I ran into a problem with my Brillelli 40GT. It started and ran great on the test stand, but I now have it in the plane and I can't get it started. It seems that the problem is that the gas is not being pulled into the carb. I've choked it with the choke, I've put my finger into the venturi to try and choke it, and no matter what I do, it doesn't pull the gas through the line.

I thought these Walbro carbs acted like little fuel pumps? Is it possible that my carb is defective? It hardly seems possible since it ran so great on the stand. I mounted it in pretty much the same position as it is in the plane, using the same fuel tank and lines.

In total desperation, I spritzed it with a little starting fluid today and it fired right up. It ran for about 5 seconds, or until the starting fluid ran out. That told me that the problem was fuel related, not ignition. I looked at the gas in the line and it never moved a bit.

I can almost guarantee you that this is somthing stupid that I'm overlooking, but I'm clueless right now. What am I missing here?

Oh, and yes, I know the spark plug wire is off in the picture, that's not the problem. I had to remove it to get the cowl off.

Thanks,

First time gasser Boy.

Well it can be numerous things.

#1 I see that you didnt use a zip tie around the fuel nipple. With gas / targon you ALWAYS want to use a ziptie and / or barb on the fuel nipples for the tank / clunk. Targon expands over time with gas contact.

#2 A small hole in a line will cause the carb not to suck fuel

#3 Double check your choke is closing all the way

#4 Double check throttle servo ATVs to make sure you are opening and closing the throttle properly.

#5 Maybe you moved your needles by mistake? - Go back to "factory" settings and retune in teh engine in the plane.


The easiest thing to do is to close the choke, full throttle, ignition on, and flip till it pops. Then go back to idle, choke off, and should start in 3-5 flips.


Hope this helps...

As sinergy has already alluded too, I also think it is an air leak.

I'd agree that it's possible your throttle linkage is not opening the carb plate enough at idle. Do as he suggested but leave the ignition off and close the choke and flip to see if it starts to pull fuel, if not then it's a definite air leak or the screen is plugged in the carb or a line may be pinched

Also, if you are using a fueler valve such as the Dubro or Sullivan, remove it because they are well known to leak air

Which line color is your fuel line?

After having some probs with my DA 100 I thought I better test the blow off perssure .
When it wes very cold it was quite hard to start , same as yours . It would fire then
stop or not fire at all . After the first start of the day it was usually fine for the rest
of the time .

So I went out and bought a pressure gauge that measures the blow off perssure
in walbro and tillitson . I raced Karts for eight years so I know that at sea level
the pressure need to be 11 to 12 psi . My carb was off the chart , it was 15+ .

Its an easy fix you just shorten the spring until you get the pressure you req . Each
time you cut the spring the pressure needs to be re tested but thats no big deal .
After the perssure was re set to 11 psi the engine is as happy as larry .

It may not be the ultimate solution but it should be tested prior to looking at the
rest of the system .

Stu

Open the low speed needle.

Ran fine on the test stand, doesn't pull fuel to the carb on your plane. Check your tank and line installation. Any chance your lines are connected incorrectly and your carb is connected to the vent line? Are you using a simple but effective fuel 'T' for filling the tank, or one of those funky 'quick fueler' devices that can leak, and actually block fuel from getting to the carb if they malfunction?

Update:

I had to change a bunch of stuff around, so I'm not sure if I've really solved the problem, but I did get it running. Here's what I did to it:

Took it out of the plane and installed it on the test stand again. I installed it so that it was upright rather than inverted.

Put on a brand new fuel tank with no fittings anywhere in the lines. Used all brand new tubing.

Removed the static pressure line from the carb.

Elevated the fuel tank to try and give it more pressure at the carb.

I started out spraying it again with the starting fluid. As before, it would start and run for a few seconds. I did that about 4 or 5 times, hoping that one of those times it would keep running. It didn't. Since that approach wasn't working, I figured I'd try something different.

I finally got so mad that I figured I'd see who gave out first, my arm, me in the heat, or the motor. I told my wife that if she looked out the window and saw me laying face down in the driveway, to just call 911 and take me to the nearest hospital. Then, as was suggested, I opened the throttle all the way and closed the choke. I flipped it until I heard it pop. (Took about 25-30 flips). I then closed the throttle, opened the choke, and after a few more flips, it started and ran. I ran it for about a minute, blipped the throttle a couple of times and shut it down. I didn't want to overheat it.

Now I have to figure out a systematic way of undoing all the different things I did, to see which one was the problem. Maybe none of them, I'm really not sure. Hopefully, now that it's run, I can get it started in the plane. I want to put the old tank and lines on there first, to see if there was a problem with any of that. Then maybe turn the motor inverted and see if it starts. Then I guess I'll put it back in the plane and see if I can get it started. Oh yeah, and I have to reinstall that static pressure line at some point. I don't believe that had anything to do with it, but who knows at this point.

arobatx, the lines were correct as installed. For filling, I simply use a "T" in the line from the tank to the carb and cap the fill line with a plug. I tested the fuel system and found no pinholes or leaks anywhere.

It almost seemed as if the carb was air bound or something. I'm hoping now that I've had the engine running, it will be easy to start. I'll keep you posted of further developments.

