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Discussion Starter · #1 ·
Slightly off topic but I know the info is here so...
Unit#1: Toro 25cc string trimmer, about 9 years old
Unit#2: Jonsered blower about 8 years old.
Both won't start today, had been running in the last 3 days.
#1 was running really rough at low speeds.
#2 ran fine about 2 weeks ago.
#1 Replaced carb, spark tester shows spark, plug out of engines shows spark, tried new plug, tried starting fluid. No firing in any case. Checked compression: about 50 - 55psi. According to MTD manual found on line indicated minimum should be above 80psi.
I am am thinking internal engine damage.
Your opinion please.

#2 Replaced carb about a year ago had been running fine since. Today spark tester shows spark, plug out of engines shows spark, tried new plug, tried starting fluid. No firing in any case. Checked compression: about 50 - 55psi.

I'm assuming same problem as #1

Another blower using same oil-gas mix continues to start and run normally. I really don't think it is a fuel problem.

Thanks in advance for any info.
Burt
 

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have you tried pulling the muffler to physically check the piston and cylinders? it would likely verify what the compression test is telling you.
On the Toro trimmer, where I just replaced the carb, I did take a look. There were some striations but not what I would call scoring.
Is it likely to be more pronounced on the exhaust side?
Thanks for the suggestion.
Burt
 

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I believe the compression numbers are either off, or true. One means the test was not working and we need to still uncover what is going on, probably ... the other means a flaw, probably repated to fuel/oil lubrication failing. So it was too much an obvious statement. But on both engines? So either the mixture failed or we have yet to find the key. My guess is it is still a fixable issue.
 

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On the Toro trimmer, where I just replaced the carb, I did take a look. There were some striations but not what I would call scoring.
Is it likely to be more pronounced on the exhaust side?
Thanks for the suggestion.
Burt
Yes. Usually things are way more visible on the exhaust side since that is where most of the damage Usually occurs.
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I agree with crazzywolfie, carbon build-up on the exhaust side is what causes the scoring and resulting low compression. Make sure the throttle is wide open when using the compression gauge and try to borrow another tester to confirm the reading you got with your tester.
Also make sure the bolts that hold the cylinder to the crank case are tight. They have a tendency of loosening and leaking compression and vacuum. I have had small two strokes run with 70-80 psi compression, but not very well. 50-55 psi is not a good sign.
Pull the mufflers and look at the piston for scoring and post a few pictures here. If scoring is minimal, the piston ring may be stuck from carbon build up and could possibly be freed or another ring installed.
 

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Thanks for all the replies. Here is the post mortem. Most of the parts are in the recycling container. After reflection I realized the Jonsered blower had been getting harder and harder to start. Not so much the Toro trimmer.
Wood Gas Font Door knocker Circle
Wood Gas Cylinder Circle Auto part
Wood Cylinder Gas Font Metal

Three views of the piston. To whoever mentioned it, yes the calibration of the compression tester is reasonably accurate and the throttle was wide open.
Next post has a few pix of the cylinder.
 

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with the compression readings you were getting i would have been expecting to see worse damage than that. some scuff on the pistons is not always a big deal as long as you don't see the same marks on the rings kind of like in the picture i posted.
 

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Here are a few cylinder pix.
inside cyl. Exh port, inside cyl Int port, cyl looking into Exh port (you can still cross hatch factory honing), cyl looking into Int port
Automotive tire Rim Gas Automotive wheel system Auto part
Head Eye Eyebrow Automotive tire Automotive lighting
Hand Automotive lighting Water Tints and shades Circle
Water Wood Building Automotive tire Font


My great kids bought me a Dewalt 20V brushless Drill and Impact driver set for Christmas.
I found a DeWalt 20 V trimmer with charger and 5AH battery on sale at Tractor Supply for only a few bucks more than a replacement gas Toro trimmer so I'm now E Trimming.
I will probably look into the ports of the Jonsered blower but I'm assuming it's a goner.
 

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like i already said i am surprised things where not worse to be causing those numbers. you can clearly see something starting but it doesn't look that bad
 
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