A Strange thing with my DA 85 Yak

[Show871]

Well I was flying today, and my plane out of the blue started having a split second rpm burst, when I had my throttle at a steady 1/4 throttle range. and at full, it actually had a split second cutout (not as often). My plane has worked fine for the 50+ flights in regards to this, and then it did it on every flight today. It was like brrrrrrrrrrrrrrrrrrrrrrriprrrrrrrrrrrrrrrrrrrrrrrr rrrrrrrrrrrrrrrrrrrrrrrrrrrrr. It did it probly like 3-5 times per ten minute flight.....I believe this is different from the other da rpm burst thread, so I am reposting. Almost like maybe an air bubble or two, maybe leaning it for a split second, but how is that possible????Anyone ever had this problem with a gasser and solved it??? any ideas????? DA 85, slimline, 85 oct 50-1 H1r. The only thing different on this day was a new mejlick 27x10th. Thanks 871

[bodywerks]

Take a look at your cylinder gasket. It should not have any evidence of blow-by. If it does, you may want to send it in to get re-sealed. That's all I can think of...

[ferocious frankie]

I don't have a gasser yet, but I've had the same problem you described on my Saito 1.80. I found out the vibration from the plane was creating bubbles in the tank causing the engine to pull air resulting in the RPM bursts in the air. You can find bubble free clunks from Turbine dealers and Troy Built Models. I believe they are made out of ceramic. There is another clunk with little brass beeds in it to keep from bubbles forming.

http://www3.towerhobbies.com/cgi-bin...?&I=LXD741&P=M

http://www3.towerhobbies.com/cgi-bin...&I=LXXF25&P=ML

Another thing to consider is if you were out of fuel and the engine was sucking air. This scenario is doubtful with gassers, but I would still consider it.

Another scenario is your fuel lines. Check all your fuel lines to see if you have any rips or holes causing your problem. There is a good chance that this is what you have.

Just some things to consider. Good luck.

[Show871]

I have a hitec 5985 mg on my throttle.....has anyone ever had those things develop a "twitch" every few minutes that could cause it????? If so, what would be the best, most hd servo for the throttle???? Is it like nitro where an analog throttle servo is better than digi??? Talked to da and they highly doubted air bubbles because the carb holds gas internally to eliminate this. Thanks

[mflander]

Mine was doing the cutout thing last time I flew it also, but only when inverted or on a partially inverted vertical climb(like a 45 degree up or the top half of a loop). If you figure it out let me know!!! I called DA from the field and he said almost every time they have heard of this the low end is too lean...

[Show871]

	Quote: Originally Posted by mflander
	Mine was doing the cutout thing last time I flew it also, but only when inverted or on a partially inverted vertical climb(like a 45 degree up or the top half of a loop). If you figure it out let me know!!! I called DA from the field and he said almost every time they have heard of this the low end is too lean...

Actually, It ended up being my fliping fuel dot. The plug had stretched out the hose just enough to let in a bit of air and create a bubble or two even when installed. This was with the blue aerotrend line, It was almost too stretchy to keep a tight seal on the dot. Hopefully a deadstick free summer for me now! 871

[mflander]

I just figured mine out yesterday... tygon fuel tubing in the tank was stiffer than a 2x4. Replaced it and all my troubles went away until the choke arm screw came out and seized up my motor....

[Show871]

	Quote: Originally Posted by mflander
	I just figured mine out yesterday... tygon fuel tubing in the tank was stiffer than a 2x4. Replaced it and all my troubles went away until the choke arm screw came out and seized up my motor....

Brutal......