manleywc

This one is long and complicated, but I'm really stumped here. Any help would be greatly appreciated.

Here's the main problem, my 3w-140 B2F quits while inverted, at low to medium throttle.

It runs fine inverted at high throttle. The engine bogs-down in the air the instant a role is initiated at any engine or air speed. This does not seem to be an overheating problem, since it will harrier forever (upright only) and climb out of sight at full throttle.

I bought the engine used, so I don't know the history on it. I've put over 40 flights on the engine, but only recently encountered the inverted quitting problem.

There's more, the engine runs perfectly in the pits, but bogs-down and blows smoke as it revs-up on takeoff. This is not a lean hesitation. It seems to be related to the forward motion. The plane has no significant speed when the hesitation starts (less than 5 mph). It only reaches full power after it is in the air. It revs to full power, without hesitation, in the pits. This happens hot or cold every time the engine is allowed to idle-down for several seconds on the ground. The bog-down at throttle-up does not happen in the air.

The fuel tank pick-up is free, and the fuel lines are tight. I checked the carb filter.

The abnormal thing is a restrictive exhaust system. The front stack is cut-off and capped on each stock, 2-stack, muffler. The exhaust restriction could be the cause of all my problems, but upright flight and static ground performance are fine. The engine also runs very dirty, blowing black residue. More residue comes from the left cylinder.

Engine setup:
3w 30x10 prop.
Ams Oil 100-1 mixed 91:1 with 93 octane pump gas.
The static pressure port is routed into the fuselage.
The bottom of the fuel tank is about 1-1/2" above the carb.
Baffled Extra 300L cowl with open hole below spinner.
Flying from sea level and 65F - 85F.

Thanks,
Cliff

bob_nj

My Feedback: (62)

Running at 50:1 as most do, and using non premium fuel? I only ask because they are the two things that immediately come to mind looking at your set up. I'm sure you'll get more suggestions along the way. I also have a 140 and am interested in the replies. Take care_bob

BBW Walt

My Feedback: (11)

Just a thought, Where is the low speed needle set? It sounds rich. Also, some have eliminated similar problems with the intake stack offered by 3W. Is the carb diaphram vented to stable air?

bob_nj

My Feedback: (62)

JPrc

My Feedback: (22)

I tried this method on my 100 twin and it did not work. Bought the carbon fiber intake and have not had a problem. I would give it a try. JMHO

manleywc

Answer to Walt:
Both needles are set rich at about 2 turns out. Original factory settings were 1-1/2 turns.

Answer to Bob:
I get a lot of mixed information on Octane. I have found very little difference between grades in my G-62 planes. Low test seems to make the engine zippy (more responsive rev-up). High test seems to run smoother, with more torque. Most flyers I've talked to use Ams Oil 100-1 (synthetic) at 100:1, and non-synthetic at 50:1.

Answer to JMHO:
I did some research on the CF intake and it seems to solve the bog-down on rolling, knife edge, and inverted flight. I will try it when I get my new problem below fixed. Thanks

The problems are growing. Here's an update:
Last night I cleaned lots of black build-up out of the mufflers. I also removed the static port vent hose. There were no bog-downs in the rolls on my first flight today. But here's the bad part. I did not get a chance to test inverted flight, because the engine nearly quit on a full throttle vertical climb. It also happened yesterday with the static port vent hose attached. This was definitely caused by fuel starvation. I richened the low end from 1-7/8 turns to 2-1/8. There was an occasional burble on the rolls during the second flight. After verifying that it could sustain full throttle level flight, I tried the vertical again, and it quit. Again, this was definitely a fuel starvation shut-off

I disassembled the fuel tank to check for air leaks in the pick-up line, but found none.

This engine ran good for over 30 flights, then the inverted quitting problem started. Now it runs out of gas on vertical climbs. The problem seems to be in the carb, and it is getting worse.

I plan to install a new carb kit.

Thanks for the advise.

bob_nj

My Feedback: (62)

Have you read the thread entitled, "3w100 dies, plane dies, vicious cycle? " I'm wondering if you've explored and read the reams of information on the warping of the phenolic carb spacer? This post is one of many that addresses that matter. I posted a couple of pictures of the DA spacers I recently aquired. I plan to retrofit them in the event that this problem crops up on my 3W 100 or 3W140 in the future. I've just not experienced this situation yet. Again, I am interested in your findings_bob

Diablo-RCU

My Feedback: (1)

One other thing to check. Are you running a felt clunk filter or an inline fuel filter? Perhaps you've got dirt in the carb?

manleywc

Answer to Diablo:
I'm using a Stihl filter. It has a cylindrical plastic housing with a fine mesh filter element. It has very low flow resistance, and is still heavy enough to stay at the low point. Remember this setup worked for over 30 flights.

