pkevinb

I'm have an odd problem with fuel starvation during inverted flight. I can fly inverted all day long with the first 2/3rds or 3/4 tank of fuel but after that if I go inverted the engine dies and when I land there is no fuel in the lines.

I checked the clunk and all fuel lines and everything is ok with that. I also tuned the engine with 1/4 tank of fuel in it and it didn't help. It flies fine straight and level and in rolls and loops when it is low on fuel, just not inverted.

The plane is a Pulse XT 40 with an Evolution .45 engine in it. The tank is in it's normal position.

Any help with this problem will be greatly appreciated.

And It Is Not A Clunk Problem. I Checked That First.

da Rock

One possibility:
Clunk won't fall to the top of the tank. Happens when the clunk line is too long. Tanks with concave bottoms inhibit the clunk with that bottoms.

Simple thing to also try. Show the tank to an experienced flyer.

Mr67Stang

Take the plane in your hands (not running) and roll it inverted, listen for the clunk to drop to the top of the tank.

Destiny-RCU

Another thing I have seen is the clunk fuel line isin't soft enough and holds the clunk off the top. I only use bladder type tanks anymore, prevents foaming and this type of problem.

But I also second with Da Rocks comment...Have an experienced pilot look it over.

pkevinb

It is not a problem with the clunk. That was the first think I checked.

Destiny-RCU

Okay i'll take a second stab at it. Most tanks of this type are very prone to fuel foaming issues especially when the tank is low...Do you have just as much padding on top of this tank as you do on the bottom? when you roll inverted, when the tank is low. Have you now caused the tank to rest on less padding and invite foaming?

gunfighterII

You might have a split at the point the clunk line goes into the brass tubing, probably on the bottom, when the tank is full it's in fuel when it's 1/4 full the split is exposed. I've split tubing at this point many times, hard to find.

pkevinb

I thought that too. I added foam to the top of the tank and that didn't solve it. I am beginning to think that it may be a problem that I may have to live with.

pkevinb

That is something I will check. Thanks!

Villa

Hi pkevinb
You will get the fuel problem figured. I noticed you live in Meadville. I used to live in Franklin and flew at a field in Cooperstown owned by Paul Deeter. Do you know if that club and field is still active? Where do you fly?

pkevinb

Yes, I fly in Cooperstown, Maple Cave Flying Club, a great place to fly. It is still owned by the Deeters. I am down there almost every Saturday and Wednesday when I can make it. I also fly at a club in Conneaut Lake.

opjose

One possibility is that you have your clunk line set up so that it is on the bottom of the stopper.

When upright the clunk is able to hit the fuel w/o problems, but when inverted the stopper end of the fuel tubing is "higher", in turn preventing the clunk from remaining submerged in the fuel itself... add to this the occasional travel of the fuel to the front of the tank, and you'll quickly end up with fuel starvation. A very minor difference in height can do this!

Check your tank, and if possible adjust and rotate things so that the clunk line and tube is on the centerline of the tank and freely able to reach the corners.

I know that most advocate keeping the clunk off the back wall of the fuel tank, but I've had luck letting it reach the extremes, provided the clunk has adecuate "cutouts" in the nose to prevent the fuel flow from being cut off when the clunk bottoms.

j.duncker

My Feedback: (2)

Although you say the tank is in the normal position still check the tank position.

If it is high relative to the carb. then it will lean out inverted. I run the center line of my tank on the center line of the carb.

da Rock

There are no problems like that.

There is the possibility that the clunk does fall to the top and then sucks itself closed against the end of the tank. Some clunks have slots in them to prevent that. Some don't.

BTW, adding foam to the top of the tank probably wouldn't solve foaming. Adding it just to the top of the tank suggests something about the way you've got the tank in the airplane. And foaming doesn't usually happen in just one orientation, and actually doesn't usually happen. And if it were a foaming problem, you wouldn't be seeing the empty fuel line you're reporting.

For a delivery fuel line to be empty when there is fuel in the tank requires that the delivery line was plugged or sealed or was out of the fuel long enough to go dry.

