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Rotax 447 RPM Varies

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WhiskeyVictor36(at)aol.co
Guest

Posted: Sat Jun 22, 2013 4:49 am Post subject: Rotax 447 RPM Varies

Problem with Rotax 447 not holding steady RPM.

  

 After climbing to altitude and reducing the RPM to my cruise setting of  5,000, the RPM slowly decreases to about 4,000.  I bump the throttle lever  and get it back up to 5,000, and then it continues on up to 5,500 or even  to 6,000 RPM.  I cannot seem to get it to stay at 5,000 RPM.

  

 I had this problem about a year ago and at that time I tried cleaning  the carb, fuel tank, installed new fuel lines and added fresh fuel (auto regular  with up to 10% ethanol but adding stabil for control of that) to no  avail.  The problem eventually went away on it's own.  Now it's  back.  Any ideas?

  

 Bill  Varnes

Original Kolb FireStar

Audubon NJ

Do Not  Archive

 [quote][b]

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undoctor

Joined: 21 Oct 2008
Posts: 212
Location: Bethelhem, PA

Posted: Sat Jun 22, 2013 3:00 pm Post subject: Rotax 447 RPM Varies

Hi Bill,

     

     This may be a bit like a house painter making a suggestion to     Rembrandt, but I had a problem like that with my FireFly with a     447.  What I found was that when it would fluctuate like that it was     mostly due to the attitude of the plane.  When I'd decrease RPMs it     seemed the FF would slowly go to a steeper angle of attack which     would put more resistance on the engine, slowing it down.  Then when     I gave it more throttle I believe the AOA lessened and I'd pick up     speed and the revs would follow.

     

     When it does it for you watch your VSI if you have one, and play     with giving a bit of back pressure on the stick.  See if that     affects the RPMs.

     

     Two strokes can be pretty cantankerous at times!

     

     Dave Kulp

     Bethlehem, PA

     FireFly 11DMK

     

     BTW, I got my wings and horiz stab back from the repairman     (following my trailer hangar rolling 1 1/4 revolutions in Hurricane     Sandy) at Shoestring and put them back on Thursday.  I've still got     a few things to take care of before I commit aviation, but I sure am     getting anxious!

      

     On 6/22/2013 8:48 AM,       WhiskeyVictor36(at)aol.com (WhiskeyVictor36(at)aol.com) wrote:

     

     [quote]                              Problem with Rotax 447 not holding steady RPM.

          

         After climbing to altitude and reducing the RPM to my           cruise setting of 5,000, the RPM slowly decreases to about           4,000.  I bump the throttle lever and get it back up to 5,000,           and then it continues on up to 5,500 or even to 6,000 RPM.  I           cannot seem to get it to stay at 5,000 RPM.

          

         I had this problem about a year ago and at that time I           tried cleaning the carb, fuel tank, installed new fuel lines           and added fresh fuel (auto regular with up to 10% ethanol but           adding stabil for control of that) to no avail.  The problem           eventually went away on it's own.  Now it's back.  Any ideas?

          

         Bill Varnes

             Original Kolb FireStar

             Audubon NJ

             Do Not Archive

               	  Quote: 	
		  

	
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Richard Pike

Joined: 09 Jan 2006
Posts: 1671
Location: Blountville, Tennessee

Posted: Sat Jun 22, 2013 7:09 pm Post subject: Re: Rotax 447 RPM Varies

If you have a variable pitch prop, try changing the pitch a bit to load the torque curve in a different location. I had a 532 that would do that when the load on the prop was too great.



Might not work, but at least it is a cheap experiment...

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Richard Pike
Kolb MKIII N420P (420ldPoops)
Kingsport, TN 3TN0

Forgiving is tough, being forgiven is wonderful, and God's grace really is amazing.

t41pilot

Joined: 05 Sep 2011
Posts: 38
Location: Howard City, Michigan

Posted: Sun Jun 23, 2013 12:00 pm Post subject: Re: Rotax 447 RPM Varies

I have a 447 with about 30 hours on it and as undoctor points out, the rpm will change as the pitch of the aircraft changes with a given throttle setting. Pitch changes the load on the engine so pitch up equals more load and less indicated rpm and vice versa. My rpm changes are 200 or 300 rpm in either direction as pitch changes. not 1000 as you are describing. So, the important thing here is whether your problem occurs  at a constant altitude or not and just around your cruise setting or across the entire throttle range. If you are maintaining a steady altitude, then you do have a problem.  If it occurs just in the 4 to 5 grand range and nowhere else, then the midrange circuit in the carb needs looking at. Check for worn needle and that the clip is still fitting snuggly in the grooves. Make sure the rubber o ring on top of the clip is secure.  Make sure your throttle cable is snug and properly adjusted at the carb inlet. Pulse line for fuel pump should be as short as possible and stiff as possible. Pump has to lift fuel quite a ways on a firefly. A partially plugged fuel filter will cause engine surges too.  I've read that paper style fuel filters are not recommended when using auto gas because of the alcohol.  Not sure how true that is but for a couple of bucks I changed mine out to a different type just for peace of mind.  So far so good on my engine. I'm presently using 89 octane auto gas.  I manage my pitch during flight with a vertical deviation indicator of my own design that works quite well. I find that I use it alot to help maintain a constant altitude which also helps maintain a steady EGT temp.

