Weedeater SST-25 (25 cc) engine only runs between Full & Half Choke


Old 05-31-16, 11:06 AM
Thread Starter
Join Date: Nov 2006
Location: US
Posts: 370
Weedeater SST-25 (25 cc) engine only runs between Full & Half Choke

Hi all,
Wondering if someone had experience with a 6 year old Weedeater SST-25 string trimmer only running without stalling out when Choke set between Full & Half setting? Aside from maybe mixing a little more 2 cycle oil in the gas than usual, I'm not sure about this effect.
Weedeater seems to start normally with a few priming bulb pumps, I pull the cord while on Full Choke and it starts but immediately stalls - I don't think it ever did run on the first Full Choke pull even when new but it always seems to at least start for a second or two.
My procedure is then to move Choke to Half and pull again; and before it would start even without any further priming gas - then, after running a few seconds at Half Choke, I could move Choke to OFF setting.
This year, I have to move the Choke to Half on the second pull to keep it running; even to use it.
The problem is, the Choke control doesn't stay there and wants to be either in the FULL or HALF Choke position - so, I'm always having to watch it.
I even had to place a piece of self-adhesive Velcro under the Choke lever to keep it in the 3/4 Close position.
Other than that it seems to run Ok! - though it seems to run through the gas faster, which is probably to be expected.
Once I was able to move the Choke to Open and run it till the gas ran out; but immediately after refilling, it wouldn't run continuously unless the choke was set to 3/4 Closed.
Any ideas or advice appreciated.
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Old 05-31-16, 03:53 PM
Group Moderator
Join Date: Mar 2003
Location: NC, USA
Posts: 17,737
The carburetor is probably dirty. There may be a speck of something partially blocking an orifice restricting the flow of fuel. Partially closing the choke restricts the air to bring the air/fuel ratio back inline so the engine will run.
Old 05-31-16, 04:55 PM
Join Date: May 2015
Location: USA
Posts: 3,138
Another possibility is that you have a leak that is allowing extra air into the carb, so you have to compensate by partially closing the choke. A common cause of this is for the screws that hold the carb on to loosen a little allowing some air to sneak in. Pretty common on high vibration equipment. So try tightening the carb mounting screws.

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