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912 UL Intake Manifold Pressures

 
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italianjon



Joined: 05 Aug 2015
Posts: 52

PostPosted: Fri Oct 20, 2017 11:28 am    Post subject: 912 UL Intake Manifold Pressures Reply with quote

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
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PostPosted: Fri Oct 20, 2017 1:08 pm    Post subject: 912 UL Intake Manifold Pressures Reply with quote

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




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klinefelter.kevin(at)gmai
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PostPosted: Fri Oct 20, 2017 8:22 pm    Post subject: 912 UL Intake Manifold Pressures Reply with quote

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






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support!

-Matt Dralle, List Admin.










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davidjoyce(at)doctors.org
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PostPosted: Sat Oct 21, 2017 1:09 am    Post subject: 912 UL Intake Manifold Pressures Reply with quote

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
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brian.davies(at)clara.co.
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PostPosted: Sat Oct 21, 2017 4:49 am    Post subject: 912 UL Intake Manifold Pressures Reply with quote

Sticking throttle cables?

Brian Davies

--


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Roger Lee



Joined: 10 Jan 2006
Posts: 1461
Location: Tucson, Az.

PostPosted: Sun Oct 22, 2017 5:20 am    Post subject: Re: 912 UL Intake Manifold Pressures Reply with quote

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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