Tuning issues. Stalls out after WOT

SteveSS · Feb 27, 2016

I just finished up kitting a Tilly HU4. The saw starts, runs, and idles well, but stalls out after coming off of WOT. I've fiddled around with the H and the L, beginning at one full turn out from lightly seated. No matter how I tweak it, it still stalls out coming down from WOT. I could use some suggestions, please.

5000+ · Mar 1, 2016

SteveSS said:
I just finished up kitting a Tilly HU4. The saw starts, runs, and idles well, but stalls out after coming off of WOT. I've fiddled around with the H and the L, beginning at one full turn out from lightly seated. No matter how I tweak it, it still stalls out coming down from WOT. I could use some suggestions, please.

What saw? Stock? Wot rpm? Usually too rich on the H.

Motorhead · Mar 1, 2016

Might have to tweak the metering valve,bend the flap up a bit

TJ the Chainsaw Mechanic · Mar 4, 2016

I agree....try the metering lever. To low will run lean...to high and too much fuel goes in and floods the saw out.

fossil · Mar 11, 2016

Make sure as well that your new pump diaphragm doesn't have a small tear or hole in it.

Agree with the metering lever set too high as well. I doesn't take much.

dbittle · Sep 27, 2016

Let me dig this thread back up. I have the same issue going on with a Husky 242. What is a reasonable amount to lower a metering lever? I think mine has the metering lever issue going on, since I also had to turn in the high side mixture screw a little more than I really wanted to get it to run right. I've got new seals and it passed vacuum & pressure testing.

AVB · Sep 28, 2016

Considering the base adjust is 1-1/4 to 1-1/2 turns on mixture screw I would not worry about having to be in more as long as the engine runs good. A lot of Stihls are only a 1/4 turn out. A too low of a metering lever setting will also cause lean out at idle; just like too high will cause flooding.

dbittle · Sep 29, 2016

I'm about 3/4 - 7/8 turn out on the H screw and the saw stalls about half the time when I let off the throttle. I went in last night and lowered the metering lever about .015". That may have been too much and I may raise it back up about half that amount before I give it a try.

dbittle · Sep 30, 2016

Ok, I got a chance to run the saw again. It did tune more normally with the metering lever slightly lower. The stalling behavior was reduced, but didn't disappear entirely for most of the tank. I may have gotten it all balanced out before I finished, but we will see tomorrow. It almost seemed like it had some throttle linkage wear as well. When I let off the throttle, it would either settle immediately into a nice idle and stay there or it would settle into to a different slower idle and die. There was no middle ground and it never went from one idle pattern into the other one.

backhoelover · Sep 30, 2016

need to do a pressure vac test and you need to make sure your nozzle check is not leaking

dbittle · Sep 30, 2016

The saw does pass the pressure and vac tests, so we are good there. I have not tested the nozzle check valve. I watched the video on the walbro youtube site the other day about the nozzle check valve, but it did not tell what that valve does or how the saw behaves when it fails.

1990Husky262 · Oct 6, 2016

i have a 246 doing a similar thing and believe it is the nozzle check valve. I haven't had the time to dig into it yet. To test the nozzle i either remove it from carburetor and hook a hose to it, you should be able to suck through it but not blow back into the carburetor. You can probably also leave the jet in and close high speed needle and use a hose and hold against the actually high speed nozzle ( if it has a axuillary feed hole on it which i believe that one does) and you should be able to blow through it but not suck through it. Sometimes if find what happens is the sealant they used to seal the Welch plugs will loosen and flake of and get stuck in the rubber flapper and prevent from sealing other times the valve just gets worn. You can try knocking out the nozzle and carefully look through the holes and see if you can see anything and maybe carefully use some low pressure are and try cleaning it out but it doesn't always work. I happen to have the walboro part number right beside me at the computer it is 86-610-1 and that is for the HDA-98 carburetor.

dbittle · Oct 6, 2016

I called a temporary halt on this project when I discovered that my 346 was missing the piston ring pin, and that said ring and piston had suffered some trauma. Since I suddenly needed to order 346 parts, I added the 242 nozzle check valve to the order. My plan is to replace it and see what happens from there.

dbittle · Nov 2, 2016

No new information to report yet on the 242 nozzle check valve. It has been backordered for about 3 weeks so far. Hopefully it will show up soon.

AVB · Nov 3, 2016

dbittle said:
The saw does pass the pressure and vac tests, so we are good there. I have not tested the nozzle check valve. I watched the video on the walbro youtube site the other day about the nozzle check valve, but it did not tell what that valve does or how the saw behaves when it fails.

I got a S100A that has a bad main nozzle right now. I got learn to do the main nozzle test instead of just cleaning carburetor, installing a kit, and then to find out that I got a bad nozzle. Now I had to order a complete carburetor as that the S100A main nozzle is not available.

Kinda hard to check this valve but it is an one way check valve and I had good lot of them being leaky here lately. The problem I having with them the priming system won't prime properly and can leak air back into the metering chamber of the carburetor. Trying to pressure check them won't work through the primer line port as the nozzle will work as intended. To vacuum check which is only a few inches of vacuum would reveal if they are not sealing on vacuum. Don't over do the vacuum as you can damage the valve or pull the metering diaphragm down enough to open the metering valve; of course you can seal off the fuel pick port to prevent this. Now you do pressure check the fuel pump side by inputting about 5 psi though the fuel pickup port which checks that the metering valve is sealing and that there is no leaks in the fuel pump side of the carburetor.

Now some carburetor the mixture ports are open to the metering chamber. In these cases you pull a vacuum while listening at the main nozzle to hear if it is leaking with mixture screws lightly seated.

dbittle · Nov 15, 2016

Ok, I just received my 242xp nozzle check valve in the mail last night (11/14/2016). I ordered the silly thing at the beginning of October, so it has been quite the delay. I will make an attempt to install it in the saw and see how it works out this weekend.

dbittle · Dec 24, 2016

Bringing this thread back from the distant past, I had a chance this week to run the 242 with the new main nozzle check valve. It didn't really do much for it. I adjusted the idle up some, which did cure the stalling issue, but allowed the chain to slowly bump along from time to time. I am going to carefully inspect for a worn throttle shaft or linkage next.

Motorhead · Dec 24, 2016

You might have a weak clutch spring

dbittle · Dec 25, 2016

That might be. It also might still not be tuned quite right on the low side. I might well have left it a little too rich. I did look over the linkage closely and everything looked ok. I will check the springs as well.

dbittle · Dec 26, 2016

It appears that the re-tune did the job. I had to work over the tuning after replacing the main nozzle check valve and had the low side too rich at first. I did it more carefully today and ran a tankful of fuel through the saw without issue. Thanks to everyone for the help!!

Tuning issues. Stalls out after WOT

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