Chainsaw bogs down under load when cutting

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  #1  
Old 08-05-09, 10:17 PM
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Chainsaw bogs down under load when cutting

I have an 18" Poulan "Wild Thing" 2375 that is only about a year old. Just recently I used it for several hours a day, for days in a row for a few weeks. (Probably used 10-15 tanks of fuel.). Starts and runs great, but bogs down when cutting. The blade slows down to almost stopping. I have a new air filter, plug, checked the exhaust is clear, and have adjusted the high and low carb adjustments screws. Runs very well until trying to cut with it. (Does this with new blade as well). I am in the process of putting a new fuel filter on it, (though I would think it would be dying and running sparatic if that were the issue). Fuel lines are in good shape, no apparent holes or cracks.

Any thoughts on what could be the issue. Could I have a problem with the parts that drive the chain, maybe?? Sprocket bearing, or brake malfunction??

I plan to take the carb off and clean it, and put a kit on it if necessary. Doesnt sound like a fuel/carb issue to me- I'm afraid it being a mechanical problem.

Any thoughts would be appreciated. Anyone have a similar issue??
 
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  #2  
Old 08-06-09, 05:45 AM
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The bearing in the drive hub = no - that's only an idle or prior clutch engagement bearing. For one year old it shouldn't need a kit = waste of money/time. If it started out running OK this cutting session, I doubt if it's gummed up.

The chain break = probably not, but make sure it isn't on or dragging. Make sure your oiler is working properly. It should throw a line of oil on a board, etc., when revved out of the cut.

You may have a problem with the high rpm adjustment, but with a little tinkering you can usually work those things out. Just start out 1 1/2 turns from light seat and try in or out a little until you find the power you lost.

The fuel if too heavy with oil can rob power. Don't use any of the generic "good for everything" oil. Get some quality oil like Stihl. It costs a little more, but you really don't go through that much of it.

Any time you're running in hot weather, use a slightly higher oil mix, shorter run times, keep the chain sharp, and make sure the air path for the cooling is clear. With the emissions standards on the Ca compliant engines, the leaner mixtures are killers on two strokes.

You may have a scored cylinder/piston. Pull off the exhaust and look in the cylinder for scores on those parts.

If you have always had this problem, keep one thing mind, that is a small saw and essentially a non professional saw. Although the ads for it like to make it out to be a wood eating monster, it's pretty tame in that line of work.
 
  #3  
Old 08-06-09, 05:17 PM
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Marbobj, thanks for the input. Yeah I dont suspect the carberator being an issue due to the saw only being a year old, and it being pretty clean, and I clean the saw pretty thoroughly after each use. Nevertheless, I figured I would take it off and clean it just to see that theres nothing that found its way into one of the tiny flow routes or anything, but I'm not even sure that the saw bogging would be caused by a problem such as that. As mentioned, it runs great, sounds fine when it is running before cutting, I can't imagine a fuel flow issue, or a spark issue or anything like that. Your input on the mechanical parts makes me think I'm okay there, too. I don't see any obvious issues with the drive mechanism or chain brake at all. I have also adjusted the high rpm and low speed adjustments. At full speed I turned the high in all the way and backed it out to the right spot, set the low to the quickest throttle response. So I should be good there. I just wonder if there may be something to the fuel oil mixture or something. I know the ratio is correct, and i use the Poulan brand 2 cycle that I have always used. The gas is fresh, but maybe its a bad tank for some reason or another. I'll take the carb apart to make sure its clean, and try a new tank of fuel and see what happens.
 
  #4  
Old 08-06-09, 06:09 PM
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Since you're starting OK, the compression (piston/rings/cylinder) is probably OK. Since you're accelerating well, the ignition = OK.

I would say air flow (intake/exhaust/throttle/choke) or fuel/(high end on carb).

This is assuming the chain is oiled and and spinning freely.
 
  #5  
Old 08-07-09, 12:24 PM
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Have you cleaned the inside of the bar out? Bar is not excessively worn causing the chain to drag in the bottom of the groove? Oiler is working ok? Nose sprocket on the bar turn freely?
 
  #6  
Old 08-07-09, 10:28 PM
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Thanks for the thoughts and suggestions!

Marbobj- I think it's gotta be air or fuel, maybe an obstruction somewhere. I'm gonna give everything a once over again, and take the carb off to make sure there's not a slight blockage somewhere. I'll try adjusting high and low settings again also to make sure I'm good there.

Bontai Joe- Good thoughts, could surely be any of those. I always clean the bar groove out really well, and I had planned to double check oil flow to the bar anyway, so I'll check the points you mentioned. I know the nose sprocket is ok, I've already checked as I've has that jam up before! Thanks again for the thoughts- I'll get back to you all!!
 
  #7  
Old 08-08-09, 06:57 AM
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Everything you need to know about your Walbro carburetor can be found at the link below. Be sure to download the manual "Diaphragm Carburetors".

Service Manuals
 
  #8  
Old 08-08-09, 10:31 PM
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Thanks Airman! Appreciate that very much!!
 
  #9  
Old 08-09-09, 02:58 AM
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Not my specialty, but didn't see the depth of cut mentioned. When you sharpen it, are you cutting down the rakers. If so you may be creating too big of a bite and that can cause it to bog down just as it is getting into the wood. A new chain with a more aggressive bite can do the same.

Just a thought
Bud
 
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Old 08-09-09, 05:22 AM
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Hi Bud. I actually have my chains sharpened by a pal that has done a great job for me for years, so I'm not sure about the sharpening details. The bog started occuring after using the saw for a bit one day. Was cutting just fine, then problem surfaced. I switched to a newly sharpened chain to find the bog occures immediately upon resistance to the chain coming in contact with the wood I'm cutting.
 
