Two stroke weed whacker primer bulb

So, about six months ago I reported on by success fixing the leaf blower. That had a bad carb and stuck piston ring. So, I finally decided to do the same with the Troy-Bilt convertible weed whacker. (It has a shaft that converts between whacker and a lawn edger widget). It hasn't run in a decade. IT is still in really good shape, wasn't heavily used.

I took the carb apart and first thing, the fuel hoses were shot, disintegrating. The carb had a little bit of fuel gunk in it, not surprising since it was left with fuel to evaporate all that time. I fully disassembled it, except for removing one welch plug. Sprayed it with carb cleaner, blew it out with compressed air, rinsed the fuel tank, cleaned the fuel filter. I thought I'd have to get new fuel lines, but then I realized it was the same size as the fuel line I had bought for the leaf blower! So, I checked for compression with my finger, pulled the plug and checked for spark, put the new hose in, put it back together. Started on the first pull.

I revved it up, all was good. But then when run at high speed it starts to struggle, like it's not getting gas, then it quits. Put the choke on give it a pull or two, and it starts right back up. And that is what it was doing a decade ago when it wouldn't run! Doh! So now I'm thinking it's likely the primer bulb. It seems to have a lot of air, like 50% in it when it quits. Also, pumping the bulb, I can watch fuel in the lines and it looks like it moves back and forth, instead of in one direction. I'm thinking that it probably has a check valve in it that's kaput and it's probably also leaking air. But there is no sign of leaking any fuel. Being old, it should be replaced and I have one on order. But in the meantime, some questions:

This bulb is separate from the carb. Do they typically have a check valve in them? There was a little plastic widget in the fuel line, but on the parts diagram it calls it a "connector" and from the size and shape, I think that's all it is. I didn't use it, opting to just run one length of fuel line instead. I think it's purpose is just that it's a bit easier to put together with two pieces of line and then join them. But since I don't have the new primer bulb, I'm thinking that I will get it fired up, then remove the primer bulb and bypass it with that old connector. I figure once it's full of fuel and good to go, it doesn't need the primer and I can find out for sure if it is the primer without waiting for the new one. Does that sound like it should work?

Reply to
trader_4
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The check valve is in the carburetor if this is the typical Walbro deal. That is the flat mylar piece under the big screw. It is not unusual to see gas going both ways but more should be going in one direction. You can usually buy the whole carb for a few bucks more than the kit. Do you have the adjusting tool? Sometimes all you have to do is run the screws in and out a little to dislodge something stuck in there, Maybe remove the screw and blow it out, then readjust.

Reply to
gfretwell

It's a ZAMA, China's finest.

That is the flat mylar piece under the big screw. It is not

This is a fancier one, they call it quick start or something. It has what amounts to a choke knob that's part of the carb that connects to a red know that comes out of the house. To start it, you twist that knob that works against a spring and locks. Once it's started, first time you give it throttle, it automatically releases the choke widget. The choke isn't the butterfly type either, it works a valve inside the carb. Funny thing, according to the part numbering, I see that same carb come up without the quick start gizmo and with it. Without it, it's a $15 carb from China. With it, it's a $35 carb.

I don't have the tools and didn't remove those screws. You're right, I said I cleaned it all out except for what was behind one welch plug, but I didn't remove the those needle valves either. But, I don't think it has anything to do with the problem. When it runs, it runs perfectly, max RPM, goes like hell. But then after 20 secs to a minute it starves out like it's not getting gas. I'm betting it;s that bulb. I found the connector from the old hose, pulled it off, it's like I thought, just that, essentially a nipple. I'm going to use that to bypass the bulb.

If I get to it. I just got a rope over a 3" tree limb that's 25+ ft in the air. Now I have the rope saw and have to cut it off, back and forth we go.....

Reply to
trader_4

There is also going to be a filter in the tank that may be plugged up. It is on the end of the fuel hose. Drain the tank and shake it out through the filler hole.

Reply to
gfretwell

OK, so here's the latest. Upon looking at the plumbing, I realized that the primer bulb, even if it's leaking, can't be the problem. It's on the after side of the carb. Fuel flows from the tank, to the carb, out the carb, to the primer bulb suctions side, out the primer bulb and back to the tank via the return line.

