Primer Bulb Question

[Freudianfloyd]

Reading a different post made me think of something my MS211 does. For some reason, the primer bulb never fills with fuel, even when pumping it, but the saw runs great, and usually starts on one or 2 pulls without using it. I am sure it isn't an issue, but can anybody think of why it does this? It doesn't leak, and the fuel lines are good. Like I said, the saw runs great. Just curious.

 

[stihl86]

The BR 4 mix series wont fill the primer completely either. Even when new. I think it has something to do with the amount of distance the system has to move the fuel.
But, if the bulb doesn't have anything in it, that could be a indicator of an partially clogged screen in the carb, on the pump side.

 

[Old2stroke]

The main reason purge bulbs suck air instead of fuel is due to a check valve in the carb that is not sealing properly and allowing air to be sucked back through the fuel jets. A simple test is to clamp the fuel supply line to the carb closed and pull a vacuum on the carb port going to the purge bulb. It should hold a vacuum if the check valve is seating properly. If the saw has a purge bulb, the carb will have at least one of these valves and there might also be another one in the main jet nozzle.

 

[sb47]

I hate primer bulbs, I will not buy anything that has one. Been there done that, nope, not anymore.

 

[rupedoggy]

switch the lines at the bulb

 

[alexcagle]

There are two check valves in the purge primer.

If either fails......no prime.

There is almost always a check valve in the outlet port of the carburetor going to the primer as well, to keep it from back feeding if the primer ruptures.

Most check valves on jets I've ran across will leak some, especially when dry.... Even new ones.

While the saw is running at a half throttle; carefully- try pumping the primer to clear any specks of debris or to help wet a dry primer to help it start working.

 

[alexcagle]

switch the lines at the bulb

Get it backwards on a cheapo carb without a backflow check valve inside the outlet, and you'll flood the crap out of the saw.....BTDT