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912 80hp violent vibration on cold start
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froghair



Joined: 22 Nov 2009
Posts: 2

PostPosted: Sun Nov 22, 2009 1:46 pm    Post subject: 912 80hp violent vibration on cold start Reply with quote

Wondered if anyone has experienced this:

On cold start, anytime OAT is below ~60F, with full choke (enricher), engine will start but shake violently as though not running on all cylinders. I have to coax it to take any throttle increase for up to ~30 seconds. As soon as it will take throttle, it breaks out of this 'harmonic' and runs normally and will do so until allowed to cool back down to ambient temperature.

Engine info:
Older (1997) engine - no clutch gearbox. ~820 hours.
Installed on RANS S-6.
3-blade Warp Drive taper-tip prop.
Carb kits (from CPS) including diaphragms, floats, float needles installed at ~700hrs.

What I've already done/checked:
Carbs balanced - numerous times.
Cold cranking RPM checked at ~325.
New belville washers and shims in gearbox.
Carburetors inspected/cleaned numerous times especially enricher circuit.
Carb boots inspected.
Ignition inspected/checked - pick-up coils checked for proper resistance.
Start on one mag, start on both mags, start with throttle at idle stop, start with throttle barely open (killed warm engine idling at 2200rpm and didn't move throttle until next cold start).

Nothing helps and I'm just about out of ideas! Keep in mind that it runs perfectly once it gets out of this ugly mode. Warm starts are no problem.

Thanks in advance,
Mick in Tulsa


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thilo.kind(at)gmx.net
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PostPosted: Sun Nov 22, 2009 2:11 pm    Post subject: 912 80hp violent vibration on cold start Reply with quote

Hi Mick,

Mine does the same at temps below 50. Take 15 to 20 sec to normal behaviour.
Engine is on the plane since 2001; so far no adverse effects found.

Cheers

Thilo

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Roger Lee



Joined: 10 Jan 2006
Posts: 1452
Location: Tucson, Az.

PostPosted: Sun Nov 22, 2009 3:50 pm    Post subject: Re: 912 80hp violent vibration on cold start Reply with quote

First narrow the gap on your plugs to .024 to start and if it is slightly better try .022. Cold starts if that is the actual problem is hard on engines. If it continues think about preheating the engine. Narrow the gap on the plugs first and let us know. What is your mag drop rpm and at what rpm is this test done?
p.s.
Once this is done you'll have to show me a frog with hair. Must be a Tulsa thing. LOL


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sdemeyer



Joined: 31 Jul 2009
Posts: 45

PostPosted: Sun Nov 22, 2009 3:52 pm    Post subject: 912 80hp violent vibration on cold start Reply with quote

Hi Mick, my 912 does exactly the same thing as well. I have determined the cause to be it's just a cold blooded beast. I think some people use a preheater to avoid the cold starting issue but I don't.

Scott

--- On Sun, 11/22/09, froghair <tim47(at)phroghair.com> wrote:
Quote:

From: froghair <tim47(at)phroghair.com>
Subject: 912 80hp violent vibration on cold start
To: rotaxengines-list(at)matronics.com
Date: Sunday, November 22, 2009, 1:46 PM

--> RotaxEngines-List message posted by: "froghair" <[url=/mc/compose?to=tim47(at)phroghair.com]tim47(at)phroghair.com[/url]>

Wondered if anyone has experienced this:

On cold start, anytime OAT is below ~60F, with full choke (enricher), engine will start but shake violently as though not running on all cylinders. I have to coax it to take any throttle increase for up to ~30 seconds. As soon as it will take throttle, it breaks out of this 'harmonic' and runs normally and will do so until allowed to cool back down to ambient temperature.

Engine info:
Older (1997) engine - no clutch gearbox. ~820 hours.
Installed on RANS S-6.
3-blade Warp Drive taper-tip prop.
Carb kits (from CPS) including diaphragms, floats, float needles installed at ~700hrs.

What I've already done/checked:
Carbs balanced - numerous times.
Cold cranking RPM checked at ~325.
New belville washers and shims in gearbox.
Carburetors inspected/cleaned numerous times especially enricher circuit.
Carb boots inspected.
Ignition inspected/checked - pick-up coils checked for proper resistance.
Start on one mag, start on both mags, start with throttle at idle stop, start with throttle barely open (killed warm engine idling at 2200rpm and didn't move throttle until next cold start).

