OutdoorKing Repair Forum Forums Repairs and Maintenance Questions on Trimmers and Brushcutters Ryobi Trimmers & Brushcutters Ryobi Lawn Hornet 1100 MK III Leaking

There's nothing like applying the scientific method when you need to solve a problem, and that is what you are doing. Personally I would not have expected the double diaphragm setup to work, because the doubled flap valves might be too thick to work, but I haven't tried it, so that is just prejudice, not science. You've found that it didn't work, but not why. If you now try the mylar one alone, and it works, the only possible reason will be something that is different between the double diaphragm and the mylar diaphragm alone.

If the interior of the carburetor was dry, no fuel was being pumped, so the problem was most likely in the fuel pump. You put the old diaphragm back in and it worked for a while, which further supports the idea that some aspect of the double fuel pump diaphragm was the specific cause.

Because the baggy old diaphragm had been working for years, it will quite likely continue to work for a while longer. Hence I do not think it would have been the sole cause of the machine flaming out and not restarting. However if the output from the fuel pump was pretty marginal with the old diaphragm, combining that with low fuel level and a lower starting throttle set-point might just keep the machine from starting. Filling the fuel tank and putting the throttle cable back the way it was originally might get it working again, for a while and in a fashion.

If you continue to go step by step and apply careful reasoning, you should get to the bottom of this. Personally I'd try the mylar pump diaphragm as the next experiment, rather than try to get some action out of the baggy diaphragm. You've said that is what you plan to do, too. I'll look forward to hearing how it goes.

yeah, getting there. Thanks for your help. I will try the mylar alone next. However just to clarify I did not use the the two diaphragms with flaps. Only the conventional has flaps. The mylar part I used is the one at the bottom right in the photo. That one on top of the conventional one gives me the shape of the mylar diaphragm with the tick (which I haven't used yet) in the picture. The problem the cutter must have had to do with the leak, The metering diaphragm was broken and a bit stiff. I replaced it and the leak has gone. I was able to use the cutter for 20 minutes. The pump diaphragm is not broken but is is stiff and not good as you say.

So you used the conventional one second from the top of the center column (with the cross on it) together with the mylar one at the bottom of the right column? Which one was in contact with the carburetor body? Remember that the flap valves can only work if they are right up against the flat metal carburetor body. If you put anything in between, such as the gasket or the mylar diaphragm, the flap valves can't work. So, the conventional item second from the top of the middle column needed to be directly in contact with the carburetor body, and the mylar diaphragm needed to be in between that item and the gasket, which would have been against the pumping chamber cover.

Have you replaced the fuel filter on the end of the pickup hose, inside the tank? If it is restricted by dirt it will reduce fuel pump performance.

Yes, I had used those two in the correct order: the conventional first(in contact with the carburetor body, then the mylar then gasket and then cover lid but it wasn't working.


When I put the old ones back, there were a couple of things I also did. Adjusted the trigger wire to make it tenser and also took the clip that holds the needle and bent the end upwards a tiny bit as it did not seem to be lifting the needle before. So perhaps this helped fix the problem.


I now tested both: the mylar type diaphragm and the conv+mylar set up and both worked. I did not notice any difference between the two. However it seems to me they both are smoking a little bit more and running slower than when I used the old diaphragm. This may just be my wrong perception but it also feels they have a smoother idle run, which is nice.





Again, I may just be wrong or perhaps that is how it is. The old set up is not good anyway, so I don't have a good point of comparison. It may have to do with the trigger wire adjustment (although I thought I kept it within range of where it was )

In short, the mylar type pump diaphragm runs ok at least for now. There is no much to do in my yard at the moment so didn't do much testing. I'll give it some more use next time I mow my lawn to see how it behaves in the long term.

My take on that report is that the mylar diaphragm alone works correctly, but you have now adjusted the metering lever height, in the metering chamber where you had already replaced the diaphragm. If you have done that, it changes the air/fuel ratio of the carburetor. However, you report that it now runs fairly well, so you may have only made a small adjustment (the metering lever height is a rather sensitive adjustment).

Here is the Walbro service manual for your carburetor:
http://wem.walbro.com/distributors/servicemanuals/WTseries.pdf

Please read the manual, paying particular attention to the metering chamber and the metering lever, then clear up a couple of points for me:
1. Did you change the metering lever height?
2. Does your carburetor have externally accessible H and L mixture screws?

If you post a picture or two showing the H and L screws, that will help also. Please do not make further adjustments to the metering lever or the H and L screws until we have these points clarified.

Thanks for the file. 1. Yes I changed the height of the lever by bending a bit the tip that lifts the neddle. But as I said before, this is what I did just before putting the old set back. I did not make any changes now when I tested the mylar diaphragms. The reason I did this is because adjusting the lever screw did not make any difference. When I pressed the spring down, the needle wasn't getting lifted. Probably the previous owner had been playing with it because it looked like the clip of the lever had been bent down. So I brought it up a bit. That is when I got the cutter working continuously for first time. It just happens that I had also put back the old pump diaphragm then. Next I just replaced the diaphragm with the mylar types and confirmed they worked too. 2. yes my carburetor has two mixture screws but i didn't touch them at all.

