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low RPM @ full Throttle

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iworonko(at)cox.net
Guest

Posted: Wed Jan 24, 2007 2:10 pm Post subject: low RPM @ full Throttle

Hi Folks,

 finally started the engine for the firs time since  I bought this Speedster rebuild project 1.5 years ago. Set the new GSC blade  pitch at 17deg. Pneumatically synched the carbs and at full throttle  I was only getting 4200 rpm. So I repitched the blades to 15 deg. (minimum  shown in the GSC chart for a 912 UL with a 3 blade 68" prop), now it maxes out  at 4300. Any ideas why I cant get anywhere close to max RPM. Could the Rotax RPM  gauge be lying to me.

 Eric N58EW

    [quote][b]

kerrjohna(at)comcast.net
Guest

Posted: Wed Jan 24, 2007 2:26 pm Post subject: low RPM @ full Throttle

those guage are notorious for drifting. I recalibrate mine every annual condition inspection. On mine there is a small hole on the back, originally covered by a sticker, into which I stick a small electronic screwdriver to adjust.  You will need to do the math for the reduction drive and have access to a digital hand held tachometer.  Check your local R/C hobby shop.

  

 Using the conversion table you created in doing the math set the prop rpm such that you will be looking for a convenient engine rpm.  Then adjust the tach. Best to have the tail tied to your pickup. Don't ask.

  

 John Kerr

  

 [quote]-------------- Original message -------------- 

From: "Eric" <iworonko(at)cox.net> 

    Hi Folks,

 finally started the engine for the firs time since I bought this Speedster rebuild project 1.5 years ago. Set the new GSC blade pitch at 17deg. Pneumatically synched the carbs and at full throttle I was only getting 4200 rpm. So I repitched the blades to 15 deg. (minimum shown in the GSC chart for a 912 UL with a 3 blade 68" prop), now it maxes out at 4300. Any ideas why I cant get anywhere close to max RPM. Could the Rotax RPM gauge be lying to me.

 Eric N58EW

 	  Quote: 	
		  

	
[b]

Float Flyr

Joined: 19 Jul 2006
Posts: 2704
Location: Campbellton, Newfoundland

Posted: Wed Jan 24, 2007 2:38 pm Post subject: low RPM @ full Throttle

Mine lied to me... but that was  2 stroke.  Check with a digital or optical tach.

  

  

 

Noel [quote]   

   --

_________________
Noel Loveys
Kitfox III-A
Aerocet 1100 Floats

lcfitt(at)sbcglobal.net
Guest

Posted: Wed Jan 24, 2007 2:59 pm Post subject: low RPM @ full Throttle

John's advice is right on.  I carry an optical tach with me in the cockpit 

and find that the tach will vary as much as 300 rpm due to temps.  I made a 

knob that is attached on the back of the tach so it can be adjusted in 

flight.  The conversion table is taped to the optical tach.



Lowell



Another thing to look at and I learned this first hand.  Make sure the 

throttle allows the carbs to go full open at the full throttle position. 

for the first little while I was flying mine, the throttle full in was 

holding the carburetor arm a bit from the stop.



Lowell



---

rdmac(at)swbell.net
Guest

Posted: Wed Jan 24, 2007 3:06 pm Post subject: low RPM @ full Throttle

Eric,  

            First, what are you using to pitch the blades? Are you using the GSC pitch protractor that came with the prop? If you are then I’d say your tach is off. Even static RPM you should be up close to 5500 RPM at 17 degrees.  

            Roger Mac        

  

From: owner-kitfox-list-server(at)matronics.com [mailto:owner-kitfox-list-server(at)matronics.com] On Behalf Of Eric

 Sent: Wednesday, January 24, 2007 4:10 PM

 To: kitfox-list(at)matronics.com

 Subject: low RPM (at) full Throttle  

  

     

Hi Folks,  

    

finally started the engine for the firs time since I bought this Speedster rebuild project 1.5 years ago. Set the new GSC blade pitch at 17deg. Pneumatically synched the carbs and at full throttle I was only getting 4200 rpm. So I repitched the blades to 15 deg. (minimum shown in the GSC chart for a 912 UL with a 3 blade 68" prop), now it maxes out at 4300. Any ideas why I cant get anywhere close to max RPM. Could the Rotax RPM gauge be lying to me.  

    

Eric N58EW  

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        [quote][b]

dave

Joined: 22 Sep 2006
Posts: 1382

Posted: Wed Jan 24, 2007 3:13 pm Post subject: low RPM @ full Throttle

What about a tiny tach ?



I have found them to be 50 times more consistant than the Rotax tachs.

The take the impluse right from spark plus lead same as you would when you 

use a timing light.

How you wire your Rotax tach I think alters the reading as well as 

electrical load.



Tiny tach is small and in my opinion you better off with a 2 1/4" G meter 

than a Rotax tach.

I have both a Rotax tach and a Tiny Tach .......  The Tiny is consistant and 

the Rotax mightbe the same one out of 100 times and other times  300 to 600 

or more off.  WHY ?

Dave



---

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dcsfoto

Joined: 24 Aug 2006
Posts: 120

Posted: Wed Jan 24, 2007 3:26 pm Post subject: Re: low RPM @ full Throttle

tiny tach    are you running a 912 and what model tiny tach are you using



thanks

lcfitt(at)sbcglobal.net
Guest

Posted: Wed Jan 24, 2007 4:23 pm Post subject: low RPM @ full Throttle

Dave,



The Tiny Tach has been mentioned before.  I just can't get my self to cut 

another hole in the panel and have a hole with nothing in it.



