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throttle back 912 uls rough

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6 months 2 weeks ago #18469 by korbike
throttle back 912 uls rough was created by korbike
Coming in to land throttling back and getting a rough engine. New plugs, carbs synced and adjusted. No problem when throttling up. Seems like when the load is gone fuel pressure is rising causing the problem? Goes up to about 7psi. however that's with the old VDO fuel sender, I'm installing the Kavlicos one to get a more accurate reading. The engine has about 270 hrs. 2007, fuel pump is 893110. Thanks for any insight. David

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6 months 1 week ago #18486 by RTX
Replied by RTX on topic throttle back 912 uls rough
David

Do you have a vapor return line installed within your fuel system?

Check your floats to make sure they aren't sinking. Weigh them together and they should not be more then 7 grams.

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6 months 1 week ago #18489 by bh0gue
Replied by bh0gue on topic throttle back 912 uls rough
I had the same problem David; 912uls running rough and a fuel leak on my right carb, but only at idle. My floats weighed 13 grams. I replaced the floats and problem solved!

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6 months 1 week ago #18490 by Pacheco
Replied by Pacheco on topic throttle back 912 uls rough
Hi

Would you explain what a vapor return line is?

Tanks in advance.

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6 months 1 week ago #18491 by RTX
Replied by RTX on topic throttle back 912 uls rough
See Link and look at attachment

www.rotax-owner.com/en/flightsafety/476-ai476

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The following user(s) said Thank You: Pacheco

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6 months 1 week ago #18493 by korbike
Replied by korbike on topic throttle back 912 uls rough
Thanks guys, no leaks but I'll check the floats. I don't have a return line (Kitfox, runs cold if anything) but I'm looking into it. thanks again, David

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6 months 1 week ago - 6 months 1 week ago #18504 by RTX
Replied by RTX on topic throttle back 912 uls rough
In this link you will find a video for the periodic inspection of the carburetor float buoyancy on Rotax 912/914 aircraft engines.

www.rotax-owner.com/en/videos-topmenu/ex...uctions/445-sb912065
Last edit: 6 months 1 week ago by RTX.

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6 months 6 days ago #18523 by korbike
Replied by korbike on topic throttle back 912 uls rough
Ok floats are both under 7 gr, 6.02 and 6.52. Looks like I'll be putting in the return fuel line, any thoughts on installing a check valve? Thanks again for posts. David

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6 months 6 days ago #18524 by Roger Lee
Replied by Roger Lee on topic throttle back 912 uls rough
Check valve or did you mean restrictor with the re-circulation line? The new Corona pump needs this line. The older pumps you may have gotten away without it. Just went to another Rotax school with the guys from KitFox.

Roger Lee
LSRM-A & Rotax Instructor & Rotax IRC
Tucson, AZ Ryan Airfield (KRYN)
520-574-1080 Home (TRY HOME FIRST)
520-349-7056 Cell

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6 months 6 days ago #18527 by korbike
Replied by korbike on topic throttle back 912 uls rough
Hi Roger,
I'm in the process of installing the restricted fuel return line. As I understand it, that fuel return line needs to be jetted at the banjo fitting (I assume this is what they mean by restricted) My question is, do I also need an inline valve (check valve) that only allows the fuel to flow in one direction, in this case to the header tank. I know other people have installed the check valves, I'm just not sure its necessary.
Don't know if I have the Corona fuel pump, mine is made in Italy, part #893110, rotax is 2007, I believe. Thanks again for all the help. David

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6 months 6 days ago #18530 by Roger Lee
Replied by Roger Lee on topic throttle back 912 uls rough
Hi David,
You do have the Corona pump made in Italy. The restrictor is usually just an idle jet soldered into the Banjo bolt outlet side. You do not need a check valve or anything else. The header tank is not pressurized and flow will be under pressure from the engine to the header tank so back flow isn't going to happen. Most think the re-circulation line with the restrictor is just for vapor lock. It's there to also help to control pressure.

