xtdsm

Hello guys, I have been having this problem with my DA 50 right after installing it into a new bird (it never did that before). I would set the low needle for the best transition and set the high to 2 full turns. She would fly nicely for 5 mins or so then when I try to transit from idle (in the air) it would want to die as if it was too lean but she would idle fine as soon as I pull back the stick to idle. it seems as it goes lean when it heats up in flight which does not make sense to me, I know as engines heat up they need less fuel or in other words they run richer but in my case it acts the opposite at the beginning of the flight it would burble and act rich, then a couple of minutes later she would run beautifully and soon after it would act as being too lean (would not transit) and this is when I land and check the engine temperature to find out that the engine is too hot. Is it only a matter of adding more fuel at idle or it's an air flow issue, and finally what the symptoms of an over heating engine, would it be wanting to die during transition?


oh I almost forget, my plane is extereme flight look alike Yak.


Thanks a lot

Rcpilot

My Feedback: (78)

Tune the carb properly. If you don't know how, then get help from someone with experience.

Josey Wales

My Feedback: (61)

.

Tired Old Man

My Feedback: (1)

The issue is a lack of understanding of how to tune a carb. Don't tune a cold engine because the settings will change as it heats up. Only tune a warm engine. Tune the high needle for max rpm and back it off a couple hunfred rpm. Tune the low needle for either max rpm or the best transition at around 3,000 rpm. Before you do any of that, go with what RCpilet said and find someone that already knows how to do it properly and learn from him or her. It's not hard, but remember that gas engines have BIG effects with small needle changes.

Yes. your engine is much too lean.

xtdsm

Ok guys, I guess I did not make myself clear enough in my first post.

First of all, let me say I do know how to tune carbs to some extent, I have tuned this carb/engine and it ran perfect in my other plane (GP 25% yak) for a couple of months or so, this problem only occurred in my new Extreme Flight Yak replica. I did set both needles to where they should be (1 7/8 high and 1 3/4 low) and peaked the RPM then backed up 200on the high, and set the low for the best transition, as I always did before.

- My real question, do these engines run leaner as they warm/heat up?
- why would my engine start off at the beginning of the flight very rich, then a couple of minutes later it will run perfect, then a little bit later it will run/act like lean?

How would I know if the engine is overheating in the air, would it not transit, or it would ?

Thanks again guys.

Flyer95

My Feedback: (1)

If the rubber parts in the this pumped carburetor are old then maybe they need to be replaced. These parts get stiff after a while and will not work as good as they used to.

Tired Old Man

My Feedback: (1)

The mixture settings of all the gasses change as they warm up. If you are setting the needles for the best power when it is cold then it will go lean as it warms up. I have never heard of needles being set to "where they should be". That location can only be detertimed by the propeller, the temperature, the humidity, and the fuel used. When the engine is running correctly then, and only then, will the needles be set "where they should be".

Go here if it will link and spend a few minutes. http://prme.nl/forum/viewtopic.php?t=10

If that doesn'y work go here, locate post #3. http://www.rcuniverse.com/forum/m_4831738/tm.htm

xtdsm

Silversurfer thanks a lot bro for the help, and everyone else, I just wanted to know if the engine will lean out as it warms up. Now I know what to do.

by the way Silversurfer, what I mean by needles are set where they should be is simply the start point suggested by DA manual, I started there and tuned from there (using a tach/ear to do so), I guess I just need to set the needles a bit richer, or wait till the engine is fully warm (I thought a 20 seconds of idling at the ground is enough to warm the engine enough, but I guess I was wrong.



Flyer95, my engine is not that old (2-3 months old) so I don't think that the rubber parts dried out already, but that would be where I would look for next if richening the needles won't do it.


Thanks a lot for solving my puzzle guys

Rcpilot

My Feedback: (78)

This is how I tune a gas engine. It takes time, but doesn't everything that you do the right way?

Lean the high end out untill it is maxed out. You can hear the engine pick up RPM and then stumble when it gets too lean. Set it right at max and then back it up the thickness of the slot in the adjustment screw. Maybe 1/16th turn on the screw. 1/8th turn is too much. You just don't want it set to peak RPM. But, you only need to richen it just a little bit. Gas needles are a lot more sensitive than glow needles.

