RevGQ

My engine is inverted in a P40 Warhawk and I simply use a small plastic bottle with fuel tubing attached to squirt fuel into the carb.

makib

Hi,
I have also MVVS 1.6 inverted on my F3A plane with original reso on and turns 17x10 Mejzlik abouth 8000rpm and more! great engine. For first time starting after long period close choke, make abouth 10-20 flips (no contact), switch on and fire at once shortly, release choke, after fev flips will run, make shure not to push hard throttle at once, let motor get working temperature.
Hope this will help.

ps
my motor is with red had and 2 magnets, previous was wit 1, but this is muuuch bether! much more tork in lower rpm.
when I have a little time I will post some pictures.

RysiuM

My Feedback: (1)

Like I wrote, it would take more than 20 flips (it will be more than 1000 flips) to get the fuel to the carb. I admit, that the fuel tank is about 10 inches behind the engine, but still the fuel moves in the line very slow. Comparing to my other engines, where every flip the fuel moves about 1/4 inch in the line for every flip, in MVVS I can't see any movement in the fuel line. Once the carb is wet, it draws the fuel without problem. Maybe my carb is bad (it was always like that) or maybe I should open the pump cover and check the membrane for contamination.

I think I have the same version (red head, two magnets, Vlach ignition). Once it starts the engine is awesome.

makib

maybe is the carb. pump sealings old, (maybe the carb. was sitting in store a few years before come to sit on your engine),
change all the carb. sealings-(2 pieces) will help for shure. Replacing is wery simple, one big screw and 4 smaler. Of course, some cleannign will help also, specially small metal net down in abouth 8mm hole. This net is wery ofen sealed with dust and old oil.
This is just sugestion for solwing some minor problems which offen occurs.

RysiuM

My Feedback: (1)

I guess, I will have something to do this weekend
BTW, I just fired up Fuji BT-43EI-2 , on my Wilga - the first time since January 2008. The fuel setup is identical to my MVVS (tank is about 12 inches behind and about 5 inches below the engine). Five flips on the prop and the engine came to live. No problem with the fuel drawing here. That proves, it is not the setup fault, but the carb itself. I will open the carb and see what's going on (it's pita, as I have to disassemble the whole front end of my Edge in order to get into the carb now).

PlaneKrazee

My Feedback: (14)

It's been a while since looking at my 26 but did you seal the hole (if there is one) in the choke plate?

Regards,

RysiuM

My Feedback: (1)

No need for that. This is the pump or mettering device causing the problem, not that the engine gets to much air.

Antique

My Feedback: (4)

The pump functions only after the engine is running and gets the pulse from the crankcase...
The choke is a separate function..A plate with no hole at all works just like a thumb over the venturi...The hole lets air through....You don't want air, you want fuel from the tank....

PlaneKrazee

My Feedback: (14)

If you put your thumb over the carb and flip the prop does it suck fuel? Solder over the hole.

PlaneKrazee

My Feedback: (14)

Yup, fuel from the tank.

RysiuM

My Feedback: (1)

I hope Pe will jump and either correct me or explain better.

We are talking about "pumped" carburetors, not a simple "glow engine" carb. The thumb over the inlet for sucking the fuel from the tank works in glow engines. Just simple action as the engine works as a pump creating a vacuum in the carburetor and therefore it sucks the fuel straight from the fuel tank.

Walbro is a little more complicated and creating a vacuum in the carb inlet does not suck the fuel from the tank - there is a system of flow and pressure regulators as well as the fuel pump in the way. If you increase the pressure in the glow engine fuel tank, the fuel will flow (overflow) through carburetor. If you increase the pressure in the fuel tank for gas engine you will not increase the fuel flow through the Walbro carburetor - there is a pressure regulator on the way.

Closing the choke (or finger over the inlet) makes the mixture just richer enough for startup, but will not free-flow the fuel into the engine. In MVVS the standard choke plate works very well for the purpose of starting the engine - as it is.

