Chainsaw is driving me nuts!

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  #1  
Old 11-28-09, 09:27 PM
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Chainsaw is driving me nuts!

Its a Husky 55 rancher and its driving me crazy. It used to run great, until I burnt the top end. It was due, this saw's been through hell and back. I put a new jug, piston, ring etc. (very easy to do) and it wouldn't run. The motor has just over 90 psi. I've changed EVERYTHING. It runs great with a quick shot of carb cleaner down the throat of the carb so I've pretty much isolated it to a fuel issue. New filter, fuel line (fuel line is nice and tight), no kinks in the line, I rebuilt the carb twice with a quality kit. It's clean as a whistle, I can spray cleaner in any passage and a distinctive stream comes out somewhere else. I bought a new base and gasket, so its not sucking air. The gas I'm using runs anything else fine. It idles decent, but dies as soon as you hit the trigger. I've been playing with the adjustments and it just won't run right.

I can't figure out what is wrong, but I think I need a new freshy carb for some reason. Does this sound right? Would buying a new carb be a smart thing to do next?
 
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Old 11-28-09, 11:15 PM
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If you rebuilt the carb & put a kit in it,, did you adjust the meetering leaver??? This is the same idea as the float adjustment on a float type carb...The carb manufacturers web sites have excellent manuals & instructions on how to adjust...How are the crank seals??? Are they new as well,, or could they be drawing air around them & making the mixture lean??? Sounds like you have most of it covered,, It'll just be some silly little thing..... Roger
 
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Old 11-29-09, 01:46 AM
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Did you replace the crank seals?
 
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Old 11-29-09, 08:37 AM
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Two-cycle engines can be a challenge. There are many little things that can impede fuel delivery. A leak somewhere may be the culprit.

The first two links below are for Husqvarna 55 service manuals. They cover every detail of testing/checking the engine, including the crankcase seals. They also cover carburetion.

The tools used to block passages for pressure testing can be improvised. I use thick pieces of Plexiglas that I drill, tap, etc. An inner tube valve stem with the rubber base makes a good pressure port. I sandwich the valve stem between pieces of Plexiglas for easier attachment.

http://www.gardening-tools-direct.co...1018855-26.pdf

http://www.gardening-tools-direct.co...5310300-76.pdf

At this link, you can learn all you want to know about Walbro carburetors. Download the applicable chainsaw carburetor service manual as well as the Diaphragm Carburetors service manual.

Service Manuals
 
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Old 11-29-09, 07:22 PM
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no I didn't do the crankshaft seals. It takes right off with a shot of carb cleaner. would it matter?
 
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Old 11-29-09, 07:32 PM
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It could if they are in bad enough shape. The fuel/air mix is drawn into the crankcase before it makes it into the cylinder, so if there is an air leak in the crankcase, the cylinder will not draw the intended air/fuel mixture. Often when a saw needs a new top end, it has overheated. This can ruin the seals, so it is a possibility. Sometimes the seal(s) will blow out and create a huge air leak and cause problems like you're having.

Going by just the description of the problem, I would start at the carb... but you've already been there so if you are satisfied you have the carb in check, take a look for crankcase leaks. If still no luck, post back.
 
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Old 11-29-09, 10:14 PM
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Hmmm....any tricks to check the seals? It has over 90 psi...
 
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Old 11-30-09, 12:39 AM
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Unless you want to build jigs like Airman mentioned, and you have a handheld vacuum pump and gauge, then I'd say just buy new ones and put them in. It definitely won't hurt and it may fix the problem. If not, you have eliminated them as a cause. I mean you went through the expense and trouble of replacing all those other expensive components, so assuming you're planning to keep and use this saw for years to come, it only makes sense to replace the seals as well. $15 worth of bad seals can ruin those parts you replaced again.
 
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Old 11-30-09, 06:03 AM
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Originally Posted by strider380 View Post
Hmmm....any tricks to check the seals? It has over 90 psi...
I posted the manuals to help you. The answer to your question is in the manuals.

I am surprised you went to the trouble to rebuild your saw and neglected the lower end. If you did not replace the crank seals I take it, you did not replace the cylinder and crankcase gasket.

With a 2-cycle engine, the condition of the crankcase and crankshaft is as important as the piston and cylinder. I am not saying you have an air leak in the lower unit but you could have. Replacing crank seals and gaskets without a pressure test is just risky, IMHO. You can use an ear syringe in place of the vacuum/pressure pump. A soapy water solution will make the leaks visible.

Are you confident the carburetor is correctly rebuilt and properly adjusted?
 
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Old 11-30-09, 01:33 PM
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Gee thanks, you guys are great. I didn't adjust the metering. I just dropped the needle in and made sure it opens and closes. I didn't know there was an adjustment on the needle like on vehicle carburators
 
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