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Hello,
On my gas trimmer if I were to let the engine run at idle for a while, at some point it will refuse to pick up speed when I pull on the throttle. It bogs down and dies. However I have noticed that removing the gas cap, fixes the issue. I thought perhaps the check valve was the issue but replacing the check valve did not solve the issue. Next was the carb itself and the fuel lines so I ended up replacing the carb, fuel lines and the filter. That did not do it either. Does anyone has any ideas what might be wrong?
Thanks,
Matt

If removing the fuel cap fixes the problem, I'd be guessing that it's the breather vent on the cap not working. Have you verified that the fuel cap vent is actually working on either cap?

Thanks for the quick reply CraigH. The cap does not have a breather vent. It is a solid, one piece cap.
I forgot to mention that I have also checked the spark arrester screen and the screen is clear.

ahdofu88 said:

Thanks for the quick reply CraigH. The cap does not have a breather vent. It is a solid, one piece cap.
I forgot to mention that I have also checked the spark arrester screen and the screen is clear.

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It sounds like a venting issue. Did you change out the vent tube filter? Most trimmers have 3 fuel lines on them. One line is the pickup line and it delivers fuel to the carburetor. There will be a small filter on that line and it goes in the fuel tank. There is one return line. There is one vent line. The vent line has a small filter on it too. This filter prevents trash from entering through the vent. If you didn’t change the fuel filter and vent filter, I would do so.
Did you use this fuel system kit?

The trimmer has a separate tank vent. That is if someone hasn't remove it and plugged the line.

StarTech said:

The trimmer has a separate tank vent. That is if someone hasn't remove it and plugged the line.
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Yep! That’s why I posted my reply and the link to the fuel kit.
The fuel kit is very similar to the one that I just put in my Echo string trimmer.

The vent valve (which I had referred to as the check valve in my post) was the first thing that I had replaced but that did not solve the issue.

IT is a 2 way system
The tank has to hold 3 to 5 psi of pressure to force the fuel into the carb
However as the fuel level drops air has to get into the tank to replace the fuel or you will get a vapour lock
Check out Joe Pace 2 stroke diagnostics on the evil You Tube

I checked out the YouTube video. On that specific application the gas cap has a vent. On mine there is no vent. It is a solid cap. Having said this, I did not think that the tank actually held any pressure. In other words I was under the impression that the carb diaphragm pulled fuel in. I'll reach out to Joe and see what he says. Thanks for sharing the link.

bertsmobile1 said:

IT is a 2 way system
The tank has to hold 3 to 5 psi of pressure to force the fuel into the carb
However as the fuel level drops air has to get into the tank to replace the fuel or you will get a vapour lock
Check out Joe Pace 2 stroke diagnostics on the evil You Tube

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Then why is there a fuel in the carburetor?

ahdofu88 said:

I checked out the YouTube video. On that specific application the gas cap has a vent. On mine there is no vent. It is a solid cap. Having said this, I did not think that the tank actually held any pressure. In other words I was under the impression that the carb diaphragm pulled fuel in. I'll reach out to Joe and see what he says. Thanks for sharing the link.

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No the pump pressurises the tank and air pressure pushes the fuel into the tank.
A fine point but you can not "pull" a fluid you can only push it . Some thing you should have been taught in high school physics .
So the pump pushed into the fuel tank .
Are you sure that you connected the carb properly ?

StarTech said:

Then why is there a fuel in the carburetor?

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No where did ahdofu88 say he ha pulled the carb apart and found fuel in the carb
What he did say is removing the cap fixed the problem and that the problem takes a while to happen
So that points to a tank venting / fuel pump problem
HE has also replaced the carb however no mention of where he got the carb from so it could be a dud carb from Scamazon

StarTech said:

Then why is there a fuel in the carburetor?

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I going have correct this since for the revision didn't earlier. Sorry I did get corrected sooner but a customer came in the shop and I got off track while I check his Echo Hedger.

It have said "Then why is there a fuel pump in the carburetor?" And I don't mean the primer either.

This is the fuel pump for Walbro WYK-353 carburetor.


There is actually a fuel pump in the these carburetors. It creates a vacuum which from negative pressure pulls the into the fuel section and as the metering diaphragm open the metering needle pushes the fuel into the metering chamber. Under negative pressure (negative atmosphere) the positive pressure (1 atmosphere of greater)does get the fuel moving. When you create enough vacuum fuel or any other liquid can flow uphill. So I have to disagree you can't pull a fluid per say if you are using a vacuum you can. But if you physically get touch it and pull then you can't; unless, you are using something that creates a vacuum.

These carburetors can even the tank return line disconnected still pump fuel into the carburetor. Just makes a mess when the excess fuel runs all over the place.

You can not pull on a fluid
It is a fundamental property of fluids
The pump pushes into the tank then air ( or tank ) pressure pushes fuel through the lines to the carb
High school physics

Then can you explain why the Honda 4 stroke I just repaired ran without the fuel cap (otherwords the tank had no pressure other one atmosphere, impossible forto build pressure when it is open.)?

Because air pressure is pushing the fuel from the tank to the carb
Put the cap back on run the engine for 30 seconds hen pull the fuel line off
Fuel will squirt out under the pressure that the pump has built up inside the tank .
The pressureised fuel delivery dates back to early aircraft practice

Oh well I just like see how happens if there is no return line. Oh you mean that the fuel pump back flows pressure to the on the same supply line.

BTW don't even have to run the engine for the fuel tank to build pressure as all you got to do to shake up the fuel. Can be done even a regular fuel can.

And that Honda brush cutter here was ran for 30 minutes without a fuel cap so I can't believe that the fuel had develop any pressure during that time. But I could be wrong.

And my hen might just pull the fuel line off thinking it is a worm.