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Drip trays...what is normal?


FlyingMonkey

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Normal is clean and no brown (91 oct) or greenish blue (100LL) residue. If you have more stains after a week then change the carb bowl gasket. When you do this make sure you bowl seats up into the groove designed for it in the carb body. If you get one edge not seated (easy enough to see) then it will leak.

You can watch the video I posted on checking for carb bow debris and just change the gasket doing the same procedure. 

 

No more residue than you have it's a good bet it's the bowl gasket.

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Since Lockwood touched the carbs last, I sent them a note with the pics I posted.  Maybe they will have an idea what's happening.  I will look everything over next time I'm out there and see if I can figure it out.  I might have to run the engine with the cowl off to get fuel flowing through and see if I can see where it's seeping.  It's time for an oil change, so I need run the engine to warm the oil before changing it anyway.  

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Andy,

 

gaskets can leak at any time. There is no time limit for a good or bad gasket. Some can leak in 50 hrs. and some may last a 1000 hrs.

 

Until proven otherwise just put in a set of bowl gaskets. That's the problem 90% of the time especially since it is so slow a leak. This is a quick easy fix and it will eliminate one possibility.  The other two places to check, but not as common is the fuel fitting on the side of the carb that feeds them . I doubt this is a bad float because of where the fuel is and the leak is way too slow. The last place that is kind of rare is the MFG machining ports that have the small ball bearing in them. These are sealed with epoxy. They can ooze, but it is usually because someone got over zealous during cleaning or used a sonic cleaner and or too harsh a liquid cleaner on them.

 

Just change the gaskets for now. I do one thing that most don't do here and don't have any repeat offenders.  I rub the new gaskets with white lithium grease. Before anyone goes crazy about grease around a fuel or oil system here is why we use white lithium grease instead of others. This grease is also what we rub our "O" rings down with. White lithium grease is fully compatible with fuel and oil When it gets hot or comes into contact with fuel it dissolves back to an oil base and that tiny little bit gets absorbed back into the fuel or oil. It doesn't clump or gum up anything. Now I said rub the gaskets down on the top, bottom and especially the edges.  Do no glob it on, just rub it in well. This just kind of pre-treats the gasket material. You do not need to get crazy here and wipe any excess off.

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What, they put in cork!?

 

If you can, get the phenolic gaskets next time you replace them. Cork sucks. I had 200 hrs on a new set of carbs and the cork was already degrading rapidly on both.

 

Oh, I don't know, I just know some Rotax bowl gaskets are cork.  Not sure what they are supposed to be for the 912ULS.  I'm guessing these are the right ones, but it does't say what they are made of:

 

http://www.cps-parts.com/catalog/rtxpages/15-00905.php?clickkey=41852

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I have no idea. I goet gaskets from leading edge air foils and they are phenolic. The only time I had seen cork was with the new engine, and they suck.

 

I was just going to order some from CPS or Lockwood (I think CPS is cheaper by a buck).  They are factory Rotax gaskets, so I guess they are whatever they are supposed to be...fiber, phenolic, viton, unobtainium...whatever.   :)

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Andy, I had wet drip trays and had fuel stains running down my engine mount from where fuel leaking from my carbs flooded my trays enough to run thru a hole in the side of the tray where a nylon zip tie to connects that helps hold the tray in place. I had new float gaskets installed and this seemed to eliminate my fuel weep. As usual, Roger's advice is sound. One thing I notice though is the small ball which is epoxied in looks kind of funky in your picture. Hard to tell by you picture and it might also be the clamp on the rubber carb socket needs tightening, but if you still experience wet drip trays after installing new bowl gaskets, you might check out these two items.

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Andy, I had wet drip trays and had fuel stains running down my engine mount from where fuel leaking from my carbs flooded my trays enough to run thru a hole in the side of the tray where a nylon zip tie to connects that helps hold the tray in place. I had new float gaskets installed and this seemed to eliminate my fuel weep. As usual, Roger's advice is sound. One thing I notice though is the small ball which is epoxied in looks kind of funky in your picture. Hard to tell by you picture and it might also be the clamp on the rubber carb socket needs tightening, but if you still experience wet drip trays after installing new bowl gaskets, you might check out these two items.

 

Thanks Dick...my slight leak is obviously nowhere near as severe as yours was.  I will get my mechanic to replace the gaskets, and we will check all of the connections and the epoxied ball when we are in there.

 

The question that has not yet been answered:  How much fuel in the trays becomes a safety of flight issue?  Mine seems to just be a little film with no ppoling at all, but is any fuel in the tray a grounding condition?

 

The weather is so perfect right now here, I hate to not fly while waiting for gaskets to arrive!

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Hmm...I checked yesterday and could not see any stains or other indication on the carbs of where the fuel in the tray had come from.  I cleaned the trays out with Simple Green, and then went flying and checked again after landing,  No fuel in the trays following that flight (6 touch and goes, about 0.8hr total).

 

The day I did noticed the fuel in the trays, I had done some particularly aggressive maneuvering, including some ~2g turns and unloading to 0.2-0.5g for a couple of seconds at a time once or twice.  Is it possible my carbs are fine in normal flight, but higher than normal positive g or less than 1g (but not negative) could cause a tiny amount of fuel to seep out?

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