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After many attemps to get the Rotec TBI to work satisfactoraly, I have finally given up on that idea and putting the standard bing carbs back on the Rotax 912ULS. Given the ridiculous price of the rotax air box and drip tray setup, I am thinking of just putting an air filter driectly on each carb.

Have any others gone down this path and if so, what did you do for a drip tray.

I would imagine if the floats fail, fuel would run down the exhaust which would probably end in tears. Being a tail dragger, I think fuel wouldn't collect in the intake system to cause hydraulic lock which is the other reason the Rotax manual suggests it needs to be drained away.

Any advice and pictures would be a great help.

I bought a couple of these used, and they work fairly well. I'm running separate filters, not the airbox.

https://www.leadingedgeairfoils.com/cat ... gory/3334/

The tube that comes out is really small, and I'm thinking of enlarging mine. For some reason, the note on the parts list says these are only for use with the airbox. Not sure if there's a reason not to use it with separate filters, or if it was just never done that way by Rotax.

I'd really like to hear more about the Rotec TBI experiments. I've been considering a homebrew EFI, or a single carb setup since I really hate the dual carbs.

13brv3 wrote:I bought a couple of these used, and they work fairly well. I'm running separate filters, not the airbox.

https://www.leadingedgeairfoils.com/cat ... gory/3334/

The tube that comes out is really small, and I'm thinking of enlarging mine. For some reason, the note on the parts list says these are only for use with the airbox. Not sure if there's a reason not to use it with separate filters, or if it was just never done that way by Rotax.

I'd really like to hear more about the Rotec TBI experiments. I've been considering a homebrew EFI, or a single carb setup since I really hate the dual carbs.

Thanks for the reply Rusty,

I looked at those drip trays and it looks like they would only capture the fuel coming out of the compensating tube and any fuel flowing out of the throat would enter the filter then drain out behind this tray, maybe they are longer than the parts illistration shows them. Do they extend very far past the back of the carb to capture this?

I will create a new topic re the TBI

Hi Murray,

Those drip trays only cover the fuel bowl and carb, so they won't catch anything from the filter. My filters are on a short angled piece of tubing since they would have hit the engine mount if they were installed like usual. That puts them behind the exhaust, so I wasn't as worried about that. Those trays fit so tight that I've thought about just making my own trays, which wouldn't be that hard to do.

13brv3 wrote:Hi Murray,

Those drip trays only cover the fuel bowl and carb, so they won't catch anything from the filter. My filters are on a short angled piece of tubing since they would have hit the engine mount if they were installed like usual. That puts them behind the exhaust, so I wasn't as worried about that. Those trays fit so tight that I've thought about just making my own trays, which wouldn't be that hard to do.

Thanks again Rusty,

I will probably do something similar to what you have and most likely make my own trays based on that

I have never experienced an overflow from by float chamber(s) so am of the opinion that the risk is low. Even so thee is no reason why the breather/overflow tubes can not be extended so that any fuel exiting would be unlikely to contact hot exhaust system.

The one proviso that Rotax require, is that the breathers pipes open in an area of the same air pressure as the inlets to the carburettors.

There is one large disadvantage to fitting a drip tray as supplied by Leading Edge - they make the job of periodic/emergency inspection of the float bowl, exponentially more difficult.

Personally I can see only one advantage to a drip tray - it may shield the float bowl from some of the radiant heat given off by the exhaust system

Heat shielding is a big reason in my mind. Even with the trays, I still wouldn't leave those vent tubes stuck under the bale like they suggest. I tried them various places, always out of dripping range of the exhaust, but ended up just fitting them into the ends of the filters as many suggest. It takes about 30 seconds to loosen the screw on the carb clamp to remove it from the intake, so not really a big problem getting to the bowl if needed.

I have seen photos of drip trays made out of sardine tins (or similar) - effective (fuel spill catch & heat shield), light weight, low cost and a useful by-product of a perverse taste.

I suspect modified aluminium fizzy drink cans may also serve the purpose.

13brv3 wrote:Hi Murray,

Those drip trays only cover the fuel bowl and carb, so they won't catch anything from the filter. My filters are on a short angled piece of tubing since they would have hit the engine mount if they were installed like usual. That puts them behind the exhaust, so I wasn't as worried about that. Those trays fit so tight that I've thought about just making my own trays, which wouldn't be that hard to do.

What filters are you using? Are the angled tubings reducing type or just 2"? I have to angle mine too but not sure if there would be too much restriction if I got straight 2" elbows

I'm using the normal tapered filters, with these 2" silicone 45 degree hoses:
https://www.amazon.com/gp/product/B085XX4HTH/?th=1

I cut the hose as short as possible to keep it from being too floppy, and kept them even in length. It's been the least of my problems. The picture I'll attempt to attach shows the offset filters. It's also a humorously warped picture. I guess I was reaching up with the phone at an odd angle. There is no engine offset, even though the picture makes it look like I have about a foot of offset to the right :-)

Rusty