bill3388

My Feedback: (18)

First of all, I really like my DLE 20. Easy starting, great power, and awesome spool up. But some of the DLE 20's mounted in a profile will run rich and lose RPM as soon as the plane goes inverted. When the plane is righted, the engine immediately returns to proper tune. This problem can be simulated by just holding the plane upside down on the ground. Mine is one of them I tried all kinds of ideas and tried searching online for help. When a profile is flying upright, the metering side of the card is towards the bottom. When the plane is inverted, the metering diaphragm is up. I read a post where one guy said the problem is caused by the difference in the weight of the fuel in the fuel chamber on the metering diaphragm. The carb is a Walbro WT. I have the Walbro metering lever gauge, and the metering lever is properly adjusted. Also, the reed block is smooth. It is baffling why some DLE 20's run great, and others have this problem.
Anybody have any ideas on what the problem might be?

w8ye

My Feedback: (16)

You could try increasing the pop-off pressure on the metering diaphragm to make it less position sensitive?

w8ye

My Feedback: (16)

To increase the pop-off pressure you would need a Walbro universal metering valve spring kit and try stronger springs until you minimize the difference between inverted and upright.

http://www.mowers4u.com/walbro-40060...nt-p-2263.html

w8ye

My Feedback: (16)

To test for the pop-off pressure you need this . . .

http://www.ebay.com/itm/Mityvac-8500...656941&vxp=mtr

ahicks

My Feedback: (2)

Or you could try running that lever just a hair higher than it's supposed to be. Better or worse, that should let you know if you're on the right track.

Higher lever is going to change your needle settings a hair.

bill3388

My Feedback: (18)

Thanks for you replies and inputs. One of my flying buddies has a really nice auto repair shop and he has that exact press/vac tester that he lets me borrow. I have checked the pop-off pressure and get about 25 psi. I can't find where Walbro really specifies a range for pop-off pressures. What range should this be?

w8ye

My Feedback: (16)

25 psi is a typical pop-off pressure for the DLE 20.

I don't usually check for the pop off pressure for that 25 psi is exerting on the pump diaphragm also.

I usually check that the metering valve needle and seat will hold 7 psi and, if you manually trip the metering valve, that the valve will re-seat and hold 7 psi. This tests the integrity of the pump diaphragm and the metering needle and seat. Beyond that I'm interested in how the engine responds to throttle and attitude changes.

In a case like yours I would begin to play around with the ultimate pop-off pressure.

Truckracer

My Feedback: (19)

It seems that many carbs these days come with a pop off close to 25, with 30+ not being uncommon in many cases. If I see 25 to 30 Lbs. for an initial test, I call it good to go as I'm mostly just looking to make sure it is not too low. As pressure bleeds off, the valve usually re-seats at about 20 - 25. Its quite rare that pop off pressure is a problem.

If the engine goes rich just holding it inverted, the spring must be very weak and can't control the regulator diaphragm at all. --OR-- Maybe there is some crud floating around in one of the fuel passages that moves allowing more fuel in that position. Can you get your hands on another known good carb to mount just for a test? This would let you know whether the problem is in the carb or not.

bill3388

My Feedback: (18)

I have actually had three different carbs on it. I also want to note that this problem is while flying inverted at a low and mid-range RPM.

The engine originally had a DLE carb on it, which was terrible. I found the metering spring was way too short, so I replaced it with a Walbro spring. This helped and I was then at least able to fly it, but it was not right.

Then I bought a Walbro from Valley View RC. This was a huge improvement, but the inverted rich problem was there. The spring was .440", so then I stretched it it .490". This really improved the inverted rich problem to where it was only slightly noticeable. But, then it was difficult to start, but only when it was cold, Opening up the low end didn't help cold starting. But, I kept wondering if I was addressing the real problem, or just compensating for it.

Then, the engine started squeaking (like a bearing noise), so I sent it back to Tower (with the original DLE carb). When Tower sent it back, amazingly, they had replaced the carb with a Walbro. So I just installed the engine with that carb. It flies pretty good with the Tower supplied Walbro, with only slightly going rich inverted. (The spring in this carb is .440")

But, this problem still continues to puzzle me. I don't see this problem on other bigger gas RC gas engines I see flying. And, I tried simulating this situation with my Stihl power equipment (Zama carb), and it does not affect them. So I wonder if this is a smaller DLE engine issue?

speedracerntrixie

My Feedback: (29)

Is the center of the fuel tank below the center of the carb? I know it's not supposed to make any difference but it actually does. I found the same issue with my DA 50 and again with a DLE 55. The issue went away with a combination of raising the tank to ease pump operation while upright and making the pump work just a little harder while inverted. The second half of the combo was leaning the low needle and not running so rich on the bottom end.

