carb not getting fuel

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So, what, exactly, does the impulse port do? Vacuum or pressure?
I tried a little oil in the port, then crank a few times. I wouldn't say oil spirts out but there was some slight movement. (The oil just flows down). Tried a dab of grease and that popped right out with a pull. The port is clear into the cyl. I tred covering the port with my thumb and cranking and didn't feel any vac or pressure. Should there be enough to feel?
Impulse port on the carb is also clear.
I'm not going to futz with the carbs any more for now...gonna wait for the new to arrive.

If the new AM carb works ill tear into the old again.
View attachment 983671
It drives the fuel pump in the carb with a pulse. Put a vac tester on it pull it over and see if the needle bounces, it should the grease popping out says it works. Once you can get the whole system air tight with vac tester ,then look at a new carb if it wont run.Did you test the fuel line to see if it will hold pressure?
 
It drives the fuel pump in the carb with a pulse. Put a vac tester on it pull it over and see if the needle bounces, it should the grease popping out says it works. Once you can get the whole system air tight with vac tester ,then look at a new carb if it wont run.Did you test the fuel line to see if it will hold pressure?
Plenty of fuel line pressure, lol...gas all over when I pulled the fitting off the hose...oops...
 
So vac test it again and when passes the test if it still wont run try a OEM carb. Also IDK about that that plug leaking you should fix that first.
Different jug now. Can't fix the other one without a lathe as the plug seat is too badly damaged along with the stripped threads.
 
Is this what you mean by pts saws?

PTS is a common, normal, and often adaptive response to experiencing a traumatic or stressful event. Common occurrences, like car accidents, can trigger PTS as well as more unusual events like military combat or kidnapping. Almost everyone who experiences a scary situation will show at least a few signs of post-traumatic stress. That’s because our brains are hard-wired to tell our bodies to tense our muscles, breathe faster, and pump more blood when we’re under intense stress. This is the “fight-or-flight” response that prepares your body to deal with a threat or challenge in the environment by pumping more blood and oxygen to your muscles, and it shuts down non-critical functions like digestion. This fight-or-flight response is a normal reflex during and sometimes even after a traumatic event, which is why PTS is considered a normal reaction and not a mental illness.

PTS Symptoms and Behaviors​

If you’re experiencing post-traumatic stress, your heart may race, hands shake, you may sweat or feel afraid and nervous. After the stressful event, you might avoid or be leery of engaging in that activity again, you may have a bad dream about the event you just experienced, or you may feel nervous in a situation that reminds you of the unpleasant event. Although they can be momentarily intense, symptoms of PTS usually subside a few days after the event and won’t cause any prolonged meaningful interference with your life. One positive outcome of experiencing PTS may be that you behave more carefully in a potentially dangerous situation in the future.

PTS Treatment​

Since post-traumatic stress is not a mental disorder, treatment is not required as the symptoms will likely improve or subside on their own within a month. However, you should talk to a healthcare provider if you feel troubled by your symptoms — if they’re interfering with your work, school, or relationships or if you’re engaging in reckless behavior such as drinking or using drugs to cope with symptoms.
PTS is an abbreviation for parts, not that. @singinwoodwackr @srcarr52 could probably fix the one jug for you. Also, are you sure the metering levers are set right? That will make a huge difference in how (or whether) the saw will run
 
Metering lever?
Yeah, the little see-saw that raises and lowers the needle. I've always heard it called the metering lever but it may have other names. Anyways, it needs to be set to a certain height, Idk what that is in your carbs but on most of the ones I deal with it's flush with the sides of the carb body or flush with the level of the carb floor around it. If that doesn't make sense I get get pics of what I mean.
 
I don't think you will feel and vac/press but the oil should show movement. The pulse from pressure to vacuum is what drives the fuel pump in the carb and causes the fuel to flow. The reason I mentioned the pop off pressure in my previous post and the atmospheric vent is that could be an issue. How is your carb vented?? If it is a hose it maybe blocked.
 
