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Duncan McFadyean
Joined: 18 Jan 2011
Posts: 219
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 Posted: Tue Jan 31, 2023 7:28 am Post subject: New engine runs a little rough when weather is cold. |
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There should be a detectable change (small increase) to EGTs if dense air is causing the engine to run lean. Or small decreases if carb ice is the culprit.
I've had a recent engine change and find the "new" motor to ice-up during the start/warm up processes, much more than the old engine this winter.
Differences in gearbox friction torque may also introduce new affects, especially for the 'picky'!
Duncan McF.
| Quote: | On 31 January 2023 at 14:36 n7188u <chmgarb(at)gmail.com> wrote:
Hi Guys (and Gals),
Haven't posted much lately but things going well with my mono. Enjoying it more every day.
One question, and a puzzler for me, regarding engine vibration (yes, I know I am picky about this subject but I hate when things are running well and then change):
My new engine (about 70 hrs now) has always ran pretty good. However, as of late, I noticed a slight (emphasis on slight) vibration when I power down to a low cruise power setting (around 500-5100 RPM). Now, I know that some people will start screaming that I should not keep the power that low but I had no issues with sensing vibration (slight) at that power level before.
Well, I started to suspect that this was happening when the weather got colder (50s-60s °F). EGT looks good at around 1400. And even though I have blocked maybe 1/2 of the oil cooler, it still runs a little bellow 180 (160-170). Coolant has been as low as mod 150s.
Sure enough, last flight the vibration was noticeable. Yesterday we had a warm and humid day, in the 80s, so I decided to test my theory. Lo and Behold the engine ran great. Absolutely no vibration at 5000 RPM.
My suspicion at this point is that the cold air from our ram air induction system is just very cold, and maybe adds a little extra pressure, and the mixture goes lean with the stock 912S carb setting. # 1 and 2 plugs look normal (slight tan) but the #3 and 4 look lean (white). Engine is stock as it came from Rotax with no changes to the carbs made.
If we get a cold day again I will try moving the needles up one notch but I wonder if anyone had an experience like this before.
Best Regards,
Chris
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kingsnjan(at)westnet.com.
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| Posted: Wed Feb 01, 2023 2:58 am Post subject: New engine runs a little rough when weather is cold. |
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Hello again Chris,
When I read your post, my immediate suspicion was carby ice hence my
query. I am not suggesting you definitely have icing problems but I do
think it is worth considering it as a possibility.
Indeed Rotax don't provide any form of carb heat and I suspect this is
because they are perfectly happy to have the engines sucking hot air
under the cowl.
I have a home made intake plenum to supply cold air with as much ram air
as I can produce. My plenum is sealed to the top cowl in an effort to
prevent any loss of ram air pressure. This is not sanctioned by Rotax
of course.
With the cold air entering, I figured that it would only be a matter of
time before I got some carb icing so I purchased a hot water type Carby
Heat kit from Lockwood Aviation in the USA their being the main Rotax
agent in the US I believe.
Touch wood, this set-up has served me well for almost 400 hrs now and I
have never had an icing problem. There is certainly nothing wrong with
the way the engine runs. The good thing about this sort of carb heat is
that it stays on permanently with an undetectable power loss as opposed
to under cowl hot air induction.
Best
Kingsley
On 01.02.23 8:05 am, n7188u wrote:
| Quote: |
Thanks for the postings guys. Some answers:
1- The carb bowl vents are located in the plenum.
2- I have no provisions for carb heat since neither the stock Europa has it nor Rotax provides it unless I go aftermarket.
3- The engine has 70 hours in it total but I did check the clutch at 25 hours. 51 NM (38 ft*lb). I can check it again.
Chris
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budyerly@msn.com
Joined: 05 Oct 2019
Posts: 286
Location: Florida USA
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| Posted: Wed Feb 01, 2023 4:21 pm Post subject: New engine runs a little rough when weather is cold. |
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Chris and Kingsley,
Keep in mind there is no choke per se on the Bing. It is an enrichening circuit (also known as the starting carb) that only works correctly when the throttle is closed.
Once above about 3500 RPM the enrichening circuit hole in the carb does not have enough suction to pull fuel from the bowl and it actually leans the carburetor, not enrichen it when the throttle plate is open.