Roger Lee
LSRM-A & Rotax Instructor & Rotax IRC
Tucson, AZ Ryan Airfield (KRYN)
520-574-1080 Home (TRY HOME FIRST)
520-349-7056 Cell

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6 months 5 days ago #18532 by korbike
Replied by korbike on topic throttle back 912 uls rough
Thanks Roger,
That makes sense, much thanks to everyone to help put this in perspective. David

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6 months 12 hours ago #18567 by jiott
Replied by jiott on topic throttle back 912 uls rough
I think I disagree with Roger. Without a check valve, on the ground with engine off, fuel will flow backwards, bypassing your fuel shutoff valve, into the carburetors. So for maintenance purposes you will have no way of completely shutting off fuel to the engine. Remember, the header tank, where the return line terminates is constantly under a pressure equal to the head of fuel up in the wing tanks, which is always above your carburetors. The Rotax installation manual calls for a check valve. You must use one without a spring so it opens easily when engine is running. I mounted mine in the return line where it turns up almost vertical into the header tank fitting. This way, gravity keeps the ball on its seat when engine is off-no leakage.

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6 months 8 hours ago #18570 by jiott
Replied by jiott on topic throttle back 912 uls rough
I am assuming a high wing type plane. A low wing may not need the check valve.

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6 months 8 hours ago #18571 by jiott
Replied by jiott on topic throttle back 912 uls rough
I was wrong about Rotax calling for a check valve in the return line-they don't say. However, my argument still stands. My Kitfox build manual DID call for a check valve in that line and it is part of the Kitfox return line package.

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6 months 8 hours ago #18573 by korbike
Replied by korbike on topic throttle back 912 uls rough
Thanks James,
I ordered the return line kit from Kitfox, and it does come with a check valve. Looks like they do recommend it. At least partly because of fire, without a fuel valve to shut off, there would be a constant flow to the engine compartment in the event of a post accident fire. I like your location for the valve, makes sense. Much thanks to everyone on this subject. David

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5 months 5 hours ago #18913 by korbike
Replied by korbike on topic throttle back 912 uls rough
Ok, synced carbs, checked floats, installed return fuel line and check valve, balanced prop, and replaced the rubber hoses on the balance tube. It turns out that the previous owner had pinched the aluminum balance tube at the end by about 50%, yep that makes a difference! Much smoother now!
However I still have an erratic fuel pressure any where from 3-7 psi? Any ideas, I have changed over to the Kavlico and mounted it to the firewall, same odd readings as the VDO. Any thoughts on replacing the fuel pump or trying another Kavlico sender? Dynon D180 firmware was just updated by the factory? Thanks David

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5 months 4 hours ago #18916 by Roger Lee
Replied by Roger Lee on topic throttle back 912 uls rough
You may need to go into the D180 menu and pick a different sensor number since you switched from VDO to Kavlico. You might try checking the grounding on the Kavlico and the D180.

Roger Lee
LSRM-A & Rotax Instructor & Rotax IRC
Tucson, AZ Ryan Airfield (KRYN)
520-574-1080 Home (TRY HOME FIRST)
520-349-7056 Cell

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4 months 4 weeks ago #18917 by korbike
Replied by korbike on topic throttle back 912 uls rough
Thanks Roger,
I changed the setting in the Dynon when I put in the Kavlico, #6 I believe. I'll run another ground from the sensor to the Dynon and report back. It will be a couple days before I can test it out. Thanks again. David

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4 months 3 weeks ago #19041 by korbike
Replied by korbike on topic throttle back 912 uls rough
No joy on changing the ground. Ran a larger separate wire to the ground on the case, same erratic moves, from (2.1 - 7-2) never really stays at one place. When it hits the alarm, its just for that second, doesn't stay there. I did accidentally drop the sensor on the floor before I put it in, but its doing the same thing that the VDO was doing before, so not sure that had any effect. It does seem like a sensor issue but I'm thinking about changing the fuel pump, at least I'll know its not the pump? David

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