Truckracer

My Feedback: (19)

OK, my post was based on your first post where you said you could duplicate the problem on the ground with the airplane held inverted. That suggests a very different problem than also having the problem in the air where airflow at different airplane attitudes can also cause issues. I suggest you try a vent line on the regulator plate on the carb and route it to a protected area or shield the opening on the plate so random airflow can't hit the plate and affect diaphragm operation. You might just try rotating the plate to where the vent hole is pointed towards the engine which would be the most protected position.

kmeyers

I tend to think it is the boost port opposite the exhaust port that is causing this. Your engine is horizontal right?

Can you tune the plane in the inverted position? Also tune only when the engine is completely warmed up.

Use the choke to start a cold engine and never expect a cold engine to run right.

That is where I would start.

daveopam

My Feedback: (9)

I wonder what would happen if you rotated the carb 180degrees??? This may make for some linkage issues. But you could run it on the ground with a hand held linkage. just to see if it made it better/worse.

David

bill3388

My Feedback: (18)

Yes, I tried raising the tank above the centerline of the carb on the first Walbro before I stretched the spring. It made no difference when simulating on the ground or numerous flights in the air. It also made no difference in the tuning. I have found leaning the low end helps the inverted rich problem, but too lean causes other problems.

bill3388

My Feedback: (18)

The problem is the same whether duplicating on the ground or flying.

I couldn't decide on whether to include everything I have tried in my first post, but finally decided to describe the problem and go into details later. I think we all have found that when people bounce around different ideas, that can trigger suggestions that lead to a solution.

When the problem was worse, I did try rotating the regulator plate in all positions, with no improvement. I also tried a shield over the carb. Other profile fliers I know have tried these too, with no improvement.

bill3388

My Feedback: (18)

Yes, the engine is mounted horizontal in the profile. I think that most DLE 20's are either mounted upright or inverted, so this problem would only be noticeable when knife edging the one way when the fuel regulator is positioned up. It wouldn't be very easy to tune the plane inverted. Can you give me more explanation on the boost port opposite the exhaust port that is causing the problem?

w8ye

My Feedback: (16)

Most reed valve gas model engines have the boost port.

Jennifer Curtis

Maybe a fuel line issue. Could be the clunk is sucking
against the bottom of the tank when upright, but hangs
free when inverted. Could also be a kink in the line
inside the tank. Could also be a crack in the line letting
air bubbles into the fuel flow, but not when inverted.

If you can, try running upright and inverted on a test
stand where the tank and lines stay in the same
position.


Jenny

kmeyers

I think at lower throttle settings that some fuel puddles or drops out of the windage area around the crank. It could enter the engine in inverted flight through the boost port but not upright. The main ports would only see this fuel in nose up or down.

There were puddling issues some had with the side mounted 30 that some could carefully tune away. Some could not.

It is just a wild guess though.

ahicks

My Feedback: (2)

Re: puddling, anything is possible, but my DLE 20 profile is tuned/running rich (bordering sloppy rich) most of the time. That's just something I've gotten used to over the last few years. It runs best like that (good power, easy start, RELIABLE), and exhibits no noticeable changes at any attitude. About the only time it's actually running in a clean 2 stroke is with a lot of power on a vertical run.

bill3388

My Feedback: (18)

I did try different stuff on the tank, including an upper and lower vent, but it never made any difference. Thanks for your response.

bill3388

My Feedback: (18)

Interesting thought. Like I said, what is baffling that this only happens on some engines. A profile flier I know has two DLE 20's. One runs just perfect and the other has this running rich inverted problem.

speedracerntrixie

My Feedback: (29)

It's too bad we read about inconsistencies like this with the little DLE. As far as I am concerned in the 20cc size it really is the only game in town. On my latest build I gave serious thought to fitting the little DLE in the nose but I just read too many issues with bottom end performance/need to run them overly rich and having a constant burble in the midrange. In the end the airplane got YS power which has its own baggage but meets performance expectations. Hope you are able to find the issue and it's something that can be resolved.

ahicks

My Feedback: (2)

If someone wanted DLE 20 power, but not the DLE, RCGF and Valley View both have great reputations and make excellent alternatives...

speedracerntrixie

My Feedback: (29)

Al, in the end I went with something I knew was going to live up to my expectations in the performance department. I would have loved to have a gas burning hand starter but I didn't want to experiment on this particular airplane, they are extremely rare and I have a year of build time invested. However watching it climb vertically with that 16x10 three blade prop pulling it is just amazing.

I will eventually end up with a little gasser but I think it will be more of a kick around sport airplane. I do have a Bucker Jungmeister of the correct size that needs to be finished.