Bob Pastorello

My Feedback: (198)

I must admit, BBBlue, that I have personally never tried this technique, although I have heard from many who say that a carb has a problem if you can push fuel through it....check valves, pop off pressures and such.
Notwithstanding, I have some down time and a spare carb or two to play around with, so I will try your procedure just to see what happens. Appreciate your post!

captinjohn

Just thinking, did you say pressing the primer bulb on your set-up that fuel would drip out the carb throat onto the muffler. That is OK with me, because I am going to try your prime system. It sounds workable to me. Capt,n John

Bob Pastorello

My Feedback: (198)

captinjohn - if you're responding to my procedure for modding the carb to add the primer access tubing...yes, with the throttle full open, choke closed, and dry carb....after about 3 or 4 slow pushes of the primer, I could see the fuel being pulled into the carb from the tank outlet line, and hear the various carb passages filling, and eventually a few drips out the rear of the venturi (this example was a DLE 30cc mounted on a taildragger, so carb was "downhill").
I did the same mod to a DLE 20 equipped pattern airplane, same result.
VERY easy for initial start after the priming.

av8tor1977

My Feedback: (6)

Well, I posted that "Sticky' quite some time ago about how primer bulbs work and how they might be beneficial for us. I am glad some people are now getting the benefit from it. Good deal.

AV8TOR

Bob Pastorello

My Feedback: (198)

And thanks to you for reminding us! That sticky is mostly my stuff, with some great insights like yours from others....It is good to try stuff and find out what others already know!
I sure appreciate it!

BBBlue

Most welcome.
Hope it works for you the same.

BBBlue

SRY double post.

Bob Pastorello

My Feedback: (198)

I attempted to "force fuel" through two different Walbros today, attempting to pump fuel into the main fuel inlet fitting, and verify that the carb primed, and fuel flowed into the venturi.
On disassembly, there was in fact NO fuel past the primary inlet chamber, so it seems that either my attempts were flawed, or the carbs really do not permit this method of wetting various air-filled passages, such as though that would be found in a stored, dried out engine.

The pumping air cyclically into the diaphragm vent orifice works, as does the AV8TOR procedure of installing a primer port and primer into the fuel chamber beneath the pump.
I'm good, and have too different methods to adapt as needed for future seldom-flown gassers.
Thanks to everyone who helped with various tips and procedures. The ones I've implemented will see me through lots of trouble free starts!

av8tor1977

My Feedback: (6)

Trying to force fuel through the inlet like that will only allow fuel to enter if you exceed the pop off pressure of the regulator. That could be anywhere from slightly less than 10 psi to as high as 30 or so, depending on the carb and its setup. If you do that, you will surely flood the engine royally....

AV8TOR

acerc

Does this pressure method also risk forcefully changing the internal components such as one way valves and even the reg?

av8tor1977

My Feedback: (6)

The way to test the pop off pressure is with a tool Walbro sells that allows you to pump pressure into the fuel inlet and see at what point the regulator "pops off".

Personally though, I wouldn't attempt it with a liquid, as the liquid is not compressible and once it enters the carb after the regulator pops off, could possibly damage something. Not likely, but possible I would say.

Keep in mind, that this has nothing to do with using a primer bulb in the original manner in which is was designed, and as described in my post and others.

AV8TOR

w8ye

My Feedback: (16)

I'm not one to test for the actual "pop off" pressure.

The reason being is that this much pressure will not do your pump diaphragm any good.

My technique is to put one half atmosphere pressure on the fuel inlet. and see if the needle and seat of the metering alve will hold this pressure.

Then to cause the metering valve to open mechanically or with air pressure to the outside of the diaphragm. Then to allow the metering valve needle and seat to close to check for complete closure.

In this situation, I'm checking the integrity of the pump diaphragm and pump cover as well as the needle and seat of the metering valve.

I use a MityVac 8500 to make the test.

fixentocrash

hello well my way of doing it is full throttle full choke flip maybe 6 times fuel get to carb open throttle back to high idle flip 2-3 times engine starts than
dies open choke flip once twice and your off Bob all that is needed is to get fuel to pump side of carb on the wt series the cover with one screw in middle, your mod is on the metering side of carb which works because it pulls fuel through the pump side over to metering side so it does work but just seems like a place to suck air if your tube or hose comes loose i rather flip a few extra times if need be.

Bob Pastorello

My Feedback: (198)

UPDATE - I've always liked to post results of procedures and techniques, particularly when "new" to me, so I thought I'd do that here. One of my DLE 20's in my 1.20 size pattern airplane was one that would dry out very fast, simply because in the workshop, it stands on it's spinner along side the others that I can't story level or nose up. So, it was always very hard to choke, even requiring an electric starter when I wore out a shoulder.
This was the first carb I modified to add the primer bulb to, and the primer bulb itself is roughly at centerline of the carb/tank, and mounted on the side of the fuse.
Today's test was normal choke on attempts....no joy. Period.
Pressed the primer bulb maybe 6 or 8 partial pushes, could see fuel going out of the primer as it was drawn through the carb pump side.
Left the choke on, it was TOO juicy, so no joy with a few flips.
Opened the choke, high idle, two flips to start, and the noise told me it just had too much gas, so now I know not to use the choke. I'll test this theory on the next one, which is my DLE 30 in my Yak, probably tomorrow.

At any rate, this thing WORKS, and works well, and makes starting VERY easy. Hoping it works as effectively on the others I've mod-ed, which is the DLE 30 and a DM55.
Thanks again to everyone who provided input on this, Particularly av8tor1977, who posted this in the sticky years ago. It's good to go back and reread stuff now and then....

w8ye

My Feedback: (16)

+1

av8tor1977

My Feedback: (6)

When you are using the primer bulb, basically once you press it a couple of times or so and see it fill with gas, it has done it's job. When you feel the bulb get stiff and can feel it pushing fuel back into the tank, the carb is full.

AV8TOR

Bob Pastorello

My Feedback: (198)

I'm using a single line remote-style primer, and the bulb seems to settle at about half full. Frankly, I don't know how a single line works, except that it does...maybe someone can 'splain it ??

w8ye

My Feedback: (16)

With the single line bulb, the suction of the bulb will open the metering valve as well as suck fuel on through the pump part of the carburetor.

When you push on the bulb it forces some of what fuel that may be in the metering chamber into the carburetor venturi.

It acts as a primer.

av8tor1977

My Feedback: (6)

I personally prefer the dual line primer bulb. Less chance of flooding the engine, and we all know how difficult a flooded engine can be to start, especially if you are not using a starter.....

AV8TOR

Bob Pastorello

My Feedback: (198)

That makes sense, and good advice for something to watch for. I chose the single line simply because it was far less plumbing, no interference with inlet line from tank to carb, and that it seemed to NOT "push" as much fuel as the two line.

Evidently this single line because of where it's tapped under the pump diaphragm, it actually pushes air out of the carb system when the bulb is PUSHED, then as it is RELEASED, evidently that is the vacuum source to pull fuel FROM the tank/inlet line into the chamber, thus ready for the next push which will be less air, and more fuel. SO if one ignored that sound, or didn't test it much, one would end up with one helluva flooded engine....clearly, that's a risk. Have to see how that works out.