Stuart G

I have a DA50 in a comp-arf 2.3 extra and whilst flying on mid range and doing aerobatics with the throttle at about half the engine burbles, I am using the MTW canister exhaust that comp-arf supply. I have leaned the low needle quite a bit but it still does it. have I got to lean it more or is this problem due to the hole in the diaphragm cover facing forwards and being effected by changes in pressure? The engine is not runin yet and not being run on fully synthetic oil yet so am i expecting too much too soon?.

Cheers.
Stu.

famousdave

My Feedback: (61)

The DA50 is going to run like crap for the first few tanks... don't sweat the burbles until after you run a gallon or two through it. You are only concerned with three things at this point - NO deadsticks, keeping the engine cool, and seating the rings. Ignore the burble.. it just means its running rich which is OK for new engine.


Once you have a gallon or two run through it and its still blubbering away...
You need to pay attention to two things - your low needle is too rich (high needle may be as well) ... and the length of the headpipe to the can may be too short.

Tune the engine so that WOT produces max RPM, then back needle off (richen) until RPM drops about 200 - do this by ear.. no real need for a tach. Once set, adjust the low needle until a rapid transition from idle to WOT produces a slight hesitation. Back off (richen ) the low needle until that hesitation JUST goes away.... low needle is set where it needs to be once transition is very clean. Re-check high RPM again. Repeat the process if necessary until engine runs smooth. FLY the engine, don't just try to get it right on the ground... take the cowl off if needed to get access to the needles.

If you cannot get the engine to stop blubbering with the needle adjustments - your headpipe is most likely too short. The headers are adjustable as are the slip collars. Cans are meant to be tuned to the engine and some times moving the pipe length out can make a huge difference. I do this only after the needle changes. In general the longer the pipe the better on cans so play with it... move the pipes out and see if there is a diff.... you might even have to move them IN and trim the headpipe to get the right length. Usually you can find the ideal length too from posts here on RCU... I found my QQ106 length this way... worked perfect first time...

Just as an FYI - there really are no "pressure" issues with the DA50 (or any rear mounted carb)... despite the chatter - its more of a myth than fact. The mods that DA made were to make needle tuning easier and to prevent fuel from pooling in the reeds at low RPM - all transition or burble issues can be resolved in the needles (assuming the carb is not bad)... all it takes is patience which most people don't seen to have...


DP

pe reivers

Desert...
I would not call it that. I think it's more like Walbro ignorance, which is a curable condition [X(]

Midrange burbling (running rich midranfe) is cured by decreasing the idle needle (and if need be richening the H-needle), until the burbling stops, and the engine runs down nicely, and will spin up nicely. Settings will change with running in, so a re-adjustment now and then is in order, until these needle things settle. It takes some feeling for the engine what is just right, and what is too lean. Too rich does not hurt much, too lean means deadsticks.

Stuart G

Thanks for your replies guy's, I guess I will just have to be patient and run more fuel through it then adjust low needle a bit more. As far as the length of header goes I have not altered the standard length and connot make it any longer as the can will not go any further back as it will hit the wing spar, but i will be able to shorten it if needle adjustments are not the cure.

DiscoWings

My Feedback: (76)

Every DA50 I have seen does this, if you are succesfull and eliminating this by tuning, it will be amazing. From what I understand this just how DA-50s run; great power on the high-end but midrange is not so great...[&o]

Josey Wales

My Feedback: (61)

Its true..I have a new one with 1/2 gallon thru it and one with 24 gallons thru it..the burbling will go away after about 8 gallons..at least it did for mine..

famousdave

My Feedback: (61)

There is a diff between a slight "ugly" sound .. which is the normal DA midrange sound and an all-out burble.... burbling is horrible.. you know it when you have it. . You are right though... DA's sound much better at WOT than in midrange.... that's the walbro. The big 3Ws use tillotsen carbs.. they have very little burble and a much better midrange... but tuning them is a PITA.... you get something but you give up something... nothing is free!

DP