DA100 acting strange
 

I have a DA100, slimline mufflers, PT 27x10 prop. It has 30 flights on it.

When it was new it ran quiet and smooth at idle and was able to idle around 1,000 - 1,100. That was at factory recommended settings... After 4 or 5 flights I tuned the top and bottom and it was running great.

After about 22 - 23 flights it began to act "weird" on the bottom end. First it was hard to start - I figured out it was a tad too lean on bottom even though it was not hesitating on run up it was not idling down properly (idle was staying up then eventually dropping after 10 seconds... sometimes goosing it would get the idle to drop.)

I should mention that the temperature had dropped from +20c to around 0c now.

So - now I have the idle backed out about 1/8 from where it was and it starts easily and idles down correctly, the top end is tuned to 6,375 RPM (thats max.)

So the issue is it runs rough at these needle settings in the bottom 1/8 throttle or so and will only idle at 1,200... no less. It's very bouncy at this idle setting and sounds rich and LOUD in the air. It is reliable though and is not over heating (at least I can't detect any signs of it.) Moving the idle even a hair makes it lean again (as in when I cut throttle the idle comes down to about 1,500 then after 10 seconds or so drops to 1,200 and almost quits... like it's loading up or maybe starving?) The power in the air is great and past 1/3 throttle it is very smooth and quiets right down (but straight and level only needs about 1/4 to 1/3 throttle.)

I don't know. I guess maybe I should re-set to factory and re-tune. It was running so great at first. Kinda frustrating.

I never had issues tuning my ZDZ80's or DA50... and I know how well it can run.

I have looked over the fuel system and throttle servo linkage. Everything seems okay.

RE: DA100 acting strange
 

Just a clarification - at 1,400 RPM and up the engine is fairly smooth on the ground. It's just below 1,400 it starts really jumping around - almost more like a miss than a loading up. Hmmm... maybe I'm still lean on the bottom?

Could be I have 2 problems? Maybe I should put a plate over the carb in case some air is blowing on the vent hole causing it to richen a bit in flight? Starting to think maybe I'm lean ont he ground and rich in the air - that would explain the symptoms I think.

I'd better check my ignition battery too ... any other suggestions?

RE: DA100 acting strange
 

The engine getting hot will cause this as well.
You may need to redirect some of the air flow to improve cooling.

RE: DA100 acting strange
 

Okay - now I feel stupid :)

I took the cowl off and gave everything a really good once over:
1. Both plugs were loose. If the DA caps didn't fit so good they would probably have fallen out! Yes I did check them but that was about 15 flights ago - my bad. They are good and tight now.
2. The plugs were too black. Not fouled but getting there... I cleaned them up and will get the needles set right this time.
3. I checked the needles - high is 1.5 low was 1.0 - so that means the high is at recommended rich starting setting and the low was getting quite lean... which means I screwed up and started with it WAY rich on the top and now I am just at factory (which might actually be the peak setting... I'll find out tomorrow.) I set the low back to factory so I know where I am starting from.
4. I opened up the cooling outlet a lot more and added a deflector to make some pressure change. The shape of the cowl itself is almost a baffle but I will make some further enhancements over the weekend to force air through the fins.

Hopefully I get it running well again tomorrow.

RE: DA100 acting strange
 

Chris,

Glad to here you got it solved.

I just bought a used DA 100 and I am having troubles as well. Won't run over 3300 rpm tops full open.

May be a stupid question but does it matter which lead goes to which plug from the ignition? I don't see any markings on the ignition indicating whch cylinder to go to.

Had a guy that knows engines trying to help me set it up but still not good top end rpm and it wants to dye if going from about 3/4 to full throttle.

Any thoughts anyone?

RE: DA100 acting strange
 

Jim,
Since both plugs fire at the same time, it doesn't matter which lead goes to which plug.
Second, I would richen the top end by one full turn and try it again.
It sounds like you are too lean.

RE: DA100 acting strange
 

OK thanx, wasn't sure of the firing order so that's why I asked.

Engine is no longer in a plane so will have to wait to find new home or mount on a stand. Thanx for advice.