Nothing helps and I'm just about out of ideas! Keep in mind that it runs perfectly once it gets out of this ugly mode. Warm starts are no problem.

Thanks in advance,
Mick in Tulsa


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froghair



Joined: 22 Nov 2009
Posts: 2

PostPosted: Mon Nov 23, 2009 7:45 pm    Post subject: Re: 912 80hp violent vibration on cold start Reply with quote

Thanks for all the input. Peter Rees sent me a PM describing an identical situation that was caused by the starter sprag clutch NOT disengaging when the engine 'caught' and thereby limiting rpm in the violent shaking mode for much longer than it should ever be. He also noticed the condition only at colder ambient temperatures and could not feed-in any throttle until the clutch eventually decided to let go. I would like to test this - somehow - any ideas?

I would expect that if the starter sprag clutch is 'dragging,' then the engine should be spinning (or trying to spin) the starter much faster than was ever intended. Have any of those who've said, "mine does that too" had problems with damaged starter motors?

Thanks,
Mick in Tulsa


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Goodone



Joined: 13 Sep 2008
Posts: 49

PostPosted: Fri Dec 04, 2009 5:57 pm    Post subject: Re: 912 80hp violent vibration on cold start Reply with quote

Why don't more folks use a primer with the 912? It would seem to me that the use of a primer would help greatly. In fact, I fly a 912UL powered Skyranger that uses only a primer and no choke. My primer works by injecting fuel into the manifold pressure output port and works well. The Bing carbs have primer ports and and I do wonder why they are not more widely utilized. It would seem to me that both a primer and choke would be best in cold weather.

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Roger Lee



Joined: 10 Jan 2006
Posts: 1452
Location: Tucson, Az.

PostPosted: Fri Dec 04, 2009 7:50 pm    Post subject: Re: 912 80hp violent vibration on cold start Reply with quote

If you live in a cold climate the best thing you can do for you engine is get a pre-heater. Heating just an oil tank on the 912 is no good because it is a dry sump. You need to heat the cylinders, block and oil tank. The engine metals on a really cold start are not a good thing. I just installed another pre-heater in for another 912 owner. On a day when it is in the teens the engine is 85F with a good pre-heat system.

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PostPosted: Sat Dec 05, 2009 3:23 am    Post subject: 912 80hp violent vibration on cold start Reply with quote

There is no choke on a Rotax 9xx, it's a starting carburettor and won't
work unless the throttle is closed.
Graham

Goodone wrote:
Quote:


Why don't more folks use a primer with the 912? It would seem to me that the use of a primer would help greatly. In fact, I fly a 912UL powered Skyranger that uses only a primer and no choke. My primer works by injecting fuel into the manifold pressure output port and works well. The Bing carbs have primer ports and and I do wonder why they are not more widely utilized. It would seem to me that both a primer and choke would be best in cold weather.




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Dick Maddux



Joined: 24 Jun 2008
Posts: 513
Location: Milton, Fl

PostPosted: Sat Dec 05, 2009 5:43 am    Post subject: 912 80hp violent vibration on cold start Reply with quote

I have a primer on my 912UL and I still get rough starts on occasion and I keep my airplane in a heated hanger in the winter (yes it does get to 25 degrees here in NW Florida on occasion) So I don't believe a primer is the total answer.
When I bought the aircraft from a guy in Mass he insisted on starting the engine during my purchase inspection and it was 17 degrees outside! It was a horror show! I tried to get him to stop but the engine finally started after many attempts and applications of primer. I finally have a method that seems to work for me when it is cold. Three primer squirts three revolutions on my throttle from full closed to open(Vernier) This doesn't always work but is close. If the engine stumbles and hangs up at 1200 rpm I shut it down immediately and try again. It will generally start idle around 1800 rpm.
These engines can be temperamental when cold. I know if my airplane was at ambient temp when cold it would be that much worse. When it is warm outside it is no problem to start except it will sometimes diesel and run backwards a few blades on shutdown when it's real hot outside. I have found a switch to premium fuel in the summer seems to help.
Dick Maddux
Kitfox 4
912 UL
Milton,Fl
[quote][b]


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rparigoris



Joined: 24 Nov 2009
Posts: 471

PostPosted: Sat Dec 05, 2009 11:46 am    Post subject: 912 80hp violent vibration on cold start Reply with quote

