The loop does prevent fuel leaks when standing the plane on nose. That's the best reason I've found.

It's the ONLY reason I've found. I did notice in a recent AMA "build" artical how someone was stating the loop prevented burbal during throttle transitions in 3d maneuvers. Nearly fell out of the chair laughing off when I read it.

Tom....notice the fuel tank in airplane is kinda high. I still say a high tank (caneffect running a tad)when full ...the fuel level is above carb. When tunning this engine on airplane,it puts the tank in a lower position. But when in flight...the fuel level is above the carb a fair amount. Remember the tune job is done with airplane on a angle....or prop would hit the ground. its close..

The pressure under the diaphragm is slightly below atomspheric pressure controlled by the spring forcethat closes the needle valve. Tank level within our size limits will have no effect on the tuning, now connected to a 20' diameter tank and you just might need to readjust as the level changes.

That's one of the things about our engines that make them such a pleasure. Tank location has zero impact on engine performance when kept within a rather wide range of allowable locations. Essentially if the tank can be installed anywhere in or on the lane the engine will function the same.

A non-pumped glow engine will experience gravity feed performance issues but that is very difficult to develop in our planes. I've seen a lot of vent tube installations that generated numerous problems. Never install a vent tube unless first determining there is absolutely a need. An improperly installed, restricted, or excessively long vent tube delays or alters the pressure sensed by a diaphragm until long after the aircraft has passed the point the engine needed the information. For a period of time there was, and likely still is, a lot of people that were automatically installing a vent tube when they installed an engine. Somewhere, someone said a vent tube eliminated a mid range burbal. That same person probably forgot to let people know they could also cause one, along with a few other irritating issues.

TOM here is question for you about Walbro carbs. What if any difference will that gasket make that goes under the diaphragm? I didn't have one. Will this gasket have much change in the needles? Dennis

Thought I'd add my two cent's. I have a test stand I built for these gasser's. It has vibration dampening and a thrust table built in. Any way the fuel is ran directly from a gas can on the ground. About 2  feet below the engine. No problem's with fuel draw here.

There are two gaskets in the Walbro..One on the pump diaphragm side goes on top of the pumo diaphragm, the one with no metal center..Other side has a gasket under the metering diaphragm, metal center, then the cover...The carb will NOT function correctly if either of the diaphragms is not positioned correctly..PERIOD,,,You can dink around all day long with changing needles and lever height,,,The engine MIGHT run, but not right...Like Rush says, "do not doubt me"

Antique, thats what I'm talking about. This carb has never had the gasket under the metering diaphragm. When I took it apart to check it wasn't there only the diaphragm. Dennis

I had this same thing happen to me with the same symptoms as you just described and it ended up being my radio going into fail safe due to a malfunctioning battery, check all your batteries and connections and do a good range test on the ground before you fly again just my 2 cents

I will admit I did intsall the vent line just in case....so I will just slip the line off it.The line was about 7-9 inches long! If that works....Thats great. Thanks, Capt,n

Thanks Ralph. The smileys aren't working again or you would have gotten a thumbs up.

same here. same exact problem as you are describing in the first post. it's not so much a loss of signal type of failsafe, it's a low voltage at the receiver failsafe and it cuts throttle to let you know you have a problem. A123 1100mah packs are prone to losing capacity with no warning. they're good one flight, bad the next. check the carb all you want but also check the capacity of your onboard flight batteries.

Bart

I am using A123 at 2300ma each. My radio failsafe is set to completely shut down the throttle. If i had a power falure it would have been both batterys and no control of the plane. I also use a data logger. When the engine went down I always had complete control of the plane.
Thank you for your advice but the radio have been gone thru and everything is working.
What drove me nuts was I couldn't get it to act up on the ground. So now I'm waiting for a carb kit.
I'll post the results when i fly again. Dennis

OK, good luck with the carb kit. I believe the radio failsafe is for a loss of signal from the radio to the Rx. The failsafe I'm talking about is the Rx's reaction to a low voltage condition onboard the plane. It has nothing to do with the transmitter. When this happens you maintain control because it's the Rx that has shed the throttle channel in order to preserve the other channels like an ESC with BEC does.
If you're using a data logger then you know that you didn't have a low voltage condition and that should be the end of that suggestion.
Regards,
Bart

In a low voltage condition the receiver it will shed load across the board. In reality it's not shedding load, it has lost ability to distribute. The power buss in receivers is common so line loss is equal. A receiver does not automatically shed just the throttle unless something has been changed I'm completely unaware of. The so called "brown out" condition experienced by so many using 2.4 has been entirely due to over use of a battery, causing a full loss of control through a system reset as the receiver lost the ability to distribute adaquate servo power when the voltage levels dropped below a certain point. A little further drop in voltage and the receiver loses its ability to process signal.