Now set the low end like this:

What your going to do is rev it up to full throttle and then back it down to 1/2 throttle and listen. You'll back it down to 1/2 throttle and listen to it. If it's smooth for 10 seconds, then you can start to back it down 1 click at a time and listen to it. If it misses or gurgles--your too rich and will have to make a small adjustment. This usually involves stopping the motor. No big deal. Stop it. Lean the low end about the thickness of a screwdriver blade. Start it up and run it up to full again. Back it down to 1/2 and hold. Now back it down 1 click at a time. When does it gurgle and miss? 3 clicks down from 1/2 throttle? 6 clicks down? Just pay attention and take note of when it starts to act funny.

Each time you start it and run it up to full throttle you will hold it for about 10 seconds. Then back it down to 1/2 throttle and hold for 10 seconds. Back it down 1 click at a time. Hold it for 10 seconds each click. Listen to it and if it sounds clean--then back it down another click. Listen to it.

You should be able to back it down farther and farther each time you make an adjustment to the low speed needle.

Make an adjustment. Start it up. Full throttle. Back it down to 1/2 throttle and start counting clicks as you throttle down. Hold each click for 10 seconds. As you lean it and make adjustments--you should be able to back it down farther and farther each time before it gurgles and misses. When it gurgles and misses, take note of how many clicks you are down from 1/2 throttle and then make a small adjustment.

Eventually, you'll get it backed all the way down to an idle and it will be super smooth. Thats what you want. No mid range gurgle or missing.

When you get the low end set--you'll need to go back to the high end and check it. If you have to lean the low end a lot--usually that will effect the high end too and make it lean. So, if you made more than 1/2 turn lean on the low end to clean it up--you'll most likely have to go back and richen the high end again. Just get in the habit of going back and double-checking the high end after you set the low end.

Set your high side again. Set it to max and then back it up the thickness of the slot in the top of the screw. About 1/16th turn. Not more than 1/8th turn. It's not necessary to run it rich like a glow engine.

Thats the only way I know how to tune them. It works, but it's time consuming.

Some guys think that you'll fry the engine by running it up to full throttle on the ground and letting it run 1/2 throttle for extended periods of time. I disagree, as long as it's got air moving over it. If the cylinder is sticking out the cowl and you got prop blast on it--no problem. If it's inside a tight cowl and you don't have good airflow, then you'd be smart to shut it down as Silversurfer suggests and let it cool between adjustments. Most of my airplanes are so drastically overpowered that my engine cylinders are sticking well out of the cowl and they get plenty of airflow while I make my adjustments. I just start them up and let them idle for 1 or 2 minutes. Then I rev them up to full throttle for about 20 or 30 seconds to heat them up. After that I start making my adjustments to the carb. Get it dialed in and go fly it.

Make all adjustments with the cowl on. If you get it all tuned up without a cowl--you'll just have to do it again after you put the cowl back on. The cowl effects the way the air flows into and around the carb. Leave it on.

An engine that surges up and down at high speed is lean. Richen the high speed needle 1/4 turn and try it again.

xtdsm

Ok people, problem solved. And no it was not tuning the needles.

to make the long story short, I tuned as you guys suggested and she overheated right away, I then made both needles super rich, waited till she cooled down then tried it, it ran like crap for the first 3 minutes or so (being too rich that is) then it leaned itself out and ran perfect for like 5 minutes or so, and over heated. And only then I knew for sure that it was not tuning problem, instead it would be fuel supply problem. so I took her home, yanked the tank out, took the fuel stopper out to check the clunk line and it seemed perfect, then I blew air with my mouth in the carb line from the other end and wallaa the hose the connects to the stopper from the outer side is leaking. The guy who put the plane together for me used a bigger ID hose than the brass tube and zip tighed it, but obviously that was not a good idea, I replaced that hose with a smaller ID one (tight fit) and the leak stopped. I have not test flew her yet tho, but I am pretty confident that that was it.