Yeah, the little see-saw that raises and lowers the needle. I've always heard it called the metering lever but it may have other names. Anyways, it needs to be set to a certain height, Idk what that is in your carbs but on most of the ones I deal with it's flush with the sides of the carb body or flush with the level of the carb floor around it. If that doesn't make sense I get get pics of what I mean.
Ah, got it. Yeah, did that but will wind up double checking all 🙄
 
I don't think you will feel and vac/press but the oil should show movement. The pulse from pressure to vacuum is what drives the fuel pump in the carb and causes the fuel to flow. The reason I mentioned the pop off pressure in my previous post and the atmospheric vent is that could be an issue. How is your carb vented?? If it is a hose it maybe blocked.
Pop off is high, over 20#
Carb has a vent port
 
- So, what, exactly, does the impulse port do? Vacuum or pressure?
...

It does a little of both, depending on where the piston is in its stroke.
 
- So, what, exactly, does the impulse port do? Vacuum or pressure?
...

It does a little of both, depending on where the piston is in its stroke.
Yea, a little reading got me up on that. This has been a fun puzzle so far.
I have a theory...supported by a couple friends who know 2cycle carburetor...that the pop-off pressure is too high. I'll play with springs tomorrow...have plenty to cut up and experiment with.
These may be OE carbs but they have been rebuilt in the past, God knows how many times and with questionable kits.
 
if the needle lever is set too low fuel will never enter the carb,, if the impulse circuit is leaking or missing it will not pump fuel into the carb body. Th fuel tank will self pressurize pushing fuel to the carb.
 
Pop-off pressure seems to be poorly understood, it has NOTHING to do with tuning and has no affect on how the saw runs (unless it is really low). Pressure builds up in the fuel tank for many reasons and can be different for any saw, the inlet valve has to stay closed to prevent this pressure from forcing fuel into the carb and upsetting the normal operation of the running saw as well as preventing a flooding condition after the saw is shut off. For most saws, 10psi for pop-off should be enough to prevent this, however, I've heard that if a hot saw is shut off on a hot day and left in the sun, the tank pressure could exceed this.
 
if the needle lever is set too low fuel will never enter the carb,, if the impulse circuit is leaking or missing it will not pump fuel into the carb body. Th fuel tank will self pressurize pushing fuel to the carb.
The inlet valve is only supposed to be opened by the diaphragm operating the control lever in response to the engine fuel demands. If the control lever is set too low, it has to be adjusted and tank pressure should never be able to open the valve.
 
Pop-off pressure seems to be poorly understood, it has NOTHING to do with tuning and has no affect on how the saw runs (unless it is really low). Pressure builds up in the fuel tank for many reasons and can be different for any saw, the inlet valve has to stay closed to prevent this pressure from forcing fuel into the carb and upsetting the normal operation of the running saw as well as preventing a flooding condition after the saw is shut off. For most saws, 10psi for pop-off should be enough to prevent this, however, I've heard that if a hot saw is shut off on a hot day and left in the sun, the tank pressure could exceed this.
I’ve only ever checked it seals and holds at least 10 psi, but chatting to a Stihl Tech at my local dealer the info I was told was spring resistance (pop off pressure) does in fact affect the tuning of an engine.

As the springs resistance increases, the level of fuel supplied is marginally delayed as a higher vacuum is required to over come it creating a marginally leaner fuel supply.

I have never tested it specifically, but I’ll take his word until I do.
 
I’ve only ever checked it seals and holds at least 10 psi, but chatting to a Stihl Tech at my local dealer the info I was told was spring resistance (pop off pressure) does in fact affect the tuning of an engine.

As the springs resistance increases, the level of fuel supplied is marginally delayed as a higher vacuum is required to over come it creating a marginally leaner fuel supply.

I have never tested it specifically, but I’ll take his word until I do.
I don't believe your Stihl Tech unless he can come up with test data to support his claim. There isn't enough variation in spring tensions to have much affect. I've never heard this theory provided by the carb manufacturers.
 

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