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  #11  
Old 06-15-2014, 05:53 AM
Avengerboss Avengerboss is offline
 
Join Date: Dec 2008
Location: Ramona, Calif.
Posts: 317
Default Rotax problem

We've experienced that also and it was the float adjustment . It was set to low and one carb was actually running out of fuel, and it always happened at take off power, not sure why those carbs do that but they do. Saw it on an older 80hp and the newer 912S.
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  #12  
Old 06-15-2014, 11:15 AM
roger lee roger lee is offline
 
Join Date: Sep 2013
Location: Tucson, AZ
Posts: 322
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The float arms should be 10.5mm from the edge of the bowl seat to the top of the float arm. You can set a MM ruler (or buy the expensive Rotax tool gauge) on the bowl edge and slide it over to the float arm. If it is too high or low the tab that the Viton tipped needle valve is attached to can be bent slightly to make the arms hang higher or lower. The carb needs to be off the engine and upside down to do this. Check both sides of the float arm to make sure each float arm is equal to the other.
Sometimes if you have an old needle valve the internal spring goes bad and it won't control the level well. Then you typically have a little flooding.

This is very easy to do.
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  #13  
Old 06-15-2014, 10:11 PM
the_other_dougreeves the_other_dougreeves is offline
 
Join Date: Jan 2006
Location: Dallas, TX (ADS)
Posts: 2,180
Default

Experienced something like this with a J3300, which uses almost the same Bing carb (single vs double). It was carb bowl contamination.

TODR
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  #14  
Old 06-16-2014, 10:38 AM
9Driver 9Driver is offline
 
Join Date: Dec 2006
Location: Fernandina Beach, FL
Posts: 61
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Have ordered float bowl gaskets. Will check/clean bowls and jets and then fly or attempt to . Will post results. Thanks to all for info/suggestions.
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  #15  
Old 06-23-2014, 10:49 AM
9Driver 9Driver is offline
 
Join Date: Dec 2006
Location: Fernandina Beach, FL
Posts: 61
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Removed carb float bowls. Found a few very small black flakes? particles? in both bowls too small to identify. Cleaned bowls, removed and blew out jets. Reinstalled with new gaskets. Ground run OK. Flew this morning - smooth on takeoff and throughout the entire flight.

Many thanks for all the help.
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  #16  
Old 06-23-2014, 12:34 PM
roger lee roger lee is offline
 
Join Date: Sep 2013
Location: Tucson, AZ
Posts: 322
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small black particles are either rubber hose specs or the floats were flaking. In another 3-10 hrs. pop the bowls off the bottom and check once more to make sure it isn't going to be a repeat issue at the wrong time.
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  #17  
Old 06-26-2014, 10:42 AM
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ScottSchmidt ScottSchmidt is offline
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Join Date: Dec 2005
Location: Salt Lake City, Utah
Posts: 1,158
Default My Experience so far

We have around 50 hours on our -12 and have experienced this exact problem. In October we replaced the old style fuel pump with the new one (just as a pre-caution). About a month ago we did a takeoff and the engine went very rough right after adding take-off power and then could not replicate it again. Then a couple of weeks ago it was happening on the ground almost every time power was added. Did the "mag check" and found that it did not change anything. So we pulled the carbs and replaced all the suspect parts everyone has talked about here. We started it up and did lots of full power run ups and everything appeared to be great so we took off and flew around. I did notice the fuel pressure dropped a little when climbing, something I had not noticed before. So, over the airport (probably should have tried this on the ground first:roll eyes I pulled the fuse of the electric fuel pump. I have done this many times and typically the fuel pressure drops a few psi and then comes right up. This time it dropped to .1 psi and the engine started missing. It came back to life after I put the fuse back in and we landed. On the ground I pulled the fuse again and it did the same thing. Went to about .1psi but this time the engine kept running and didn't go rough.

We have a new mechanical pump coming and will update everyone on what we find. We may check the float adjustment as well.

Everyone may want to try this test on the ground and see if there was a bad batch of the new style fuel pumps out there.

The other thing we cannot figure out is the fuel smell on takeoff during this time. We never had it until these past few flights and can sometimes see a little fuel in the aluminum catch under the carbs. If the mechanical pump is bad, why would that cause fuel to come out of the carb. It does not look like anything has come out of the overflow tube on the mechanical pump.

I will update after the new pump is added and more checks are carried out.
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  #18  
Old 06-26-2014, 11:22 AM
RFSchaller RFSchaller is offline
 
Join Date: Oct 2010
Location: Phoenix, AZ
Posts: 2,820
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I think this illustrates the downside of not having a fuel pump switch. If the electric is running all the time you may not find a mechanical pump failure until both are inoperative. I've posted before on the mod I did to wire the electric pump into the unused Nav light circuit that gave me a simple way to add a control switch. I conduct run ups on the mechanical pump and then turn on the electric as a backup for takeoff and landing.

I understand the argument that a continuous run pump is one less switch for a pilot to forget, but in this case I believe the switched pump is the better design.
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  #19  
Old 06-26-2014, 01:52 PM
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WingedFrog WingedFrog is offline
 
Join Date: Mar 2010
Location: Raleigh, NC
Posts: 863
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Quote:
Originally Posted by RFSchaller View Post
I think this illustrates the downside of not having a fuel pump switch. If the electric is running all the time you may not find a mechanical pump failure until both are inoperative. I've posted before on the mod I did to wire the electric pump into the unused Nav light circuit that gave me a simple way to add a control switch. I conduct run ups on the mechanical pump and then turn on the electric as a backup for takeoff and landing.

I understand the argument that a continuous run pump is one less switch for a pilot to forget, but in this case I believe the switched pump is the better design.
I agree with the fuel pump switch but I believe that leaving it on during flight is safer to avoid vapor locks in the fuel line upstream of the mechanical pump. I do not switch the fuel pump on during ground operations or during run-up. I switch it on just before takeoff and check its impact on fuel pressure before going WOT. I believe this mode of operation allows to detect potential failures on both the electrical and mechanical pumps in a safe place i.e. on the ground on a routine basis.
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  #20  
Old 06-26-2014, 05:53 PM
paul mosher
 
Posts: n/a
Default switch

Perhaps a guarded switch for electric pump and a added item to pre take off check list to ensure mech fuel pump is operating normally
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