Poulan S25 not picking up fuel from tank

[Lawn Masters]

This $#@$@ing saw is getting me very frustrated. it will run with fuel poured down the throat of the carb, but wont pick up fuel from the tank. even if it will pick up fuel from the tank, it will reach the carb, then just fall back down the line to the tank again. I've checked EVERY single seal, every possible problem, I cant figure it out. I've narrowed it down to something in the carb leaking, but I cant figure out what. every gasket in the carb was just replaced with new, and nothing should be leaking, but it is. Now I need help figuring out what to do to fix it.

I also need a new piston and ring for this saw too, and air leak in the original fuel line caused a lean run condition really making a mess of the piston.

 

[Al Smith]

Well sir,the only thing that will cause that phenominum is leaky fuel pump check valves,commonly refered to as the fuel pump diaphragm.

 

[Lawn Masters]

I tried about 4 different ones, nothing worked.

 

[Stumper]

First thought is the diaphram. Since you say it is new there are 2 possibilities- wait make that three. Ii it is installed backward. 2. The diaphram was installed on the wrong side of the carb. 3.the metering needle and it's lever are out of whack.
There have been some carbs with an passageway check valve in the carb body (a little bronze plug gizmo). I don't remember one in the S25 carbs though.

 

[NWCS]

had problems like this on a friends mostly restored Mac SP125C, it would run.. but try to cut she stalled every time.. i tried adjusting the carb.. few others tried.. nothing would work.. i just slapped a NOS Tillotson HL124B on it to replace the walbro SDC.. she runs like a beast and cuts anything now!
very rare that i break down and say just get a new carb.. but this would be one of those times. baileys has the complete carb for my stihl BG85 blower (what i consider the legendary POS from hell) for $37 or so.. everybody else wants $65. not even going to bother rebuilding that carb.. bought the blower brand new and it only ran for about 3 months.. to me that screams horrible defect (rest of the engine is still NEW condition NO wear)

 

[lostone]

I am wondering the same thing as Stumper, was the diapham installed next to the carb body then the gasket? I rebuilt a HU tillotson and put it on back wards (gasket then diapham) but luckily I found out that it was wrong before I tried starting it.

 

[Dadatwins]

Beside carb problems listed, bad fuel line will cause problem, no pin holes or pinched places? Also bad fuel cap, not venting will cause fuel to suck back into tank. Those older poulans had a small rubber bladder inside the fuel cap that would vent the tank enough and not allow the fuel to spill out when inverted. Fill the tank with fuel and lay it on its side and see if it leaks from the tank. good luck.

 

[Al Smith]

Generaly speaking,if the thing will pump fuel,and then dump back towards the tank,it's the intake check valve.I have a Tilley Hu,breakdown drawing,but this danged thing will not let me load an attachment,for some reason.Take a look see on Tillotson's web site.I don't remember,for sure,but I think that the Hu,is one of them that you can get the diaphrams in bass akwards.Another think I just thought of.Some of the kits contain a soft diaphram,that goes next to the fuel inlet,and also a fiber type harder one,that goes over top of the softer one.I once put an HL together,out of kilter.The saw would run for about 5 seconds,then die.As far as a piston,and ring,it would be cheaper to get the entire saw from e-bay.They don't fetch too high of a price,usually.

 

[ray benson]

Here is a pic of a Tillotson HU
http://www.rowenacarbs.co.uk/HU_noform.htm

 

[Lawn Masters]

Thanks guys. I'm beginning to suspect a new gas cap, and some other parts are in order here.probably a new carb to go with it. it will spray some gas out of the cap on the tank when you try to pull it over, so that may be a problem right there.