We are getting there, we just have a bit further to go.

I am not sure what you mean by adjusting the lever screw. I think you mean you were loosening the retaining screw that holds down the metering lever pivot, circled in red in this picture:



That screw should be tightened firmly to hold the pivot in place - it is not an adjustment. The metering lever is adjusted ideally by using a plastic tool, like this:



You can easily make your own gauge out of sheet metal. For WT and WA models, the center bar, which touches the top of the metering needle, should project 0.065" (1.65 mm) below the other two bars, which rest on the flat body of the carburetor at the sides.

It seems from what you have said that you have the metering lever height close to correct, but it worries me that you may not have had the pivot retaining screw tight when you measured it. Because the metering lever is spring-loaded, it rises up when the screw is loose. Unless the screw was tight when you finished your adjustment, it looks as if you need to go through the process with a home-made gauge.

Once you have the metering lever height adjusted, we can talk about making any necessary fine adjustment of mixture by using the H and L screws. If you had the pivot retaining screw tight when you did your test, it sounds as if all that will be needed is some fine-tuning of the high speed mixture screw, but please do not touch that until we have finalised the metering lever discussion.

yeah, I realise I had the wrong idea. However I was pretty sure I tightened the screw firmly. I checked this again and I had done so. All i did was "correct" a bit the clip that lifts the needle as it seemed twisted/stretched.

I made (sort of) the gauge and measured as in the photo ( middle bar resting on the lever) It is quite close. Close enough I would think.

On a side note, I can't help but think this tool would only be useful if I knew my lever had got the right shape. As I said, mine did not look so. Also if you saw the lever was too high, how would you adjust it. would you use a screw driver or something to bend the lever?

At this point, to be honest I am not sure what I should be looking for. It is true I have the feeling the mylar diaphragms made the cutter run slower but I could be wrong, and if not maybe that how it is supossed to run. I don't have much experience with one of this.

I will be interested in learning about the fine tuning even though I may not need to apply at this stage.



Thanks again for all your help, I had fun bringing the cutter back to life and more importantly avoiding it to go to landfill.

Remember you are applying the special gauge to the rounded top of the fuel needle, not the lever itself, so the shape of the fork on the lever is not critical, except that the needle should be supported by both sides of the fork.

Post-edit: The above instruction is wrong, the gauge is applied to the opposite end of the metering lever, directly above the spring. My error. I must be getting too old for this stuff, it isn't long since I last adjusted one of these.

In principle you can adjust the fork either by holding it and bending it in place, or by taking it out. I prefer to take it out, because it is rather springy (it is not dead soft steel) and I do not like to risk having the tip of the needle pushed hard against its seat. If you take the lever out to adjust it, you can be quite careful to bend both sides of the fork evenly. On the downside, putting the lever back in without the spring going ping and disappearing, requires care.

Once the metering lever height is set, adjusting the mixture is theoretically easy but can be rather frustrating in practice. You do it like this. If the carburetor has been stripped completely, you simply reinstall the H and L needles by screwing them all the way in until they very lightly bottom. Then you turn them both anti-clockwise one and a quarter turns. That gives you fuel settings that will allow the engine to start and run, though probably not especially well. Then you set the idle speed screw fairly high, start the engine using the standard procedure, and let it warm up. Once it is warm you reduce the idle speed as low as you dare, or ideally, until the clutch disengages and the cutting head stops rotating. Then turn the L screw (idle mixture) slightly clockwise a bit at a time until the engine suddenly runs smoothly (that is, 2 stroking - it will have been 4 stroking initially). Move the needle clockwise and anticlockwise until you find the most anticlockwise position that allows it to 2 stroke, or just a bit richer (more anticlockwise) than that.

Next step is the H screw (high speed mixture). Open the throttle wide and turn the H screw clockwise until it suddenly smooths out and 2 strokes. Feel around to find the most anticlockwise position (that is, richest mixture) that allows it to two stroke fairly steadily. However do not dally on the clockwise (lean) side of the best position, where it stops 2 stroking and starts 4 stroking. Lean mixture at full throttle can damage the engine. (This is especially true of high performance chainsaw engines, but you should always avoid running on the lean side at high speed/heavy throttle, for any engine, 2 stroke or 4 stroke.)

That is the official tuning procedure. In practice, you may find that when you have done that, there is a lean zone somewhere between idle and the "starting" throttle position. Consequently if you open the throttle suddenly from idle, or if you linger for a while anywhere below the starting throttle position, the engine may hesitate or stall. If that happens it is best to make the L screw just slightly richer than the 2 stroking position, to overcome the problem.

wow, I am glad I did not touch the L and H screws. Great info but I will have to read it a few times before I try that. thanks again!

