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I am still pondering the "innocent looking hole"...
I see that now. Forgive me, I’m still learning this. Yes, the impulse has nothing to do with fuel directly, it’s not really even a fuel line, just an air pressure line that “heartbeats” the pump side. This carb gets impulse signal through the flange inlet pipe it mounts to, it doesn’t have it’s own hose nipple.So we are confused. Does this carb get the impulse signal from a separate line directly from the crankcase or does it get it from a hole in the flange where the carb mounts to the engine. If you are actually testing an impulse port on the carb, it just operates the pump chamber diaphragm and should hold both vacuum and pressure, has nothing to do with the fuel inlet from the tank and cannot be used to test the fuel inlet valve in the carb, this valve has to be tested by applying pressure to the fuel inlet port and applying vacuum to it is a meaningless test. The nozzle check valve should be easy to blow through going from the fuel chamber into the carb throat and should hold vacuum going in the other direction. These devices have a little rubbery disc that is often distorted and becomes intermittent so "bench testing" it doesn't mean it will continue to work in a running saw.
You are right, the fuel inlet should hold a minimum or 7 or 8 psi for normal operation, however if the pressure in the fuel tank builds up (hot day, saw sitting in the sun), the inlet valve should not be forced open until the pressure exceeds anything the tank can produce, this is called the "pop-off" pressure and usually 15psi is enough. A vacuum test has no meaning on the fuel inlet.I see that now. Forgive me, I’m still learning this. Yes, the impulse has nothing to do with fuel directly, it’s not really even a fuel line, just an air pressure line that “heartbeats” the pump side. This carb gets impulse signal through the flange inlet pipe it mounts to, it doesn’t have it’s own hose nipple.
So the test for the metering needle is on the fuel inlet (should hold min 7psi pressure and vacuum). The other inlet is for the purge. That should hold pressure, but not vacuum?
BLACK HOLE? nothing gets out..they say even lightI am still pondering the "innocent looking hole"...
Now to remember all of this and/or be able to reference it when needed ThanksYou are right, the fuel inlet should hold a minimum or 7 or 8 psi for normal operation, however if the pressure in the fuel tank builds up (hot day, saw sitting in the sun), the inlet valve should not be forced open until the pressure exceeds anything the tank can produce, this is called the "pop-off" pressure and usually 15psi is enough. A vacuum test has no meaning on the fuel inlet.
If you are applying a p/v test to the purge port on the carb, it should not hold pressure, the air being forced in would just dump out through the main jet and the idle ports. If you apply a vacuum to the port, it probably won't hold, the main diaphragm will just be sucked down and open the inlet valve, however, if you block the fuel inlet port and apply a vacuum, it SHOULD hold a vacuum if the check valves in the carb are working properly (main jet check valve and may be another body check valve, depending on carb)
The purge bulb contains 2 check valves that keep the fuel moving in one direction only, from the carb to the tank, so the suction port of the purge should hold vacuum but not pressure. Generally, the purge is hooked up with clear lines and if you can see fuel being pumped through in the right direction, it's fine.
tree monkey did a ut vid on a 359 carb (199?) and 15 psi popoff as the saw impulse is a problem The video helped me a lot.Now
Now to remember all of this and/or be able to reference it when needed Thanks
Yes YOU get to be right "AGAIN"Not as desirable as an "innocent looking ho'".... Those are very rare.
There is merit in learning, especially hands on, making mistakes and learning from those, which makes it easier to remember (been there done that kinda situations).Thats about 40 bucks...and you are spending 10 x that in personal time.....for a simple fix, on a chainsaw...maybe you just like to chat?
popoff pressure is a test done on the fuel input port and has NOTHING to dp with the impulse that operates the fuel pumptree monkey did a ut vid on a 359 carb (199?) and 15 psi popoff as the saw impulse is a problem The video helped me a lot.
When you say it like that There is no argument from me ... I will go back and read thru this thread . I am reading it to learn like "Pudsy" on post #31popoff pressure is a test done on the fuel input port and has NOTHING to dp with the impulse that operates the fuel pump
From me +1 for this discussion - thanks to OP and all involved!
Not everyone appreciates your humor, but I do!I am still pondering the "innocent looking hole"...
With all the details in your replies I still let that get by me. Posts # 9 - 14-19 - 20 - 24 and 32 breaks things down for me. I read post #19 The OP ordered a new carb and now I will have to assume the nozzle/check valve part "Woodslasher" mentioned was(IS) the culprit. I have read other threads discussing the fuel circuits, nozzles, welch plugs and from lack of hands on use they grow fuzzy.popoff pressure is a test done on the fuel input port and has NOTHING to dp with the impulse that operates the fuel pump
The disc part being intermittent is new to me (Thanks) and is the main reason for OP buying a new carb.These devices have a little rubbery disc that is often distorted and becomes intermittent so "bench testing" it doesn't mean it will continue to work in a running saw.
I am still working on a joke involving the word "Pudsy"......Not everyone appreciates your humor, but I do!
Are you inferring your humor is precalculated??I am still working on a joke involving the word "Pudsy"......
Premeditated a bit.Are you inferring your humor is precalculated??
The cogs upstairs turn slowly as downstairs gets all the lubePremeditated a bit.
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