Hi Dick" So I don't believe a primer is the total answer."This is given from a guy who has yet to start my 914, but have experiance with type 64s and other carbs on motorcycles. First off on my 1988 BMW R100GS, the first thing to snot up is the enriching jet that is located in the float bowl. You don't need much to hurt cold weather starting. If I get stuck in cold and can't get it to start, it is difficult on that bike to remove air cleaner duct to hand choke, thus if I blow into overflow on each carb it forces raw fuel into carb and i have always gotten a start after that. If you got stuck and don't have a primer this is an easy to do alternative in an emergency. Rotax has information on starting problems in real cold temperatures, and they have alternative parts that enrichen further, however they say you should switch to original parts when temps rise. You want good RPM cranking, thin oil and good battery and a heavy duty starter are not going to hurt. It is true best have entire engine warm when starting in cold, but if I were stuck warming up spark plugs has always done wonders. In short, before anything further make sure your carb is absolute clean, spins motor fast, and make sure gap on plugs are not too large.Ron Parigoris [quote][b]

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michaelrosenberg



Joined: 25 Aug 2015
Posts: 3

PostPosted: Tue Aug 25, 2015 2:55 pm    Post subject: Re: 912 80hp violent vibration on cold start Reply with quote

Hi guys, I know this thread was from a while ago, however did you ever find the solution Froghair. This is the only post I have found with identical problems to mine. It is only on cold start.... However, I am from South Australia and a cold day is in the order of 60F. Hardly cold enough to warrant preheating the engine.

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Roger Lee



Joined: 10 Jan 2006
Posts: 1452
Location: Tucson, Az.

PostPosted: Tue Aug 25, 2015 4:46 pm    Post subject: Re: 912 80hp violent vibration on cold start Reply with quote

Most of the time these starting issues come from only a couple of things.

Weak battery and or too small a size wire for the starting system and or battery.

Carbs not synced,

Ignition modules going bad. The starter circuit in one module may be dead and the second is trying to make due. Usually the 2006-2007 modules,

Idle rpm too low or too high,

Old black colored starter. The newer gold colored high torque starter is better. It doesn't turn faster just harder.

Using a primer system instead of the regular choke setup. (This is a big one.)

Air filters too dirty.


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michaelrosenberg



Joined: 25 Aug 2015
Posts: 3

PostPosted: Tue Aug 25, 2015 5:16 pm    Post subject: Re: 912 80hp violent vibration on cold start Reply with quote

Cheers,

The battery is brand new, cables are fine etc. Carbs are synced and floats are fine. It does have the black start motor however it cranks over quite hard and starts almost instantaneously,

The issue is when it starts it has an ungodly resonance for around 10-30 seconds. In that time it won't accept any throttle response until it comes out of that period then it runs smooth.

There are a few reports on the forums of indentical issues, however none seem to report back with the issue or solution.

Michael


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PostPosted: Tue Aug 25, 2015 5:54 pm    Post subject: 912 80hp violent vibration on cold start Reply with quote

Try increasing the idle speed or open the throttle a touch more at startup

Dave

Quote:
On Aug 25, 2015, at 8:16 PM, michaelrosenberg <mickyrosenberg(at)icloud.com> wrote:



Cheers,

The battery is brand new, cables are fine etc. Carbs are synced and floats are fine. It does have the black start motor however it cranks over quite hard and starts almost instantaneously,

The issue is when it starts it has an ungodly resonance for around 10-30 seconds. In that time it won't accept any throttle response until it comes out of that period then it runs smooth.

There are a few reports on the forums of indentical issues, however none seem to report back with the issue or solution.

Michael




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rickofudall



Joined: 19 Sep 2009
Posts: 1314
Location: Udall, KS, USA

PostPosted: Tue Aug 25, 2015 6:09 pm    Post subject: 912 80hp violent vibration on cold start Reply with quote

Micky, What is your startup procedure? How do you set the starting carburetors and the throttle? What is your normal, all warmed up idle speed?

