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912 UL Intake Manifold Pressures

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italianjon

Joined: 05 Aug 2015
Posts: 68

Posted: Fri Oct 20, 2017 11:28 am Post subject: 912 UL Intake Manifold Pressures

Hi All,



I've been tracking a vibration for a while, and it has been very difficult. Carburettors have been sync'd more than I've had hot dinners, plus other areas of the engine. So far I've eliminated the propeller, gearbox



I noticed a strange effect today, and I'm unsure about it. Today, as a result of a vibration plot taken last weekend, decided to carefully check the carburettor sync again. The vibration plot is showing the vibration at half-crank and twice-crank frequency.



I connected two vacuum gauges, so that I am reading absolute vacuum (i.e. 0" is ambient and 10", for example, is 10" of vacuum).



From about 10" up to 0", which corresponds to rpms of about 3400 up to 5400, the carburettors are in sync. Below that they aren't.



At idle of about 1750/1800 rpm i get 12.5-13" in the port carb, and 15.5" in the starboard carb.



I found Roger Lee's very good guide and thought that I could take out this idle difference with the idle mixture screw. But it didn't really change anything, no matter where set on the port carb. On the starboard carb it did have an effect.



The other strange symptom that I found is that if I take the engine to a fair speed, say 4000 rpm and then quickly idle the throttle, then both carbs come down to 15" in sync before the port carb raises to 12.5/13".



Compressions were checked 12 months ago, all ok. Carburettors we overhauled 12 months ago, all ok. Carb mounts renewed 12 months ago.



Any one seen this effect before?



I'm thinking of taking off the manifold and checking the O-rings between the engine and manifold for leaks. And also stripping back the carbs, cleaning and rebuilding them.



Anything else I should be thinking?



Best



Jon

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williamtsullivan(at)att.n
Guest

Posted: Fri Oct 20, 2017 1:08 pm Post subject: 912 UL Intake Manifold Pressures

Check the Viton seals in the enrichers.  One could be deteriorating.  Cheap and easy fix, if that's it.

--------------------------------------------

On Fri, 10/20/17, italianjon <jon.catilli(at)gmail.com> wrote:



 Subject: 912 UL Intake Manifold Pressures

 To: rotaxengines-list(at)matronics.com

 Date: Friday, October 20, 2017, 3:28 PM

 

 

 "italianjon" <jon.catilli(at)gmail.com>

 

 Hi All,

 

 I've been tracking a vibration for a

 while, and it has been very difficult. Carburettors have

 been sync'd more than I've had hot dinners, plus other areas

 of the engine. So far I've eliminated the propeller,

 gearbox

 

 I noticed a strange effect today, and

 I'm unsure about it. Today, as a result of a vibration plot

 taken last weekend, decided to carefully check the

 carburettor sync again. The vibration plot is showing the

 vibration at half-crank and twice-crank frequency.

 

 I connected two vacuum gauges, so that

 I am reading absolute vacuum (i.e. 0" is ambient and 10",

 for example, is 10" of vacuum).

 

 >From about 10" up to 0", which

 corresponds to rpms of about 3400 up to 5400, the

 carburettors are in sync. Below that they aren't.

 

 At idle of about 1750/1800 rpm i get

 12.5-13" in the port carb, and 15.5" in the starboard carb.

 

 I found Roger Lee's very good guide and

 thought that I could take out this idle difference with the

 idle mixture screw. But it didn't really change anything, no

 matter where set on the port carb. On the starboard carb it

 did have an effect.

 

 The other strange symptom that I found

 is that if I take the engine to a fair speed, say 4000 rpm

 and then quickly idle the throttle, then both carbs come

 down to 15" in sync before the port carb raises to

 12.5/13".

 

 Compressions were checked 12 months

 ago, all ok. Carburettors we overhauled 12 months ago, all

 ok. Carb mounts renewed 12 months ago.

 

 Any one seen this effect before?

 

 I'm thinking of taking off the manifold

 and checking the O-rings between the engine and manifold for

 leaks. And also stripping back the carbs, cleaning and

 rebuilding them.

 

 Anything else I should be thinking?

 

 Best

 

 Jon

 

 

 

 

 Read this topic online here:

 

 http://forums.matronics.com/viewtopic.php?p=473713#473713

 

 

 

 

 

 

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 7-Day Browse, Chat, FAQ,

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klinefelter.kevin(at)gmai
Guest

Posted: Fri Oct 20, 2017 8:22 pm Post subject: 912 UL Intake Manifold Pressures

To check the intake manifolds for leaks you can spray ether around them with the engine running. If the RPM goes up you have a leak. 

Kevin



 	  Quote: 	
		   On Oct 20, 2017, at 2:06 PM, william sullivan <williamtsullivan(at)att.net> wrote:

 

 

 

  Check the Viton seals in the enrichers.  One could be deteriorating.  Cheap and easy fix, if that's it.

 

 

 --------------------------------------------

 On Fri, 10/20/17, italianjon <jon.catilli(at)gmail.com> wrote:

 

 Subject: 912 UL Intake Manifold Pressures

 To: rotaxengines-list(at)matronics.com

 Date: Friday, October 20, 2017, 3:28 PM

 

 

 "italianjon" <jon.catilli(at)gmail.com>

 

 Hi All,

 

 I've been tracking a vibration for a

 while, and it has been very difficult. Carburettors have

 been sync'd more than I've had hot dinners, plus other areas

 of the engine. So far I've eliminated the propeller,

 gearbox

 

 I noticed a strange effect today, and

 I'm unsure about it. Today, as a result of a vibration plot

 taken last weekend, decided to carefully check the

 carburettor sync again. The vibration plot is showing the

 vibration at half-crank and twice-crank frequency.