  #11  
Old 08-12-09, 10:14 AM
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Update- still having a problem- have question

Well, I checked the saw thoroughly again to find that I definitely have an issue with oil getting to the chain. Obviously this must be fixed but I don't necessarily believe this is causing the saw to slow down while cutting. I could be wrong, I think it could be possible for a saw to do this, but I also know that in the past I have had oil passages get blocked while cutting and the chain would start to smoke but the saw never slowed down when cutting like it does now.

All the obvious oil passages are clear but oil is not getting to the bar for some reason. I have always been very careful to not let any debris get into the oil tank, so don't know if the blockage started there.

Anyone know how to determine if it is an oil pumping issue, versus plugged supply lines? I think the oil is gravity fed on my saw, no oil pump. Any thoughts on where to look for blockage or how to clear this problem up??

I have also noticed that the chain doesnt "spin freely" when I turn it while the saw is not running. (Feels like the drive sprocket is not turning without resistance). Shouldn't it spin on the bar without any resistance? I'm wondering if there is an issue with the brake hanging up or something. FYI- when I run the saw, (with and without the chain on it), it seems to run without anything hanging it up- no sign of resistance like smoke or burning smell or anything.
 

Last edited by Visser; 08-12-09 at 10:52 AM.
  #12  
Old 08-12-09, 08:17 PM
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The oiling is not gravity fed. You have an oil pump that sits under the bar. It's easy to find with the bar and the metal chain guide off. Run the engine without the bar/chain on it to see if oil is coming out of the oil port from the pump.

Lack of oil on the chain will cause it to seize, just like an engine which has been ran out of oil. This will show up first when cutting.

With an oiled chain the chain should spin freely in the bar groove. To prove the fault to yourself, manually oil the chain to see if it makes a difference. If it doesn't, check the chain brake.

Your whole problem is likely a dry chain.
 
  #13  
Old 08-13-09, 06:47 AM
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Thanks marbobj. I'll take a look into it later today and report back. Appreciate the great help!

Even without oil getting to the bar, the chain spins freely around the bar, but the chain drive does not spin freely when I turn it, which led me to think there might be a problem with the chain brake or drive assembly.

I'll let you know what I find. Thanks again!

Visser
 
  #14  
Old 08-13-09, 07:19 AM
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OK, let's back up.

The chain needs the oil, without it, you can have the problem you're describing.

However, without the chain on the drive sprocket, you're saying that sprocket drum drive isn't spinning freely? It should.

If it doesn't it's an indication the brake has a problem or the spring that holds the drives together inside the drum is broken. That usually doesn't happen. Pull the drum off the crank end and take a look at it.
 
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Old 08-13-09, 07:25 AM
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Marbobj, thanks for the quick reply to make mention of the sprocket drum. Thats what I figured, I thought I knew enough to know that it should spin freely without resistance of any kind and it definitley seems to not be doing that.

I knew I would have to fix the oil problem regardless of any other issues, but i will indeed pull the drum of the crank and see whats up there.

I'll post my findings later today!

Thanks again for the help.
 
  #16  
Old 08-15-09, 06:53 AM
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Update

After pulling the sprocket drum I found a few interesting things. There was a small screw behind the clutch assembly, melted into the plastic case housing that surrounds the clutch assembly! This was causing the resistance that I felt when turning the sprocket by hand. Kind of interesting that i hadnt felt or heard any sign of this while the saw was running. I have no idea where this screw could have come from until I noticed in a parts diagram that my saw doesn't have a chain catcher as pictured. This sits below the bar mounting nuts and held in place by a tiny screw. Its possible that the screw had come loose and worked its way behind the sprocket drum and clutch assembly. I dont see anything that it could possibly be. I was able to get the screw out without removing the clutch assembly, and the sprocket drum turns freely. AND I am NOW getting oil at the oil port when I run the saw without the bar and chain. That screw must have somehow been blocking the oil pump from operating, or oil from pumping. That part of the problem solved. I do have one slight issue in that when I went to work on the saw I first observed that the chain brake was not working. The band is not tightening around the sprocket drum when I engage the chain brake. Figure I can take the clutch assembly off and look into this and fix it, and while the clutch assembly is off, I can check out that there is no other damage caused by the rogue screw.

On a sad note- I now have another issue that will prevent me from finding if the lack of oil was the cause of the blade stoppage when cutting, (or if it had to do with the screw stuck in there where it didn't belong). When I put the chain back on to try a cut, I was having a problem with the chain loosening up while the saw warmed up. I observed that the bar mounting nuts were not tightening enough to hold the chain taught. Come to find that the bar mounting bolts are pulling through the cheap plastic housing that holds them in place!! Okay, I get what I deserve here, I knew I bought a cheaper, less quality saw for occasional use when I purchased this thing but it was what I could afford at the time. I knew it had plastic where other saws had metal. However, I would think that there might be some foresight to this potential problem, and some metal reinforcement in place to prevent this from happening.

So I obviously cant operate the saw until I get this fixed to know if I solved the initial problem. I'm going to contact Poulan to discuss a manufacturer's defect and warranty replacement!!

I'll report back when I get the saw fixed.

Thanks to all for the great help that led me toward what I think could be the solution.

Visser
 
  #17  
Old 08-15-09, 12:48 PM
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If you have the chain drive off (the center drive mechanism is turned counter clockwise to remove), you'll see a place for a small screw to hold the oil pump in place. That's a possibility.
 
  #18  
Old 08-17-09, 04:21 PM
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Thanks marbobj, that's probably more likely where the screw came from. I'll check it out.
 
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