Gas string trimmer starts, then dies


Old 08-19-17, 12:31 PM
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Gas string trimmer starts, then dies

I've got an 18cc Weedeater Featherlite, the same one Moses used to cut his way through the bullrushes when he crossed the Red Sea, so it's seen some use. I've probably been through this a hundred times with this trimmer and before it's always come down to either something in the filter screen or I did something wrong the last time I put it back together. The normal procedure is to R&R the carb until by some coincidence I manage to get it A) clean and B) reassembled properly, after which it runs fine again. But this one's got me thinking it might be beyond fixing.

Now it starts, runs a few seconds, then dies. It repeats that maybe 1-3 times and then refuses to hit again until after it's had a rest.

When it began this start-then-stop business, I checked the plug and it was a bit sooty. So I removed the carb, disassembled it and soaked it in OMS for a couple of days. And I replaced the plug.

While I was at it I also cleaned the air filter, confirmed fuel lines were clear, the tank was pressurizing, and just for good measure I bought a can of store-bought premix to eliminate the variable of my homemade gas.

I tested the spark and it looked weak, but I can never get a good blue spark with this thing because the lead is too short. In order to get a ground I have to stick a screwdriver into the plug hole and touch the plug to the screwdriver, which also means I only get a half-hearted yank on the starter cord because I don't have a third hand for holding down the trimmer.

The rubber diaphragms are getting a little stiff but I put in a rebuild kit a couple of season's ago and it's not yet anywhere near as bad off as it was when I did the rebuild. They're still reasonably pliable.

One thing that seems to be sort of creeping up on it is I can sometimes get it to start but only by pulling several times, really, really fast, almost spinning it continuously like an electric starter before it'll hit. Which has me wondering if the ignition fire on these things can go bad gradually. Seems to me that also would account for the soot.

Slight change of topic, I have a second featherlite of the same model that's identical except for the brand of carb. It's major malfunction is that the pull rope doesn't catch. So if the problem with the other trimmer turns out to be non-carb related, is it a shade tree mechanic-level job to swap everything above the recoil mechanism?

Ideas? Hoots and jeers?
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Old 08-19-17, 06:18 PM
Join Date: May 2006
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I would say although it may be the ignition module, I would lean toward a leaking diaphragm/valve in the carb. I would replace the carb with a new one. They're about 12 bucks.
Old 08-20-17, 04:36 AM
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I just did a carb replace on my trimmer, after the shop wanted $85 plus parts I opted for the $20 kit on ebay. Took 10 minutes to swap.

It was not pre set so that took another 5 min after watching a video on youtube but it's running better than ever now!
Old 09-21-17, 02:55 PM
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Nobody ever accused me of being the sharpest tool in the shed, and I couldn't be convinced the carburetor had become effectively "dead" so abruptly, or that my rebuild had gone bad after just two seasons when the original parts had lasted fifteen or thereabouts. So I turned to the disused weedeater, the one with the broken recoil mechanism (hereafter referred to as "Weedeater B") and commenced to cannibalizing.

First I tried to repair Weedeater B's starter, but it kept jamming again on the first pull, and I can't figure out why. So either there's some bit on it I don't recognize as broken or I don't know what I'm doing (odds are 3-to-5 on the latter). In any case, getting that spring wound back up and re-installed is not my favorite leisure-time activity, so I am not about to unwind the one that's working to see can I figure out what's broken on the other one.

So I transferred the complete engine from Weedeater B into the trimmer that I had most recently been using, hereafter known as Weedeater A. I did not swap the coils, just the engine. And I only have one carb, a Walbro, that I can find all the pieces to.

And guess what? It pulled the same trick as Weedeater A had been. Started, then died in two seconds or less.

But as mule-headed as I am, it then occurred to me that I still hadn't eliminated the possibility that Weedeater A's coil was going bad. So I transferred Weedeater B's coil to the setup, so the new set-up was the "chassis" from Weedeater A with the engine and coil from Weedeater B. And the Walbro carb. But before I gave it a test-run, I thought to soak the carb one more time in OMS, then rinsed it in denatured alcohol.

It started and would idle just fine, but would bog at the slightest application of throttle. It did this maybe 10 times, and it always restarted on the first pull, and idled like it would have been happy to run forever. Then I managed to get it up to operational RPMs by partially opening the choke and the throttle. Sometimes the power fluctuated cyclically (which had me jiggling the trigger throttle to relocate the "sweet spot") and other times it ran like a scalded dog, usually at half choke and with just a touch of throttle. But the engine vibration moves the choke lever and it's hard to weedeat without moving the throttle even the tiniest bit.

