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914 falters and drops 500 revs over 37 on the map gauge ease the throttle back and runs ok drained and replaced fuel no difference but I think it is fuel related, runs bad at 40 which is full boost , any ideas?

 

 

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914 falters and drops 500 revs over 37 on the map gauge ease the throttle back and runs ok drained and replaced fuel no difference but I think it is fuel related, runs bad at 40 which is full boost , any ideas?

Long shot but check there is no crud build up around where the main jet is. I once trouble shoot similar on an 80 hp UL 912 (Took six goes, carb rebuild bits, float bracket adjustments etc over 6 weekends) and found a crud build up that looked a bit like an 'o' ring at the main jet recess. ( You will need to have a real good look for it; Or I should say I missed it on the first carb and discovered it on the second and then re checked the first; and bingo there was the crud / gremlin.) When cleaned engine ran sweet as.

Cheers

 

Mike

 

 

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Tried everything but I think it may be the right carby bowl leaking noticed fuel wet on the outside so l guess on full boost it may be loosing some air pressure which I guess would throw the engine way out of balance as those cylinders would be lacking some fuel , previous owner has overtighned the bowl ,apparently a common problem, now I have to figure how to fix it, maybe some sealer any ideas?

 

 

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Tried everything but I think it may be the right carby bowl leaking noticed fuel wet on the outside so l guess on full boost it may be loosing some air pressure which I guess would throw the engine way out of balance as those cylinders would be lacking some fuel , previous owner has overtighned the bowl ,apparently a common problem, now I have to figure how to fix it, maybe some sealer any ideas?

I have seen a Rotax 914 operating quite normally with a leaking carby bowl, but it is still possible depending on whether it's just leaking or the fuel level is too high causing flooding.

 

I had a problem with similar symptoms on a 912 UL that turned out to be a faulty muffler. Of course that was the last thing checked, after we'd already turned the carbies inside out several times.

 

 

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Tried linishing bowls using wet and dry on a glass table , it was out a bit , bolted every thing back up but it still weeps when I turn on the pump , I didn't think the fuel level in the bowls would be near the top , anyway ordered new gaskets, hope it fixes it

 

 

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Couple of things from experience,

 

1. Your floats are not set correctly or your fuel metering needle teflon tip is worn, ( there was a batch of floats that ere replaced under warranty due sinking).

 

2. I suspect that the throttle position potentiometer needs calibration, to do this ( and should be done whenevr you balance the carbs) you need software and a dongle.

 

3. The TCU ( turbo control unit) has a logging facility that record exceedances and faults suggste a download and view of that data would be first step.

 

If you are anywhere near Tamworth NSW, I am happy to plug into the TCU and check it out as well as set the carbs up.

 

 

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If the floats are set correctly the fuel level in the bowl should not be at the gasket join. to test this remove your bowl gasket, refit and turn on your pumps if it overflows then the floats are not right or the seat is U/S. the 500 rpm spool back I have seen on a few occasions with this engine and it has always been TCU calibration or wastegate calibration related, there is also a bleed hose located on the right upper intake plenum that feeds a pressure signal to the rising rate fuel regulator, these have a habit of splitting at the join and the result is eratic fuel pressure under load, usually presents as an engine cut when it goes on turbo. the potentiometer in the carb tells the TCU aht percentage of throttle you are at and correlates this to a programmed atmospheric pressur inside the manifold, if its not set right you get a boost spike and the TCU tries to protect itself. when you downloaded your TCU data how many boost exceedance events did it collect?

 

 

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Thanks , I will refit the carby and try the pump test have removed the old gasket which fell apart , reading on other forums it seems to be a common problem , if the bowls are leaking engine runs lean on those cylinders resulting in rough running , apparently if both are leaking engine runs smoother but lacks power , I will check the data , the map gauge stops at 40 , when it passes 37 it starts to die . If I leave the bowl off and hold the float leaver up then turn the pump on would that should show if the needle and seat is leaking.

 

 

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Depending on the hours total time you will find that you have to adjust the floats due to wear on the needle and seat. I do exactly what you have described, hold the float up and have some one turn on the pump. If it does not let fuel through you will have to adjust your float height to put more pressure on the seat.

