bmp01

A brief update/summary for anyone visiting this thread in the future looking for a conclusion: The saw now runs with the original parts pictured above. That is to say it does not have a check valve in the high speed circuit. It idles, accelerates, returns to idle totally predictably. I did not expect this. Hi speed circuit is not providing any fuel at idle - I can close the high speed screw completely with no change to engine. And there is obvious no air going up the hi speed jet because the engine idles happily and forever. I wonder if the wire gauze filter is behaving like a check valve once it’s coated in fuel…? Dunno, but in this carb, with this saw there is no need for a ‘normal’ check valve in the hi speed circuit.

Sounds like you’ve got that bit sorted. I was thinking I could wind in the hi speed screw…. that would block it. Engine ought to idle on the low speed circuit. And buy the optional check valve 🙂

You’ll need a short length of flexi hose, so you can blow and suck through the drillings in the metering chamber. You should be able to blow through the main jet (and check valve) in the direction fuel flows but not draw air in opposite direction. The fun begins when you find air travels in both directions…. the problem could be the check valve or the accelerator circuit.

Okie-dokie.

Oops I didn’t spot the /c bit in the title… it has a purge bulb? Check the bulb operation and pipes for leaks. Worth noting: if the one way valves in the purge bulb assy stop working you effectively have the carb’s metering chamber connected to tank pressure.

Items 56 filter, 1 retaining ring, 23 plug are the same as mine ( I shouldn’t have removed the jet (LH part in my pic above) apparently 🙄 Item 20 check valve is an alternative fit part (that’s why it’s not highlighted). Weird, a carb with the option of no check valve ??? 🤔🤔

I happened across some WJ parts list that suggest the WJ carb had the option of not having a check valve.

I think this will be of little interest to most but I’m wondering - does anyone know about these old Walbro WJ carburettor’s…. I have this Partner 7000 pro saw, bit tatty but it’s all there and has frightening compression. It will pop with some fuel thrown down the intake so I headed to the carb to see what’s what. Well, all looks surprisingly good, no fuel rot, no dirt in filter, diaphragm and pump all good blar, blar…. But the main jet check valve doesn’t work (surprise given general condition). And here’s where I ran into ‘issues’ - it seems like it was never supposed to work…. there is nothing in there that looks like it could act as a check valve. See picture of items that came out.

It’s part of the high speed circuit, the brass bit that pokes into the carb venturi. It delivers the ‘hi speed’ fuel into the carb. Check valve description because it stops (or checks) the air in the venturi from flowing the wrong way through the hi speed circuit and into the metering chamber at idle. Did you check the fuel line in the tank for leaks, does it run ok on a full tank? 🙄🙄….or is it accelerator piston o ring shagged again….🥱🥱

Yes that should happen. Now open each screw, one at a time and tell us which one is allowing the air through…. I think that’s ok too. You are blowing into the metering chamber only, so long as you have the little valve and it’s gubbins plus the diaphragm in place. That’s the chamber where fuel is supplied to the jets….. So here you are creating a little bit of pressure on the fuel side of the jets, you are blowing through the main jet and low speed jets in the direction they are supposed to work. The one way valve in the main jet should be open in this direction. With the low speed circuit there is sometimes a little one way valve at the entry to the low speed circuit, which would also be open in this direction. What is not ok is the purge bulb (or you) being able to suck through the main jet one way valve. And it’s not ok, being able to suck through the low speed circuit one way valve if there is one, less of a big deal, but still not good. Worth mentioning, both one way valves are often a little leaky with air, less so with fuel in them. Secondly, if the purge button pops back really slow and fills with air, its likely the fuel filter inside the carb is probably blocked …. bulb can’t suck fuel so it does what it can and sucks air, through the jets. And finally, leaky fuel line (between carb and bulb) or the bulb itself will allow air into bulb, I think this is pretty obvious. But less obvious maybe is that a leak in this area can easily allow air to be sucked into the carb metering chamber when engine is running…. Food for thought.

Had a bit of time this afternoon to clear away some sawdust, sluice out the bottom end with some fuel and inspect the main bearings and cages with a mirror on a stick. Tried one of those endoscope connect to you phone thingees - waste of time only focuses down to 4 or 5 cm. Seems like everything is sound, rotated it through a couple of revolutions to make sure I didn’t miss any sections of the cage hidden by crank weights. There must be some regions of the inner race I couldn’t get to see but I’m going to say it’s good.

Yes, I understand that, amazed the bit(s) didn’t leave a single mark left on its way, but if that’s what experience says then I’ll check the brgs. Maybe I’ll find some damage in the bottom end if/when I end up splitting the cases. My blow-by question was relating to the black on the crank weights. Same shade of black as the carbon deposits on the piston skirt above and below the ring. Which is combustion gas getting past the ring. (Piston hasn’t been hot enough to cook the oil). Thanks for your reply’s.

Thanks for comment. Two or more suggestions for bearing - ok, better get over my laziness then …. Blow by past the piston maybe?

Thanks for that, can’t fault the logic. Have to admit to being negligent as far as checking further, I know I should but it looks pristine in the bottom end. Plus I can’t think of anything in there (brgs, cages) that would provide flat debris like that. I like the screw driver theory ….. right opposite the spark plug hole. Ties in with a DIYer trying a Chinese replacement plug sourced from an online store, cheap as chips. Why am I leaning towards boggery rather than mechanical unreliability ? 🤔🙄

Ring got forced back into the groove about 1/2 mm, I was surprised there was enough depth in the groove for that to happen.