So, two things to remember: To start the engine cold, throttle closed and starting carb engage (choke to most of us although it is not a choke valve). Once the engine hits we have two choices, slightly advance the throttle and or hold the choke out until the engine begins running smooth or: For those who have their idle set at 1600 RPM hot, and fine pitch, this means the throttle is not set for idle per the Rotax manual. (You know that initial setting when rebuilding the carb!) With this combo the throttle is closed hard, and little fuel and air gets by the throttle plate and starting can be problematic unless the throttle is cracked open a bit on start. When normally set up with an 1800 RPM fixed pitch prop pitched for a full power static of 5200 RPM (an average pitch between climb and cruise) all starting procedures are by the book. Throttle closed, choke out (enrichening circuit/starting carb engaged) and the engine start is quick. (Provided the starter is cranking above 300 RPM anyway.)
Pulling the choke at higher RPMs tends to cause the engine to run lean for the above reasons but to recap, with the throttle plate open and MP high, the float bowl is now slightly depressurized and the main jet loses some flow because of the lowered bowl pressure and consequently the carb leans a bit.
Refer to the Understanding the Rotax series by Phil Lockwood some 20 years ago and a later set from Rainbow Aviation. The Rotax video series is pretty good. Better than watching the news, or Hallmark Channel now days.
But first, look at your carbs and exhaust system. A slight jet of hot exhaust gas can cause roughness at full or cruise power. Pay attention to soot lines coming off the exhaust staining. If there is any soot on the carb bowl you've got serious issues. I will fly and put my hand in the cowl access doors and touch the carb bowls after a test flight (if I can) to see if the bowls are cool. Gas evaporates, so even in a hot cowl, the bowls are not hot to the touch. If one of the bowls is warm....Exhaust leak! Because the CKT exhaust systems don't seal absolutely tight and sometimes the head to downpipe is not a tight seal. I've had to actually use lapping compound to get a good seal.
Mid range roughness can be hard to troubleshoot. Normally compare EGT's, keep the fuel fresh and of proper octane. Remember very old car gas won't burst with a match, it just burns on the surface. Heck of a thing.
Next thing on roughness is carb cleanliness, balance tube leak, bowl vent leak, manifold gasket leak / carb rubber connector socket cracked, compressions significantly different, but usually, it's a dirty, improperly adjusted throttle plate, carb or air leak. One culprit if the hoses and interior mechanicals are clean, is a partially open enrichening lever. If one or both of the carb "choke" cables do not allow full closure (on the stop) of the starting carb arm, the engine runs rough midrange.
On the subject of carb ice in humid Florida, when the temps get into the 40-60F range, carb ice is a real issue in a normally aspirated engine. If you run a 912 or 912S XS (cold air intake), carb ice is a real issue if the throttle is fixed at one RPM. The Classic warm radiators preheat the air in the cowl so it was less of a problem. One reason motorcycles don't get carb ice often is the throttle is constantly moving. If you are looking for an idea to keep you busy for a while, why not put in a temp probe in the Bing carb. In the Bing Carby, there is a manifold tap that can be used to troubleshoot the throat temperature. I've never installed a carb temp probe or considered it is because the 912S XS models I have done all had the water jacket carb heat running at all times.
Should you want to experiment (I know of no one that has done a true carb temp probe), there is a screw hole that is plugged for our Rotax Europa's in the carb I think it is an M3 screw for a manifold pressure tap on single carb engines, but you can just as easily put in a Harbor Freight thermocouple drilled in a brass screw and some JB Weld or similar, and check your throat temp but that is not really an easy thing to do.
Enough of my tomes,
Bud Yerly
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n7188u
Joined: 15 Nov 2015
Posts: 404
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| Posted: Thu Feb 02, 2023 6:29 am Post subject: Re: New engine runs a little rough when weather is cold. |
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Thanks for the info Bud. I was indeed familiar with the enrichment feature of the Bing, as compared to a regular choke, but didn't know that it could actually lean the mixture if applied in the air. Interesting.
It is clear from all the feedback that the 912S can suffer from carb ice. The reason I didn't quite jump to the conclusion that this is the issue I'm having is because I have experienced carb ice in airplanes with Lycoming engines and it presents itself in a different way, much more violent and over a broader RPM range. Also, last time I had this issue, it showed itself when I powered back from a brief climb to 1000' (from SL) and it manifested itself immediately when I moved the throttle back to midrange. I would think carb ice would take a little longer to build up (but what do I know).
Something I am going to check is to make 100% the "choke" is closing fully. I have checked it many times but will be more discerning. I am also going to check for any hot carb bowls as you recommend.
Still, I am going to explore the possibility that the mixture is going lean. This is a tough one for me to believe because the EGTs don't seem to show that is happening but the plug color is. I do know the Bings have aggressive midrange economizer settings (lean) so I want to experiment with that. Low engine temps are also bugging me.
And yes, I will look at the hot water jacket although not a fan right now of the idea of having to install these.
