Walbro carb problem

[openspaceman]

2 hours ago, bmp01 said:

 

I agree with adw, the check valve (red circe) is to stop the purge bulb from sucking air through the various jets - its so much easier to suck air than fuel.

Where's the fuel feed to the low speed circuit ? Is that through the same check valve (red circle) as high speed circuit ? 

Also agree the brass main jet looks odd, looks like its pressed in too far. Does it protrude a long way into the carb throat?

 

 

I think you are both right in that the check valve should prevent air being sucked back from the choke tube when the purge bulb is used and as there was a very  fine stream of bubbles in the purge circuit this check valve leaking would explain that. The jet protrusion looks okay.

 

 

 

The red circled check valve looks like it is the only exit from the metering chamber and definitly connects to the main jet. There is one idle drilling forward of the butterfly and a few under it when closed. These latter must have been drilled before the large welch plug was fitted.

 

Either way this check valve is passing fuel in both directions and if I cannot get the thing out and replace it the carb is toast.

[openspaceman]

17 minutes ago, spudulike said:

This is an interesting turn of events as if that check valve has been pushed in too far, it will most likely cut off the petrol feed to the thing.

You could tap it through with a drift and then refit it so it is level with the lip you can see in the pic. If you are careful, you may be able to lever it out from inside the bore if it isn't too tight but I would knock it through if there is internal clearance to do so.

I think the brass jet is fitted okay. This is a cheap carb and maybe they have used this check valve as the only way for fuel to exit the metering chamber to the idle and main jets as a cost cutting exercise??

 

Once I decide there is no way to repair the check valve and the carb is scrap I will knock it out and post a picture.

[spudulike]

If all else fails, you could try plugging the purge circuit so the carb can work without it if it is faulty. Perhaps a little gasket seal may do it so it can be removed if it doesn't work. It may make the machine harder to start but at least it would prove the point.

Have you compared the good carb with this one? I know they are different carb manufacturers but they may operate in a similar way.

 

 

[spudulike]

Just looked at the carb pics again and, unless I am wrong, that check valve supplies the fuel to the high and low circuits from the look of it as there are no other jets present so blocking it would stop the machine running.

 

Is it definitely a check valve? It does look like the type you get in a typical plastic purge bulb housing but not seen one like this but have spent the last 10 years avoiding them

Do you think someone stuck a pin in it thinking it was a jet and fooked it? 

[openspaceman]

19 minutes ago, spudulike said:

 

Do you think someone stuck a pin in it thinking it was a jet and fooked it? 

Very likely as we are all inveterate "fixers" at the repair cafe, and everything was very clean.

[adw]

I have never seen a main jet nozzle that deep before.

[openspaceman]

15 minutes ago, adw said:

I have never seen a main jet nozzle that deep before.

I doubt you have had the misfortune to work on an Einhell saw either

[spudulike]

I did an Einhell hedge trimmer once, the gearbox had locked up. Turned the gears over backwards and it all freed up so handed it back fast and legged it. Great quality

[bmp01]

You dont need the purge line gubbins. I'd argue youre better without and have deleted it many times on my saws. Just put a short bit of hose on the carb (in place of the purge hose) and blank the end of short hose. Blank off he purge line too.

So long as that oneway valve passes fuel without restriction your now good to go.

 

Regarding the main jet/one way valve .... small parallel punch and hammer.....tap it through into the centre of the carb. I hold the carb in vice jaws with the choke in closed posn, bit of something soft to protect the faces of the carb. Keep the punch in the midldle of the jet. The jet will pop out into centre of carb, you can retrieve and inspect jet for its one way operation. Also have a look at the drillings in the carb and the groove around the jet and see how far the jet should be installed. Just tap it back into place when you're ready, it alignes itself easily with a little care. Theres no rocket science here. 

 

 

[openspaceman]

1 hour ago, bmp01 said:

You dont need the purge line gubbins. I'd argue youre better without and have deleted it many times on my saws. Just put a short bit of hose on the carb (in place of the purge hose) and blank the end of short hose. Blank off he purge line too.

So long as that oneway valve passes fuel without restriction your now good to go.

 

Regarding the main jet/one way valve .... small parallel punch and hammer.....tap it through into the centre of the carb. I hold the carb in vice jaws with the choke in closed posn, bit of something soft to protect the faces of the carb. Keep the punch in the midldle of the jet. The jet will pop out into centre of carb, you can retrieve and inspect jet for its one way operation. Also have a look at the drillings in the carb and the groove around the jet and see how far the jet should be installed. Just tap it back into place when you're ready, it alignes itself easily with a little care. Theres no rocket science here. 

 

 

I''l push it through next year but I think it will not have a check valve in it and its annular groove will just take fuel from the un serviceable check valve I ringed in blue, as does the idle circuit, we'll see.

 

In the mean time HNY to all and especially @bmp01,, @adw and @spudulike for help on this thread.