Outdoor Power Equipment and Small Engines - Poulan 2150 primer bulb working backwards!

Poulan 2150 chainsaw. All fuel lines are in their original position. Primer bulb is marked tank and carb side. Tank side is for larger line and runs into tank and fuel filter. Carb side is smaller diameter line and runs to carbs lower fitting. Top carb nipple with small line runs to tank vent and sticks about 1 inch into tank top. Pushing on primer bulb PUSHES air OUT of fuel filter and sucks from carb side of bulb. Pulled out primer bulb and verified action separately. Definitely pulls from carb side and pushes into tank side which makes no sense to me at all. Going backwards like that would require source of gas to be from "vent" line in tank which isn't low enough into tank and would not be filtered. Pressing on the bulb pressurizes the fuel tank. The fuel sprays out when you open the tank!! I can't believe primer bulb is suddenly working backwards. The saw just stopped working in the field and has not run since. Has anyone else had experience with this? Hope you can help. Thanks.

If all fuel lines are in original position then they were wrong. The line with the filter should go to the carb, then from carb to suck side of primer and return to tank from the blow side of primer.

Correct...they are not in the original position, it can't work that way. The port marked "tank" goes to the return line in the tank, not the supply line with the filter on it.

Thanks for the responses! How do we explain that the Primer bulb is marked carb and tank. The Tank side line is larger than the carb side line! Cannot get them mixed up. The larger line when the bulb is pressed is blowing air into the tank and pressurizing the fuel tank. Is it possible that something in the primer bulb assembly has broken and some how reversed its function? If someone out there has one of these I sure would appreciate someone looking at it to confirm how it works. I know what you guys are saying is right about it not working the way I found it when I disassembled the saw. Yet you need to believe what I am telling you about what I have found. The saw just suddenly stopped working in the field and nothing has been disturbed of changed from the original configuration except it just started working backwards!! (No human intervention) Thanks for your help. Of course I will purchase a new primer assembly and I will let you know what I find out. All comments, observations, experiences and advice is greatly appreciated.

Well why would you want to filter the return fuel line over the inlet?
The return line is not meant to pressurize the fuel tank and the primer system is only meant to purge the air bubbles from the lines and carb.
Of course I can't explain what you found but I don't believe it is correct.

The line marked tank blows air out when you press the primer. That's the way it's made and how it is supposed to function. It connects to the line with no filter going to the tank. The suction side of the primer goes to the carb. This is all regardless of how big the primer fittings are. That doesn't indicate what lines go to it although it would seem that way. I have some to look at in the shop, but I don't need to look at one to verify how it is connected...I work on them for a living. That's the whole of it....there is no other way for it to work. I don't think it suddenly started working backwards, I just think you have the wrong impression of how it works and should work. The check valve in the primer is put into place in one direction, and it can't come out and turn around. It's not physically possible for multiple reasons. The only way the primer can function backwards is if someone reverses the lines on it.

I'm looking at the primer pump from my poulan 2150 chainsaw right now and the larger fitting marked 'tank' is connected to the blue tube going to the carburetor. The smaller fitting marked 'carb' is connected to the clear tube going to the tank. There is a much smaller tube (vent?) which is not sealed going from the carb directly into the tank. I have pulled this tube out of the tank and the chainsaw continues to run fine so it may be a pressure relief for the tank. It appears to me that the pump is marked backwards. Go figure!

If it helps,, These are NOT really primer bulbs... They just got a bad name along the way!!! They are really a fuel system purge bulb.... They will never give a squirt of fuel into the carb as most people are used to seeing on lawnmowers...All they are designed to do is to pull the air from the carb when you release the button,, & push it into the tank when you push the button.. I've seen lots of people get mixed up because of the term ""Primer"" bulb... Hope this makes it clear & helps some ??? Roger

If you have a line running from the carb to the tank and it runs fine with it removed, something is wrong. The return line should go from the primer to the tank. The supply line should go directly to the carb. It sounds like your return line is connected to the carb? With it removed from the tank, you risk fire/explosion.

No matter what the primer says, the fitting that blows out when you push it goes directly to the tank. The fitting that sucks in when you release the primer goes directly to the carb. The line with the filter on it goes to the carb inlet. Every time, no matter how it is marked.

My Poulan 2150 chainsaw's primer/air purge bulb is marked 'Primer' on the side of the chainsaw. It is labeled an air purge assembly on the parts diagram. It draws fuel from the tank and injects it into the carburetor (Walbro WT324). I know, because I can easily flood it with the primer and I've watched the fuel spray into the carb throat whenever I press the bulb. The primer valve also blocks fuel from draining out of the fuel line back into the tank. There is a third line, approx. 1/16" ID which runs from a small black plastic fitting on the carb into a small hole in the fuel tank. The saw will run with this removed but fuel will splash/dribble out of the hole in the tank into the area under the carb, so it needs to be there to plug the hole. All I know is what I have observed on my particular saw.

OK, my bad, after fooling around with my 2150 a little more I seem to have found my error. The person who owned this saw before me had swapped the primer source tube (unfiltered) with the normal run fuel tube (filtered). What I thought was a vent tube was actually the primer fuel source tube. What I thought was the primer fuel source was actually the normal run fuel line. I would prime the saw and it would run but not very well or for very long. I also have replaced the primer bulb as it was getting cracks and leaking air, which I thought was the reason for reduced runtime. Hope this helps someone else.

Oh yeah, as noted by others on this thread, the primer draws air and/or fuel out of the fuel chamber (behind the diaphragm) which then draws fresh (filtered) fuel into the fuel chamber from the fuel tank. The unfiltered line just returns any air and/or fuel back to the tank. If you have the tank/carb lines hooked up backwards on the primer assy then you will pump unfiltered fuel into the carb. This may get you started but it can't be good practice. Besides drawing dirt into the carb it can cause flooding and much cussing.

Thanks to everyone for their input. I learn something new almost every day!:thumbup: But usually only after lots of head scratching.