 

 

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The amount the float drops is adjustable. The float level is a fixed amount specified in the books. Needle and seat wear shouldn't be a lot. Are the floats contacting the bowl or free to move. There could be a piece of lint, rubber or sliver of metal not letting it seat . Check if the float floats in fuel. Your gasket could have damage somewhere. Is fuel pump pressure the amount it should be? Nev

 

 

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Floats are OK to check float height do you measure the gap between the tang and the carby body ,the needle and seat are sealing ok pump on and holding the tang up the fuel flow stops and I can hear it diverting back to the tank via the reg. Ordered the gaskets last night at 5.30 and they turned up this morning ,no complaints about the service as l live 2hours north of Melb.

 

Apparently permatex make a sealer unaffected by fuel unsure whether I should try that as well. I will let you know how I got on ,fingers crossed , getting sick of taking the cowls on and off.

 

 

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Tried everything but I think it may be the right carby bowl leaking noticed fuel wet on the outside so l guess on full boost it may be loosing some air pressure which I guess would throw the engine way out of balance as those cylinders would be lacking some fuel , previous owner has overtighned the bowl ,apparently a common problem, now I have to figure how to fix it, maybe some sealer any ideas

 

q 1 does this aircraft have return line from carby to main tank q2 what is the part number on the fuel pump q3 have the fuel lines been recently replaced q4 what do you mean by common problem apparently for crist sake find a l2 that knows what he is doing before you kill your self blunt enough neil

 

 

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Still leaked with new gasket talking to Wal he seems to think the float height may be to high as the fuel in the bowls which I didn't know ,is nearly at the top so it doesn't need to be out much to make it leak

 

 

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Fixed the leak ,didn't need much adjustment but after blowing down each breather the right one is loosing air past the gasket maybe the body is out of shape left one holds pressure

 

 

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Floats are OK to check float height do you measure the gap between the tang and the carby body ,the needle and seat are sealing ok pump on and holding the tang up the fuel flow stops and I can hear it diverting back to the tank via the reg. Ordered the gaskets last night at 5.30 and they turned up this morning ,no complaints about the service as l live 2hours north of Melb.Apparently permatex make a sealer unaffected by fuel unsure whether I should try that as well. I will let you know how I got on ,fingers crossed , getting sick of taking the cowls on and off.

Hi rhtrudder

Just for info you can get a tool to assist in setting the float hinge bracket. Flood's sell them. You screw it to the carb body and with feeler guage you set the position of the float hinge bracket, this way you get it correct as doing it by sight the bracket may look level / parallel to the carb body but you can get the bracket a little bit out of level and conformity when looking from the end. The tool is well worth the money; I bought mine when getting carb parts at the time of the second service. I should have got them as soon as I needed them the first time. About $30 from memory.

 

I've got no knowledge about the 914's or read about thier maintenace so disregard if not applicable.

 

Cheers

 

Mike

 

Carb Float bracket tool.doc

 

Carb Float bracket tool.doc

 

Carb Float bracket tool.doc

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Wal did mention that I will have to get one I just dropped the level a small amount and it stopped leaking but now are still loosing pressure ,the gasket is made out of paper material and seems to be to hard to seal ,back in my motorcycle mechanic days I reckon they were made of neoprene can't understand why Bing don't do the same. The 912 engine don't pressurise the float bowls so it doesn't matter , starting to reach for some sort of sealer don't know what else to do.

 

 

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Wal did mention that I will have to get one I just dropped the level a small amount and it stopped leaking but now are still loosing pressure ,the gasket is made out of paper material and seems to be to hard to seal ,back in my motorcycle mechanic days I reckon they were made of neoprene can't understand why Bing don't do the same. The 912 engine don't pressurise the float bowls so it doesn't matter , starting to reach for some sort of sealer don't know what else to do.

Don't like to use non rotax part but better than using goo on your carbs. Have a look here-

http://www.ebay.com/itm/Rotax-Reusable-Float-Bowl-Gasket-Nitrile-830-727-/321586624037?hash=item4ae00e7625:m:m6ZZ-OQdP_zWSpmlT9Z28YQ&vxp=mtr

 

 

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