Walbro Carb Check Valve

[landlubber]

Hello,
I'm working on some 026's with the Walbro 194. New kits installed. Starting at 1 turn out L/H.

I have a saw that will start, idle OK for a bit but gets unstable a bit if you tilt the saw on it's side (holds vac and pressure post rebuild). Runs OK in the cut but seems a bit lean. When you let off out of the cut, the saw will take a while to spin down like its lean and it will die and not restart easily. Choke doesn't seem to help. Sometimes the saw won't rev up easily without hitting the throttle a few times. Fuel line and impulse are new and I vac/pressure test from outside the boot so all that should be leak tight.

My thoughts were that the check valve was leaking and allowing air into the L-speed circuit. I've tried to check the check valve and the little disc is loose and I can blow through it but can't pull vac against it. It blows through freely and restricts flow in reverse but isn't leak tight. I tried a few other carbs and they are the same, the check valves don't seal but provide some 'one way action'. Is this normal?

I'm testing with the L screw seated, a nipple into the H screw hole and my thumb over the little hole in the metering area. I can see the check valve disc dancing in the brass retainer when I blow into it.

Thanks
LB

 

[merc_man]

Sounds to me like the check valve is ok.
Ther is a thread on these 026. Type in 026 carburator and that should bring it up. Sounds like some of these are finicky from factory. I have one now that im trying to figure out. Its about same as yours. Passes vac and pressure. Will idle and soon as tip forward it dies. I have replaced impulse and made a fuel line for it. Just got the oem one in so gonna put it in this weekend.

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[merc_man]

https://r.tapatalk.com/shareLink/to...hare_fid=1392778&share_type=t&link_source=app

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[merc_man]

That link should get you ther.

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[landlubber]

Interesting, thank you.
I pressure tested the inlet needle, it was good. I remounted the carb with some hylomar around the metal ring/boot and the carb face and reset the needles to 1-1/2 and started over. It's taking a lot more fuel now and not seeming so touchy. It ran quite well but I didn't have time to run more than 1/2 a tank through it. It's much better.

 

[drf256]

Great efforts to diagnose. Well done.

I can only tell you that the 194’s can just go bad on occasion. You can rebuild them all you want, but sometimes you just need to get a new one.

Did you pull the Welch plug and chase the holes clean with a micro bit when you rebuilt?

The check valve sounds to be functioning correctly. Don’t forget it is normally wet, so it will seal better. It only stops negative pressure in the metering area from pulling sit back through the nozzle instead of pulling up the diaphragm and opening the needle for fuel. The Low circuit (and transition) is fully fed via the area under the Welch plug. The only reason that they don’t back feed the metering area with air is that there is some constant negative pressure in them at idle via Venturi effect.

See the thread Merc Man referenced above and also check those transition/idle holes out.

 

[Brewz]

I've had a few carbs that just wouldn't work right no matter what I did.... multiple ultrasonic and chemical baths, multiple rebuild kits and welsh plugs.

Punched out the main nozzle and replaced with a new OEM one and they were like new again.

I now replace them as part of a carb rebuild on a performance build, just a few $ for insurance

 

[landlubber]

I did test the check plate wet but did not pull the welch plugs as everything else was very clean. I'll keep testing it and if there's any more strange behaviour I'll pull the plugs.

 

[fossil]

Sounds to me like the check valve is ok.
Ther is a thread on these 026. Type in 026 carburator and that should bring it up. Sounds like some of these are finicky from factory. I have one now that im trying to figure out. Its about same as yours. Passes vac and pressure. Will idle and soon as tip forward it dies. I have replaced impulse and made a fuel line for it. Just got the oem one in so gonna put it in this weekend.

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There's a good thread on here about some 026 cylinders that have a little lip in the intake that causes the fuel to puddle in there. When you tip the saw forward it will dump the puddle of gas into the cylinder and die.
The thread shows how the carefully grind or sand that lip out.

 

[merc_man]

Great efforts to diagnose. Well done.

I can only tell you that the 194’s can just go bad on occasion. You can rebuild them all you want, but sometimes you just need to get a new one.

Did you pull the Welch plug and chase the holes clean with a micro bit when you rebuilt?

The check valve sounds to be functioning correctly. Don’t forget it is normally wet, so it will seal better. It only stops negative pressure in the metering area from pulling sit back through the nozzle instead of pulling up the diaphragm and opening the needle for fuel. The Low circuit (and transition) is fully fed via the area under the Welch plug. The only reason that they don’t back feed the metering area with air is that there is some constant negative pressure in them at idle via Venturi effect.

See the thread Merc Man referenced above and also check those transition/idle holes out.

So what goes bad on them? My BIL just ordered a new one for his cause the dealer told him that too. I had never heard of a carb going bad befor till now. 130 bucks for a new wt 194.

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[merc_man]

There's a good thread on here about some 026 cylinders that have a little lip in the intake that causes the fuel to puddle in there. When you tip the saw forward it will dump the puddle of gas into the cylinder and die.
The thread shows how the carefully grind or sand that lip out.

You wondnt happen to be able to find the link for it. I cant find it.

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[drf256]

You mean the recent one?

https://opeforum.com/threads/026-carb-question.23692/

Not sure what goes bad in them. I suspect it’s generally debris or varnish in the idle/transition holes. I guess it could be the check valve flapper as well. I’ve seen oem some kits supply the little disc for them while others don’t.

To the OP, if you pull the Welch plug and chase those holes without enlarging them I bet your issue gets resolved. Hit them with some carb cleaner as well.

 

[fossil]

You wondnt happen to be able to find the link for it. I cant find it.

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The link in drf256's post above this post. Start on page 2

 

[merc_man]

Ok that one. Im in that one too lol.

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