Craftsman Weedwacker flooding

[KE4AVB]

If you get gas coming through the main nozzle in the venturi by using the purge bulb, something definitely ain't right, and line hookups will have nothing to do with that. The high speed check valve in those carburetors is the final point which fuel can reach un-aided. Do a teardown of enough of these carburetors, and really look at the check valves and how they work, it's easy to see. Now, if the check valve is bad, then, YES it is easily possible for the situation you describe, (and a backwards check valve is a bad check valve) - But otherwise, no.

I think your overlooking something here. Now if this was a cube with a built in primer then operation is different as all the check valves are in the cube but this is two piece system where the priming system check valves are separate. The separate primer has two check valves in it and this carburetor has no check valves in the discharge port going to the primer to prevent backwards flow. The main nozzle does contains a check valve. Now with the primer lines reverse and fuel is fed into to the discharge port it will pressurize in the diaphragm chamber. Now think of the main nozzle as an one way side street. Since the fuel mix can not go back though the needle valve (check valve) which would closed it has no choice but to open the main nozzle check valve and push into the throat of the carburetor. In this configuration as the fuel expands fuel will leak out of the carburetor. Engine can be started and run a short time until fuel in the carburetor and primer line is used up. With the carburetor leaking sometimes there will excess fuel mix in the crankcase that would also be available to burn.

[bgsengine]

Actually looks like we're both wrong - me more than you, but...

Just sold a new Echo, about 20 minutes ago- customer traded in (token 20 bucks) one of these they had bought by mail order - they ran straight gas through it but it ran fine before it blew up. I stripped the carb off and noted that the configuration is different from the ones I had been thinking of and worked with before (I think they must have been Zama, perhaps.)

I am wrong in that it does not hold pressure when applied to the return port , but you are wrong in that it does not go through the main nozzle check valve (I'm still right on that point- they do hold the pressure, I just destroyed the carb by filling the idle ports with solder!) - The fuel WILL leak out into the carburetor, but it goes through the idle ports which do not have any check valves involved. Once I filled the idle ports with Solder, carb would hold pressure no matter which way the pressure came from. But it is true that they DO leak - now I am trying to figure out which carburetors I must have been thinking of that did NOT - I believe it may have been off a fixed adjustment (no idle /low speed adjustment, just a check valve) but for this particular model, which Is now sitting on the scrap heap, it is true that they can leak, but it comes out the idle ports, not the main nozzle.

[KE4AVB]

That one on the mixture ports is one source that I overlooked but as for main nozzle leaking I actually seen that with my own eyes here even with ilde mixture screw fully seated which can still leak. When I corrected the plumbing the problem went away. At least now you can see how they can leak if connected backwards. I not going argue over if you or me is right about the main nozzle as it is an open possibility either way and really depends on the manufacture's design and what has happen to the equipment since it was assemble.

The only comment I can make here that I have seen things happen that I was told were impossible for piece equipment to do over the years and had to come a fix on my own.

One question though what kind solder did you use? My regular electrical solder here will not stick to aluminum other than by leftover resin.

[KE4AVB]

I have some spare time on my hands today so I pulled the Zama Tech manual and Walbro should be close inline with this.

A picture is worth a thousand words...although it doesn't include the fuel line plumbing. The labeling isn't mine either.

Copied Zama Tech Manual

[bgsengine]

That one on the mixture ports is one source that I overlooked but as for main nozzle leaking I actually seen that with my own eyes here even with ilde mixture screw fully seated which can still leak. When I corrected the plumbing the problem went away. At least now you can see how they can leak if connected backwards. I not going argue over if you or me is right about the main nozzle as it is an open possibility either way and really depends on the manufacture's design and what has happen to the equipment since it was assemble.

The only comment I can make here that I have seen things happen that I was told were impossible for piece equipment to do over the years and had to come a fix on my own.

Yes, but again, the main nozzle check valve, new ones - should *NOT* leak like that - Minor seepage is tolerable, but they are intended to prevent fuel from feeding uncontrolled into the main nozzle. - It isn't *impossible* for them to do that.. but it isn't *right* if they do.

One question though what kind solder did you use? My regular electrical solder here will not stick to aluminum other than by leftover resin.

[/quote][/quote]
popped out welch plug, heated idle ports with butane pen torch, painted with plumber's flux, then melted in some regular rosin core solder and drop it in the ultrasonic tank for a quick cooling. Trick is to heat the aluminum enough for the solder to melt and remain liquid so it would flow into the holes, it doesn't need to "stick" and as soon as (you got to work fast) it spreads out, cool it before the heat gets to and melts the rest of the carburetor parts. Those little butane pen torches let you get a lot of heat in a very small spot very quickly. Couldn't have done it with a regular propane torch or soldering iron.

[Deere2me]

oops, Model 316794400, somebody else did do the fuel lines, but I think that if they where hooked up wrong, it would not run at all or pump gas from what information I have. Check valve sounds most likely, I appreciate your fast responses.
Pat

OK now, did ANY of the preceding babble answer your question????

[plpitts1]

Looks like when I get back to work in the morning I need to check the fuel line hookup. I’m pretty sure they are right as I double checked them when it was brought up at the beginning of this conversation.
Thanks for all the input, and information.
Pat

[plpitts1]

Fuel lines hooked up correctly. Fuel line with filter to pump side of carb, fuel line from diaphragm side to (short) vacuum side of bulb, return line from other side of bulb to tank. So what I get from reading these posts is that my Carb is no good.
Thanks again.
Pat

[KE4AVB]

Thanks Pat for the update. It does sound your going to need a new carburetor. Depending on the condition of the trimmer it might be better just to replace it considering the new carburetor cost. All that depends on the customer too. Here I got a couple chainsaw collectors that are willing pay well to get an old saw back into running condition if possible. They just want them in running so they show them off at meets. Once I get them in running condition they have them repainted at another shop.

I have only had two carburetors that flooded when connected correctly and both had leaky needle seats which are non-replaceable. One was a Zama and the other was a Walbro. The Zama carburetor was still available so it got replace but the Walbro was NLA and its replacements were also NLA; needless to say, that chainsaw died. It was left here in the shop as donor for others so it may live on in parts.