Lowell



do not archive

---

Float Flyr

Joined: 19 Jul 2006
Posts: 2704
Location: Campbellton, Newfoundland

Posted: Wed Jan 24, 2007 4:27 pm Post subject: low RPM @ full Throttle

My Kitfox tach is way off but at least it's linear  It reads about 20% too

high..  Imagine take offs at 5120rpm on a R582, 2.58 B box....(Reads

6400rpm) Also imagine the boost in performance when I installed the Tiny

Tach.   Take offs are now in the realm of 7680 - 7800 rpm on the Kitfox

tach.  No wonder I couldn't get the plane to climb!  It's a wonder I was

able to get off the water at all.



Noel



[quote] --

_________________
Noel Loveys
Kitfox III-A
Aerocet 1100 Floats

Float Flyr

Joined: 19 Jul 2006
Posts: 2704
Location: Campbellton, Newfoundland

Posted: Wed Jan 24, 2007 5:03 pm Post subject: low RPM @ full Throttle

Lowell:



My Tiny Tach was flush mounted on my panel for the trial.  I still have the

Kitfox tach but I could have removed it and made a plate to fill the hole

with a mounting hole for Tiny Tach in it.  I find it's easier to follow

trends in rpm on the analogue instrument... The digital one is for accuracy.



Noel



[quote] --

_________________
Noel Loveys
Kitfox III-A
Aerocet 1100 Floats

dave

Joined: 22 Sep 2006
Posts: 1382

Posted: Wed Jan 24, 2007 5:33 pm Post subject: low RPM @ full Throttle

Lowell,



That is why I said put in a G Meter.

The tiny is a surface mount -- 



or better yet.



Run both and recrod the results for your self .

Dave

---

kirkhull(at)kc.rr.com
Guest

Posted: Wed Jan 24, 2007 5:51 pm Post subject: low RPM @ full Throttle

Any good shop ( and most A&P ) can test your tach with a laser devise and a

piece of reflective tape on the prop.  If you are in the Kansas City

Missouri area I can check it for you.  I need another reason to fly 205AK

anyway.

 	  Quote: 	
		  >

> I have found them to be 50 times more consistant than the Rotax tachs.

> The take the impluse right from spark plus lead same as you would when 

> you use a timing light.

> How you wire your Rotax tach I think alters the reading as well as 

> electrical load.

>

> Tiny tach is small and in my opinion you better off with a 2 1/4" G meter


	


[quote]> than a Rotax tach.

> I have both a Rotax tach and a Tiny Tach .......  The Tiny is consistant 

> and the Rotax mightbe the same one out of 100 times and other times  300 

> to 600 or more off.  WHY ?

> Dave

>

> ---

roncarolnikko(at)hotmail.
Guest

Posted: Wed Jan 24, 2007 6:42 pm Post subject: low RPM @ full Throttle

Eric I was trying to get up to rpm's when a hobby tach from an RC freind 

found the problem.  My tach was way off.   I was turning 6000 rpm's and 

looking for more. Now at 3500 rpm's it flys great.  How many rpm's are you 

looking for?   I'm not used to 912's redline, but you say your at 4300 rpm 

now.  Ron NB Ore   do not archive

 	  Quote: 	
		  From: "Eric" <iworonko(at)cox.net>

Reply-To: kitfox-list(at)matronics.com

To: <kitfox-list(at)matronics.com>

Subject: low RPM (at) full Throttle

Date: Wed, 24 Jan 2007 16:09:56 -0600



Hi Folks,

finally started the engine for the firs time since I bought this Speedster 

rebuild project 1.5 years ago. Set the new GSC blade pitch at 17deg. 

Pneumatically synched the carbs and at full throttle I was only getting 

4200 rpm. So I repitched the blades to 15 deg. (minimum shown in the GSC 

chart for a 912 UL with a 3 blade 68" prop), now it maxes out at 4300. Any 

ideas why I cant get anywhere close to max RPM. Could the Rotax RPM gauge 

be lying to me.

Eric N58EW


	


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Float Flyr

Joined: 19 Jul 2006
Posts: 2704
Location: Campbellton, Newfoundland

Posted: Wed Jan 24, 2007 6:53 pm Post subject: low RPM @ full Throttle

Tiny tach is about $60.00.  How much is a laser tach??



Noel



[quote] --

_________________
Noel Loveys
Kitfox III-A
Aerocet 1100 Floats

iworonko(at)cox.net
Guest

Posted: Thu Jan 25, 2007 7:01 am Post subject: low RPM @ full Throttle

Thanks to everyone who responded to my low rpm (at) full throttle problem.

Ron, I am getting 4300 and Rotax 912 redline is 5600-5800 rpm.

Looks like my options are either an optical tach or TinyTach. I am going to 

go with a TinyTach because its cheaper, reads eng.rpm not prop rpm, and it 

leaves both hands free to fiddle with buttons and knobs.

Eric

dave

Joined: 22 Sep 2006
Posts: 1382

Posted: Thu Jan 25, 2007 7:15 am Post subject: low RPM @ full Throttle

Will be an interesting comparison,  looking forward to hear the results.



Dave

---

kirkhull(at)kc.rr.com
Guest

Posted: Thu Jan 25, 2007 6:52 pm Post subject: low RPM @ full Throttle

Don't buy a laset tach just have a shop or someone  use one to test your

tach to see if it is correct



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