 

 I connected two vacuum gauges, so that

 I am reading absolute vacuum (i.e. 0" is ambient and 10",

 for example, is 10" of vacuum).

 

> From about 10" up to 0", which

 corresponds to rpms of about 3400 up to 5400, the

 carburettors are in sync. Below that they aren't.

 

 At idle of about 1750/1800 rpm i get

 12.5-13" in the port carb, and 15.5" in the starboard carb.

 

 I found Roger Lee's very good guide and

 thought that I could take out this idle difference with the

 idle mixture screw. But it didn't really change anything, no

 matter where set on the port carb. On the starboard carb it

 did have an effect.

 

 The other strange symptom that I found

 is that if I take the engine to a fair speed, say 4000 rpm

 and then quickly idle the throttle, then both carbs come

 down to 15" in sync before the port carb raises to

 12.5/13".

 

 Compressions were checked 12 months

 ago, all ok. Carburettors we overhauled 12 months ago, all

 ok. Carb mounts renewed 12 months ago.

 

 Any one seen this effect before?

 

 I'm thinking of taking off the manifold

 and checking the O-rings between the engine and manifold for

 leaks. And also stripping back the carbs, cleaning and

 rebuilding them.

 

 Anything else I should be thinking?

 

 Best

 

 Jon

 

 

 

 

 Read this topic online here:

 

 http://forums.matronics.com/viewtopic.php?p=473713#473713

 

 

 

 

 

 

 The RotaxEngines-List Email Forum -

 Navigator to browse

 List Un/Subscription,

 7-Day Browse, Chat, FAQ,

      - MATRONICS WEB FORUMS -

 via the Web Forums!

     - NEW MATRONICS LIST WIKI -

 Email List Wiki!

    - List Contribution Web Site -

 support!

                

     -Matt Dralle, List Admin.

- The Matronics RotaxEngines-List Email Forum -

Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:

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davidjoyce(at)doctors.org
Guest

Posted: Sat Oct 21, 2017 1:09 am Post subject: 912 UL Intake Manifold Pressures

Jon, I believe I had a rather similar thing quite a few years ago when my throttle cables were run in a not symmetrical pattern with one following tighter bends. Regards, David Joyce, GXSDJ 

   

 

On 2017-10-20 20:28, italianjon wrote:  	  Quote: 	
		    	  Quote: 	
		  --> RotaxEngines-List message posted by: "italianjon" <jon.catilli(at)gmail.com (jon.catilli(at)gmail.com)>



Hi All,



I've been tracking a vibration for a while, and it has been very difficult. Carburettors have been sync'd more than I've had hot dinners, plus other areas of the engine. So far I've eliminated the propeller, gearbox



I noticed a strange effect today, and I'm unsure about it. Today, as a result of a vibration plot taken last weekend, decided to carefully check the carburettor sync again. The vibration plot is showing the vibration at half-crank and twice-crank frequency.



I connected two vacuum gauges, so that I am reading absolute vacuum (i.e. 0" is ambient and 10", for example, is 10" of vacuum).From about 10" up to 0", which corresponds to rpms of about 3400 up to 5400, the carburettors are in sync. Below that they aren't.At idle of about 1750/1800 rpm i get 12.5-13" in the port carb, and 15.5" in the starboard carb.



I found Roger Lee's very good guide and thought that I could take out this idle difference with the idle mixture screw. But it didn't really change anything, no matter where set on the port carb. On the starboard carb it did have an effect.



The other strange symptom that I found is that if I take the engine to a fair speed, say 4000 rpm and then quickly idle the throttle, then both carbs come down to 15" in sync before the port carb raises to 12.5/13".



Compressions were checked 12 months ago, all ok. Carburettors we overhauled 12 months ago, all ok. Carb mounts renewed 12 months ago.



Any one seen this effect before?



I'm thinking of taking off the manifold and checking the O-rings between the engine and manifold for leaks. And also stripping back the carbs, cleaning and rebuilding them.



Anything else I should be thinking?



Best



Jon





Read this topic online here:



http://forums.matronics.com/viewtopic.php?p=473713#473713

ist">http://www.matronics.com/Navigator?RotaxEngines-List

ics.com

.com

.matronics.com/contribution

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brian.davies(at)clara.co.
Guest

Posted: Sat Oct 21, 2017 4:49 am Post subject: 912 UL Intake Manifold Pressures

Sticking throttle cables?



Brian Davies



--

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Roger Lee

Joined: 10 Jan 2006
Posts: 1464
Location: Tucson, Az.

Posted: Sun Oct 22, 2017 5:20 am Post subject: Re: 912 UL Intake Manifold Pressures

Hi Jon,

Give me a call and let's see if we can work this out and eliminate a few things. I need to ask some questions.

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_________________
Roger Lee
Tucson, Az.
Rotax Instructor & Rotax IRC
Light Sport Repairman
Home 520-574-1080 TRY HOME FIRST
Cell 520-349-7056

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