It ran like that for about 20 minutes, during which time I got through trimming about half of the worst overdue parts of the lawn, then it died and refused to restart. The insulator on the spark plug was still slightly gray and the rim of the jacket had a fair dusting of soot, which wiped off easily with a shop towel. Not a hint of cinnamon.

All that said, my first question is, would you agree that these further tests pretty much unequivocally put the blame on the carburetor? My thinking is that it could not have run at full strength, even briefly, unless both the engine and the coil were performing at least marginally well. Which only leaves the carb

So even if the carb is bad, now that I've bought myself a small margin of time on the overdue trimming, I can afford to start out with the cheapest fix, another rebuild kit. And if that doesn't fix the problem, I won't have lost anything because if I then buy a new carb, I can remove the slightly used rebuild kit parts from the old carb to conserve for when the new carb needs them.

Which leads me to my second question, interchangeability of carbs. Which I think is made a little more ticklish by the fact that most newer gas string trimmers are 25cc or more, but mine are only 18cc, so I'm concerned that newer carbs all would be unduly oversized.

According to documentation from Weedeater, this model took Walbro part number Wa-223, Wa-224, or Wa-226, or the Zama part number is C1U-W7, which has been superseded by the C1U-W7C or C1U-W7D. The problem is all the replacements I can find for those models cost upwards of $50. I can get a nice, new 25cc 2-stroke Ryobi that comes both with a warranty and recommendations of personal acquaintances for less than $100 OTD from Homie's depot (with my 10% veteran's discount). I see no future in paying half that to keep an old trimmer on life support (and all the headaches that carries with it).

However, in searching eBay for a Wa-226, I find an ad for a genuine NIB Walbro WT-631-1, which claims to be interchangeable with the Wa-226, and for $25, delivered. However, the 9-digit part number for that carb doesn't match that for any of the known-compatible Walbro or Zama carbs. And I can state to a certainty that the one depicted in the eBay photo is NOT identical (in external configuration) to the existing carb.

Or even better, there also is a Zama C15-51 C1S-S3D (apparently made for Stihl) that claims to be interchangeable with the Walbro WT-223 for $16, delivered. The WT-223 is nowhere on Weedeater's list but apparently the same identical string trimmer was sold under the brand names of Weedeater, Craftsman and Poulan (and maybe others). And Poulan lists the Wt-223 as interchangeable with the Wa-224 and Wa-226.

I am at a loss to find anything "authoritative" to tell me which carbs are interchangeable, which leaves me in analysis paralysis. Ideally I would like to get the $16 Zama C15-51 along with a $5 rebuild kit for the existing Wa-223, which barely breaks $20 and hopefully would allow me to get a few seasons more use out of the existing weedeaters.**

So if anyone would care to share your expertise on carb interchangeability, or to offer an specific opinion on the $16 Zama, I would be eager to hear it.

**I admittedly am overly attached to the two weedeaters I currently have because 1) they were paid for years and years ago and 2) having two identical trimmers has given me no end of flexibility regarding parts swapping to keep at least one of them in service for better than 15 years. Were it not for that I'm pretty sure I would have binned the both of them years ago and bout something new.

Last edited by Fred_C_Dobbs; 09-21-17 at 03:12 PM.
Old 09-21-17, 03:34 PM
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I would buy the $16.00 job and be done with the fixit kits.

Old 09-21-17, 06:06 PM
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You apparently have more time than money and hopefully you are enjoying the tinkering venture. If it will bolt up, and the throttle cable/linkage is of the same type (z-bend/hook/bullet etc.) then is should be ok. The other thing would be the size of the throat/venturi.
Old 09-23-17, 11:09 PM
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Running it like you did with it scalding fast and partial choke, then the grey plug, you probably toasted the engine. Running lean like that will kill a 2-stroke in short order.
Old 10-05-17, 12:54 PM
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Photo that needs no caption:

Differences in rigging aside, compared to the Walbro Wa-223 (right), the throat on the Zama C15-51 (left) looks like it was made for a Striaght-8 Studebaker.

Pay the Stupid Tax. I'm giving up and going to Homie's this evening to buy a new one.

Thanks to all for your help.

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