You are correct TOM, but since the subject wasn't about my problem I left in alone. I didn't want to divert the thread to radio systems and how they work.
But I will say this. My radio system is a JR 11X and servos are on separate channels. Two A123 at 2300ma ea. on the receiver and one a123 on the engine. The fail safe if programed to return all flight controls to neutral and the engine to idle. This happens when you loss link. If you loss total power to the radio you have no power for failsafe to work, but you still have power to the engine. the throttle may or may not stay the same. The flight surfaces will just flap in the breeze and down you go.
To have brown out both battery's would have to drop below 3.2v.
In my case when the engine lost power I always had control of the plane and was able to make a good landing. Had i had bad battery's it would have shown up on the ground when I did my preflight. I always check both battery's during the preflight by turning each battery off one at a time making sure I have control. Dennis

Hi all:
I have been reading this thread and if I may add to Antique's message and throw in a question for the original poster as well.

As Antique stated. Walboro designed the carb as per the illustrated parts manual. If something is missing from the carb that should be there, it is not right. Get all the gaskets from a carb rebuild kit and ensure they are on the carb per the IPC (illustrated parts catalog)

If your carb is a side mounted carb it is always good insurance to run a tube from the carb back plate to the inside of the fuse to equalize the carb and keep it from getting pressure pulses from the prop while in flight.

For my 2 cents If everything is right with the carb and the engine is sagging off right after takeoff, May I suggest that you ensure the overflow/vent line is not partially clogged. If it is clogged or partially clogged it will cause the engine to run lean and one of 2 things can happen.

1. The engine will sag and either keeprunning or die(lean condition caused by a partial blockage of the vent line).
2. The engine will sag and die (full blockage of the vent line) if this is the case your fuel tank will collapse as well.

I had this happen to me on a maiden and the fuel tubing got next to the muffler and completely blocked off my vent tube. Engine died, fuel tank was collapsed but we made a good landing.

Dont know if this helps you or not but is something to look for.

Good luck and I hope you get it sorted out.

Glenn Williams

I think what he wants to know, is that once his carb is repaired and assembled correctly, WILL his needle settings have changed. The answer is definitely yes.

Some people are terrified of losing their needle settings, as they don't like to retune. No offense intended, just stating a fact.

You will have to retune the carb.

AV8TOR

Agreed. Yes you will have to retune your carb. Once tuned it should be ok until you have a major climate change or the carb gets dirty. If the carb is needing constant adjustment after warm up the screens are more than likely partially blocked.

Glenn Williams

This is what i found when i took the carb off. Look at the page on the attachment.
http://www.ereplacementparts.com/wal...67_140808.html
Parts # 19 and 21 are missing.
This engine was bought new and I have never taken the carb apart.
And no I'm not afraid to tune a gas engine, I just hoped it would stay the same. It was tuned so good hate to start over
Dennis

Other than the missing parts, did you discover any other problems to cause the sagging?

The screen had some dirt in it. not sure if was enough. And the servo arm on the carb was loose but not by much.
Can't explain the missing parts. the only time I have done anything with the carb was removing it to add the new updated plate. Dennis

There are times that a manufacturer deletes a part. However are you sure the gasket ismissing? The reason I ask is that the gasket is sometimes stuck to the diaphragm. It is very small and sometimes goes unoticed during disassembly. This has happened before by others.

Might take a little closer look.

Glenn Williams

It may have been just functional enough the way it was to run acceptably. Once time had accumulated the existing parts likely degraded to a point they could no longer provide the additional capacity needed to overcome the deficient condition. New parts always work better than old parts and if there is enough additional capacity new parts can often overcome a deficiency that would otherwise be evident.

This situation reinforces points I've made in other threads noting that we do not know what we are getting when we buy a new carb or engine with a new carb and to trust in a factory to assemble an item to be ready for flight to be ludricous. Never, ever, trust the needle position on a new carb, and hope they put all the parts in the right places inside the carb. Be prepared to correct deficiencies that arrive with new coarbs. They are never, ever assembled by the most competant or intelligent people.

DadsToys,

Thanks for the opportunity to take advange of this situation to make mention of it again.