Last weekend my Troy Bilt 4-cycle gas trimmer (TB425cs) wouldn't start. I had been using it earlier that day but it was conking out every once in a while. Later that day I couldn't get it started again.



This weekend I replaced the spark-plug (haven't done this as long as I've owned which has been something to the tune of 5+ years). I was going to replace the muffler and whatever else but they didn't sell replacement parts at Lowes. That alone was a pain in the ass. I took the spark plug to 4 different places, including the place where I bought it. I guess normal spark plugs have the number written on the side. This one had some nonsensical number engraved on the side. I eventually found the parts guide and Googled that number with the model number and came up with the one i needed, which Lowes had... after they told me they didn't. The one that it came with was just longer than the one that replaced it.








Changed and added new oil.

Then  I swapped out the plug. Nothing.



So then I just started taking screws out of things. I took the valve cover off, looked at the parts in there, kind of like opening the hood of my car and just kind of staring at what's there, not having a clue what I'm looking at. The parts looked oiled and functional. I might have done that a couple times throughout the "repair" process.

Put the cover back on.



I took the spark-plug out and shined a flashlight into the "cylinder assembly", again, not knowing what I'm really looking for. My thinking at this point is, the spark plug goes in here, so this must be where sparks ignite fuel or something. But there was no fuel in the "chamber". I thought about pouring some in there... probably would have been a bad idea. Put the plug back in and reconnected it.



Next to took the air cleaner cover off. That little foam thing is the filter? How lame.

Nice big hole in the middle of the carburetor. Looks like a good place to spray some starting fluid. So I did.



Tried starting it. It fired up, but wouldn't actually run more than a second. I figured I must be moving in the right direction. Did this a few more times. Same results.

Then I popped the spark plug off again, sprayed some starting fluid in the cylinder assembly, popped it back on and tried it again. Same results.



Hmmm...



So then I start taking more screws out. This time I disconnected the carburetor from the "cylinder assembly". Neat, it comes off. Better put it back on.

At this point I found the choke... never noticed that there in the last 5+ years. Must have just grown that part. No other explanation.

Thought about taking it apart further where the primer (bulb) is. Thought being the operative word.



Took out some more screws, this time on the starter housing assembly (where the pull cord is). Got them all off, wiggled it around but it doesn't come all the way off until more things are off with it. Put it back on.



Then I went back to the carburetor. I'm thinking it's gotta be something with the fuel... I pulled the fuel return line off the nipple, looked at it, put it back on. It was indeed a fuel return line that goes on the nipple assembly thing part. Not that I knew that yesterday... it was a little blue hose yesterday (in case you haven't noticed I'm now reading from the parts diagram, mostly).



I hit the carb with some more starting fluid. THIS time it actually ran for a little bit. Must have been the return line. Something I did with that... which was exactly nothing. Tried it again... ran for <60 seconds. Now I'm getting more confident.








So now I start playing with the screw on the carb... the one on that black piece at the top of the picture. I'm assuming it's some sort of idle control since it seemed to control how fast it idled. This kind of seemed to work with keep it running... not sure how this is different than just pulling up on the trigger but it apparently is. I also started playing with the choke at this point.



Somehow I got it to stay running for >60 seconds. Then after it died I got it running again for 60 more seconds. I played around with it a little more and then it just stayed running. I stopped it and it started right back up. So I was able to run through an entire tank of gas plus some of a fill-up doing what I had to do.



AMAZING!!



Another weird thing was the cut-off switch didn't work and the thing was stuck running. I ended up just choking it out until it stopped. Started it back up and after that the cut-off switch worked fine.



So... do I get a patch or a certificate as a master mechanic?

Is this how the guy that fixes my car does it or was it just blind luck?



I was looking over a parts replacement site to see how much it costs. I'm assuming a lot of these parts won't wear out of break for the "life" of the trimmer because just for the hell of it I added 1 of each to the cart to see what it would add up to and it was about $1,600. That's about 7-8x what I paid for the thing.



Is it even worth replacing parts on these things v. buying a new one?

We live in such a disposable society now that it seems like people just throw things away once they stop working. I could see replacing parts like the carburetor that would be relatively easy, but anything that's "inside" it I kind of think I could replace, but I would have no idea how to tell when it needed to replaced or what needed to be replaced even if I took the whole thing apart.

Try using 89 or 93 octane gas in your fuel mix and see how much of a difference that makes. You'll be surprised at how easy it is to start with 93.

I'm going to guess by the
that you're joking... otherwise I might have actually considered it



 

Not joking at all, high octane mix is the way to go. Stihl and Husqvarna recommend 89 or greater for use in their chainsaws. Trimmers generally don't need it, but they start and run better that way. I was having a lot of trouble starting my trimmer, but then I got a chainsaw and switched over to 89 octane gas for all the two cycle engines. The trimmer started right up with no problems. Fresher fuel works better too.

Could have had some crap in the carb and when you choked it to kill it because of the faulty switch you pulled the crud through the carb, clearing the passage.

While the carburetor itself could be quite expensive to replace, the rebuild kit for it is only a few bucks and will resolve any issues it may have for the most part.  Most tech schools offer a course in small engine repair, I highly recommend it for anyone who owns and maintains their own property.

ETA:  Congrats on the successful repair of your trimmer, feels pretty good, huh?

Bryan

The trimmer is one of two gas operated things I own, the other being the lawn mower. I am going to have to at least sharper or replace the blade on that thing. Probably some other minor things like the oil.



I'm happy the trimmer works again... as long as it stays working.




 

Don't know much about 'Octane rating' do you?

Yes,  I do actually. I didn't see that this trimmer is a 4 cycle, though.

How does that change things?



 

I use AV gas w/ oil mixture, don't know the mixture though, maybe 30:1. It's "dirty" gas from my friend who races ATV's and he uses AV gas..

Starts up and SCREAMS... It was free from the dumpster and it has been running this way for 2 years.

I would think AV gas would work nicely.

It actually specifically says it's not a mix engine. It has it's own oil "tank".



 

DO NOT use gas that has any methanol . It will screw it up bad.

Does the gas cap have a rubber vent on it?  Mine has broken twice.  The gas tank is so small that the pressure from the motor cucking gas causes it to starve itself.  Next time unscrew the gas cap and see if it makes a sucking sound.  Run some SeaFoam through the next tank fill.

Clean your air filter or replace it.

Get fresh gasoline.