DA 100 Transition Question

[aviti]

I've got a fairly new DA 100. Been running fine except a few times I noticed some hesitation while transitioning from a harrier into a hover. It was so infrequent that I figured the low end was still a tad rich and it was loading up. I decided to tweak the needles on the ground today and the transition is fine unless you let it sit at idle for say 20 seconds and then quickly go to full throttle. It dies instantly like it is lean on the low end. I started richening up the low end and although it started sounding richer on transition, it will still die abruptly if you go from a low idle to full throttle quickly. I tried everything from the factory setting of 1 3/8 out to 2 full turns out and even to 1/4 turn in from the factory setting (and everywhere in between). The high end seems fine and is 50-100 rpm from peak. It doesn't lean out on up lines and turns about 6300 peak on the ground.

My other DA 100 doesn't act like this so I think something may be wrong. I pulled out the needles and nothing clogging, checked the screen in the carb and it was clean. The next thing I might try is to replace all my tank and plumbing in case there is an air leak but I am tempted to just send it off to DA and see what they say. I don't normally go full throttle quickly from idle in the air so it has never quit while flying but I think you should be able to quickly advance the throttle from idle and not die. Any ideas?

[TheTank]

Try going the other way, make sure you are not loading up when its idling. Usually, if you have your low end to lean, you wont be able to start the motor even after it has popped on the choke, it will run a few secs on the prime and die. Try leaning out the bottom end a 16th turn at a time and see if it helps, it it wont start, you have gone too far.

[aviti]

OK, I already went in a ways also. I went about 1/8 turn in from the the factory 1 3/8 and it seemed to die quicker. I will say that it never got to the point that it wouldn't start though. I'll try leaner and report back (plane is in my garage ready to fire up).

[aviti]

I turned the low end in 1/16 at a time until I got to where it would only start on the prime. That was at about 1 1/4 turns out. The I opened it back up 1/16 at a time to where it would start and idle again. This was at about 1 5/16. At this point it still died when I transitioned from idle to full quickly. I then kept opening it 1/16 at a time and it would still die at every step all the way out to almost 2 turns. It will not die if you advance the throttle more slowly but I should be able to hit it pretty quick and go from idle to full right? My other DA never quits even if I'm a tad rich on the low end.

[yakattack]

my engine did this also, turned out to be rich on the high end.

[JimC-MD]

Have you pulled the plugs to check them? The heaviest Kv requirements are durring transition and snap throttle applications. You can see it on an ignition scope when you snap the throttle on a gas engine. If the plugs are getting fouled, this would be the time it would be most likely to fire down the side to ground and not ignite the fuel. You may try cleaning them or burning them off to see if the response improves.

[aviti]

I got the high end needle to a peak of 6300 so I don't think that is the issue. I have not checked the plugs though. It's only got 2 gallons through it but I can pull the plugs and check them. DA's are so easy to run that I have to think there is a problem somewhere. I will probably just send it back to DA. I appreciate the tips though. I'll keep fooling with it tomorrow and if no avail then back to DA (weather turns cold again Monday so I won't miss it for a bit).

[TheTank]

You are letting it warm up for a while before you start testing it... its probably a stupid question, but I wanted to make sure...

[aviti]

Yes, letting it warm up. I probably need to go back and read one of the good threads about how to tune a carb. The more I think about it, the guy that said to try leaning the high end may be onto something. I figured the high end was fine as I was getting peak just under peak RPM but perhaps its still too rich and when I pour on the throttle from idle the high end quickly dumps in enough gas to just kill it. It's worth a try. The engine runs so good otherwise that I hope its just the needles.

[3Dkid330]

Hi Tony,

I had a very similar problem a few months back; no fast transitions, would die out within a few seconds, and power was steadily decreasing at full power runs. (DA 100) We also attempted to retune the engine, but whatever we did didn't work; plus, as far as I know, Gas engines should pretty much be set it and forget when there are no problems, so I figured that something was up. We took out the carb screen, found a little bit of film on it, cleaned it, but still had somewhat of the same result. My dad backed out the needles and found a small piece of red plastic inside one of them (high end if I remember correctly?) which turned out to be the problem; it also explained the bogging in high power runs and overheating. (After all of this, had to retune which was basically like starting from scratch)

Your problem sounds similar but not exactly the same-usually when problems like this happen, it's not the tuning or the engine, so I would check anything else that could be causing it. Possibly a pinhole in a fuel line, or an air leak somewhere? If you can view the fuel line to the carb, it might be a good idea to check it to see if bubbles are flowing to the carb. (With my engine, I did not find any bubbles in the fuel line since the problem was inside the carb and was a small clog) Also your problem sounds like it might just be that it is loading up, but I am hesitant to call it that because it came on fairly suddenly after running fine for a while. (since gas engines usually don't need significant retuning unless something is wrong)

Hope you get it resolved as soon as possible! My engine runs awesome now, not a problem at all with it since the clog in the carb; I'm extremely happy with it.

Hope this helps,
Brandon

[aerowiz]

aviti,

i had the same problem with my da100. i tried everything, made a cover for the hole on the carb plate, changed fuel, changed filters etc.

it was the main needle that was too rich, only slightly but it caused a really bad transition. hope this helps.


aerowiz.

[Diablo]

Rich needle settings never make a gasser quit. Since yours still quits when you richen the needles up, something is wrong. It is going lean on acceleration. Remove the cowl and watch the fuel line with the engine running to see if there are any bubbles in the line. You may also have a leaky gasket between the carb and reed block, or if you have had the covers off the carb, you may have installed the metering diaphragm incorrectly.

[aviti]

Brandon - My problem sounds similar but different also. Top end power is very good even on up lines. Also, I think the problem has been there from day 1, it's just that I didn't find it right away. It's only hesitated a couple times in flight and been so quick you'd barely notice it. I normally don't let an engine sit at idle for 20 seconds and then jam it full throttle so even on the ground I didn't notice it. When I did test it previously, I be pulling the throttle up and down and it still did fine. I pulled both needles and nothing in there, checked the carb screen and it was perfectly clean. I have not ruled out an air leak in the fuel system and will check today for bubbles.

Aerowiz - I'm gonna try leaning out the top end. I thought it was fine as my RPM seemed to peak but I will gradually go leaner. I had a buddy tell me that he had the same problem in his race car and it turned out to be the high end.

Thanks for the help guys.

[aerowiz]

aviti, my main needle is 1 turn out. i have no problems on the uplines and the engine has transformed into a smooth runner.

[aviti]

I leaned the high end down to about 1 1/4 and it still quit on quick transition. It seemed better though (not really sure). I checked the fuel line for bubbles and it looked clean going to the carb. I pulled the plugs and there was quite a bit of black carbon on them. I'm hoping this could be the problem...running too rich and fouled the plugs. I cleaned them and will try it one more time, continuing to lean the high end also.