dditch

Rebuilt the carb. I thought I did it right but now I'm questioning my work.
Got it to start and it would run for about 2-3 seconds then die.
Started w/ 1 1/4 turns on the low end and worked out to about 2 turns before stopping.
I choke the engine and it will pull gas all the way up to the carb.
But when I start her up after most of the spins of the prop (spring starter magneto), air will come back out of the carb and start filling up the fuel line.
I removed the fuel filter and same thing.

What should I look for.

TlMMAAY

My Feedback: (1)

Mine did that when the gas cap wasn't tight enough. Check your fuel lines for an air leak.

dditch

What gas cap?
My tank has a vent on it.
Do tanks have caps on them sometimes?

My thought is that it is from the Car because I have the cowl off. I can see the air back feed from the carb.

RC Extreme power

My Feedback: (24)

Float valve under the cap with 4 screws not closing.

Milton

pe reivers

assembly:
??????????????????
pumper gasket on top of pumper membrane. non-curled valve petals?
regulator membrane on top of the regulator gasket. nice and flabby?
regulating lever about horizontal when fuel is admitted. f forked lever, hooked up to regulator membrane OK?
??????????????
pop-off pressure test without leaks? IOW, does it hold pressure?

RC Extreme power

My Feedback: (24)

Just a little suggestion, Dump the old carb and get a new one, Most think they are easy to rebiult but to many things that can go wrong.

That is what I do, If carb is bad dump it and put on a new one. Saves hrs of frustration.

Milton

dditch

pop-off pressure test without leaks? IOW, does it hold pressure?
Any more info on doing this test?
I've never rebuilt a carb before.

Truckracer

My Feedback: (19)

How deep did you get into your carb? Did you do more than just replace the rubber parts?

Here are a few tips for things to look for. If you are talking about the Quadra 75 you posted about elsewhere, you have a Walbro SDC carb .... pretty much similar to most other Walbro carbs. Gas leaking back to the tank can really only be caused by two things ..... a leaking pump membrane or a leaking internal needle valve. Most common would probably be the diaphram.... it should lay flat against the carb housing the the two pump flaps that are part of the diaphram should be flexible and not be curled and should lay flat against the housing. If a separate gasket it used it should be between the diaphram and the cast pump cover. In many cases, the gasket will be part of the diaphram. Under this same cover, you'll find a very fine screen pressed into a recess in the carb body. You can usually just clean this screen without removing it (recommended for most users). On the other side of the carb and under the stamped steel cover, the regulator diaphram should be very flexible. On the SDC carb you have to be very careful with assembly as there is a sort of slotted nub on the underside of the diaphram that has to engage a slot on the arm that controls the internal fuel metering needle valve. If this arm / slot is not engaged (just pushing on top of the arm) the needle valve will leak usually causing engine flooding or dripping of fuel out the carb. The engine will usually run if this is not assembled correctly ..... but it won't run right and you will have a very hard time getting the engine to idle. On this side of the carb, a gasket will go between the diaphram and the carb body.

Lots more to these carbs but these basics should stop any leakback you migh have.

dditch

Thanks SOO much Gentlemen for all the suggestions.
Truckracer had it right.
It was the little part on the diaphram plate that was to hold onto the U channel of the rocker arm. It was not attached as I assembled it. I missed noticing that when I dissasembled it and when I put it back, just put it on top. Attaching it, what I did was to not screw in the rocker arm holding screw all the way so the rocker could pivot out more, I then put the diaphram plate to it and folded the diaphram gasket back to tighten the screw.
Mine came w/ a 2nd thicker and harder gasket. Rightly or wrongly, I assembed the side in this order.
1) Main Body
2) Thick gasket
3) thinner diaphram gasket.
4) outer Plate.
(Is this correct)

I"m wondering if I was to put the diaphram on the body side or the plate side?
Since I put it on the body side, I had to fish the diaphram gasket through the hole of the thicker gasket after attaching the diaphram gasket plate to the arm.
An exploded view of the Carb assembly would help.

I like to post info so that others who search this forum can hear the whole story.
Engine was first run up and flew 10 flights, then mothballed for about 9 years I estimate.
I purchased a rebuild kit from the local small engine parts store for the Walbro SDC Carb of the Quadra 75. ($11 for the kit).
I had replaced the 3 main rubber parts, pin on the other side of the rocker arm, rocker arm & Pin but not the fuel screen which as said, just needed to be wiped clean.
After tearing it apart, I think it would have been fine if I had left it alone. The Plane had been in my basement all this time so there was no dry rot but I felt the $11 was a good investment in $$ and a little time.

I ran it this morning and it started up reasonably quickly and held the fuel in.

Now, I'm onto adjusting the High and Low ends (I'll make a new post so that future searches from others will yeild good results) "Setting H and L needles in a Walbro carb"

dditch

I really want to know if I assembled the thicker diaphram gasket right w/ the Diaphram.
This is not my same carb but it shows how the thick gasket goes next to the carb body and the thin diaphram after it.

http://wem.walbro.com/walbro/product...milyName=ROPER

If anyone can confirm this please for the SDC (80?) carb that is used w/ the Quadra

Truckracer

My Feedback: (19)

On the regulator side of the carb (side with the stamped steel cover) the gasket goes on the housing first followed by the regulator diaphram, then the cover. Just the opposite on the pump side where the diaphram goes against the carb body first. The diagram you refer to illustrates this assembly. Hope this helps!