# Chainsaw carb/fuel problem driving me nuts



## AlexP (Aug 26, 2006)

I am at my wits end with my old in age but almost new Poulan 2800 Chainsaw.
After many years of non use stored inside my garage I decided it was time to crank it up. The saw was stored completely free of fuel. Obviously the fuel lines were dry rotted and so I had to replace them. I figured the carburator diaphragms would be shot so I bought a rebuilding kit for the Walbro HDA-49 carb on my saw. The kit was a Walbro OEM K20-HDA.

The carburator was spotless inside and I saw no signs of varnish or dirt anywhere. I removed the needle and metering lever and cleaned the needle tip gently and it was in great shape but I replaced it anyway. The high/low adjusting needles on the side of the carb were also removed and tips cleaned even though they looked clean. The carburator was sprayed thoroughly with carb cleaner and everywhere I sprayed the passages were clean and showed no signs of clogging anywhere. I then used canned air to spray out all of the orifices. The carb body looks pristine like it was just made. 

I assembled the lower metering lever diaphragm with a new needle and lever from the kit reusing the original factory lever spring. Height of the lever was about even with the base of the carb body barely making contact with a straightedge held across. Needle moved easily up and down with any minor move of the lever. The mesh micro screen in the carb was left spotless.

The upper fuel pump diaphragm and gasket were replaced but the only thing different that I noticed was that my original fuel pump diaphragm was black rubber and the new one from the Walbro kit was a whitish looking mesh type fabric. All the holes and cut outs lined up perfectly with my old diaphragm. I reset the high/low needles to 1.5 turns out from fully closed. 

I checked to make sure the spark plug had spark and I would have bet money it would crank right up. WRONG. The engine will fire immediately if I squirt some gas/oil mix down the carb or in the cylinder but will shut down almost immediately. I did manage to keep it running for a couple of minutes by continuously misting fuel mix into the carb but as soon as I stop squirting the engine died. So I definitely have a carb/fuel problem. 

I have pulled the carburator off several times now becoming very familiar and quick with the procedure and it seemed like it was dry of fuel inside each time. Almost like the fuel was not being sucked into the carb. The fuel filter is definitely clean and I even removed it one time completely and just left the fuel hose in the tank with no filter but still no luck sucking fuel. I can see no fuel coming out at all thru the return line. I also tried leaving the return line with no hose thinking that maybe the gas tank was pressurising and not allowing any venting causing a vacuum preventing fuel flow but that didn't work either. The spark plug was always dry also. The fuel does make it to the top inlet fitting because I can see it.

The only thing I have not tried yet is switching the fuel hoses. I have them connected with the main line with the filter end connected to the top of the carb and the shorter return line connected to the fitting on the side of the carb. The return line hose has a little plastic end with a rubber cap type thing on the end. I put this hose thru the bigger of the two holes in the tank and the fuel line thru the smaller of the two holes. Is this hose routing correct?

I am almost completely out of theories, patience, and I am at my wits end. I am ready to throw in the towel and go to a lawn equipment mechanic but I might never be able to live with myself if I did that. Can any of you mechanical wizards offer any technical advice before I break down and admit defeat? (I think I hear my chainsaw laughing ). Thank you.

Alex

P.S. I did do many searches and read many great posts and even printed out the great Walbro Service manual. This was a big help to me in this whole ordeal.


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## big ed (Jul 29, 2006)

check the cylinder and make sure thatit is not loose and seals have not deteriorated also it is very important that carb impulse passage is working by hose or passage at the intake below the carb a misplaced gasket turned 180 can make a big difference good luck


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## AlexP (Aug 26, 2006)

Big Ed,
The cylinder is tight and the compression is good. The saw will run if I mist fuel thru the throat continously. The carb gaskets are definitely correctly installed having checked that several times. Also, the carb base gasket to the cylinder is correctly installed. 

I am not really sure what you mean by checking the carb impulse passage by hose? 

Thanks.

Alex


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## peppy (Jul 19, 2006)

AlexP said:


> The only thing I have not tried yet is switching the fuel hoses. I have them connected with the main line with the filter end connected to the top of the carb and the shorter return line connected to the fitting on the side of the carb. The return line hose has a little plastic end with a rubber cap type thing on the end. I put this hose thru the bigger of the two holes in the tank and the fuel line thru the smaller of the two holes. Is this hose routing correct?


Yes it is correct. Have you tried looking at your gas cap? Is the gasket in it dry rotted? Sounds like there is not enough pressure to help push fuel up into the carb.


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## hankster (Jan 1, 1998)

Does the primer prime correctly? Fill tank about 1/4 full and see if it will suck fuel... if not it is a sign that you may have the fuel lines backwards.


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## AlexP (Aug 26, 2006)

In reply to Peppy: The tank cap has an o-ring and is in good shape and holds the pressure. 

Hankster, there is no priming bulb at all. This is an older saw and it didn't come with one. The tank is pretty much full to the brim so I will empty out the tank to about 1/3 full and try again. I will also reverse the fuel lines if that doesnt work. 

I will check back with you guys in several days since we are in the middle of Hurricane Ernesto preps down here in Miami. I'll let you guys know the results.
Thank you all for the advice.

Alex


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## AlexP (Aug 26, 2006)

*Finally got it running!*

Well after putting the saw away for a week or so I finally got my patience back and looked around the web for more data on my saw and carburetor. I found lots of old info on Mike Acres Chainsaw Collectors website. 

I definitely had the inlet line reversed but the real problem was that one of the hoses was strictly a breather hose to vent the tank with no connection to the carb at all. The second carb hose connection went to a fitting well hidden on the crankcase underneath and behind the carburetor which I found using a small light. This was the impulse line that Big Ed hinted at in his post. Put everything back together, a few tugs on the starter rope, and the saw fired right up. Tuned up the carb and it is running great now. Many thanks for the help guys.

Alex


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## 13EJ54 (Sep 14, 2011)

i posted up in new member but would like to give credit to this thread for helping me with a chainsaw problem. the final clue just posted by AlexP led me to the solution for my troubles. when i took my saw out of storage, the fuel and impulse lines crumbled before i could tell their origination. AlexP found the impulse line terminated in the crankcase but i could not see the place for connection thru the hole behind the carb. after much searching, i took the pull to start assembly off and then could see the connecting point (a brass looking nipple for about a 1/16 inch inside diameter plastic tube protruding from the crankcase). once i made this connection between carb and crankcase the saw starts and runs normallyl. thanks to all for this thread.


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