Rick Girard
On Tue, Aug 25, 2015 at 8:16 PM, michaelrosenberg <mickyrosenberg(at)icloud.com (mickyrosenberg(at)icloud.com)> wrote:
Quote:
--> RotaxEngines-List message posted by: "michaelrosenberg" <mickyrosenberg(at)icloud.com (mickyrosenberg(at)icloud.com)>

Cheers,

The battery is brand new, cables are fine etc. Carbs are synced and floats are fine. It does have the black start motor however it cranks over quite hard and starts almost instantaneously,

The issue is when it starts it has an ungodly resonance for around 10-30 seconds. In that time it won't accept any throttle response until it comes out of that period then it runs smooth.

There are a few reports on the forums of indentical issues, however none seem to report back with the issue or solution.

Michael




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michaelrosenberg



Joined: 25 Aug 2015
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PostPosted: Tue Aug 25, 2015 6:31 pm    Post subject: Re: 912 80hp violent vibration on cold start Reply with quote

I have tried many different options for starting from a lot of different advice. All options end with the same issue which is perfectly describe from Froghair on the initial post of this thread.

Basically, cold weather starry is:

Fuel pump on (5secs or leave on)
Enriched on
Throttle closed
Start

Engine cranks over well and immediately fires and starts, resonance or shacking happens for 10-30 seconds. Slowely removing enriched or adding throttle has no effect. I can pith the throttle to the firewall and has zero response. Engine probably resonated at around 1000RPM(ish)...... No throttle response means I can not effect this.

Once everything smoothed out I warm it up at approx 2000RPM and it will idle around 16-1800RPM.

Once it moved out of this resonant time, it purrs.

I can only put it down to a fuel delivery or enriched issue. Once I get the engine running smooth at idle, I added some enriched to see what would happen and exactly the same symptoms occurred. Engine wound back to low RPM and resonated again. I kind of expected it to happen in this scenario, how ever the starting issue I have no control over.


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peteohms



Joined: 31 Oct 2007
Posts: 224
Location: Leander, TX

PostPosted: Tue Aug 25, 2015 7:05 pm    Post subject: 912 80hp violent vibration on cold start Reply with quote

I may have had something similar. It turned out to be a sticking float that took a few shakes to unstick.

Pete
Leander, Tx
Kitfox 3


Quote:
On Aug 25, 2015, at 8:16 PM, michaelrosenberg <mickyrosenberg(at)icloud.com> wrote:



Cheers,

The battery is brand new, cables are fine etc. Carbs are synced and floats are fine. It does have the black start motor however it cranks over quite hard and starts almost instantaneously,

The issue is when it starts it has an ungodly resonance for around 10-30 seconds. In that time it won't accept any throttle response until it comes out of that period then it runs smooth.

There are a few reports on the forums of indentical issues, however none seem to report back with the issue or solution.

Michael




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http://forums.matronics.com/viewtopic.php?p=446419#446419












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PostPosted: Tue Aug 25, 2015 8:05 pm    Post subject: 912 80hp violent vibration on cold start Reply with quote

Michael,
1000 RPM is way too low for idle on the Rotax 80 hp engine.  It will always run rough below about 1800 RPM, and idle speeds lower than that are very hard on the gear box.  I am not at all surprised to hear that your idle is quite rough at 1,000 RPM.  Your idle should be 1800-2000 RPM, minimum.  If it runs smooth at that speed, it's fine.
Regards,

Paul Kuntz
On Tue, Aug 25, 2015 at 7:31 PM, michaelrosenberg <mickyrosenberg(at)icloud.com (mickyrosenberg(at)icloud.com)> wrote:
[quote]--> RotaxEngines-List message posted by: "michaelrosenberg" <mickyrosenberg(at)icloud.com (mickyrosenberg(at)icloud.com)>

I have tried many different options for starting from a lot of different advice. All options end with the same issue which is perfectly describe from Froghair on the initial post of this thread.

Basically, cold weather starry is:

Fuel pump on (5secs or leave on)
Enriched on
Throttle closed
Start

Engine cranks over well and immediately fires and starts, resonance or shacking happens for 10-30 seconds. Slowely removing enriched or adding throttle has no effect. I can pith the throttle to the firewall and has zero response. Engine probably resonated at around 1000RPM(ish)...... No throttle response means I can not effect this.

Once everything smoothed out I warm it up at approx 2000RPM and it will idle around 16-1800RPM.

Once it moved out of this resonant time, it purrs.