I looked at the thread mentioned above by Bob. I removed the insulator and valve block. The fasteners attaching the insulator were not very tight, and there was some evidence of leakage between the insulator and valve block. I can't see where warping could be a problem, since the seals are very thick. I can see where the seals could have compressed over time, effectively loosening the fasteners. I put a light coat of red RTV on all seal surfaces, and reassembled everything. I did not have a chance to fly today. I still plan to get the carb kit.

Thanks
Cliff

rc bugman

My Feedback: (30)

When you have the carb apart, also make sure to check and clean the fuel intake screen. Even though I use an inline filter and filter the fuel before filling the tank, I have had problems with this screen becoming partially plugged and causing fuel problems.

Elson

Kris^

My Feedback: (1)

Manley, I've been experiencing similar problems with one of the new 3W150b2ss engines. I have a TOC'd 140 that I REALLY love, though. It's the most dependable 3W I have. BUT. . as to your problem. . it sounds like fuel is puddling inside the crankcase, just above the reed valve assembly, and then when you roll inverted it falls into the engine, effectively flooding it and probably killing it. Your symptom of it blowing smoke and gurgling/running badly upon acceleration for takeoff tends to support this. I do not know if you NEED it this rich (two turns out on the low end), just to get it started, but if you do it's indicative of a warped phenolic carb mounting block.

If the engine will start at a leaner low-end mixture adjustment, I'd advise setting it that way, since your symptoms are of an overly-rich bottom end on the carburetor. If, however, it NEEDS to be this rich to run properly, take the carb block off, flatten it with some sandpaper, reseal it with some 3M "yellow weatherstrip adhesive" available at any automotive parts store, and reset the needles once you have the engine running again. The yellow adhesive is tenacious and pervasive, adn we in the automotive busines nicknamed it "Yellow Death" since you will probably die before it comes off your skin.

Really, about 3/4-1 turn on the bottom and 1.25-1.5 on the high end is the "normal" adjustment range for the needles on your carburetor. Anything outside that range, especially richer, would support your having an airleak under the carburetor.

Hope this helps.

manleywc

Thanks for the reply Kris. I did find evidence of a leak at the thick neoprene seal between the valve block and fiberglass insulator. It was wet with gas across the seal in two places. the 4 screws were not very tight either. I think age, heat, and exposure to gasoline caused the seal to shrink. I have resealed all surfaces, but have not had a chance to fly it.

Don Lowe

Most guys resolve this problem by running a vent line from the regulator port(hole) to the inside of the fuse. This solution presumes that the problem is a change in the atmospheric pressure reference when maneuvering which gererates achange in this ref pressure. The regulator sees venturi pressure on one side of the diaphram and atmospheric on the otherside. If this balance is changed the engine may run rich(or lean). A friend has a 3w-100 which does this and this correction did not resolve it. The engine does the same thing on the ground when rolled inverted-only when the engine is at reduced throttle. I'm beginning to think that the problem is fuel that is pooling above the carb when upright and runs in to the engine when rolled inverted. I have a 3w-140 which shows a slight hesitation when rolled inverted but very quickly returns to normal when held inverted. What we need is a fuel injection system which runs the same no matter what. If my theory is correct a rear induction system would be best like the ZDZ line

Kris^

My Feedback: (1)

The best "version" of what Don is describing is probably the 3W CF intake extension that goes above the carburetor, and has a vent line that attaches to the front of the pressure diaphragm. This system basically balances the pressure at the carburetors throat with that at the atmospheric reference port on the fuel pressure regulator diaphragm. I've always felt that the "balance" line going into the fuselage does not properly reference the pressure drops and changes associated with the air entering the carburetors throat and venturi. Add to that the length of the balance line/tube, and you now get a less responsive diaphragm since the long, but small diameter tube tends to damp the pressure changes that a shorter tube would allow, effectively making the diaphragm too unresponsive to the pressure and flow changes the carburetor is experiencing.

Personally, I'd rather see a totally enclosed carburetor housing that prevents pressure fluctuations and high velocity air from striking the carburetor in any way, such as a large air cleaner assembly on a race car. This, plus making sure that the carburetor, reed cage, and gaskets, are totally sealed, would go a long way toward smoothing out our engines no matter what flight attitude.

