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HI,
I have a 25cc model: 3HCPS.0254AE

Symptom: If gas tank is really full, string trimmer works fine for a while. Right now my tank is about 75%full and when I do get it started, it
usually stalls engine quickly. It seems to have something to do with the angle I hold trimmer at.

I will try to add a couple photos I just took.
Other info: the filter just disintegrated in my hand, so I will buy another one, running without an air filter did not help the problem.
Also, about two years ago I replace the gas tank lines to the carb and bulb. I admit, the black round rubber gas tank seal ( where two gas lines pass thru)
does leak gas by that seal when gas level is high enough in the tank.

I am willing to buy some parts right away to solve this stalling symptom. I like repairing my equipment, but not sure how to solve this stalling issue.
TIA,
Greg

Hi Greg,

When you replaced the fuel lines, it's easy to make the fuel lines too long. The fuel filter (in a string trimmer) is known in R/C airplane circles as the "clunk" witch finds the lowest center of gravity in the tank to ensure fuel pickup at any angle the airplane is flown, even upside-down . I'm thinking the fuel line may be too long.

Tygon tubing (the yellow fuel line) is also known for hardening after even a short period of time making fuel pickup at certain angles impossible. See if you can hold the gas tank up to a strong light source and rotate the trimmer to see if the fuel filter is in fact at the bottom of the tank regardless of angle.

If you happen to live close to a Hobby Shop, they sell a different version of Tygon tubing that supposedly stays flexible.
Regards

Jeff

Replace the grommet in the tank and the fuel lines.
Go to a mower shop and get genuine Tygon tubeing not "popular yellow colour" tube from evilbay or amazon which will be the wrong grade of plastic which will either go hard and crack or worse go to mush and destroy the carb.

The fuel system is pressurised and if it leaks pressure you will get very poor running and difficult starting.

Hello,

The faulty grommet will cause fuel leaks, but the operation of a diaphragm type carb relies on pulses from the crankcase to generate fuel flow into the carb/engine, AKA a fuel pump.

As far as I know the fuel system isn't pressurized per se. A leak at the grommet shouldn't cause your issue, of course you don't want gasoline dripping from your trimmer, either.

Regards

Jeff

The fuel system on cube carbs runs at 7 to 10 PSI
THE FIRST THING YOU DO WITH ONE IS TO DO A PRESSURE TEST OF THE TANK & CARB.
This saves ripping apart perfectly good and properly functioning carbs for no reason other than stupidity & ignorance.
If there is a return line the system is pressurised.
If there is no return line it is not pressurised.
GENUINE TYGON FUEL LINE does not go hard and crack when used for the liquid it is designed for.
Fake Tygon does as does the wrong tubing like using petrol tubing for ethanol engines will go hard & crack.
Even tubing that has TYGON printed on the side might not be TYGON.
Because it is a premium product & gets sold at the premium price it gets counterfitted
FWIW I fix about 100 trimmer/chainsaw/blowers each year all of them get Tygon and not a one in 6 years has come back with hardened tube.
I have also used it on dozens of British Motorcycles where they are exposed to extreme heat & lots of UV and once again it has outperformed the usual Butyl / Neoprene black fuel line hands down.

People buy Tygon off ebay / Amazon /Craigs list for 1/4 the regular retail price thinking they are really smart & got a Bragan where in fact they have bought geletein plastic tubing at twice it's normal retail pricing.
This is regardless of weather it has Tygon printed on the side or not.
I have even seen some supposedly genuine Tygon fitted by a customer where the printing has washed off where fuel has leaked onto it.
IT never twigged that real Tygon petrol tube would be printed with fuel proof ink .
People will also buy Tygon air line & sell it as fuel line, they are not the same.

jp1961 said:

Hello,

The faulty grommet will cause fuel leaks, but the operation of a diaphragm type carb relies on pulses from the crankcase to generate fuel flow into the carb/engine, AKA a fuel pump.

As far as I know the fuel system isn't pressurized per se. A leak at the grommet shouldn't cause your issue, of course you don't want gasoline dripping from your trimmer, either.

Regards

Jeff

Click to expand...

All,
I did what Jeff suggested, but it's clear the end of the tubing with fuel filter does stay on the bottom.
I do have a new update about the original symptom...
1. I lay the trimmer down with the bottom of the gas tank on the ground, cap up. I start engine, it runs for a few seconds and stalls.
2. I lay the trimmer down in various positions. I start engine and give it throttle at the same time, it revs up to high speed, but once I let go of trigger , it stalls!

I'm also wondering if the carb has any adjustment screws, it's a model: Walbro WYA32.
Thanks for the tips on the Tygon tubing and grommet, I'll get those.

TIA, Greg

jp1961 said:

Hello,

The faulty grommet will cause fuel leaks, but the operation of a diaphragm type carb relies on pulses from the crankcase to generate fuel flow into the carb/engine, AKA a fuel pump.

As far as I know the fuel system isn't pressurized per se. A leak at the grommet shouldn't cause your issue, of course you don't want gasoline dripping from your trimmer, either.

Regards

Jeff

Click to expand...

Jeff,
Because curious minds need to be fed and experiments are much better than words
Run your trimmer for a few minutes then pull off the fuel pick up line.
Enjoy the fuel shower.
OR just remove the fuel cap and you should hear the pressure releasing.
IF not then you have a pressure leak or faulty fuel cap.


Below are the first 3 things you do when presented with a faulty hand held power tool with a fault that you can not recognise from the sounds it is making.
If not running then you start with external fuel & in line spark tester.
But assuming it will start & you do not have sufficient exposure to these engines to work out what is wrong by ear then you do the following in the order presented.
I wish I had come across Joe Pace's videos when I first took over the repair business, but like a lot of things, the boring fact videos get smothered by all of the "sexy ones" from great actors with very limited knowledge or skills
People seem to value the entertainment factor substantially higher than facts.


https://www.youtube.com/watch?v=V9vTjBeEgQE
https://www.youtube.com/watch?v=iOwhMFx8wp0
https://www.youtube.com/watch?v=I5fQ4_jJP5Q

Looking at your pics,

I believe that you have the fuel lines hooked up incorrectly.

The line from the primer/purge bulb needs to be the short one. It just returns the excess fuel to the tank. The other one should go to the filter in the fuel.

All who posted,
Ya'll were correct, I had the lines reversed!
I got a good piece of tygen and use that for the bulb line.
Then look at attached photos,
you can see how I solved the grommet leak by using a small piece of rubber from a physical therapy exercise band!
Problems solved, works great, no stalling, no fuel leaks.

thanks again for the help and other educational videos, I learned mucho.
Greg

ggratecc said:

All who posted,
Ya'll were correct, I had the lines reversed!
I got a good piece of tygen and use that for the bulb line.
Then look at attached photos, View attachment 45962View attachment 45964
you can see how I solved the grommet leak by using a small piece of rubber from a physical therapy exercise band!
Problems solved, works great, no stalling, no fuel leaks.

thanks again for the help and other educational videos, I learned mucho.
Greg

Click to expand...

Glad to hear it!!

Yeah, it is a common mixup everyone has made.

Glad to hear you have it up running.
Just watch that green tube.
If it is silicon rubber as most medical rubbers are then the fuel will soften it over time & it will break up then fall into the tank.
Long term the grommet should be replaced they are not expensive, just make sure you get one from a mower shop.
Most of what is available on line are neoprene which is not suitable for use with fuel.