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Craftsman 2 stroke 25cc string trimmer only runs on 80% choke

#1

T

TylerFrankel

Hello! I am working on a string trimmer for my neighbors, which is a craftsman branded 2 stroke. Seems to be pretty new. When he gave it to me, he said it would start but promptly die. It did that. I changed the fuel out of it, took the carburetor sides off (both the metering and fuel intake diaphragms looked ok, felt silky), and nothing looked too dirty. Cleaned it up with some water, reassembled it and still doesn't run right. Spark plug is fine. When I adjust it to having the choke almost completely on, it will revv up, thought it seems to "hesitate too". It dies at idle though. If I open the choke it idles but bogs down and won't rev up. I don't know what the problem is. I don't suspect the idle screws because they're those kind that can't be adjusted without a special tool and my neighbor doesn't have on as far as I know, nor do I. If it comes down to it, I'll use a Dremel to turn those stupid screws into flatheads. But I don't know what the issue is. Anyone have advice? Thanks!!!

-Tyler


#2

B

bogdaN

Do those stupid screw and open up some.(counterclockwise).Dan


#3

tom3

tom3

Get a hook and pull the fuel hose out of the gas tank, check the filter and the end of the hose for a crack. I did the dremel deal on my mixture screws and the housing and it really helps to keep it running right to adjust those. Mine are marked H and L for high speed and low. My trimmer has the noisiest muffler of any two stroke yard machine ever.


#4

primerbulb120

primerbulb120

Just get the adjustment tool, they're cheap and easy to find online. Dremeling the screws can damage them and prevent them from sealing properly, making the carburetor impossible to adjust.

Tom, what kind of trimmer do you have?


#5

T

TylerFrankel

TylerFrankel said:
Hello! I am working on a string trimmer for my neighbors, which is a craftsman branded 2 stroke. Seems to be pretty new. When he gave it to me, he said it would start but promptly die. It did that. I changed the fuel out of it, took the carburetor sides off (both the metering and fuel intake diaphragms looked ok, felt silky), and nothing looked too dirty. Cleaned it up with some water, reassembled it and still doesn't run right. Spark plug is fine. When I adjust it to having the choke almost completely on, it will revv up, thought it seems to "hesitate too". It dies at idle though. If I open the choke it idles but bogs down and won't rev up. I don't know what the problem is. I don't suspect the idle screws because they're those kind that can't be adjusted without a special tool and my neighbor doesn't have on as far as I know, nor do I. If it comes down to it, I'll use a Dremel to turn those stupid screws into flatheads. But I don't know what the issue is. Anyone have advice? Thanks!!!

-Tyler
Click to expand...

Thanks everyone! I'll try and adjust the screws. Lucky for me, they aren't labeled so I guess I'll just turn them around until it starts working :laughing: If a dremel will damage it, then.... welll... I'll do it anyway and risk buying a new carburetor. It feels wrong to fuel the EPA and corporate greed.


#6

T

TylerFrankel

tom3 said:
Get a hook and pull the fuel hose out of the gas tank, check the filter and the end of the hose for a crack. I did the dremel deal on my mixture screws and the housing and it really helps to keep it running right to adjust those. Mine are marked H and L for high speed and low. My trimmer has the noisiest muffler of any two stroke yard machine ever.
Click to expand...

I've looked at it, it looks ok to me. It can't be more than 2-3 years old, its very clean and looks new. The carb gaskets are pristine and the EPA screws tells me its not too old


#7

B

bertsmobile1

The L needle is Longer and is the one closest to the engine
The H is generally shorter and always closest to the air filter end
The EPA carbs have a much longer taper section on the needle so generally their initial settings are 2 to 4 turns off sealed


#8

primerbulb120

primerbulb120

The EPA doesn't make any money off the tools, in fact they would prefer if you didn't know the tools existed or where to buy them. However, they aren't able to regulate the Chinese manufacturers who mass produce them.

Don't just mess with the screws randomly. First, begin with the H screw and open it (turn counterclockwise.) Then do the "L" screw the same way if it still hesitates when getting off idle.


#9

tom3

tom3

primerbulb120 said:
Tom, what kind of trimmer do you have?
Click to expand...


Straight shaft Craftsman 25cc. Red, model 315.794470. All around good machine but not the best for in the neighborhood here. Tried to fit a different muffler on it but couldn't rig one up.


#10

T

TylerFrankel

bertsmobile1 said:
The L needle is Longer and is the one closest to the engine
The H is generally shorter and always closest to the air filter end
The EPA carbs have a much longer taper section on the needle so generally their initial settings are 2 to 4 turns off sealed
Click to expand...

These screws are parallel to the engine for some reason, neither being closer to the engine nor air filter. I'll see what I can do with adjusting the screws.


#11

primerbulb120

primerbulb120

That's not possible. You either have the wrong screws or are looking at them incorrectly. Could you post a picture of what you're referring to?


#12

T

tbzep

Every time I've had to run a trimmer or saw with the choke open the cause was air leaking into a cracked fuel line or primer bulb.


#13

T

TylerFrankel

primerbulb120 said:
That's not possible. You either have the wrong screws or are looking at them incorrectly. Could you post a picture of what you're referring to?
Click to expand...

You were right. I don't know what I was thinking, but there was one closer to the engine than the other. I got the dremel on the screws and adjusted them, until the engine stayed idling and ran smooth at max RPM without bogging down on no choke. Had to slightly increase idle screw. The engine takes time to warm up, like a normal 2 stroke, but after it warms up it stops bogging and runs fine.


#14

B

bertsmobile1

VEry Very Very important on these engines is to adjust them properly.
The H screw is done first, wound in till the engine faulters then out till the engine faulters then set 1/2 way between these two .
Most people adjust it till the engine runs fastest which is too lean and the engine will overheat & sieze.
I do this without the air filter on so with the filter the settings will be just a touch on the rich side which keeps the engine cooler.

After the H is done then the L gets done, the same way.
Finally the idle screw gets screwed out till the head stops turning.

Depending upon just how far the engine was out of adjustment the whole process might need to be done a couple of times.

The other rookie mistake is to tune the engine with no load.
You must have the line out full length or the trimmer will run great in the workshop but have no balls in the grass.

Some times I have needed to move the guard out of the way and run the line out longer to put enough load on the engine.


#15

primerbulb120

primerbulb120

Another thing to watch for, if you richen the L circuit it will affect the H circuit too. So after adjusting both, check the H side again to make sure it's still correct.


#16

T

TylerFrankel

bertsmobile1 said:
VEry Very Very important on these engines is to adjust them properly.
The H screw is done first, wound in till the engine faulters then out till the engine faulters then set 1/2 way between these two .
Most people adjust it till the engine runs fastest which is too lean and the engine will overheat & sieze.
I do this without the air filter on so with the filter the settings will be just a touch on the rich side which keeps the engine cooler.

After the H is done then the L gets done, the same way.
Finally the idle screw gets screwed out till the head stops turning.

Depending upon just how far the engine was out of adjustment the whole process might need to be done a couple of times.

The other rookie mistake is to tune the engine with no load.
You must have the line out full length or the trimmer will run great in the workshop but have no balls in the grass.

Some times I have needed to move the guard out of the way and run the line out longer to put enough load on the engine.
Click to expand...

Well I guess I'll go get it back from him, I had no idea about these things. Plus, he had like no string in the trimmer so I bet its wrong. I'll get back to you all soon. Thanks!


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