I’m hoping someone can help me resolve a rather frustrating issue(s) I’m having with my DA-50 (newest version). A little background.. I have about 10 gallons through the engine. For break-in, I ran 5-6 gallons of Lawn Boy Ashless at 32:1 with an NX 22x8. Throughout the break-in, I left it a little burbly rich on the bottom end. The engine performed flawlessly with incredible power but would almost deadstick intermittently on downlines and would always deadstick in inverted harriers/elevators and inverted flatspins. I attributed this to being possible too rich and loading up. Now that I’ve got ~10 gallons through the engine the problem still exists..

Tuned for solid idle, snappy transition and peak RPM the engine at acts like it is very rich on the bottom end. It will burble, sputter and cough at anything under half throttle. I could deal with the sputtering as the engine runs awesome otherwise. Unfortunately, tuned like this, it will also quickly load up and die in a low-throttle inverted situation like an inverted harrier/elevator. If I lean the low end out enough to take away almost all of the burbling and sputtering, the engine will not idle reliably. The idle RPM will slow decrease until it dies. If I let it idle for several seconds (if it hasn’t already died) and increase the throttle it will either not respond and die or it will cough sputter and then slowly increase in RPM.

I’ve found that the engine richens significantly in flight. If I tune the low end so it will not idle and/or transition well on the ground it seems to be better in flight (in fact, it’s almost too rich, still). The is annoying because I have to start her up and keep the goosing the throttle to keep it running before taking off.. I soldered a brass tube over the carb vent and ran a piece of fuel tubing into the engine box but it didn’t seem to make much difference. I’ve tried every single needle combination possible with no real productivity. I’ve tried both the stock muffler and a Slimline Pitts. I’ve tried different octane gas, different mixtures of oil, etc.. The engine has incredible power (turns an NX 22x8 at 7440RPM rich and a PT carbon 23x8 at 6900) but I’m limited to what I can do because I’m afraid of a catastrophic deadstick. Low, slow, inverted and deadstick is not a good combo!

Sorry for the long-winded post but I’m overly frustrated at this point.. Any assistance would be greatly appreciated.

Thanks,
Abram

The best idea might be to call 520-722-0607 and ask for Brian Hueffmeier
and have him go thru each and every adjustment...

Also may VERY sure your clunk line is not stiff in the tank... That when
you do go inverted it falls to top<which is now bottom> so it can still
pick up fuel...

The tank plumbing is all good. I even eliminated the filling 'T' from the carb line so it's a straigh shot from clunk to carb.[&:]

Hello

I have new DA 50 with very similar problems in QQ yak. I have beat my brains out trying to figure something out. I have spoken to Brian at DA and plan to send the engine back for him to look over. He reminded me that the Internet is terrible place to try to find reliable help. The one thing that I found that changed the behavior was adjusting the pop off valve spring in the carb. I am really suspicious about this being part of the problem. You can at least entertain yourself by searching on !QUOT!pop off pressure!QUOT!. There are not too many posts, but what's there is kind of interesting. You can seach on by screen name to find some of my earlier inquiries.

RJM

When you are making your adjustments make sure they are very small..Im talking a screwdrivers width..the carbs are pretty sensitive..Both of mine have a SLIGHT burble between idle and 1/2 throttle but not enough to load up..What kind of clunk are you using ? Maybe some gunk clogging up the carb?

Does he mean RC Universe in particular?

Find a different place to run your vent line to. If it will run fine on the ground and goes rich in the air that is your problem. Changing the pop of pressure will help, but you are still having a pressure build up problem.

This might not help but my DA50(s) idle and run perfect out of the box. They do burble during break-in but never a deadstick or unreliable idle. After ruling out any fuel or air supply issues, I'd send it back to DA. You should only accept an excellent running engine, which they usually are.

Thanks for the input, all. I have a few updates. I found there was a small leak at the solder joint where I soldered the tubing on the carb vent plate. I patched it up so the vent tube is airtight. I switched to an NX 23x8 prop as I think the 22x8 was not enough load. I went through a complete retune of the engine with a fresh mix of 87 octane and Amsoil 100:1 mixed at 90:1. I have the engine running fairly well turning the prop at 6800RPM’s with a few exceptions. With the low end lean enough for a clean transition with little popping/burbling on the low end the engine will barely idle at all on the ground. I have to keep goosing the throttle or the idle will slowly drop and die. This is huge annoyance when I’m waiting for my turn onto the flightline.. It seems fine in the air, though. If I richen the low end just a little for a solid idle and snappy transition, it’s still very rich in the air – like popping and missing rich. I believe my assumption that the engine was loading up and dieing in an inverted, low-throttle situation was false. I’m now fairly certain it’s leaning out and dieing. In an inverted elevator or flatspin the throttle becomes unresponsive and the RPM’s quickly drop (like it does on the ground idling..). If I’m lucky I can catch it in time, drop the nose and avoid a deadstick. Throttle response also seems a little funky in rolling harriers, but it’s manageable.

