need walbro carb. help

[tomdcoker]

I am rebuilding a walbro wt or wa 038 carb. on a dolmar ps 401 chainsaw and I have run into a problem. The diaphragm was bad and the only way it would crank was pour gas in the carb. throat. I rebuilt the carb, choked it and after the third pull it cranked and I adjusted it to where it was running good. Set the carb. while cutting wood. It would open up good and idle fair, but when I killed it and tried to restart it the saw went down hill from there one time after I had it running fair I checked where the needle settings were and the high speed jet was open about a half turn. I put a new stihl fuel filter on it, it is getting fuel, I blew through the impulse tube and air came out the carb. I also raised the arm on the metering needle a small amount. It has a blue white spark on the plug and I tried a different plug. Now the only way it will crank is when I pour gas in the carb. Any Help would be very much appreciated. Tom

 

[JohnL]

Maybe check that the fuel tank is venting right, not building a vacuum.

 

[timbrjackrussel]

Air should not come out the carb when you blow in the impulse tube.Check the pump diaphram,gasket positions and bolt tensions.

 

[timbrjackrussel]

I may have misunderstood,air should not come out the carb when you blow on impulse line ON the carb.If you blow on the line that goes to crankcase air could come out carb depending on the position of the piston on the intake port.

 

[Lakeside53]

I am rebuilding a walbro wt or wa 038 carb. on a dolmar ps 401 chainsaw and I have run into a problem. The diaphragm was bad and the only way it would crank was pour gas in the carb. throat. I rebuilt the carb, choked it and after the third pull it cranked and I adjusted it to where it was running good. Set the carb. while cutting wood. It would open up good and idle fair, but when I killed it and tried to restart it the saw went down hill from there one time after I had it running fair I checked where the needle settings were and the high speed jet was open about a half turn. I put a new stihl fuel filter on it, it is getting fuel, I blew through the impulse tube and air came out the carb. I also raised the arm on the metering needle a small amount. It has a blue white spark on the plug and I tried a different plug. Now the only way it will crank is when I pour gas in the carb. Any Help would be very much appreciated. Tom

Put the metering arm back to standard. There is little to be gained with raising it unless you're modifying the rest of the saw.

With the carb not holding pressure, it can only be two things:
1) metering diaphragm is pressing on the needle arm.
2) Gaskets are not in the right order.

It sounds like you have may have assembled the carb wrong. Check the order of the gaskets

- metering cover->metering diaphragm->gasket->carb body.

- and particulary in your case, Pump cover->gasket-> PUMP DIAPHRAGM-> Carb body.