secret_squirrel

Pics attached.

kmeyers

I would block off the stock air intakes on both sides of the spinner. These only supply air that has to compete with air going over the engine head. Very easy little fix. A lip in front of the exit creates a low pressure area for the air to get sucked out.

secret_squirrel

thank you for your response. I am not sure I understand the part about, "lip in front of the exit creates a low pressure area for the air to get sucked out". Do you mean on the bottom of the cowl at the rear? If so, how tall would it need to be?

kmeyers

That's what I mean. The lip can be very effective at very small heights 4 - 6 mm.

secret_squirrel

x

thank you sir. You are correct, that would be an easy fix.

secret_squirrel

So this weekend, someone at my local field helped me tune my engine. It isn't perfect but I was able to land without changing the throttle trim. So the end result 1) new plug 2) repaired the muffler gasket and 3) properly tuned. From there I am left with a couple conclusions. 1) engine needs to warm up a little so I set the throttle trim for landing and give it a little throttle to start and 2) the engine is close to breaking in but not totally there.

i may also add a little balsa to the back opening lip of the cowl to see if things improve but I am pretty happy for now.

av8tor1977

My Feedback: (6)

I would definitely add that lip to the cowl, as without one your exit area looks a bit small.

Definitely do the remote vent mod on the carb. I just do this as a matter of standard procedure on all my planes.

This definitely sounds like a slightly hot engine and/or lean idle problem, along with a pressurized cowl, but just to be thorough, you might check the reed valve seating as well.

Note: You won't mess up that carb cover by soldering a tube into it. Just use a Dremel tool and clean up the underside afterwards so nothing can touch/damage the diaphragm. If by some wild mistake you ruin the cover, I'll send you another one for free.

AV8TOR

ahicks

My Feedback: (2)

Rather than curing problems that may not be there, it would seem that running this thing without a cowl might be a simpler approach. If it's not broke, don't fix it?

secret_squirrel

Two things I am going to try:

First, I kinda think my low end is to lean. Going to try a couple clicks of rich. I am also going to try the lip on the cowl. These are two easy things that dont do any damage to the engine.

My confussion is, if it was an air flow problem, wouldnt the engine ultimately come back to its original idle after landing on the ground and returning to ground conditions? My engine does not, it stays at the same idle as if it was still in the air.

After trying the easy fixes, I will venture into the carb cover fix. Weather has been terrible so hard to test stuff. I feel fairly comfortable that I will be able to do the carb mod without issues, just want to make sure it is in fact the issue before I go down that road. Thank you very much for your offer though :-) Makes me feel better knowing if I screw up, someone will bail me out!!!

secret_squirrel

Yes sir, I agree. Problem is, there are people all over the place running this engine with a cowl on without issues. Last time I flew with both the cowl on and off after someone at the field "properly tuned" my engine and there were no differences in the idle upon landing. Both with the cowl on and the cowl off, the idle was higher after a couple laps around the field. It was noticable less of a change than prior to having my engine tuned,

kmeyers

SS I like to make the final idle setting at the end of a good flight when the engine is "heat soaked".

This is done after landing and without shutting the engine down.

ahicks

My Feedback: (2)

SS- You failed to mention you had already flown with and without the cowl. Judging by your results, carb cover fix not necessary. If you had seen a difference in the way the engine runs with/without the cowl, then it possibly may have been the issue - but it could still have been a heat related issue.

Regarding other people running around with cowls without issue - assuming yours has been correctly located/cut out not a good assumption at all. Improperly installed outlets a big deal when it comes to overheating/engine inconsistency. The only way to know for sure is to fly without it. Actually, your OUTLET appears to be on the small side in the pic. It looks like you're stuffing much more air into the cowl than what is being allowed to escape.

kmeyers advice makes sense.

So does your idea of trying a click or 2 rich on the low speed. -Al

av8tor1977

My Feedback: (6)

If the carb senses pressurized air in flight, it is forced to provide a richer mixture. If a person doesn't realize this is happening, they logically start leaning the engine out, usually on both the high and low needles, to get proper performance in flight and to eliminate the midrange burble. Then when you throttle back and slow down to land, the ram air pressure drops and your tune becomes lean. That's when you can experience "idle hang" where the engine won't drop down to a normal idle. The problem is exacerbated by the fact that if there is ram air pressure in the cowl, the engine is also probably running hotter than normal, which also contributes to an "idle hang" problem.

AV8TOR

av8tor1977

My Feedback: (6)

As far as yours seeming to run the same with the cowl both on and off, I agree; then you probably need to richen the idle a touch more. If this then results in a midrange burble in flight, you might try going to a larger prop, and re-tune. Quite often with these carbs, the idle has to be set a bit richer than ideal to get acceptable all around performance out of the engine.

AV8TOR

ahicks

My Feedback: (2)

To this thought, I say simply, Amen.....

