# Homelite 25cc Problem



## tburner (Sep 16, 2008)

What should the compression of a 25cc Homelite Weed Eater engine be? I tested my Trimmer that I am having trouble with and I am getting less than 50 psi.


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## Spit (Nov 3, 2006)

Below 90 psi and you have a problem....you have a problem since you're almost half of the minimum. I've always thought that as a rule of thumb 90-125 psi is close to the minimum for almost all makes and models of 2 cycles.

Spit


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## tburner (Sep 16, 2008)

Spit,
I was thinking the same thing after reading some postings similar to mine. The thing that perplexes me is, I have have a 25cc Craftsman blower that I get the same compression reading, and it runs just fine? I did check my compression gauge for accuracy with my air compressor and it is right on, Go Figure!


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## mfcjr1 (Sep 6, 2008)

I have a 25cc sears that has low compression (around 60) and it will not crank for nothing. I can usually feel the difference in low versus good compression when I pull the rope. What I do not understand is why did the sears blower run good one day and the next has no compression. The cylinder and piston have been replaced twice before and I am giving up on this on now. I have 2 older blowers (10 plus years) that still have great compression and are running good. Seems the older motors run much better than the newer ones.


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## pyro_maniac69 (Aug 12, 2007)

its all in the quality of the motors nowdays, you get what you pay for, its simple at that


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## tburner (Sep 16, 2008)

Can anyone explain why the 25cc Craftsman blower that I mentioned earlier can even run 
(it runs really well as a matter of fact) with a compression reading of about 45 psi? I have checked it's compression several times (scratching my head and lol) Maybe it is just an anomaly or it is possessed LOL! 
P.S. It is about 5 yrs. old.


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## geogrubb (Jul 28, 2006)

Possessed or bad compression guage, take your pick, I go with a bad guage. Have a good one. Geo


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## pyro_maniac69 (Aug 12, 2007)

I agree with bad gauge, 45 is pushing it for a 4-stroke motor


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## tburner (Sep 16, 2008)

The gauge is not bad as I mentioned in an earlier post, I have checked it with my air compressor at 50psi, 60psi, 100psi, 110psi, and 120psi each time it is right on the money.
This is the first thing that I suspected, that the gauge was wrong. Hence my wondering how could this 2 stroke craftsman 25cc run as it does, which is that it runs very well?


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## dawgpile (Apr 28, 2008)

The reality is, (at the risk of starting an unintended flame war), the issue of small engine compression is not as black and white as people would like. What you have is a lot of legend, folklore, and tribal knowledge, not that any of it is bad. Just about everyone I know who has worked on small engines has their own personal 'rule of thumb'. However, you need only look at Briggs or Tecumseh service manuals to see they specifically don't state compression figures(even though Tecumseh talks about using a standard compression gauge!). Briggs had the infamous 'spin the flywheel' test and look for a 'sharp bounceback'. Now they recommend a cylinder leakdown test as opposed to compression.

The reason for this is because a small engine will run under an extremely wide number of operating conditions, not the least of which is engine compression. And yes, 4 cycle engines typically can operate across a wider spectrum of conditions.

The bottom line, while 90 psi for a 2 cycle is a nice ballpark figure to have, I feel the best way to use this is as a single data point. It's fair to say if you have close to 90 or more, compression is probably not the source of a problem. However, the converse is not necessarily true. IOW, if you have less than 90, it doesn't mean this IS the source of your problem or that the engine will not run.

Most 2 cycle service manuals will recommend a leak down test also, as opposed to a direct compression test. Unfortunately, this is not easily accomplished by most shade-tree mechanics like us because you need to block off the intake and exhaust ports and this is not necessarily easy to do because it involves the fabrication of parts. Much easier to connect a standard compression gauge.

It stands to reason that if it were as simple as using a standard compression gauge, the engine folks would publish the spec and this conversation would be moot! Enjoy!:thumbsup:


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## tburner (Sep 16, 2008)

PILE,
Thanks to your post I looked into other possible problems with this weed eater. I invested $6.00 in an ignition tester and found that the coil was the problem. After replacing the coil for $40 it runs just fine. The compression like I said is below 50 PSI,
your advice was what was needed! Thanks !


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## chuck_thehammer (Oct 24, 2007)

There is one point that has not been talked about,
the choke must be wide open and the thottle wide open as well. this will change the compression.

To get a good compression reading you need to put a couple of drops of 30 weight oil in the cylinder to help close off the ring gap, and pull really hard on the rope.

Chuck


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## hankster (Jan 1, 1998)

Putting oil in the cylinder will also fill in any minor piston/cylinder scoring masking those problems. 

Over the past 5 years I have repaired well over 7000 2-cycle products. I have never seen one run with only 50 psi compression. I guess anything is possible.


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