starts. As an example if your idle rpm is 2000 then it is harder to start than it would be at 1750 rpm. too much fuel at the higher idle rpms. If your idle is already a little high try less choke next time.
Roger Lee
Tucson, Az.
LSRM-A, Rotax Instructor & Rotax IRC
(520) 574-1080 (Home) Try Home First.
(520) 349-7056 (Cell)
Tucson, Az.
LSRM-A, Rotax Instructor & Rotax IRC
(520) 574-1080 (Home) Try Home First.
(520) 349-7056 (Cell)
- FastEddieB
- Posts: 2880
- Joined: Wed Jan 07, 2009 9:33 pm
- Location: Lenoir City, TN/Mineral Bluff, GA
Thanks, Roger.
At 40º, how much "choke" would you use?
I know from BMW motorcycles with essentially the same "choke" that they start best with full choke and no throttle. In fact, I've heard that opening the throttle defeats the effects of the "choke".
Yesterday what I tried was very brief boost pump, full "choke" and no throttle. After about 4 or 5 tries, advancing the throttle got her to stay kicked over. Then she settles down immediately into a smooth idle where very little "choke", if any, is needed to keep he running.
In the "Soft Start" literature, there's a long list of things to check prior to installation, all of which they recommend checking first. It's on page 6 of this document:
http://www.bullyhawk.com/docs/Bully%20H ... 202009.pdf
There's a ROTAX mechanic at a nearby airport, Tim Dawson of http://www.optimum-improvement.com/. I may call him today to discuss this and maybe have him guide me through checking my engine regarding the items in the bullyhawk list.
Of further note is that I do not recall my Sky Arrow being this hard to start when I first got it - it seems to have been a progressive problem.
Note to others (Roger knows all this already): Why do I put "choke" in quotes? Well, a choke is a specific engine-starting device that enriches starting mixture solely by reducing airflow to the engine, literally "choking" it for air. Bing carbs (and many other modern carbs) introduce a secondary circuit for the fuel, resulting in a richer mixture, rather than restricting the air. They really shouldn't be marked "CHOKE", but I guess they still are for the sake of convention.
At 40º, how much "choke" would you use?
I know from BMW motorcycles with essentially the same "choke" that they start best with full choke and no throttle. In fact, I've heard that opening the throttle defeats the effects of the "choke".
Yesterday what I tried was very brief boost pump, full "choke" and no throttle. After about 4 or 5 tries, advancing the throttle got her to stay kicked over. Then she settles down immediately into a smooth idle where very little "choke", if any, is needed to keep he running.
In the "Soft Start" literature, there's a long list of things to check prior to installation, all of which they recommend checking first. It's on page 6 of this document:
http://www.bullyhawk.com/docs/Bully%20H ... 202009.pdf
There's a ROTAX mechanic at a nearby airport, Tim Dawson of http://www.optimum-improvement.com/. I may call him today to discuss this and maybe have him guide me through checking my engine regarding the items in the bullyhawk list.
Of further note is that I do not recall my Sky Arrow being this hard to start when I first got it - it seems to have been a progressive problem.
Note to others (Roger knows all this already): Why do I put "choke" in quotes? Well, a choke is a specific engine-starting device that enriches starting mixture solely by reducing airflow to the engine, literally "choking" it for air. Bing carbs (and many other modern carbs) introduce a secondary circuit for the fuel, resulting in a richer mixture, rather than restricting the air. They really shouldn't be marked "CHOKE", but I guess they still are for the sake of convention.
Last edited by FastEddieB on Fri Mar 05, 2010 8:52 am, edited 1 time in total.
Idle rpm
Hi Eddie,
What is your idle rpm? If it is already at 1750-1800 then you may have another issue.
What is your idle rpm? If it is already at 1750-1800 then you may have another issue.
Roger Lee
Tucson, Az.
LSRM-A, Rotax Instructor & Rotax IRC
(520) 574-1080 (Home) Try Home First.
(520) 349-7056 (Cell)
Tucson, Az.
LSRM-A, Rotax Instructor & Rotax IRC
(520) 574-1080 (Home) Try Home First.
(520) 349-7056 (Cell)
- CharlieTango
- Posts: 1000
- Joined: Sat Jun 10, 2006 10:04 am
- Location: Mammoth Lakes, California
- FastEddieB
- Posts: 2880
- Joined: Wed Jan 07, 2009 9:33 pm
- Location: Lenoir City, TN/Mineral Bluff, GA
- FastEddieB
- Posts: 2880
- Joined: Wed Jan 07, 2009 9:33 pm
- Location: Lenoir City, TN/Mineral Bluff, GA
My idle seems to be about 1,700 to 1,800 unless I pull it back hard against the stop. Then I can drop it back to about 1,500 rpm.
Saturday I had a ROTAX mechanic give it a quick look. We checked the carb balance dynamically and it was perfect. We went ahead and gapped all the plugs a little tighter, from .070mm to .060mm.
He said he had better results starting on just one mag. Not sure why that would help, but it seems to (on two not-so-cold startups yesterday).
Someone else recommended cranking the engine over a few times with the mags off first, before mags on. I'll try that as well.
BTW, the mechanic found this:
It's a clamp that helps support the starter. Hard to spot unless you're looking. He was, because he says its a common failure.
Though its just a glorified hose clamp, I'm ordering one today (at about $26!)
Saturday I had a ROTAX mechanic give it a quick look. We checked the carb balance dynamically and it was perfect. We went ahead and gapped all the plugs a little tighter, from .070mm to .060mm.
He said he had better results starting on just one mag. Not sure why that would help, but it seems to (on two not-so-cold startups yesterday).
Someone else recommended cranking the engine over a few times with the mags off first, before mags on. I'll try that as well.