Long story short, too rich upright and too lean inverted. I can’t find a happy medium. The engine runs like a champ as long as I’m not inverted with a low throttle setting – which very much limits my 3D repertoire.. I’m at the point where I almost don’t enjoying flying my 50cc plane because I fear a deadstick…

If you are still seeing differences between ground idle quality and flying low speed or idle then you must still have some sort of pressure issue or air turbulance near the carb intake.

Send it back. I have 100% confidence in my DA's and fly low inverted harriers all the time. If you have no confidence in the engine flying the plane will be no fun. Right now you are just buying time until you crash it low and slow in a deadstick.

You should be able to just bolt the engine on and fly with confidence, no modifications or pressure plates/tubes should be needed.

I agree

This site is pretty useful for info on Waldbro carb's. See if any of the problems they list fits yours.

http://tech.flygsw.org/walbro_tuneup.htm

Also not sure if you want to do this but maybe you can flip it over and start it to see if it runs the same on the ground inverted (with the help of a few friends). This would eliminate any pressure problems. BTW, I did notice that you plumbed your vent to the inside of the fuse.

Hey AH
How far away from the carburator is the tank mounted? In relation to the carb, is the tank on the center line? How far off the DA factory needle setting are you on the carburator?

Almost sounds like you are lean on the low end setting... Slowly decreasing in RPM at a idle till it dies. And possibly a touch rich on high end when you richen the low end up to keep it running, causing the gurgling while flying at higher RPM's. Would be interested to know where the needles are currently set.

Oh, have you checked the small screen in the carb for blockage? If you haven't, you might want to before your next outing.
KJ

Update! I popped the motor off and removed the carb. The 2 carb bolts were just barely snugged up so there could have been a potential leak. The gaskets looked well-seated, though. To my suprise, I did find a bunch of crap in the carb screen. I flushed it out, wiped everything down and bolted all back up. I reset the needles, fired it up and when through the tuning and I think it might be fixed! I was able to get a solid idle with a clean transition with little to no burbling/popping. With the engine idling I picked up the plane and held it inverted, sideways, did the hokey pokey, etc.. without a single miss or fluctuation in RPM. If I can scoot out of the office earlier enough tomorrow I'll get some flights in and put it to the real test. We'll see!

AH,
Great job! Since DA reworked the case pressure problems on this motor, it really is a great performer, all most bullet prof. I recommend using the ultra fine Dubro filter in the supply line between the tank and carburetor. (Preferably mounted inside the cowl where it can be accessed for periodic inspection) Ensure that the fuel can line is also ultra screened.
KJ

Thanks, KJ! If this doesn't fix it, my last resort is shipping it off to DA for a check up. I should know tomorrow. It sure ran great in my garage![&:] I'm suprised there was so much junk in the carb. My fuel can clunk is filtered, my fuel filler fitting is filtered and I have a filter in my fill line to the tank. You can never be too careful!

I think you will find tomorrow that you will have a great day flying with an engine that just loves to run now that she can get some fuel.

I'm not sure how or where the gunk comes from, always thought it might be from the moisture drawn into the fuel tank, where it emulsifies to a slim...
Have fun tomorrow, and report back if all is well.
KJ

The very same thing happened to my G45, fuel filters everywhere and yet crap reached the carb screen [:@].

Sure hope that was your problem, and good luck on your next flight.

Karol

Are these the real fine filter screens or those corse metal screens? I use those dubro ones that are really fine. If stuff is getting through those there must be a leak in the screen around the edges.

I use the Dubro #162 Final Filter which has the 130 micron screen. They seam to work really well, but after experiencing the same characteristics with a carb that I was having problems getting dialed in, I found gunk on my carb screen as well.
KJ

I use a weed wacker clunk / felt filter on my fuel jug's pickup, then an automotive filter in the hand pump's feed line and a 130 micron mesh filter in the carb's feed line...still got gunk in the carb screen.

Karol

You almost wonder if the gunk is back feeding from the engine into the carb. That or the gunk is solidifying right there at the screen.

Seems like the thing to do is to periodically check the carb screen before a major problem develops.

Karol

Same story for the most part.. The bottom end richens significantly in flight it still deadsticks inverted at low throttle. I can replicate it every time by doing an inverted elevator at or near idle - as soon as I begin to advance the throttle it immediately leans out and dies. I tried several different needle settings all with similar results. The engine runs great except in the aboved noted situation. I even tried moving my carb vent tube to different locations with no change. Once it got too dark to fly I continued to troubleshoot on the ground. I can repeat it on the ground every time as well. I did, however, find if I richen the bottom end a lot (as in nasty burbling/sputtering/popping) it will not lean out and die when advancing the throttle. With the engine being so rich on the ground, I can't imagine how it would run in the air, though. I guess it's time to send it to DA.[:@]