What's on your bench today?

[openspaceman]

49 minutes ago, bmp01 said:

No,  that's wrong.  Check valve is typically only on high speed circuit, as part of the high speed (or main) jet. So while the jet is out make sure you can blow through it in one direction , as per the fuel flow , and not in the reverse direction.

Low speed circuit doesnt have a check valve but sometimes there is a one way valve on the whole fuel circuit ...I think....

 

Edit, the logic for check valve in high speed jet is ironically for idle operation.  It stops air going back down the high speed jet, passing through the fuel circuit and out the of the low speed jet

 

Thanks for the explanation, I thought it affected idle jet.

 

I have checked the screen between the pump diaphragm and the inlet needle valve and that is clear.

 

With the main jet out and the Hi needle screwed in to stop air from getting past its hole in the metering chamber and a fuel tube pressed against the main jet hole there is no discernable difference  whether sucking or blowing though I think it is no more restrictive than the needle jet when the fork paddle is fully depressed.

 

I think if I take out the welch plug to get at the check valve the repair will have become too uneconomic.

[bmp01]

14 minutes ago, openspaceman said:

With the the main jet out and the Hi needle screwed in to stop air from getting past its hole in the metering chamber and a fuel tube pressed against the main jet hole there is no discernable difference  whether sucking or blowing though I think it is no more restrictive than the needle jet when the fork paddle is fully depressed.

 

I think if I take out the welch plug to get at the check valve the repair will have become too uneconomic.

Here's how I test main jet, hope you still have it out of the carb....

Put a hose over the outlet end of the main jet.... If you try to blow through the hose that's trying to flow air the wrong way through the jet - the check valve (in the jet) should shut and stop any airflow.  If you suck on the hose air should flow through the jet (in the same direction as normal fuel flow). 

 

In your first paragraph, if i have it correct in my mind you are blowing into the main jet hole from the metering chamber side ? And youve blocked the main jet hole at t'other end (where it comes into the carb 'venturi' ? And you can still blow through the hose ? I dont see how.... unless accelerator jet piston is missing.

Second paragraph, the only welch plug i can picture is the one over the low speed jets, there is no check valve under there. If it's another welch plug then it's a different carb to the ones I've seen, can you post a picture? 

 

[bmp01]

Oh hang on, I've got a picture of a main jet with the check valve parts next to it. ...here you go. ....

(This is not the exact one from your saw / carb but they are all the same as far as I know).

Edited January 13, 2022 by bmp01

[bmp01]

And here's a sketch of how those bits go together.

 

Edited January 13, 2022 by bmp01

[openspaceman]

@bmp01 That's all very helpful but I take it that last picture is a check valve and main jet and it probably sealed beneath the welch plug.

 

See picture:

The red ring is what I take to be the main jet hole and the its brass jet. The green ring is the bypass to the main jet controlled by the H screw directly above it with the damaged limit cap. The yellow under the needle valve lever is the idle jet and welch plug. I don't know what the purple brass plug is and the blue is the welch plug under which I suspect is the check valve. Green and red are connected as carb cleaner bubbles out of both when squirted through the H screw hole.

[spudulike]

DO NOT REMOVE THE WELCH PLUG....YOU WILL NEVER RESEAL IT PROPERLY......

The blue is the check valve and can often be pressed out in to the carb choke. I have never seen a welch plug covering one and I think what you are seeing is the backside of the valve.

The removed jet is a simple two way jet and has no one way valve in it.

If you blast carb cleaner down the H screw hole with the red and green holes covered, you should get a good spray from the check valve in to the carb choke.

The machine idles...the welch plug and the void underneath must be clean and doesn't effect the high speed at all.

 

Edited January 13, 2022 by spudulike

[bmp01]

Picture paints  a thousand words. ... and it seems like what I call the main jet (with its integral check valve) you are all calling a check valve.

 

So, Spud is right (of course), in the blue circle is the check valve. If you have any mechanical dexterity you can just tap it out with a drift straight into the carb ventrui. Even better news; you can just refit it by tapping it back into place from the metering side. I typically clamp the carb in a vice, leather on the faces to protect. Note the depth and orientation of the check valve before you start.

Check valves are replacable and have their own part no.

One note of caution - if the carb venturi is small you need to be confident the check valve will travel all the way into the venturi and not bump into the far wall before its released from its bore. I think i did a 211 carb which is most likely the same.

 

Looking at the carb picture and thinking about your hose blow /suck test plus the 2 apparant feeds to the check valve....it's a bit of a puzzle. 

2 feeds, the jet feed,  therefore a constant fuel feed, probably suppying most of the fuel. That leaves the high speed screw to fine tune the small additional flow supplied through the second hole. I suspect when you sprayed carb cleaner  through the high speed screw the stuff went down to the check valve and some of it bounced back up fix jet drillng. How about you refit the high screw and bottom it, then spray down the jet feed....does any spray come out the second feed?

 

Your earler blowing down a hose test: with the high speed screw bottomed as you did, you should be able to blow through the check valve. You should not be able to suck through the check valve though. But wait, before you conclude check valve is knackered you need to know the accelerator circuit also feeds fuel to the check valve..... 

 

Do you know where the accelerator piston is?

 

 

 

 

 

 

Edited January 13, 2022 by bmp01

[spudulike]

I have changed numerous check valves on MS200t C1Q carbs using the technique above. It isn't for the uninitiated but is dooable.

I am not convinced (but is possible) that this is the issue and would get some carb cleaner through it and see if the cleaner sprays out of the valve. If it does, it is most likely OK.

[bmp01]

I'm not convinced either.

Another question for openspaceman, when the saw was idling, is the idle screw at factory setting or adjusted way rich?

 

I'm thinking 'check valve on high speed circuit is needed for idle operation'...if saw idles ok, this says check valve is closed at idle, either it's completely blocked or working as it should.

 

.....200 carb has a much bigger venturi compared to these strato saw carbs....

 

 

 

 

 

 

 

[openspaceman]

3 minutes ago, bmp01 said:

Another question for openspaceman, when the saw was idling, is the idle screw at factory setting or adjusted way rich?

Well thanks again for top input from you both. Idle was on near enough factory setting.

 

I've not done more with it today and as I said  I don't intend taking the carb apart any further as repair is uneconomic if the carb is the faulty bit.