HardDeck

Hello all

Have DA 50 in QQ yak 54. Engine is great and plane flys great -- but with outside maneuver push (eg outside loop) at low to moderate power setting -- the engine really fades and struggles and sounds like it is going flame out. I've had one flame out with this set up and I think it may have been a result of a 3D outside maneuver. The engine is still breaking in, but otherwise seems to be performing well. Called DA and they suggested may be air flow problem (within the cowl). Somehow I doubt it, but I am looking into this possibility - perhaps with baffles. Seems more like could be a carburetor problem, but I am looking for someone who has had experience with this problem.

Thanks
Dick

mwick

We've been experiencing the same problems in inverted harriers. Extreme Flight Yak. Turns out that about 95% of the problem is the low end being rich during break-in. We are waiting to complete break-in and fine tune the engine with decent synthetic before making any final determination. We have leaned the low end quite a bit from where DA had it set, but still no lean runs. I don't think we are going to get the fine tuning on a 32:1 mix that we will with 100:1.

Josey Wales

My Feedback: (61)

Yep its the low end most likely..When I first was flying my Edge I did a blender and the engine almost quit..I leaned out the low end and 20 gallons later it runs awesome!

rmh

Run a smaller prop -something that cranks at least 6500 min -then lean low end till it it just recovers nicely - leave top end a wee bit rich.
We ran into this same thing on ZDZ years back -on newer engines - It all has to do with air flow changes and the tank position -one or both but -it was always helped by letting the engine run up a bit faster.
This lessens the sensitivity of the mixture.
It's worth a shot.

JoeAirPort

My Feedback: (41)

Just curious, from where and when exactly did you buy the engine? I assume it was brand new.

Tired Old Man

My Feedback: (1)

Another item that I have ssen cause this problem as recently as last weekend is tygon fuel lines that have stiffened up inside the tank and not remaining in the fuel resevoir. That's happened on at least two different planes that I'm aware of.

HardDeck

TThanks all-

I got the engine from DA rebuilt. It is in break in, and my feeling is that low end is probably rich - but why problem with just outside accelerated maneuvers? I don't think its the fuel line clunk cause flys fine inverted. Its just just during outside push maneuvers that it falters. I did move the tank back couple of inches, and I'm using slightly smaller tigon than during first flights. Didn't notice the problem during first few flights, but that may have been just over-site. Just 2 gallon into break in so will need to avoid mishap til change to synthetic and adjust the needles and see what happens. Think I'll try the low end tweak leaning tweak now as suggested. Has anyone resorted to baffles to deal with so called airflow problems DA50?

Thanks for comments!
Dick

By the way - had similar issue with ZDZ 80 - sent back to RC showcase and they modified the carb with full resolution of problem.

Antique

My Feedback: (4)

If the rings haven't seated after 2 gallons they never will..How come no one ever sets the needles on a new engine ?
Good luck expecting a change going from 32-1 to 100-1 if you don't reset the needles at the same time...
If the low end is too lean it won't transition and can't possibly run fast enough to hurt it, it will die first, probably on take off...

HardDeck

Just following manufacturer's recommendations as confirmed with DA by phone, but what do they know?

Josey Wales

My Feedback: (61)

OK..heres what I did on mine..Set the needles to 2 turns out both high and low...Lean the low end 1/8 at a time until it dies when you give full throttle from idle..then ease off about 1 1/6 on the low end and recheck the transition..once you get it where it wont quit from idle to wo..turn the high end out 1 1/16 and fly..Get a Menz NX or MSC 22-8 prop and you should be turning at minimum 6500 rpms as per the manual..Im getting 7200 on a MSC 22-8 and Slimline pitts..Taker her up and fly full throttle straight up..if the engine doesnt sag your good...I got 20 gallons thru mine and it runs better each tank

airbr

My Feedback: (4)

Guys to me this sounds like a high G problem. Like one fellow said about the fuel lines not staying in the fuel sounds about right. A way to find out is to try the same maneuver on a full tank. Also make sure that you have addiquate defferential pressure venting on the tank. See what the manufacture recommends the motor should turn with a specific size prop and that can determine if your needle settings are right. Or do the GLow fuel test by running up the engine on the ground in a vertical and level position then down with help from a friend if the rpm changes you can make the necessary adjustments on the ground.

peso

I have two planes that exhibit exactly the same problem. Both planes have ZDZ 40 engines with canisters and the engines run very well indeed with the exception of the outside loop problem. I have flown with Menz S 20x10, 21x8 and 22x8 props with no difference.
I have found that if I do not throttle down completely during the diving part of the loop the problem is less. Is seems that the engines do not like to be loaded down heavily during the last quarter of the outside loop. Setting the idle lean makes it worse.
Starting the outside loop from inverted also works well. Quite interesting.
One of the engines is 3 years old and has been run quite a bit. The other one is new.

Antique

My Feedback: (4)

The manufacturers DON'T know what prop you're going to use, and what altitude you fly in...I don't care who they are, they don't have ESP...They will typically set the needles at a setting that will be RICH, for people who can't or won't set the needles for their situation...It's called CYA....
The altitude in Tucson is low enough that whateve rich setting they use will be at least rich enough anywhere in the country...An engine set correctly in Tucson, about 1000 feet, will be hopelessly rich at my altitude here in Williams, 7000 feet..
FWIW...Since you seem to be in communication with Dave Johnson, you might ask him who helped with his very first order of 3W(yes, he had those first) engines from Germany..Picked up at Sky Harbor Airport in Phoenix...Somewhere in the early 1990s, I think...
He had to go through customs, and put "made in Germany" stickers on all the pieces/parts in the boxes...