Hi grumpy, Ok, after some more testing and some troubles getting the cutter to start after stalling, I decided to revisit your instructions and here is what I am to so far. The position of the needle was sitting somehow 4 to 5 mm below the flat part of the carby body. I realised this wouldn't come to meet the 1.65mm you say it should be, no matter how much I fiddle with the lever. If I bent it too much i was compromising the spring mechanism. (at 90 degrees the needle would unhook or the spring would come lose. Anything less that that would not lift it enough to be at 1.65mm from the top. I assumed that perhaps my carby is different, so lifted the needle as much as i could and went ahead trying to adjust the mixture screws. The problem I have now is the cutter wouldn't start for the initial settings ( 1-1/4 turns CCW on both screws). I tried a bit more turn and a little lees turn in either or on both screws with no luck. This is just after I had been using it. One good sign is, in the choke position I get a positive response. So much that it sometimes runs on full choke for a few seconds. I'll die if I switch to partial choke. Similarly when I manage to get something out of it in the partial choke position, it is just a fast burst that dies out in no time. I have tried to switch this quickly to the run position but it dies anyway. Is it possible that my carby needs different initial L and H settings. It was running some minutes before I played with the screws. I didn't actually take note but it seems i had to screw them in more than 1-1/4 turns to get them to the bottom.

Lifting the needle makes the mixture richer. If you lift it too far, the carburetor will flood, which will be pretty obvious if it happens. However there is something wrong with the process if it measures 4 to 5 mm down, and runs as well as you had it running initially. You didn't by any chance put the lever in upside down the last time you assembled it, did you? The spring end of the lever has a feature to center the spring, if you have it the right way up.

Using different L and H settings will not hurt anything, but needing to use them tells you that your metering lever height setting is wrong. If you need to use a lot more than about 1 1/4 turns it tells you that you have the needle too low, and if you need to use a lot less it tells you that you have the needle too high.

Nope, the lever is not upside down. For my type of carburator it is just practically impossible to lift the needle that much. It sits at about 4-6 mm below the flat part of the body. So I did some more research and found a couple of sites that say the walbro tool is to measure the height of the lever arm(not the top of the needle) That makes more sense to me, at least for my type or carb and it is consistent with the photo you attached and other photos I have seen. I also found out that the tool is not needed for WT carbs as the lever sits flush with the surface right beside it. This can be set with the end of a small ruler. I will try readjusting the lever back to where it was and see. I know I am spending too much time on an old cutter that people say is not worth the money but this has been a great learning exercice, which is what I am really after.

It seems the 2 months since I last set a metering lever is too long for my memory to hold up: I gave you an incorrect instruction. Yes, you have to set the height of the lever arm directly above the spring, not the height of the tip of the needle.

Now, let's run through the process with that correction. The WA model does not require a measuring tool, for the reason you gave: you can just lay the end of a ruler across the surrounding metal and it has to just touch the end of the lever, right above the spring. However that is because the WA has a flat surface lower than the surrounding surface. Here is the instruction from the WA manual:


Here is the one from the WT manual, which you will notice applies also to the WA:


The measuring tool you made is supposed to be the same as the one in the WT manual: it spans all the way across the end of the carburetor. What you may be saying is that the dimension I gave you (1.65 mm) is incorrect.

Here is the Walbro Service Manual's instruction for setting the lever height:


So, if you use the 1.65 mm gauge you made, applying it to the lever arm above the spring, not the tip of the needle, does everything suddenly work correctly? Or are you saying I gave you the wrong dimension for the gauge? That 1.65 mm figure did not come from Walbro, it came from a repair technician on the internet, so it could perhaps be wrong - I'd very much like to find out if it is.

I found this:

Apparently there are two types of WT: Circuit Plate Type and Welch Plug Type. The first one doesn't need the tool, the second one does.




I am not sure what this all means but from the diagram above and photo below (taken from outdoorpowerinfo.com) my carb seems to be a Welch Plug Type. So it may need the tool after all.



However, there seems to be on line speculation that when you use the tool, the height of the lever arm comes to be flush with (if not very close to) the internal flat part of the carb around the lever. My carb has that flat section. I haven't yet tested this.

In regards to the distance (1.65mm), I didn't mean to imply it was wrong. In fact I found it is supposed to be between 0.060" and 0.070" You gave me 0.065" so you are spot on.

Had to edit to add this last pict showing the position of the straightedge for the WA WT WTA Welch Plug Type one.

Now that you have made the gauge, it seems like a good idea to use it - it works on any WA or WT, as I understand it. Then having set the lever correctly, you can check whether the lever height does correspond with the nearby flat surface on the carburetor body. On the WA, the flat surface does work, and that is the way I set WA lever height, but WT is not quite so straightforward because there are variants. That seems to be why Walbro recommends the tool, which works for all of them.

For future reference, remember that your tool is for WA and WT: some other models use other dimensions for the distance between the top of the lever and the height of the carburetor body.

Referring to a couple of posts ago, I think it is well worth persevering with getting this carburetor, and this trimmer, working properly. You are learning something as this goes forward. You never learn anything by giving up, you just lose confidence in yourself.