Chainsaw Repair
Husqvarna - Stihl - Poulan - Jonsered - Dolmar chainsaws and more => Poulan => Topic started by: 3000 FPS on March 12, 2014, 07:44:07 pm
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So I have been working in a Poulan 2300. I put in new fuel lines and rebuilt the carb. The saw will start and run but at full throttle I noticed a spray of fuel mix blowing back up thru the carb. I took the reed out and made sure nothing was holding it open and flipped it over but when I put it back together it still is doing the same thing.
So I bought another reed valve and put it in and still the same problem. The spray is enough that if I hold my fingers over the carb I can feel the spray and my fingers get wet within 10 seconds.
So my question is what else can cause this. Maybe blow by on the rings or to much back pressure from the muffler?
Suggestions?
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The purpose of the reed valve is to be a one way valve (The other way)
Look at them carefully and through the light?
Prop the carb open and move the crank around by hand and listen in the carb intake for the reeds to pop open and snap shut.
If there is any wheezing in the carb while the reeds are supposed to be closed, you have trouble in the reed area.
I have put a piece of Tygon into my ear and held the other end to the carb intake to hear this.
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I guess it could be possible the surface the reed lays against is warped and not completely sealing. I looked at it once but maybe it needs more scrutiny.
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If it was a piston ported engine and doing this you would know you had a worn piston.
Some engines tend to have a reflection plume of air-fuel mixture that stands proud of the carb entrance at engine speed.
Just so you are aware.
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I have 4 saws with this same design and the last time I had this problem it was because a wood chip was lodged in the reed keeping it open.
I do have a tendency to agree that it is a reed problem not sealing when closed.
Thanks for info on piston ported engines.
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I have had the reeds stuck open by debri on these as well. can these reeds be flipped? I have had to flip the reeds on a few of my later model pioneer saws..... On another note I have also had the same thing with the mixture blow back on these poulans as well, never worried about it as the saw still ran fine.......
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Roger, make absolutely sure the reed is flat when relaxed. You will have to remove the reed and lay it on a dead flat surface. Then make sure there are no bows in the reed either concave or convex.
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I have had the reeds stuck open by debri on these as well. can these reeds be flipped? I have had to flip the reeds on a few of my later model pioneer saws..... On another note I have also had the same thing with the mixture blow back on these poulans as well, never worried about it as the saw still ran fine.......
I tried flipping the reed already and a little bit of blow back I would not mind but this is excessive.
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Roger, make absolutely sure the reed is flat when relaxed. You will have to remove the reed and lay it on a dead flat surface. Then make sure there are no bows in the reed either concave or convex.
Two different reeds and one is brand new. I am going to take it apart again and check the surface the reed lays against reel close.
Good feed back is giving me some ideas and things to look at.
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There's nothing wrong with the saw. These saws just plain spit back some. Normally it's collects on the underside of the AF cover and is drawn back into the engine. Many other older saw designs have a small shield, 'filter', or pad mounted over or near the carb throat to collect this 'spitback' so it can be drawn back into the engine. Seen it on reed valve Homelites as well as both reed valve AND piston-port McCulloch's. Mac even called the parts installed for this purpose "spitback collectors". This spit back is just some of the A/F mix that is forced back through the intake tract before the reed or piston port closes.
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Look up "boost bottles" for lots of reading regarding reversion, charge inertia, and other things in two-stroke engines. They were used on many 2-stroke motorcycles in the 1970's and 1980's...
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Ok I have fixed my blow back problem today on the 2300. I have worked on enough of these things to know when it is excessive and when it is not.
The first thing I did was to pull the reed assembly out of the saw, take the reed off and put a straight edge against the plastic. I could see a small amount of warping, so I cut a small piece of a file off so it would fit and filed all the surfaces flat.
Then I noticed the carb sits right above the reed valve and decided not to over tighten it thinking it could be distorting the plastic.
I see absolutely no blow back through the carb now. The saw also idles better.
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+1
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Good going Roger!
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Thanks guys. Sometimes a little feedback makes me put the thinking cap on.
When I was working and when any of us came across a tough problem, we always started discussing it with fellow workers to try and get fresh ideas. It works.