I can only put it down to a fuel delivery or enriched issue. Once I get the engine running smooth at idle, I added some enriched to see what would happen and exactly the same symptoms occurred. Engine wound back to low RPM and resonated again. I kind of expected it to happen in this scenario, how ever the starting issue I have no control over.




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PostPosted: Tue Aug 25, 2015 8:10 pm    Post subject: 912 80hp violent vibration on cold start Reply with quote

Oops, sorry, I missed the part about no throttle response, which is obviously the real problem.  Yes, it sounds like a fuel delivery issue, but I don't have any good ideas to offer.
Paul Kuntz
On Tue, Aug 25, 2015 at 9:03 PM, Paul Kuntz <paul.r.kuntz(at)gmail.com (paul.r.kuntz(at)gmail.com)> wrote:
[quote]Michael,
1000 RPM is way too low for idle on the Rotax 80 hp engine.  It will always run rough below about 1800 RPM, and idle speeds lower than that are very hard on the gear box.  I am not at all surprised to hear that your idle is quite rough at 1,000 RPM.  Your idle should be 1800-2000 RPM, minimum.  If it runs smooth at that speed, it's fine.
Regards,

Paul Kuntz
On Tue, Aug 25, 2015 at 7:31 PM, michaelrosenberg <mickyrosenberg(at)icloud.com (mickyrosenberg(at)icloud.com)> wrote:
Quote:
--> RotaxEngines-List message posted by: "michaelrosenberg" <mickyrosenberg(at)icloud.com (mickyrosenberg(at)icloud.com)>

I have tried many different options for starting from a lot of different advice. All options end with the same issue which is perfectly describe from Froghair on the initial post of this thread.

Basically, cold weather starry is:

Fuel pump on (5secs or leave on)
Enriched on
Throttle closed
Start

Engine cranks over well and immediately fires and starts, resonance or shacking happens for 10-30 seconds. Slowely removing enriched or adding throttle has no effect. I can pith the throttle to the firewall and has zero response. Engine probably resonated at around 1000RPM(ish)...... No throttle response means I can not effect this.

Once everything smoothed out I warm it up at approx 2000RPM and it will idle around 16-1800RPM.

Once it moved out of this resonant time, it purrs.

I can only put it down to a fuel delivery or enriched issue. Once I get the engine running smooth at idle, I added some enriched to see what would happen and exactly the same symptoms occurred. Engine wound back to low RPM and resonated again. I kind of expected it to happen in this scenario, how ever the starting issue I have no control over.




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PostPosted: Tue Aug 25, 2015 8:20 pm    Post subject: 912 80hp violent vibration on cold start Reply with quote

Have you tried this. This technique was developed by a neighbor and fellow
Kitfox builder owner. His engine is one of the very early 912 ULSs - long
before slipper clutches and soft start modules. I also use it on my 80 hp
and it starts running very smoothly. This is the method. Throttle full
out, pull choke - ignitions off, crank for ten to fifteen seconds. Wait ten
or fifteen seconds throttle in one to 1-1/2 turns. Ignitions both on, pull
choke crank. Mine usually starts over revved a tad but smooth as glass.
Lowell
--------------------------------------------------
From: "michaelrosenberg" <mickyrosenberg(at)icloud.com>
Sent: Tuesday, August 25, 2015 7:31 PM
To: <rotaxengines-list(at)matronics.com>
Subject: Re: 912 80hp violent vibration on cold start

Quote:

<mickyrosenberg(at)icloud.com>

I have tried many different options for starting from a lot of different
advice. All options end with the same issue which is perfectly describe
from Froghair on the initial post of this thread.

Basically, cold weather starry is:

Fuel pump on (5secs or leave on)
Enriched on
Throttle closed
Start

Engine cranks over well and immediately fires and starts, resonance or
shacking happens for 10-30 seconds. Slowely removing enriched or adding
throttle has no effect. I can pith the throttle to the firewall and has
zero response. Engine probably resonated at around 1000RPM(ish)...... No
throttle response means I can not effect this.

Once everything smoothed out I warm it up at approx 2000RPM and it will
idle around 16-1800RPM.

Once it moved out of this resonant time, it purrs.

I can only put it down to a fuel delivery or enriched issue. Once I get
the engine running smooth at idle, I added some enriched to see what would
happen and exactly the same symptoms occurred. Engine wound back to low
RPM and resonated again. I kind of expected it to happen in this scenario,
how ever the starting issue I have no control over.


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