Engine stalls

[Britfellow]

Hello forum members,
I am working on a couple of line trimmers for a friend, the current project is a Murray 225 line trimmer, I have rebuilt and cleaned the carburetor, the motor now starts and runs fine with the choke engaged … as soon as I squeeze the throttle the engines stalls. The carburetor is a Walbro 115, what do I need to do to have the motor respond to the throttle ?

Thanks for any and all advice

 

[bertsmobile1]

115 is the number, what is the series WA, WY, WT ?
Early carbs were usually set with the H & L needles at 1 turn out from lightly seated.
Latter carbs have finer tapers and are mostly set at 2 turns out from lightly seated.

Nowhere near enough information provided to give you a meaningful reply.
Did you remove both the needles to ensure the H & L passages were clean ?
What was wrong with the carb in the first place ?
If the carb was gummed up from being left for years with fuel in it then it can be near impossible to clean out the stuck one way valves.
I have cooked some for days in the ultra sound using a very agressive solution and they are still not clean.
Some carbs require removal of the welch plugs every time to clean them out, some don't & we have no idea which carb is fitted.And not meaning to be insulting to you,
Rebuilt means absolutely nothing to us as it could be anything from pulling it apart & putting it back together again, up to replacing all of the welch plugs, check valves, diaphragms & gaskets, or anything in between.

There is a methodology to working on these engines.
You start with the spark then go to the exhaust then go to the tank then look at the carb.

What you describe is exactly what a trimer with a perfectly functioning carb but blocked exhaust will do.

 

[Britfellow]

115 is the number, what is the series WA, WY, WT ?
Early carbs were usually set with the H & L needles at 1 turn out from lightly seated.
Latter carbs have finer tapers and are mostly set at 2 turns out from lightly seated.

Nowhere near enough information provided to give you a meaningful reply.
Did you remove both the needles to ensure the H & L passages were clean ?
What was wrong with the carb in the first place ?
If the carb was gummed up from being left for years with fuel in it then it can be near impossible to clean out the stuck one way valves.
I have cooked some for days in the ultra sound using a very agressive solution and they are still not clean.
Some carbs require removal of the welch plugs every time to clean them out, some don't & we have no idea which carb is fitted.And not meaning to be insulting to you,
Rebuilt means absolutely nothing to us as it could be anything from pulling it apart & putting it back together again, up to replacing all of the welch plugs, check valves, diaphragms & gaskets, or anything in between.

There is a methodology to working on these engines.
You start with the spark then go to the exhaust then go to the tank then look at the carb.

What you describe is exactly what a trimer with a perfectly functioning carb but blocked exhaust will do.

Thank you for your reply, the carburetor is a Walbro WT 115, I took the carburetor apart, I sprayed carburetor cleaner through the various orifices, I replaced the diaphragm and gaskets, replaced the small metering needle, spring and operating lever …. I did not remove the High / Low needles ..yet. The machine was used last year and ran ok at that time … I am told by the owner. I cleaned the spark arrestor screen. The owner told me that the machine would not start at all. I got the machine to start after cleaning the carburetor, it runs well on the choke, but stalls when squeezing the throttle. The spark plug is new and gives a good spark . Thanks again.

 

[bertsmobile1]

Pull the carb off but leave the fuel lines on
Turn it sideways and blow through it with compressed air turned down.
You want low pressure high volume.
See if you get a strong fuel /air stream coming out of the carb.

Usual precautions , outside, no flames , ignition sources etc.

If you do then the carb is OK

Loosen the muffler and try to run the engine.
Mud pluggers, coked up screens & rust can all block off enough of the outlet to choke the engine when speed increases.

Pull the return line off the carb and work the purge bulb.
See if you can empty the fuel tank.
You should get a bulb full of fuel with each & every depression and the bulb should pop back up very quickly.
If the bulb is sluggish then the fuel line /filter is blocked.
If you repeatidly get air in the purge valve then you have an air leak in the fuel system.

Run the trimer for a few minutes on the choke if you have to then turn it off and crack the fuel cap.
You should hear a pressure release hiss, if not you have a pressure leak in the tank or cap.

Put a very small amount of fuel down the plug hole or tip the trimmer carb up and put about 1/2 teaspoon of fuel down the carb so it runs into the crank case.
Hold the trigger wide open & pull the starter a dozen or so times .
If the trimer burst into life then the L needle is out of adjustment or the L jets are blocked.
It is better to do this with a hot plug so you might need to run the trimer choke on for a minute or so to warm the plug.

No implied order for these tests, just as they came to mind so you can sort them from easiest to hardest.

Carb cleaner is not actually carb cleaner ( sounds funny I know ) but spraying it on rubber parts can destroy the part, that is why Walbro formulated their own spray cleaner which is safe to use on cube carb needles & diaphragms.

 

[Britfellow]

Pull the carb off but leave the fuel lines on
Turn it sideways and blow through it with compressed air turned down.
You want low pressure high volume.
See if you get a strong fuel /air stream coming out of the carb.

Usual precautions , outside, no flames , ignition sources etc.

If you do then the carb is OK

Loosen the muffler and try to run the engine.
Mud pluggers, coked up screens & rust can all block off enough of the outlet to choke the engine when speed increases.

Pull the return line off the carb and work the purge bulb.
See if you can empty the fuel tank.
You should get a bulb full of fuel with each & every depression and the bulb should pop back up very quickly.
If the bulb is sluggish then the fuel line /filter is blocked.
If you repeatidly get air in the purge valve then you have an air leak in the fuel system.

Run the trimer for a few minutes on the choke if you have to then turn it off and crack the fuel cap.
You should hear a pressure release hiss, if not you have a pressure leak in the tank or cap.

Put a very small amount of fuel down the plug hole or tip the trimmer carb up and put about 1/2 teaspoon of fuel down the carb so it runs into the crank case.
Hold the trigger wide open & pull the starter a dozen or so times .
If the trimer burst into life then the L needle is out of adjustment or the L jets are blocked.
It is better to do this with a hot plug so you might need to run the trimer choke on for a minute or so to warm the plug.

No implied order for these tests, just as they came to mind so you can sort them from easiest to hardest.

Carb cleaner is not actually carb cleaner ( sounds funny I know ) but spraying it on rubber parts can destroy the part, that is why Walbro formulated their own spray cleaner which is safe to use on cube carb needles & diaphragms.

Thank you for that comprehensive list ! …. excellent, I'll be working my way through those items.... Thanks again...much appreciated !.

 

[Britfellow]

My apologies for the long delay …. I had to buy a special " D " tool for the Walbro WT carburetters. I went through the list of possible problem area's, it turned out to be the Hi / Lo needles, I removed them, blew carburetter cleaner through the galleries, reinstalled the needles, all three of the machines fired up on the second pull of the starter cord, I adjusted the Hi / Lo needles to get smooth running and good pick up on the throttle .... spot on.

Thank you for your invaluable help .... I would be still scratching my noggin !.