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Gregg Kaat
2011 Firefly

jbhart(at)onlyinternet.ne
Guest

Posted: Sun Jun 23, 2013 2:38 pm Post subject: Rotax 447 RPM Varies

From: WhiskeyVictor36(at)aol.com

Date: Sat, 22 Jun 2013 08:48:59 -0400 (EDT)

 	  Quote: 	
		  Problem with Rotax 447 not holding steady RPM.

After climbing to altitude and reducing the RPM to my cruise setting of 

5,000, the RPM slowly decreases to about 4,000.  I bump the throttle lever 

and get it back up to 5,000, and then it continues on up to 5,500 or even to 

6,000 RPM.  I cannot seem to get it to stay at 5,000 RPM.

Bill,

I had similar problems with both the 447 and the Victor 1+.  The Victor did 

better than the 447 at holding a steady rpm but had they both had similar 

problems of not holding steady EGT's.  It drove me nuts and that is why I 

went to an adjustable air/fuel control on the Victor.  But not all the 

problems went away.  

I removed the Bing and looked at the barrel and plunger/needle assembly and 

noticed an odd wear mark inside the barrel bore.  It looked like the plunger 

and needle, return spring, and the control cable assembly were letting the 

plunger and needle dance or resonate inside the barrel bore and the main 

jet.  As an experiment, I found another spring that I could slip inside the 

ordinal spring and ran the two springs.  Much improvement.  I called the 

Bing guy and found out that they produce three different strength springs. I 

ordered the strongest spring, installed it and all my rpm and EGT variations 

disappeared.

I hope this helps.

Jack B. Hart FF004

Winchester, Indiana

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rickofudall

Joined: 19 Sep 2009
Posts: 1392
Location: Udall, KS, USA

Posted: Mon Jun 24, 2013 7:08 am Post subject: Rotax 447 RPM Varies

Gregg, Page 15-2 of the Rotax Installation Manual for two strokes says, "A suitable fuel filter of .15 mm mesh size must be fitted between pump and carburetor. DO NOT USE PAPER FILTERS. (my emphasis). Regardless of the reason that's the requirement from the white coats in Austria.

Rick Girard

do not archive



On Sun, Jun 23, 2013 at 3:00 PM, t41pilot <t41pilot(at)frontier.com (t41pilot(at)frontier.com)> wrote:

  	  Quote: 	
		  --> Kolb-List message posted by: "t41pilot" <t41pilot(at)frontier.com (t41pilot(at)frontier.com)>

  

 I have a 447 with about 30 hours on it and as undoctor points out, the rpm will change as the pitch of the aircraft changes with a given throttle setting. Pitch changes the load on the engine so pitch up equals more load and less indicated rpm and vice versa. My rpm changes are 200 or 300 rpm in either direction as pitch changes. not 1000 as you are describing. So, the important thing here is whether your problem occurs  at a constant altitude or not and just around your cruise setting or across the entire throttle range. If you are maintaining a steady altitude, then you do have a problem.  If it occurs just in the 4 to 5 grand range and nowhere else, then the midrange circuit in the carb needs looking at. Check for worn needle and that the clip is still fitting snuggly in the grooves. Make sure the rubber o ring on top of the clip is secure.  Make sure your throttle cable is snug and properly adjusted at the carb inlet. Pulse line for fuel pump should be as short as possib!

   le and stiff as possible. Pump has to lift fuel quite a ways on a firefly. A partially plugged fuel filter will cause engine surges too.  I've read that paper style fuel filters are not recommended when using auto gas because of the alcohol.  Not sure how true that is but for a couple of bucks I changed mine out to a different type just for peace of mind.  So far so good on my engine. I'm presently using 89 octane auto gas.  I manage my pitch during flight with a vertical deviation indicator of my own design that works quite well. I find that I use it alot to help maintain a constant altitude which also helps maintain a steady EGT temp.

  

 --------

 Gregg Kaat

 2011 Firefly

 

 

 

 

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Ducati SS

Joined: 15 Oct 2009
Posts: 93

Posted: Mon Jun 24, 2013 7:01 pm Post subject: Re: Rotax 447 RPM Varies

Unless the composition of paper filters has changed recently their main difference from screen filters is that they will not pass water. Up side - no water in carb, down side- no fuel in carb , and we all know about Ethanol and water.

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WhiskeyVictor36(at)aol.co
Guest

Posted: Sat Jul 06, 2013 7:46 am Post subject: Rotax 447 RPM Varies

To: Dave Kulp, Richard Pike, Gregg Kaat, Jack Hart, Richard, Girad &  Ducati SS

  

  Thanks for your input regarding my problem with the RPM not staying  in place.  If the rain and nasty hot and humid weather ever clears away, I  might get a chance to experiment with the suggestions you all gave.   When and if I find the cure I will let the list know the results.

  

 Thanks again,

  

 Bill  Varnes

Original Kolb FireStar

Audubon NJ

Do Not  Archive



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