And it's not just the clunk that could be high and dry. If the clunk line had a hole in it at or nera the tank stopper the cut could actually be delivering the fuel. That is, until the fuel level in the tank dropped below the cut. And if the cut was in the underside of the line, the weight of the clunk and curve of the hose would help to hold the cut closed. When the airplane was inverted however, the clunk would then pull the cut open, and since it was now out of the fuel, it'd suck air. It's happened before. And might be happening again. edit.... just noticed that gunfighterII had already suggested this last bit of advice. It's good advice.

Villa

Hi pkevinb
Thanks for the info about Cooperstown. I flew there from about 1972 to 1980. You have received great advice on solving your lean fuel problem. After many years of flying I found that my tank clunk sometimes contacted the rear of the tank. I now cut the line so the clunk is about 1/4 inch from the rear wall of the tank; plenty of clearance. Since I always land with fuel, this is not a problem for me. On my Canard I was having erradic engine RPM changes during manuevers, including flying inverted. I traced it to the fuel tank being too far away. I solved it by adding a 2 once header tank very close to the engine. The muffler pressure connects to the main tank. Fuel flows out of the main tank and into the pressure connection of the header tank. The header tank outlet connects to the carburator. Absolutely zero fuel problems.

AA5BY

If the problem is not solved, it also could be that the tank is not setting level but is aft down, which when inverted is aft up where the partially filled tank will then have the fuel forward and the clunk going dry.

da Rock

For a delivery line to go dry, the delivery point (where the line is actually drawing fuel) must be out of the fuel.

Some point on the line is out of the fuel when your engine stops. That is, if the delivery line going dry is what's happening.

If it's still happening, that suggests that you've simply not found why the delivery line winds up high and dry. What you've checked so far hasn't found out why. Check farther. You've not mentioned that you've opened up the tank and checked those lines.

pkevinb

Well, I feel real stupid! I checked the plane on the ground, turned it upside down and the engine was getting fuel while inverted. It was just siphoning back into the tank before it got back on the ground. It wasn't a fuel problem at all.

It was a simple glow plug problem. I think the engine richened up just a bit when inverted and the plug was on the weak side and the extra fuel put it out. I put a new plug in and the problem disappeared.

Thanks for all the help everyone.

opjose

Yup, this happens a lot. People who complain about not being able to tune an inverted engine are having the same problem.

The inverted engine gets a bit more fuel on the plug, so if it is set too rich the plug will be bathed in fuel shutting off the engine.

The key is to lean it out just enough so that this doesn't happen, but not so much as to overly lean the engine.

On inverted engines the tolerances are just a bit finer, that's all.

Longer shaft plugs also tend to help. I frequently use 4 stroke plugs on inverted Evolution, Tower, SuperTigre and GMS engines w/o problems.

pkevinb

The engine is an Evolution .45 and I replaced the plug with the Hangar 9 plug that came with it. That helped some, so I tried it with an O.S. type F, 4 stroke plug and it runs great. In fact I flew it out of fuel inverted. Another club member mentioned a Fox Miracle plug so I am going to get a few of those as well.

When the plane is inverted the tank sits a little higher than the carb too and I think that helped richen the engine even more.

I never thought to turn the plane over on the ground an check it. And I was going to try a new plug in the engine because with the glow driver on the plug it ran much better, but I just never got around to doing it.

There sure is a lot to learn in this hobby, that was the first glow plug to go bad on me. I just didn't recognize the problem early enough. It was funny too because after I got that problem solved the 4 stroke in my bipe quit on me. Sure enough it was a glow plug. Now I need to get some extra plugs.

opjose

I've been using the Fox "Miracle" plugs on my 4 strokes with great success too.

It works on most 2 strokers, but always remember to check the clearances.

The Evolution, SuperTigre and T.H./GMS engines seem to have no problems with the slightly longer plug.

There is ample clearance, and all three of these engines seem to come with longer plugs from the factory.