# Stihl Trimmer Carb Hose Routing



## ccrider966 (Jul 8, 2006)

I picked up a Stihl fs 36 line trimmer that is not getting gas to carb. The tank filter is good, the primer bulb is good but will not manage to get gas from the tank into the carb. I am not sure of the hose routing. Does the primer bulb suck gas into the carb and exhaust it into the tank or does it force gas into the carb from the tank?
I am not sure which tube on the carb is meant to hook to the suction line from the tank or which tube on the carb is meant to go the line connected to the suction side of the primer bulb.
One of the tubes on the carb is on the diaphragm side of the carb and the other is on the other side of the carb. 
Normally on trimmers I have repaired, I have found the primer bulb us used to suck fuel thru the carb from the tank and exhaust the excess directly into the tank. The fuel enters the carb on the side with the filter screen.
This trimmer has 90 psi compression and good spark and will run if I put gas directly into the cylinder till it is gone. The carb is clean and I have blown out all the passages but I cannot get the primer bulb to bring gas into the carb!
This carb has a brass removable jet which I new to me also. It has 4 cross drilled holes and some sort of ball check at the end. I assume it is just screwed in full with no adjustment.


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## ccrider966 (Jul 8, 2006)

*Problem Solved!*

I spent some time looking at the carb and its gaskets and found that the one thin gasket that has the flapper tabs on it for the pumping action was missing the tabs! The owner had tried to rebuild the carb and apparently got a defective rebuild carb kit! It is a miracle that I discovered this but once I put a gasket with the flapper tabs on it, the trimmer starts and runs good! 
You need to always look at and compare new parts to the old ones! 
By the way, the primer works like the others I have rebuilt. The primer sucks the gas into one side of the carb and exhausts it back into the tank.
I hope this thread will benefit someone else!


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## Sir Thomas (Dec 7, 2013)

Primer is really a bad name for it. It is actually a purger. It purges the air from the carb which is quickly replaced by the fuel. If the primer (purger) is on top of the carb the most likely the port closest to the primer or on the primer body is the one connects to the line to return to the tank (no filter). It doesn't need to go very far into the tank. Most likely the in port is towards the metering diaphram side of the carb and connects to the filter line.
If there is an external (snap in) primer, the in line from the filter is again closest to the metering side of the carb. The out line is closer to the top or reed valve side of the carb. That line connects to the SHORT nipple on the snap in primer and the longer nipple connects to the line that returns to the tank.


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## paulr44 (Oct 14, 2008)

ccrider966 said:


> I spent some time looking at the carb and its gaskets and found that the one thin gasket that has the flapper tabs on it for the pumping action was missing the tabs! The owner had tried to rebuild the carb and apparently got a defective rebuild carb kit! It is a miracle that I discovered this but once I put a gasket with the flapper tabs on it, the trimmer starts and runs good!
> You need to always look at and compare new parts to the old ones!
> By the way, the primer works like the others I have rebuilt. The primer sucks the gas into one side of the carb and exhausts it back into the tank.
> I hope this thread will benefit someone else!


Actually, a pump diaphragm flap valve failure isn't rare - they can curl, or although very rare I've seen them be "shredded" along the edge of the flap. Either way, those flaps are 1 of the 2 functioning parts of the fuel pump - the diaphragm has a bellows area that provides the pump action, and the flaps are the inlet/outlet valves.


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