Chainsaw Repair

Sounds like it is not pulling fuel. Are you sure you have the diaphragms and gaskets in the carb in the right order? If backwards the carb will not pull fuel. They go in different order depending on which side of the carb you are working on.

Have a look here:

http://chainsawrepair.createaforum.com/ported-saws/walbro-carb-info/

     Howdy,
   When you disconnect the line at the carb, do you have fuel?
   As far as starting goes, 50's have a funky choke system. It has a slide in the top cover that uses a piece of spring steel to partially collapse the air filter thereby covering the intake opening, and causing the choke. Take the top cover, and air filter off. Place your thumb over the intake opening when you crank the saw. If it primes and starts, you have a choke issue.
Regards
Gregg

Did you try what Grande Dog suggested in the previous post? What he is suggesting is systematically eliminate each part of the fuel delivery system starting with the fuel supply. Disconnect the line from the carb and turn the saw onto the clutch side to see if fuel flows. If fuel can flow from the tank when not connected to the carb you know that the pick up hose is not kinked. If fuel does not flow then it is either a kink in the line or the tank vent is blocked. If when you try this fuel does not freely flow out the line, then open the tank cap, if fuel flows then it is most likely that the vent is clogged.

OK, so now we know that the problem is beyond the tank and fuel delivery from the tank to the carburetor. We will leave the carb internals alone for now since you just put a diaphragm kit in it. The carburetor is essentially a pump, it uses pressure from the spinning engine to pump fuel from the tank and delivers it to the engine.

There is what is called  a pulse tube that connects the engine to the carburetor, in the case of the 50 Special this tube is built into the heat shield (501 77 11-01) it is the rather pointed tube that protrudes from the cylinder side of the heat shield. (See attached picture). There are two rubber parts that connect the heat shield to the cylinder that are notorious for failing. They are ( 503 16 16-02 induction pipe) and ( 503 31 07-51 pulse grommet), there is also a carburetor gasket (501 77 00-02). The pulse grommet for the 50 Special is NLA however I believe that the grommet from a 50 Rancher will also work (505 31 07-51).
 
If the grommet is bad (or missing!) between the cylinder and the heat shield you will not get enough 'pulse' to draw fuel. Like wise if the gasket between the heat shield is not aligned properly with the carb side of the heat shield the pulse will not get to the carb and pull fuel. If you look closely at the engine side of the carb you will see a small hole in the front face of the carb (pulse inlet) this must not be blocked, the gasket also has a small hole that must be situated such that it does not block off the pulse inlet to the carb otherwise no fuel!

Hi, brand new member here-
Does anybody know if the OP solved his problem? I have exactly the same saw and problem; changed the carb, fuel line, filter etc; saw starts, runs 5-10 seconds and then dies out of fuel. It will start up again in a few minutes with the same results.  Once it ran and cut for 15 mins, thought it was good and shut it off, problem returned. Sounds like I should go to the pulse tube next?