Seems it's the hardest concept for many to accept. -Al

Truckracer

My Feedback: (19)

Most accept the concept when the engine quits running at a very bad time! Whether they choose to do anything about the problem is another issue. As with many things mechanical, a good running engine is a collection of acceptable compromises.

av8tor1977

My Feedback: (6)

If someone would develop a Walbro type carb with a midrange adjustment, at a reasonable price, I believe they could sell thousands of them. I keep wanting to sit down and attempt to modify a carb as such, but just never get around to it.

Too many interests, too many ideas, not enough time and motivation. Oh well....

AV8TOR

Truckracer

My Feedback: (19)

Several years ago when BME was having major problems with the 115 or 116, whatever it was called, before BME redesigned the intake system some guys in California did exactly what you're suggesting .... modified a carb for midrange control. They no longer come to this forum but occasionally show up on other forums .... though sadly, I believe they largely avoid the forums most of the time these days.

It is fairly easy to modify a Walbro for a richer midrange but not so easy to make it leaner which is usually what is needed. I've just learned that certain carbs run better in midrange or just above idle than others so I avoid those I don't like.

Chris Nicastro

My Feedback: (3)

Fully cowled engine present certain challenges.
First the engine may or may not need to be baffled for good cooling performance. If the flow thru the cowl is sufficient then it's not needed. If the pressure in the cowl is high then you need proper exit area to reduce this condition.
Another condition that happens in a cowl is called vapor lock. The carb has a diaphragm that pumps based on back pressure from the piston skirt in the manifold. When the diaphragm is stalled the engine looses power and then quits "mysteriously". The silver plate with a tiny hole in it is the diaphragm cover. You can drill and solder a brass fitting and attach a short length of fuel tubing which you can redirect thru the firewall to another compartment for fresh air.

Theres a misconception, I believe, about the midrange burble or down leg burble being a carb setting problem. What you hear are the reeds flapping between open for flow and closed. When the engine is not loaded enough the reeds oscillate and that causes the noise and some hesitation. On a DLE55 and DLE55RA I have tested many props and the Xoar 22x10 is the best match as far as I can tell. The mid range burble goes away and engine response is normal. I fly both the wood and carbon versions.

For the last 4 plus years I've been using only DLE engines in a variety of planes, mostly scale, and have to say the 20,35RA, 55 and 55RA are great right out of the box.
On a couple of these engines I've done the reed and manifold update to blueprint the parts better. I don't think the engines really needed it but it's not a bad minor tweak to make.

Some notes on my set ups;
Oil - Bellray synthetic at 32:1 or Klotz at 32:1
Gas - 92 Octane NON-Ethanol - best match for these engines compression ratios
Temp - 165/185F
Battery pack - 2S LiFe packs or LiPo for higher voltage - either work fine, 1500mah is plenty for three 8 minute flights
Spark Plug - NGK CM6
On the day watch the moisture in the air and adjust the high end needle accordingly.

I have a DLE55 in a P-51 right now I fly regularly and I have the idle set to one setting all the time. I start it at this setting and shut it down never touching the idle trim. I use the cut off button on my Rx. This stock older engine always starts easily and runs hard the whole flight.
When I start it I let it warm up for a couple minutes before I open it up while tethered. On this plane I'm going to push it a bit and see how it pulls a 22x12 prop. On the Carbon Xoar 22x10 this plane clocks just about 98mph. Looking for just over 100!

ahicks

My Feedback: (2)

Chris, when the guy runs the engine cowl on and cowl off with no change, the cowl (or it's baffling) isn't the issue.

Myself, I think this is somebody that just needs a little more experience under his belt. Until then, I hope he continues asking questions. -Al

av8tor1977

My Feedback: (6)

Sorry but I beg to differ about your opinion about hearing the reeds. For one thing, you could never hear those reeds operate over the exhaust, intake, and prop noise. Secondly, even at only 2000 rpms, they are opening and closing 33 times a SECOND. You're not going to hear that as a burble either. What you are hearing is the engine going rich, either due to a carburetion fault or misadjustment, or a lack of load causing a richer mixture than had been set on the ground. It's not just reed valve engines that do it anyway; the problem is just as prevalent, if not more so with piston ported, non-reed valve engines.

AV8TOR

kmeyers

+1

secret_squirrel

I appreciate all the advice. Waiting on good weather and spouse approval to fly to try some of this stuff. :-).

secret_squirrel

just to further explain what I did at the last outing:

1). Had someone tune my engine, on the ground without the cowl.
2) flew without the cowl. On landing, the idle was higher but not significant enough that it needed to be adjusted down to land
3) next, I put the cowl on and flew again without touching either the HE or the LE needle. The landing was exactly the same. The idle was higher, but not so much that I needed to adjust the trim to land.

secret_squirrel

this is in fact what I ended up doing, adjusting idle after the flight. Subsequent flights required about a quarter idle to start the engine though. Another reason I think my low end is just a little lean. In the end, not a big issue if I have to bump the throttle a bit to start and warm the engine.