If you want to save your arm, turn the ignition off, and grab the bottom of the prop at the bottom of the stroke and just pull it around till your about half way through the compression or wherever the momentum takes you. Then return it back the other way and do it again...kind of like a pump. Watch the fuel till it gets to the carb. 25 flips is excessive but doing it your way I think its possible to have to do 12-15 flips for the first run of the day just to get the fuel pumped all the way to the carb. If you hand pump the fuel up to about an inch before the carb, you will only have to do 2-3 real flips usually.

Where is the Tygon loop of line connected? It looks as if a nipple was installed in one of the raised bosses on pump cover plate. Where does the other end terminate? If it is picking up the pulse externally on the carb adapter, is the internal pulse route plugged?

When you ran it on the stand you left some gas in the carb. It evaporated and left some gummie stuff behind. This kept the flapper valves from working, flapper valve no workie, no pump workie, no gas. Like the fuel in the tubing does not move.
When you went to wot and full choke the vacuum was strong enough to draw fuel past the valves and the fresh gas unstuck everything and your engine runs just like it used to.

[sm=wink_smile.gif]

This makes the most sense of anything so far. I kept thinking that the carb seemed like it was air bound or something. So what's the solution? Do you always run the engine dry at the end of each session? How about over a long period of down time, like during the winter?

Sounds like you've got to keep those flappers flapping for the engine to start. Is it possible to disassemble the carb and free those flappers somehow if this ever happens again?

Thanks [8D]

The small loop of Tygon tubing goes from one side of the carb to the other side-you can actually see both ends in the second picture. This line was installed by Brillelli-the line was on the carb when I took it out of the box. Not sure what it's purpose is, but I never touched it.

I believe the nipple that my pink tubing is attached to (removed in second picture, you can see it in the first picture) was a modification by Brillelli. I was told that this is the static pressure line and to just attach a piece of tubing to it and run it into the engine box and leave it open to the atmosphere. I hope that's correct.

The valves are under the side that is a casting. They can be unstuck if your carefull and don't tear the gasket.
Run the carb dry for long term storage, if you flying next weekend the nevermind.

Could you show a picture of the side of carb with your pink tubing. I'm stilled puzzled on the attachment of that end of the loop.
The 'static pressure tube' should work just fine.

Something else I've recently come across for future reference.

For those that run an engine on a stand without a radio then install the engine and have a throttle curve set up in the transmitter, look out. It's very easy to have the curve set up in such a manner that will prevent the butterfly from opening but a tiny amount at stick positions up to over 1/4 throttle. That's another reason an engine run on a stand and later mounted on a plane may not start.

Check the picture attached to my initial post. You can see it there.

Brillelli used an external pump line. The loop should go from the carb to the intake manifoild.

tkg Terri OK it's clear now. Maybe the carb is mounted 180 degrees rotated from factory and the nipple in intake manifold provides an external routing to the pump side of carb.

Just to add the final chapter to this book, I put everything back in the airplane, EXACTLY as it came out. Same lines, fuel tank, nothing different. Took it out today and it started right up. Still not sure exactly what the problem was, I've had guys tell me that they never run their gas engines out of fuel and they've never had a problem similar to mine. For some unknown reason, I could not get the gas to flow into the carb, and that's why it wouldn't start. Once I got the gas to flow, no problems with starting.

FWIW, the carb and all the lines are exactly as it came from Brillelli. If any changes were made, it was made by them. All I did was hook up the feed line and the line I've been calling the static pressure line that runs into my engine box.

Doesn't matter, it's running now.

Thanks for all the help and suggestions.

How did you finally get the gas to flow???

In all my limited experience if gas will not be pulled into the carb then either the choke is not closing, an air leak exists or the pump diaphram is bad. I had a 3W55i that would not pull fuel if I emptied the tank. I did everything I could think of then one day I pulled the carb from the engine and noticed the carb block had a tiny crack in it on the side that mounted to the engine block, replaced it and it pulled fuel right away. I have a 3W80xi that would not pull fuel after installing it but did OK after you primed it but was kinda hard to tune and seemed to be a bit lacking in power. Did all of the above and never figured it out, then one day it would only run on the prime. I took the carb off and looked at the reeds to find a very small piece of plywood jammed between the one reed and block. It wasn't much but it was holding the reed open just a small bit. I slapped my head for a few minutes after I remembered cutting out a small piece of wood for the servo mount and forgot to pull it out of the airframe so when I stood the plane up take a guess where the wood went [:'(]

Anyway, I'm glad to hear you got it running [sm=thumbs_up.gif]

Good question. I don't really know the answer, that's part of my frustration. I'm a mechanical engneer and tend to look at things logically. This particular problem makes no sense to me. As I mentioned, I took it out of the plane and put it on my test stand where I kept spraying it with starting fluid. It would run for a few seconds and then quit. It was nasty hot and I was getting exhausted. I really figured that there was something wrong with the carb. I finally put the starting fluid away and just kept flipping it. It eventually started, and since that time, it's started every time for me.

I could see the fuel line had an air bubble right where it attached to the carb and it wasn't pulling the fuel into the carb. That bubble finally disappeared, but I don't know what actually caused the fuel to start flowing. As someone mentioned before, perhaps the little flappers weren't flapping for whatever reason and then they finally started doing their job. Who knows?

It seems fine now.