Troy-Bilt TB425CS Grass Trimmer. The purge/primer bulb does not pull fuel from the fuel tank.... There is no visible fuel in primer bulb when the bulb is pushed.

be sure fuel filter is on the primary fuel line in the tank.check primer bulb and fuel lines.also check fuel tank cap.vented cap may be stopped up

Hi plomelino...

Maybe this diagram will help determine which fuel line goes to what connection
Please take time to rate me

The small diameter line out of fuel tank (has filter in-tank on end) connects directly to the side of the carburetor that has the fuel pump....that is the cover without the hole in it. Other larger diameter fuel line out of tank connects to the longer nipple on the external purge/primer bulb. The bulb "pulls" fresh fuel from the fuel tank to the carb and then out of the carb to itself, where it then "pushes" any air/old fuel back into the fuel tank. The remaining larger diameter fuel line in this setup goes from the metering chamber (has cover with writing on it and a vent-hole) side of the carburetor to the smaller nipple on the purge/primer bulb. Again, on the primer bulb, the longer nipple has a line going directly from it to the tank. This is the return line. The shorter nipple on the bub has a line from it going to the metering chamber side of the carb. If the purge/primer bulb is on top of the carb...small line from carb body to small hole in tank with filter. The larger diameter line goes from the bulb on the fuel pump side of the carb to the larger hole in the fuel tank where sometimes the line is held in place with a nylon nipple connector that keeps the line from pulling out of the tank. Otherwise, the line should enter the tank for about 1/2" or so.

You will need to do a complete inspection of the fuel system. Start with the in-tank fuel filter, all the fuel lines,and to the fuel purge/primer bulb. The bulb is an easy fix. This problem indicates aging of the fuel system and its componets. Check here for the parts. See Items 9, 17 & 18
http://www.partstree.com/parts/?lc=troy_bilt&mn=TB70SS+41ADT70C711&dn=769014720001

Try taking out the spark plug,see if its wet,is the primer bulb ok?does the bulb fill with petrol when you press it,if this is ok,check the carb for dirt,and or the tank,is your petrol mix correct,as this makes a big difference to the run ning of the machine,rgds

The gas lines probably broke because of the ethanol-laced gasoline we have to use nowadays. It deteriorates them. If the unit has the external purge/primer bulb, the way mine did, it is not that hard. Just remember...the primer bulb "pulls" fresh fuel from the fuel tank to and thru the carb, thus pushing out any air/old fuel in the metering chamber of the carb back to the fuel tank in the return line...that said..
Fuel tank...2 lines...smaller diameter line goes directly to the carb body. There are probably 2 brass nipples on the carb. This line goes to the one on the body opposite the end of the carb with the vent-hole in the cover. This is the fuel pump end...where fresh gas enters the carb.
The larger line out of the fuel tank connects to the longer nipple on the purge/primer bulb. This is the fuel return line.
The remaining fuel line (larger diameter) goes from the vented-cover (has writing on it) end of the carb to the shorter nipple on the purge/primer bulb. This line carrys air and old fuel OUT of the carb to the bulb where it is then PUSHED back to the fuel tank via the return line...so you have a small diameter supply line to carb...an intermediate larger diameter line from the carb to the bulb and finally the larger diameter return line from the bulb BACK to the fuel tank.
Go to a small engine shop and purchase about a foot each of the 2 different diameter fuel lines needed and install those new "Tygon" fuel lines as your fuel line replacement.

Fuel filter in tank with line going directly to the fuel pump side of the carburetor This is the end of the carb with a solid cover. . This line should have length in it inside the tank where it can flop around and stay on the bottom to collect fuel. The other line in the tank should have one of the little connectors on it and can be right up to where the hole in the tank is to hold it there.. This line should connect to purge/primer bulb on the longer outlet nipple. Another fuel line should run from the metering chamber side of the carb (the end with the hole in the cover) to the purge/primer bulb with the shorter outlet nipple.
The purge bulb "pulls" fresh fuel out of the tank via a vacuum created after depressing the bulb and the fresh fuel flows completely thru the carb and any air or old fuel ahead of it are drawn to the purge bulb which then "pushes" this mixture back to the fuel tank.

Can't help with the tank, but your better auto parts stores do sell an epoxy that is designed to seal plastic fuel cells.

far enough so that you can reach through filler cap and pull the line out to attatch fuel filter.
then you can pull it back in and let it rest on the bottom of the tank

it sounds like the filter on the fule line is cloged try to remove the filter and then try to prime the trimmer. it it does you need to replace the filter. just about any filter that will fit will do.