But, just to be sure, I did bypass it and the symptoms don't change. Starts right up idles, runs up as you give it throttle, but at speed after about 15 seconds, it just dies out. Further suspecting a fuel problem, I tried running it with the return hose disconnected. While it's running, no gas is coming out of the return. So, logically what's happening, it's barely getting enough gas to run and when I advance the throttle, there isn't enough so it quits. This is the same problem it had ten years ago, when I gave up on it.

So, the only remaining two possibilites are:

1 - The carb isn't pumping properly

2 - The fuel filter in the tank is clogged.

The fuel filter, I had out. It had a kind of red, oily look to it, I presume from the remaining gas evaporating over ten years and the oil and some residue being left behind. I sprayed it out with carb cleaner, blew it out with compressed air and it looks OK from what I can tell. I doubt that's the problem, but it's still possible that it's partially clogged and can't flow enough. I will diagnose further.

The carb, IDK. Taking it apart it looked OK, a little residue that came right out, no corrosion. I'm no ace with regular carbs, let alone these two stroke gizmos. It has two plastic gaskets, one on each side. I guess one or both vibrate to pump the fuel? One has a dime size dome to it of the same material, no metal. The one on the other side has a nickel size piece of metal in the middle. IDK how flexible they are supposed to be, if they can stretch and no longer work, etc. All I know is there isn't any cracking, no missing pieces, they look OK, so what's wrong?

Here is a link to a rebuild kit on Ebay. The two plastic diaphragm gizmos in mine are the two on the left side of the first/main photo. The other similar ones are for other models. I guess I can buy a rebuild kit. All the other pieces in mine, eg the valve, spring, etc in that kit in mine look OK. Is there anything I should look for in those two parts that indicate they are bad and the source of my problem?

Another question, on welch plugs, I remember on a Tecumseh, the service manual said that after you put them in you should coat them with nail polish. I did that. Seemed kind of nuts, like you'd think gas would dissolve it, no? What are you supposed to do with welch plugs after you replace them?

I guess another option is just shell out $35 for a whole new carb.

TIA for any help.

Reply to
trader_4

Is this the regular Walbro. One big screw with the mylar flappers and

4 small screws on the other side with a rubber looking diaphragm? If so the diaphragm is the fuel pump and the mylar deal is the check valves. It is a pretty simple thing. Manifold vacuum operates the diaphragm and the check valves keep the fuel going the right way. You can try a kit but I usually just throw a carburetor at these things. I am about 50:50 with the kit so it is a wash. You should get the adjusting tool tho. Sometimes you can just tweak the HS needle and get them running right. I have a weed whacker that I screw with all the time. Some days it runs a half a turn more open and the next time I use it I have to close it a half turn. I also like the manual choke because you can play with that to see if it is too rich or too lean. Some days that weed whacker will only run with about 1/4 choke, no matter what I do with the jet. The problem is I really don't use it much.
Reply to
gfretwell

To update one more time, I tried using the prime bulb to pump fuel. It seems to do a lot of sloshing back and forth, which leads me to believe there is a bad check valve, either in the bulb or carb, IDK where it is. But it does pump some, and I tried to imitate a check valve by using a pair of plier to clamp off the hose to the carb while I depress the bulb, then take the pliers off, let it suck fuel. There is always air in the line coming from the carb and no air in the supply line from the tank to the carb. So, I think we can rule out a filter issue, that wouldn't put air in there. The lines are all new, so the only thing left is somehow air is getting in inside the carb. But maybe that's normal, but I wouldn't think so. Plus with the real problem being fuel starvation, it's consistent with the problem being the fuel pump in the carb.

Reply to
trader_4

It's a ZAMA used on Echo, MTD, Troy-Built, etc.

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Or just put 301821427313, which is the item number, in the ebay search bar.

One big screw with the mylar flappers and

No, two screws on each side. The parts are shown in the rebuild kit on Ebay. Sorry, I meant to give the link in the prior post:

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If that link doesn't work, just go to ebay and put the item number in the search bar: 172218406466

I guess that's what I don't understand. Those two plastic material diaphragm things look OK to me. I wonder if there's some passage that I didn't get to that's involved with pumping? I wouldn't think so, the passages from the connection pipes going into the interior are all clear. In my latest post, I said that it looks like a lot of air is in the return line from the carb, which sounds like something is hosed up, I would think it would be all gas.

You

Yes, I know what you're saying. There's so much going on inside that damn thing.