I'd also like to see a TRUE FI system developed. . but I really don't think anyone is going to invest a couple of years and $25-50K to develop a system like that which will not sell very well and be expensive if it does sell. I have parts for such a system laying all around. . injectors, low and hi-pressure pumps, a couple of controllers, but its all focused toward automotive usage and way more than I'd ever need for a 150cc "Fuelie" system . .Oh well. . back to the drawing board.

bob_nj

My Feedback: (62)

Now here's a celebrity and long time RC'er. Introduce yourself with a little biography please sir...
I've been at it since 1976. How about you?

Don Lowe

Kris, you are absolutely right about the best solution. If the inlet is rammed the engine will lean and if the reg sees a varying reference pressure it will lean or richen. Its best that both inlet and reg reference see the same press. a lot of modelers run a ref line from the ref port to a point adjacent the inlet. That is essentially what the intake manifold add on is doing. We made this mod to engines flown in my RPV military project and it worked well

Kris^

My Feedback: (1)

Yup. . KISS as they say. . I'm designing in a "carb box" for my cowls now that establishes a "dead zone' around the carb to keep pressure fluctuations to a minimum and surrounds the entire thing. Since it's part of the cowl, you don't have to worry about something interfering the way you do with add-ons for the carb.

One other thing to consider, in the case of these engines puddling gas right above the reed valves, is that it takes inlet charge velocity to keep the fuel in suspension, and overly large reed valves drop that velocity by a very good margin at low rpm settings. Best design would be to inject gas only at the base of the cylinder ports, and move only air through the reeds, so that little or no dropout of fuel particles would be taking place. We are a long way from that, though.

BTW. . Welcome to RCU Don!!! Bring some of your friends along!!! I'm sure you guys have a ton of knowledge to share.

Antique

My Feedback: (4)

Seems like if the low speed needle is adjusted correctly the engine would use it all and there would be no excess fuel to puddle......Or if the engines were piston ported there would BE no problem....
But then the carbs would stick out of the cowl.....

Kris^

My Feedback: (1)

yeah . .a la "junky looking muscle car wannabe's" with tunnel rams, blowers and twin carbs sticking out of the hood. . . YUCK.

how bout . . remote reed valve and intake tract attached to the bottom of the transfer ports on the engine, bent 90 degrees to face aft and located under the motorbox?? Or, rotate the cylinders to face 45 degrees aft with the same setup? it would clear up a lot of room under the cylinders. not exactly a "rear" induction setup, but not a bottom induction either. Just an idea I've been kicking around.

Antique

My Feedback: (4)

You wanna see a "junky looking muscle car wannabe" airplane, click on www.rcignition.com.. goes 230+ mph...
With carbs sticking out the cowl...

manleywc

Hi everyone,

I fixed the engine. It was an air leak at the phenolic block. Sanding did not fix it. I had to buy a new block. The recess where the thick black seal sits can not be sanded flat. A mill could be used, but if I had access to one I would make a new block.

My opinion is that the dark red/brown block is a poor design made from the wrong material. 3W apparently knows this, since the new engines come with a redesigned block made from what appears to be G-10. The replacement blocks are still made from the dark material.

Warning to all, this failure happened over only a few flights. Due to the block design this failure will eventually happen to all of these engines.

If anyone wants to make a redesigned block made of a better material, I be first in line to buy it.

Thanks to all for the help.

Cliff

Kris^

My Feedback: (1)

DA has a carb mounting block, that by drilling one hole, can be used with the 3W reed cage and you can throw away the recessed gasket. Call Desert Aircraft for more details.

cnbhome

My Feedback: (2)

I have followed this thread hoping for someone with the same problem as mine to show up. I have had the same type of problem with a 3W 150 in a Carden 330, when inverted it runs rich, the attitude is exactly the same as upright so there appears to be no included airflow condition. Here's the kicker, it will run blubbering forever, I am talking minutes here, it doesn't die and as soon as I role back upright it clears up. I am having a hard time believing it is a carb block leaking. The needles are set at 3/4 and 1 1/2 any lower on the low and it won't start. I do have the carb vented to the fuselage with a short line, 6 inches or so.

Does anybody have any suggestions.

Chris

Diablo-RCU

My Feedback: (1)

Put a new metering diaphragm in the carb and use the 3W carbon fiber intake horn plumbed to the diaphragm. Reset your needles.