Will report back.
Chris
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Hitchflight
Joined: 22 Feb 2018
Posts: 94
Location: Derbyshire, England
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| Posted: Thu Feb 02, 2023 11:27 am Post subject: Re: New engine runs a little rough when weather is cold. |
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Hi Kingsley.
Good comments. Just a reminder that last weeks in depth Europa Club Tech talk Zoom session may be a useful companion to this discussion. A few moments ago the video went live on the Club website. (Carb heat, icing, vapour lock). Good well attended interactive session.
At the popular request from your fellow Australian Members we now routinely record so that you guys can enjoy at a more civilized time of day.
https://www.theeuropaclub.org/the-europa/video-log-in-required
Best wishes
Regards
Bob
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Mallard
Joined: 22 Oct 2019
Posts: 49
Location: Ireland
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| Posted: Mon Feb 13, 2023 3:15 pm Post subject: New engine runs a little rough when weather is cold. |
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Hi Chris,
When you balanced the Carbs, what RPM was the engine running at?
Cheers
James
Sent from Outlook for Android
From: owner-europa-list-server(at)matronics.com <owner-europa-list-server(at)matronics.com> on behalf of n7188u <chmgarb(at)gmail.com>
Sent: Monday, February 13, 2023 7:04:15 PM
To: europa-list(at)matronics.com <europa-list(at)matronics.com>
Subject: Re: New engine runs a little rough when weather is cold.
--> Europa-List message posted by: "n7188u" <chmgarb(at)gmail.com>
Hi everyone,
I promised an update so here it is.
In a nutshell, I decided to follow my eyes, which were looking at very white rear cylinder plugs. So I decided to move the needle from position #3 to position #4 and enrichen the mid-range mixture.
The jury is still out since I only did two flights since the change but the difference is notable in terms of engine smoothness. But too early for final conclusions. I did pull the plug and it looks a more reasonable light tan now which I think is an improvement. I will report back on the mid-range adjustment once I do a few flights in different conditions.
But what really caught my attention is that for the last three years, even with changing to a new engine, I had to put up with crappy idling 912Ss (at least by my picky standard). I always thought that that was the way these engines idle, particularly the high compression 912S.
Well, I finally decided to play with the idle mixture. I had moved the idle screw a flat or so in the past to see if anything happened but not much did. But this time around I decided to move the screw in or out one flat at a time until something happened. Well, what a pleasant surprise when the engine started to get smoother as I screwed the needle in but not until you are at less than one turn from fully closed. And I mean HUGE improvement. All the roughness went away and now it idles smoothly.
Again, I still have to fly more with these settings but what a difference so far.
I told a Rotax 912S owner friend of mine all this and he recommended I watch this video. I think it exemplifies my newly acquired conviction that the carbs in the 912S have to be tuned beyond just the simple balancing.
https://www.youtube.com/watch?v=GxEORpdJp0w
Best,
Chris
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Mallard
Joined: 22 Oct 2019
Posts: 49
Location: Ireland
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| Posted: Mon Feb 13, 2023 4:21 pm Post subject: New engine runs a little rough when weather is cold. |
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I've a 914 Chris, initially I tuned it at 2500 but found it was rough at idle & at full power. After reading reports & watching videos by Rotax engineers who advised balancing at 3500, I rebalanced my carbs at 3500. The engine became very smooth all RPM settings & still is 30 hours later!
Btw
I used a standard Analogue Gauge Balancing Kit.
Regards
James
Sent from Outlook for Android
From: owner-europa-list-server(at)matronics.com <owner-europa-list-server(at)matronics.com> on behalf of n7188u <chmgarb(at)gmail.com>
Sent: Monday, February 13, 2023 11:53:22 PM
To: europa-list(at)matronics.com <europa-list(at)matronics.com>
Subject: Re: New engine runs a little rough when weather is cold.
--> Europa-List message posted by: "n7188u" <chmgarb(at)gmail.com>
I’m going to stick to this version of the tread. Why are there two?
Anyway, I do my carb balance at 2500 but also check at 3500. Found that if I make it perfect at 2500 I get smoother low rpm operation but if at 3500 a little nicer at cruise. I’ve been told to split the difference. Not much difference between the two though. My electronic balancer is very sensitive.
Unfortunately sync will go out as I get to 1800 and just a little off at 4000. Sometimes it is better, sometimes worse. But overall runs nice. Better now after the idle mixture adjustment. Just being picky. I am convinced that if a butterfly farts in front of the airplane the tuning changes 
Just came back from a flight. Runs good.
Chris 
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