Reply to
trader_4

I am not sure who is knocking whom off but they are very similar carbs. On a Walbro there are 4 screws holding the sheet metal cover on and one big screw holding the cast metal cover on. The only difference in the models seems to be the main jet size. They are so simple looking it is just frustrating why I can't fix one. You are probably right, one passage is partially clogged. I have had some luck using a piece of fuel hose sized to fit over the main jet port in the venturi and blowing carb cleaner backward through the system. Just be sure you have the carb body stripped when you are blowing it out.

Reply to
gfretwell

Well, guess what. I was going to pull the carb again and have another look inside. I started to take it off and they have this curious flat plate that's bolted to the carb face, using the same bolts that hold the carb on. Never saw anything like it, wasn't sure what it's purpose is. I noticed there was a bit of oil at the bottom of it, that also had oil on it from years ago, when I first took it apart. So, after taking it apart I took a closer look to see what that thing does. The only thing I see is there is a hole coming out the top of the carb face, above the carb throat, and a little channel machined out that goes from the hole to the throat. The plate covers that channel. Remember this carb does not have a conventional choke. Instead it has this knob you twist, that lifts a valve. So, what I think happens is when the choke is on, the valve allows additional gas to come out that hole, across the channel in the face and down into the carb throat. On the parts diagram, they call this mysterious plate the "choke plate", which confirms it's purpose.

Before removing the carb, I decided to run it with that plate off, to see if I see any gas leaking out, etc. So, I put the two carb bolts back in without the plate, started it up and it seems to be working fine! I do smell gas though and it looks like gas might be dripping down to below the carb face. Will have to take a better look today. But my thought at this point is that the choke valve is leaking and it's supplying excess gas when the choke is off. So it will start up cold run for 15 secs, but eventually it craps out because it's too rich. Taking that plate off, instead of the gas going into the carb throat, maybe it's just dripping outside the carb. That's the only explanation I can figure for what I'm seeing. My main thought at this point is to put it together without the choke plate and start using it. Then I can take apart that choke knob/valve and inspect it again. It has what looks like a rubber cup on the end that fits over some plastic doo dad inside the carb to form the valve, I guess. I had it out and it looked OK to me, but maybe it's shrunk or something.

Reply to
trader_4

...or just grab it with a stiff wire bent into a small hook at the end- or use a similar tool- and pull it out.

Reply to
Wade Garrett

So, I determined that it runs better with that choke plate thing off. But it still winds up crapping out. I actually edged about 7 ft of sidewalk. I analyzed how that choke plate works together with the quick start choke valve. It looks to me like that mysterious hole in the face of the carb goes from the carb throat in front of the throttle butterfly to the quick start valve, to the carb throat on the other side of the butterfly. So, when the choke is activated, it forms a small path around the butterfly. Once it starts and the choked comes off, the valve just closes that path. It must be working. Why taking that flat plate that just completes that path made it run better, IDK.

I was going to fiddle with the adjusting screws. These are some weird kind. It looks like one, problem the main, can be turned with a screwdriver but only for a limited distance. The other one, must be idle, can't be turned at all. I assume if I break this plastic crap off that limits it all, there are screws with some no-tamper head under it. I was going to try to fiddle with the one I think is the main, but the more immediate problem is this. The fuel lines were shot, but fortunately I had some extra left from working on the leafblower and it's the same size. I had enough for the main line, but not the 4" for the return. I hoped to use the old return long enough to get it working, but with the screwing around, it's breaking.

So, I decided to order the carb rebuild kit and hose. It's on it's way from China, ~$3.25 for it all. As I said before, I don't know how tight or loose those plastic diaphragm/gasket material is supposed to be. I'm wondering if it's supposed to be tighter, like a drum and maybe it's stretched enough that it flops around instead of working like a pump. With the new parts in the carb and fuel line and the new prime bulb which is on it's way, I'll resume. I'm not desperate to get it going now and for $2.50 trying the rebuild kit seems like it's worth it. I figure I can probably break the plastic anti-tamper crap off and figure out a way to turn the screws more if I have to.

A question, should the return line normally be flowing gas when it's running? This one, no gas comes back, leaving me to believe it's not getting enough gas, which would explain it crapping out. Or is that normal and the return is only there for when you're using the primer bulb to get it loaded up with gas before it starts?

Reply to
trader_4

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