The pump works from the pressure pulse from the crankcase. Flipping the engine by hand creates a single pulse, that moves the pump membrane and pushes some fuel. So when you flip the prop and the fuel is in the line, but did not get to the carb yet you should see the fuel move. As soon as it gets to the carburetor, the fuel pressure regulator in the carburetor stops the fuel from moving fast. This is how I understand it supposed to work.

PLANE JIM

My Feedback: (109)

I disagree R, When I put my thumb over my carb hole on my walbro carb it gets real wet-real quick, I think there maybe some effect on fuel flow other than shutting the air off to make a rich mixture.

pe reivers

soldering the choke hole shut WILL improve initial fuel suction to the point that it will start in three flips. With choke fully closed, the pump will be bypassed and fuel is drawn directly from the tank.
Just be sure to have ignition on, so the engine will fire when it gets fuel.
This is a carb issue, and changing the carb will often solve it. Closing the choke hole with the thumb also works, privided the carb (strainer mesh) is clean inside, and idle needle is not too lean.

RysiuM

My Feedback: (1)

Thanks Pe for the input.

I tested the "finger over the carb" on the bench and indeed the fuel was pulled through the line - like in the old glow engine. So I was wrong. I admit that. However with the engine inverted this is not really safe way to flip the prop, so indeed closing the hole in the choke butterfly should improve the action.

What I noticed, that as soon as I stopped turning the engine the fuel retracted back to the tank - very fast (about 6 inch/second). It means the pump did not hold. I could see the pump was doing something as every flip the fuel went up the tube about 1/4 inch and immediately returned back to the tank.

I opened the pump cover and I checked everything for leaks. There were no any. The only thing I did not like at all was that the pump diaphragm is made out of some kind of fiberglass-like material. It is very stiff and has a fabric-like texture on both surfaces. I've never seen the thing like that. Maybe it was MVVS modification to make this carb working with gas and glow fuel.

I took 1500grid wet sandpaper and started to wet-polish both sides of this diaphragm between two glass plates. I finally get rid of the fabric-like texture both surfaces became semi-glossy smooth. Then I continue wet-sanding to get rid of little warps until the diaphragm was lying flat. I installed this back into the carb and surprise-surprise the pump works like it should now. It holds the fuel in the line and every stroke moves the fuel about 3/4 inch in the line. This is even without choke closed. Few more flips and the fuel started to drip from the carb (the engine is mounted inverted).

I will leave the plane overnight and see if the fuel stays in the line. Even if it works now, I'm going to buy new G/D kit and replace the diaphragm with the original one.

For your information the carb is Walbro WT-409, G/D kit is D10-WAT.

pe reivers

MVVS does no alteration whatsoever to their carbs. They are fitted as received from their supplier. You have walbro with dried out inner works as you found out. That can be caused by oxygenators added to the fuel. Get the repair kit, because the regulating membrane also will have hardened. The number you quoted is the right one. If you can't get one, I have them in stock.
Modern Walbro's have a blue Mylar pump membrane which is resistant to all fuels.

Edit:
One more note Richard:
The fact that the fuel flows back so quickly indicates that the regulating needle valve inside the carb leaks as well. This is a one way valve, and should not allow the fuel to flow back. When this valve leaks, a stable idle needle setting will be impossible! You may need a complete repair kit, and not just the membrane kit. Check first if you can clean the needle tip and the seat. (located unther the spring loaded regulating lever)

The engine being inverted helps a lot in flooding prevention. Excess fuel just drips out of the carb instead of dripping into the engine. Only if there is an air flow like in a running engine, will the fuel be drawn up and into the engine. This is one of the BIG advantages of the MVVS front carb construction.

RysiuM

My Feedback: (1)

Thanks Pe for all the info. I have never seen such membrane before. Most of carbs I've opened so far had either mylar-like or rubber-like material. This one was odd.

I just ordered the entire repair kit (K20-WAT) like you advised for $11.51 shipped (it is only 3 dollars more than D/G kit). As you said, the other parts might need to be replaced so I will have everything on hand. And like you wrote I just made sure, the kit I ordered has blue mylar membrane.