Just thought I would let you guys know since one of us could run into this problem again they would know what to look for.

Thanks for all the tuning posts tho.

mradcliff

My Feedback: (3)

Help
I am flying an Aeroworks P51 with a DA50, Jtech Pitts muffler, Xzoar 20X12 prop, RedLine 40 to 1 on reg gas. Engine runs great for about 5 minutes then will lean out overheat and die. When I take off the engine is slightly on the rich side and as the flight progresses it begins to run stronger (leaning out) and then will quit. I know a gasser shouldn't start out the flight rich and go leaner like a regular 2 stroke non pumped nitro engine. I checked out the plumbing and clunk in the tank and its perfect. No leaks. I pulled the carb apart and the screen looked dirty and I removed it and have been flying it without the screen. The problem worsens when the ambient temperatures get hotter. It's overheating. I have the cowl opened up as much as possible. I flew it 3 flights Saturday before noon and no problems then afternoon temperature increased 10-15 degrees and then it started acting up again. I have lots of experience with DA100 & 150 and have never had this problem. Any ideas?

MTK

Mark,

If it's an overheating problem, then you should consider ducting on thefront side of the engine. Ducting should start at the chin cowling edge and get as farback as the first 1/4 of the cylinder; further back doesn't buy much but too far fore and air will leak around the fins andbecome ineffective. You want to try to eliminate any free air passages around the cylinde, head and crankcase.....

Ductingdoesn't need to be elaborate. I use 1/32" balsa sheet which I often will build up in situ, to guide the ram air directly onto the fins. I've used cardboard stock before too. The sheeting could actually touch the fin edges or it can be 1/8" away...it will be effective either way as long as it steers the air into the fins. Just as important, the hot air discharging from the cylinder needs a clear path to the exit holes.

The exit holes don't have to be huge either but for most effectiveness, you want to put a short dam in front of them creating an area of air deflection. It creates a slight negative which draws air out of the cowling. This is similar to the lip that's raised in the front of amoon roof in a car.

I've described this with photos in my Derivative thread in the Pattern Forum. Very effective in hot ambient conditions.

mradcliff

My Feedback: (3)

Thanks MTK for the advice. I've attached pictures of the cooling area on my P51. Would you put the air dam at the very back of the cowel or on the cross bar just behind the cyl head?I really believe it's a fuel draw issue but haven't been able to prove it yet.

speedracerntrixie

My Feedback: (29)

is there a cool air supply to the carb at all? If not it could be just recirculating hot air coming off the cylinder. Poor fuel draw usually shows up as hard to start on a gasser as even with the choke it will be slow to draw fuel. How many flips with the coke on and cold engine does it take to get her to pop? My DA 50 would usually pop between 6 and 8 flips. Remainer of the day was choke off and 1 to 2 flips. It may be that the clunk line inside the tank had dropped off or has a split.

mradcliff

My Feedback: (3)

Interesting you mention the carb air. I have been thinking this may have something to do with it. As near as I can tell it's recirculating hot air and I know that can't help horsepower. The clunk is perfect along with the lines. It will usually pop cold on about 6 flips and then start in about 3-4 flips. If I could get clean air to the carb it might help. Maybe the little spoiler mention in a previous post would help this. I guess I need to experiment with the air dam and see if this helps. I appreciate any and all suggestions.Thanks.Mark

3136

You need to create negative pressure to draw air from the cowl, also baffling around the side of the cyl. You don't want air to flow around the head, it needs to go right through the fins. I use a foam type material CA glued to the cowl. At the hardware store you can buy aluminium vents, they are perfect for creating negative pressure.

MX240

My Feedback: (4)

Hi Mark,
I had the same problem as you with my TF P-51 with a DA 50.
I think these type airplanes have good enough air flow past the cylinder head.
The problem I think is the tight cowl up by the carburetor.
I didn't like doing it .....but I took my Drimel tool and made a small narrow slit on top of the cowl to force air down to the carb.
I also have between the engine supports a sheet metal air dam zip tied to keep the muffler heat down.
I went back to DA factory needle settings also that helped.
It work for me.