Troy Bilt Bronco TB70SS doesn’t run

My Troy Bilt gas powered string trimmer decided to quit on me this year.  I’ve only had it for 8+ years so I wondered why it picked this year to want attention.  8 years is a long time in cheap string trimmer years so here are a few things I did to help it get this far:

  • Only use non-ethanol fuel.  I’m fortunate that the closest gas station to my house has conventional gas – Commerce and 51 in Hernando.
  • Change the spark plug at least every 2 years
  • Do not keep mixed fuel longer than 8 months (much shorter if you use ethanol)
  • Empty the gas tank after you finish using it – back into the gas can

That is really all I did and my trimmer lasted 8+ years before it started to not run.  It started to not run well unless I had the choke in position #2, and after a few weeks of that, it stopped running any time I’d give it more than a light throttle.  I had several options without doing any work and I have an edger attachment for the Troy-Bilt trimmers so I’d need to either replace with a Troy-Bilt or get an edger attachment :

The first option was to buy a new string trimmer.  If you check the reviews at Amazon.com on the Troy-Bilt trimmers – same ones they have at Lowes’ – they are horrible.  $150 – $200 for a trimmer that looks better than the one I have (bigger head, better grip, etc..) but from the reviews, I’d be lucky if I got 2 years out of them.   I could have purchased an Echo trimmer at Home Depot for $300+tax which includes an edger attachment.

The second option was to take it to the small engines shop and have them rebuilt the carburetor (what I thought was wrong) for $120 and it would take 3 weeks due to busy season.

I decided to tinker with it and do some cheap maintenance things to see if I could make it work.  First, I ran some ‘mechanic in a bottle’ which the small engine shop suggested.  This didn’t help much at all (you’ll see why later).  The second thing I did was take the carburetor off, open it up, and clean it out with carburetor cleaner.  A phillips and flat screwdriver is all you need for this.  The carb wasn’t dirty or gunky and didn’t have any varnish on it – I believe this is partly because I haven’t ever run ethanol through it.

I was about to quit and buy a new trimmer, but I searched on my problem and found that it may be a result of a High/Low fuel mix.  From what I understand, the all powerful EPA has dictated that these new carburetors cannot be adjustable by the consumer and small engine shops are fined heavily if they sell a tool to make the adjustments.  Several videos and blogs suggested using a Dremel tool to notch out some screw slots, but I don’t have one and I’m not crazy about the potential for sparks near a gas engine – so I used a hacksaw.

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There are two small fuel adjustment needles on the top of the carburetor, one for the high RPM fuel mix, one for the low RPM full mix (look for H and L stamped on the carb – in my case, the one furthest from the trimmer body is the Low).   Once I had the notches cut, I started the trimmer, adjusted the idle screw so that it would run, and then backed off the “H” needle 1/2 turn while testing the throttle.  Once I could give it full throttle without the trimmer dying,  I slowly backed out the H needle until the trimmer sounded like it was at full power.   This really works and saved me some $.  I did replace all the fuel lines and the fuel filter and I’ll probably replace the primer bulb – although I don’t think it is necessary.

  • $6 for fuel lines & fuel filter at any small engine shop (get 2′)
  • $2 spark plug
  • $2 for a can of carb cleaner (probably not necessary for me)
  • $2 for an air filter
  • A hack saw, 20 minutes of driving, 20 minutes of actual work, 1-2 hours of trial and error before I figured out the problem.
  • $280+ saved over buying a reputable new trimmer

I only have ~1/2 acre so this trimmer is powerful enough and works very well to get the job done fast.  I hope I’ve saved someone 1-2 hours of trial and error.

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