This MVVS engine is on very nice Edge 540 but the PITA during startup has placed it very low on my "frequent flying" list. I hope it will change soon.

BTW the fuel still stays in the line - the pump is holding all right

pe reivers

the old type rubber membrane is fabric reinforced. When it dries out, the fabric structure shows.
You will be happy after you exchanged all parts. The new needle will have a Viton rubber tip, also resistant to modern (carb) gas. (Californian air resource board). These guys are to blame for the troubles we have [:@]

BTW,
I found that adding an extra shim under the head both improved performance range and increased reliability of the 1.60 engine old style (whitehead + redhead), at the cost of a mere 50 rpm top end.

Jezmo

Pe,
My Zenoah G26 came with what looks like a very thin fiberglass pump diaphram. I've never torn down another walbro with a diaphram like this. The rest were all rubber, as you stated, with a cloth reinforcement molded in. I think this is some sort of attempt to offer improved performance with oxygenated fuels. Something is definitely wrong with R's pump diaphram though as my fuel DOES NOT flow back to the tank after priming. Not sure what he and I have but it was made that way from the factory and it looks like a very very thin fiberglass reed. You can see right through it and even though it is flexable it is not as flexable as the rubber ones. It works great though on my Zenoah, at least so far.

pe reivers

That was an intermediate honey colored fabric reinforced polyester design of Walbro, because the rubber petals curled badly. Later they switched to mylar (non-reinforced polyester sheet). The mylar solved all problems.
The fuel flowing back is not only the pump section, but also the regulating section not closing well. Some carbs had the black neoprene needle tip which hardens with oxygenated fuels. New needles have a reddish rubber tip which is OK. A wipe with tissue, and a quick toothpick rotation on the seat now is all it takes to get the carb to hold pressure until pop-off.
The new fuels also have better detergent properties so gumming is less. Not all is bad, though it sometimes feels that way!

RysiuM

My Feedback: (1)

I think we are talking about the same material.

One thing, that I might not be precise about. The fuel was flowing back to the tank before priming the carb (when there was no fuel in the carb). As soon as the fuel got into the carb it did not retracted - at least not as fast. But for sure next day after the last flight the fuel retracted from the carb - there was no fuel in the fuel line. So saying short the carb did not hold the "preasure" (or rather vacum) when it was dry, and even wet did not hold the fuel for as long as all my other engines do.

Jezmo

Thanks Pe,

I've seen the mylar one but mine is the only reinforced polyester one I've seen. Wasn't sure what the material was, glad you brought me up to speed.

R,
Yes, I think we are talking about the same material.

Mine holds fuel for weeks after running. I don't normally drain my tank after flying unless I'm going to let it sit for an extended period and the fuel is still up to the carb when I get ready to start. Hope the kit fixes you up...[8D][8D]

RysiuM

My Feedback: (1)

I flew the Edge today (with this engine). After I polished this membrane the priming problem disappeared. Two flips with ignition off, choke on, throttle max and the fuel is dripping. Then two flips with ignition on, choke on, throttle idle and the engine starts for about two seconds. Then after two flips ignition on, choke off, throttle idle the engine starts like a kitty. No problem with idle - it was so low (and stable) that I had to add few clicks "just in case". If the valve leak causes the "idle problem" then my engine does not have this leak. It runs just great. I'm going to love this plane

pe reivers

Anything will become a problem if the amount present exceeds tresholds. I did not want to talk you into a problem when there maybe is none. Just wanted to make you aware of the possibility. Now that the carb functions as it should, the valve seating probably is restored back to nomal.
Flying season is here.

Jezmo

Yes flying season it here and it is gorgeous out there today.

Wiltshire1

thanks for the advice guys, soldered up the hole in the choke plate and ... choke on, 3 flips to first fire, choke off, 1 or 2 flips - runs sweet! Now for some tuning, think it may be a bit peaky at the mo, but need more flying to pin-point.