Another chainsaw that won't start - with checklist

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  #1  
Old 08-16-07, 12:43 PM
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Another chainsaw that won't start - with checklist

Hi all Ė

First post here, and like most first posters, I need help. Iíve read over a lot of great info on this site, but still canít solve my problem, or at least all of it. I have an 18Ē 42cc Craftsman chainsaw. Model 358.350280 (Poulan). I think itís about 7-10 years old. My gut tells me to just go buy a new, better, saw, but I love a challenge.

Basically, the saw has run great for years. I put it away the same every year Ė I run it dry of stabilized gas and clean it up. This year, no go. No start and not even a sputter. Hereís a list of what I think I know and know for sure:

1. I have a blue spark (not yellow) so that seems good. Plug is new and gapped to .030.
2. Iím not sure if Iím getting fuel flow through the carb. I donít think I am. I took it apart and while it appears ok (no obvious varnish or clogs), the diaphragm is suspect. So a rebuild and good bath appears to be in order.
3. But considering #2, I assumed a little fuel squirted into the cylinder would allow it to at least sputter for a few seconds. I did this and still got nothing. No life at all. I thought this was odd.
4. Fuel lines seem ok Ė flexible with no leaks
5. Compression seems ok, but I will check it tonight to be sure.
6. I need to check the inline fuel filter if it has one.
7. Air filter and muffler are clean, no clogs or overly dirty.

Some questions I have are:

1. What else can I look for?
2. How do I know if there is no flow through the carb? When I press the primer bulb, I do see the fuel moving. Can I look someone to be sure? The plug seems dry when I pull it, so maybe Iíve answered my own question.
3. If I have spark, but donít get a sputter from fuel poured into the cylinder directly, what could I be missing?
4. Through Sears, the rebuild kit for the carb is $15. A whole new carb is only $25. Would you rebuild or just buy new? I assume the new carb is complete with gaskets and diaphrams.

My estimate is I need to spend around $30-50 on various parts to spruce this machine up. (Iíd replace the muffler gasket, etc and some other things If Iím going to place an order).

Thatís about all I know right now. Would you fix it, or junk it? Itís in great shape, so I think itís worth the repair.

Thanks for the help.
 
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  #2  
Old 08-16-07, 01:17 PM
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Smile

Check the compression you should at least have 90# or better for it to run.Take the pump side of the carb. off you will find a little screen take care to remove it and put it on a paper towel and use a eye dropper with a drop of water to see if water will go through the screen,I have a lot of carbs that have a clog screen.Hope this helps.

Jerry
 
  #3  
Old 08-16-07, 01:28 PM
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I'm going to check the compression tonight. Thanks.

Regarding the "pump" side. I assume you mean the plates on the top and bottom of the carb. This is under the little rubbery/tyvek like diaphram right? There are two actually, one is white and one looks like a screen. I don't see how to get it out. See the attached diagram of the carb too, I assume you're talking about the two little discs you see on the right on the bottom?

Thanks for the help.

http://www.sixsyllables.com/miscpics/carb.jpg
 
  #4  
Old 08-16-07, 04:05 PM
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Well, before I waste my time on the carb rebuild, maybe it's junk. Compression is only 60psi, repeatedly.

No good?
 
  #5  
Old 08-16-07, 05:40 PM
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Compression is low but, if all else were in order, it should run. I'd pull the muffler back off and have a look in at the piston and cylinder through the exhaust port checking for any scratches and score marks. Remove the spark plug to enable easy movement of the piston. Also take a small, flat bladed screwdriver and see if the piston ring can be pushed into the ring land at all. If it does, it will be rather minute and can be deceiving if you don't know the exact feel for good/no good. If, on the other hand, it moves not then it is safe to assume that you have a heavy carbon buildup in the ring land and with such you will have no/little compression and vacuum. Yes, the engine should definitely have fired the fuel you squirted into the cylinder, by the way.
 
  #6  
Old 08-16-07, 06:31 PM
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So a little movement of the ring is good. I'll have to check it tomorrow. For curiosity, I checked compression on my gas blower. 120psi.

So any ideas why it didn't fire the fuel I squirted into the cylinder? Could the spark be too weak? It looked good, but I think I have to rebuild the carb, replace the coil, etc, etc, I"ll buy a new saw.

Thanks by the way, for your help.
 
  #7  
Old 08-19-07, 05:26 AM
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Here's some more info...

Th piston ring seems pretty tight, very little to no movement.

Also, I don't really see any scoring of the piston or anything bad.

Would the low compression prevent the firing of fuel poured into the plug opening?
 
  #8  
Old 08-20-07, 04:11 AM
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Yes, low compression will cause a no-fire situation.
 
  #9  
Old 08-21-07, 07:46 AM
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Thanks for your help. I think I'm not going to bother with this, and buy a slightly used Husky or Stihl.

To the scrap heap with this one. At least I can reuse the plastic case.
 
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