BTW, the mechanic found this:
It's a clamp that helps support the starter. Hard to spot unless you're looking. He was, because he says its a common failure.
Though its just a glorified hose clamp, I'm ordering one today (at about $26!)
Hard start
Hi eddie,
reducing the plug gap to .023 will help. During cold weather reducing the plug gap always helps. When you said you balanced the carbs dynamically did you mean pneumatically with gauges? If yes then good if it was mechanically that is not near enough and only gets you in a ballpark for starting. The carbs can still be way off. Pneumatically is always the best way to go.
You should not be able to get extra rpm drop on the cabin throttle by pulling back hard. This means that you are bending the idle stop arms on the carbs. You do this once and the idle balance on the carbs are out of sync again. The throttle in the cabin should bottom out at the same time the carbs hit the idle stop. If you do not have a throttle stop in the cabin you should install one and if the throttle does eventually bottom out then you need to make the proper cable adjustment at the carbs so they bottom out at the same time. The cables at the carbs would need to be lengthened a small amount to accomplish this.
reducing the plug gap to .023 will help. During cold weather reducing the plug gap always helps. When you said you balanced the carbs dynamically did you mean pneumatically with gauges? If yes then good if it was mechanically that is not near enough and only gets you in a ballpark for starting. The carbs can still be way off. Pneumatically is always the best way to go.
You should not be able to get extra rpm drop on the cabin throttle by pulling back hard. This means that you are bending the idle stop arms on the carbs. You do this once and the idle balance on the carbs are out of sync again. The throttle in the cabin should bottom out at the same time the carbs hit the idle stop. If you do not have a throttle stop in the cabin you should install one and if the throttle does eventually bottom out then you need to make the proper cable adjustment at the carbs so they bottom out at the same time. The cables at the carbs would need to be lengthened a small amount to accomplish this.
Roger Lee
Tucson, Az.
LSRM-A, Rotax Instructor & Rotax IRC
(520) 574-1080 (Home) Try Home First.
(520) 349-7056 (Cell)
Tucson, Az.
LSRM-A, Rotax Instructor & Rotax IRC
(520) 574-1080 (Home) Try Home First.
(520) 349-7056 (Cell)
- FastEddieB
- Posts: 2880
- Joined: Wed Jan 07, 2009 9:33 pm
- Location: Lenoir City, TN/Mineral Bluff, GA
Roger,
We used a home-brew dual-vacuum gauge with the engine running. Both gauges read the same from idle to 3,000 rpm. About a month ago they had been set statically, so at least in this case that got it spot on.
I have a 4-tube vacuum gauge that I bought for balancing Bings on airhead BMW's. I may dig that out. I recall I might have lost the mercury at some point, but I'm sure that can be obtained somewhere.
Good point about the throttle stops. On the Sky Arrow, it's like I hit the "stop" on the throttle lever, but a little extra force causes a little extra drop - maybe some flex there. But you're right - a tiny bit more slack in each cable might alleviate that.
Then again, is it a "bug" or a "feature"? It's kinda nice having both a "normal" idle and a "low" idle. The "low" is useful on shutdown and approach.
We used a home-brew dual-vacuum gauge with the engine running. Both gauges read the same from idle to 3,000 rpm. About a month ago they had been set statically, so at least in this case that got it spot on.
I have a 4-tube vacuum gauge that I bought for balancing Bings on airhead BMW's. I may dig that out. I recall I might have lost the mercury at some point, but I'm sure that can be obtained somewhere.
Good point about the throttle stops. On the Sky Arrow, it's like I hit the "stop" on the throttle lever, but a little extra force causes a little extra drop - maybe some flex there. But you're right - a tiny bit more slack in each cable might alleviate that.
Then again, is it a "bug" or a "feature"? It's kinda nice having both a "normal" idle and a "low" idle. The "low" is useful on shutdown and approach.
carb balance
Hi Eddie,
Next time you do a carb balance and it looks good at 3000 rpm run it on up to at least 4000 rpm. You will find the balance is out the higher you go. You fly at the higher rpms so this is the important place to check to make sure they are really in sync. I always check at the end to make sure they are good up to 4500 rpm. i usually only care about idle and high rpm sync. I may start at 3500 to get them closer, but after they are set at 3500 I go up to 4500 for a quick check.
Next time you do a carb balance and it looks good at 3000 rpm run it on up to at least 4000 rpm. You will find the balance is out the higher you go. You fly at the higher rpms so this is the important place to check to make sure they are really in sync. I always check at the end to make sure they are good up to 4500 rpm. i usually only care about idle and high rpm sync. I may start at 3500 to get them closer, but after they are set at 3500 I go up to 4500 for a quick check.
Roger Lee
Tucson, Az.
LSRM-A, Rotax Instructor & Rotax IRC
(520) 574-1080 (Home) Try Home First.
(520) 349-7056 (Cell)
Tucson, Az.
LSRM-A, Rotax Instructor & Rotax IRC
(520) 574-1080 (Home) Try Home First.
(520) 349-7056 (Cell)
- FastEddieB
- Posts: 2880
- Joined: Wed Jan 07, 2009 9:33 pm
- Location: Lenoir City, TN/Mineral Bluff, GA
Roger,
Good thoughts - will do!
As a data point, neither LEAF nor Lockwood nor California Power Systems has that starter clamp in stock. All said end of April at the earliest.
I'm going to see about getting mine brazed and reinforced locally.
I just mention this because its apparently a common failure point. It does not bode well for the parts supply chain for our ROTAX engines
Good thoughts - will do!
As a data point, neither LEAF nor Lockwood nor California Power Systems has that starter clamp in stock. All said end of April at the earliest.
I'm going to see about getting mine brazed and reinforced locally.
I just mention this because its apparently a common failure point. It does not bode well for the parts supply chain for our ROTAX engines