Bing 64 vent tube discoloration

Sean Griffin wrote:

I agree with Rogers other possible contributing factors.

I note that he also included - "Vibration can cause the bowls to over flow too."

After checking all other factors (including sending my new engine carburettors away for inspection) the only remaining factor, was the non Rotax Airbox & its direct attachment to and support by, the carburettors. Once this had been clanged to a more Rotax like configuration, the amount of fuel being expelled fell to a very small amount 😈

Thanks Sean.  Your post and discussion by Roger among others was very informative.  If after matching the lengths and a carb sync I still have issues, I’ll definitely look at changing the configuration to match a Rotax type instillation.  As mentioned, the orientation of each tube is drastically different from each other so we’ll see what happens after I fix that.  Thanks again!!!

V/r

Alex 

A few inches of rubber hose on the intake between the carbs and the airbox supported elsewhere would work much better for the carbs smooth operation. 

A few inches of rubber hose on the intake between the carbs......."

Would certainly be an improvement however be careful with the rigidity of the "rubber hose". Too stiff & you will only get a marginal improvement.

The joiner between airbox & carb is a low pressure air duct, need only be lightweight and should be as flexible as possible, consistent with durability.

If your installation is as "tight" as mine you will not have space for a "few inches of rubber hose". From memory, I was only able to move my airbox back, from the carb's about 15-20 mm. As stated I used SCAT tube as my duct. The idea being to remove any tendency of the airbox or duct, to restrict the freedom for the carbs to move.

I found the wire "stiffener", on such a short piece of duct, did nothing but make the installation difficult, so removed it.

I made the SCAT slightly long, so when installed had a slight "concertina" /fold to allow relative movement between airbox & carb, without any tendency to be pulled off.

😈

This brings up a question for me.... I used high-temperature, flexible rubber (i.e. black, not translucent) fuel vent lines from my carbs to my Rotax airbox.  So I won't be able to see any discoloration...  I was going to use the "poly" hoses, but thought they might melt...  I started down that path because the drain lines from the carb drip trays were too close to the exhaust.

Hi Michael,

I have used yellow Tygon fuel hose for my breather carb/airbox & airbox drain lines.

Most Rotax owners do not use a fuel drip catch can, as I do, so would not know if any fuel is in fact being expelled. Now that I have modified my airbox/carb arrangement, I have very little fuel in the catch can.

The drain lines from airbox/ drip tray can be routed anywhere you want (away from the exhaust system) as there is no requirement for them to terminate in a similar air pressure zone as the carburettor air intake. 😈