Steve

My Feedback: (54)

I got to see the new DA 85 in Barry's new SD Yak and it was disapointing. The motor ran good on the ground, but once in the air it ran very bad. He tried tuning the motor to run better but it ended up causing a mishap with the plane and an end to the testing. Once the plane took off, the motor started surging. We know it was a little rich to begin with, but it sounded good on the ground. The motor was tuned twice after the first flight to try and get it to clean up in the air and the final result was the throtle not responding once in the air. The carb is in the motor box and the cowl is open with no baffeling. Is there anyone going through the same thing with this motor that has found the cure?? Thanks.

Steve

bubbagates

My Feedback: (32)

Steve,

Sounds like the vent hole on the carb plate needs to have a tube soldered over it then a host connected to it and run into the fuselage to a place where it will not get direct airflow over it. It sounds as though the air in the cowl is changing pressure to the vent hole causing it to go lean (surging) in the air.

Once you do this then set the needles back to factory and retune.

Yes, even rear carb engines have this problem especially in a round cowl. A round cowl plays havoc on carbs

Steve

My Feedback: (54)

Thanks Bill,
I let him know he may have to block off the engine box where the carb is and run the vent tube past that into the fuse, or even outside the pane by the landing gear. Its worked for me on other engines, but I have no first hand knowledge with the DA 85.

krayzc-RCU

My Feedback: (31)

can you send a pic just to make sure on one spots anything from the pic. I 2 have the 85 and its smooth on the ground and in the air this is how my motor/carb area looks.

Steve

My Feedback: (54)

Thanks for the photos. Did you run a diaphram hose?

krayzc-RCU

My Feedback: (31)

no hose on any of 3 of 4 of my gassers

3dd

My Feedback: (6)

one thing that might help.a lot of people think you have to run a gas engine rich like a glow engine.that is not the case,you are only doin harm to a new engine.the amount of oil 32:1 for the mix is how you richen a gas engine up.set it to top rpm then back it down 2 or 300 rpm at the most and set the lowend so there is just a hint of burbble at the 1/2 or 1/3 throttle stick range and i bet it cleans up and runs better.in the most extreme cases i have seen you will need to make a cover plate to go over the vent plate on the carb so air can't blast straight on the vent hole.i hope this helps but really rich is not good at all on a gas engine

Steve

My Feedback: (54)

Thanks. We'll definitly use a tach and get the engine tuned better. I think the hose, or plate will be needed on this one as bad as it was running in the air.

3dd

My Feedback: (6)

you can buy a carb plate from tbm's or i take the cover off the carb and cut a soda can the same size and shape drill the four holes and reinstall it .the soda plate will form to the carb plate very easyly and works great

TheEdge

My Feedback: (788)

Sounds like your problem could be more complicated than what comes to my mind but,

Alhough I'm not a huge believer in having to run engines in on the ground with a gallon or so before flight, I have found with some new gas engines that until several tanks of gas are ran through the engine they tend to be unstable, as in eratic RPM's. Getting things worn enough for parts to achieve maximum squish band distribution around the ring and cylinder wall is when the engine runs at its best.

How much fuel had been ran though the engine on the ground to get it to achieve stable reciprocation?

jerdavis

My Feedback: (3)

How about a bad throttle servo?

JD