HardDeck

Thanks for comments and suggestions - I tried several of them -- No change re full tank of half empty. No problem with inverted flight. Further update if anyone is interested. I leaned the low end just as Josey suggested. No change. Dies like its going to quit (but so far has not) with outside loops. Sputter is always at same point in the loop - at the bottom - no matter how entered. Of interest, does not occur on first loop, but does on second and thereafter. The radius of the loop and speed doesn't seem to change anything. Does not happen when pushing to inverted after long down line. I'm still clueless. I am going to baffle around the carb intact - thinking it may be an airflow issue - pressuring air into the back of the cowl cut out.
Dick

rmh

Well - 2nd /3rd loops require more power to complete the loop so -carb is opened, climbing up backside of loop and carb is possibly causing puddling as engine then windmills down frontside of loop- just a thought.

Tired Old Man

My Feedback: (1)

I had EXACTLY the same problem in one of my planes. Then saw the same problem again in another plane last weekend. At least check the darn fuel lines inside the tank to see if they have stiffened up! One other thing, is the vent getting pinched in certain maneuvers?

Your carb is at the back of the engine. How the heck can it be experiencing drafting?

Check the easy stuff first.

HardDeck

Hello all - Update observations

Still frustrated with problem - as plane is great and I know the DA50 is great engine -- just can't get the little bugger to run well. I have tried virtually everything suggested here including:
1. leaning the low end (till dies with throttle advance), then tried on rich side -- same with high end.
2. complete revision of fuel system with clunk check, new (larger diameter) tubing throughout.
3. baffles around intake, then without cowl --- no change
4. took the carb apart and didn't see anything obvious - ran the same afterward.
5. moved fuel tank from over the wing spar - back to stock position -> no change.
Few more observations in flight: runs fine normal flight and inside maneuvers. Still all but dies at bottom outside loop and continues to blubber - but barely runs - until plane is righted. I didn' think there was problem with roll to level inverted flight, but now note that if inverted flight is continued for perhaps 30 seconds -- then the engine condition develops and persists until the plane is righted.

I am quite puzzled. Wondering if this could be something in the Walbro carb? I am not sure how this carb works, but it is clear that there is some gravity / g force component to the problem. I have a ZDZ 80 that used to do something like this on outside maneuvers, there was a fix on RC universe web site that involve adjusting the spring in the carb. ZDZ was overhauled and I ask them to address this fix and problem resolved thereafter. Could the spring or reeds or some other gravity sensitive aspect in the walbro be an issue??

Thanks to all for thoughtful suggestions and comments
Dick

rmh

Is your carb a 102 or a 76? They are calibrated differently

Shogun

My Feedback: (2)

If I remember correctly one of the guys here, Nogyro I thinks it was.... had an issue like this and found that the fix was to solder some 5/32 tubing to the center of the carb diaphragm cover. He drilled out a new vent port in the cover and soldered the stock one shut. Then he ran tubing into the fuse out of the cowl. It seems that inside and outside maneuvers will produce different air pressures inside the cowl and the carb will meter differently as the air pressure changes.

On a similar note I had a Cline regulator mounted in a Saito 100 powered 65 inch Kangke Cap that did some odd things like this. I had the Cline mounted on the left side of the firewall, opposite the cylindar which was mounted horizontally to the right side of the fuse. Get this....on a right side knife edge the plane flew fine and the engine ran strong but on a left side knife edge the engine would go rich and lose power. I moved the Cline and the problem went away completely. The reason I'm bringing this up is because the Cline is baically nothing more than a plastic housing with a Walbro needle and diaphragm mounted to it, operation is almost identical to the way the needle/diaphragm works on a gasser. when flying the Cap on a KE I never could get the nose higher than 30 degrees which shows that it doesn't take a huge deviation from level flight to alter the pressure in the cowl on some planes.

JoeAirPort

My Feedback: (41)

I think some cowls actually create a negative pressure on the bottom with those flares. It's there by design to help cool the engine. Draws air out the bottom of the cowling.

HardDeck

In answer to Dick Hanson's question - don't know which type. Looked after your question, don't see any markings on the casing.?

Re cowling issues - this is one of the first things I looked at - but the problem is unchanged with / without cowling in place. As you all know, the rear intake carb is just 1/2 inch from the firewall, but can't see how any problems related to this would vary upright vs inverted and cowling makes no difference as noted. Besides - no one else in noting this problem in the QQ yak (as far as I know).

Still thinking
Thanks
Dick

Antique

My Feedback: (4)

Unless Dave changed carbs, it's not a WT76, although the 76 seems to work better..The numbers are stamped on the casting, usually on the side next to the inlet fitting...

stunt-man

I would agree that it is a carb issue. I had a similar problem with a BME 44, the sagging at the same point certain high G manoeuvers, and it ultimately turned out that the high speed needle was set too lean.

Modified

I have the same issue with my G-62. Tried the vent tube fix( didn't work ), Baffling around the carb( didn't work ), tried a velosity stack( didn't work ). I'm running out of ideas. Also mine sags when inverted for any amount of time, even in a roll. Makes rolling harriers extremely difficult.

peso

Could it be that the gravity will put a force on the diagram in the cab. This force will have a different sign when the plane is inverted.
/PO