Primer bulb issues

[old2stroke]

Quite a few smaller saws and trimmers have a primer bulb that lets you get the thing running with fewer pulls after it has been unused for some time, however the bulbs seem to have a short lifetime (ethanol again?) and I have seen problems with their replacement.  There is a misconception of how these things work.  On modern engines they do NOT inject fuel into the engine and they cannot flood the engine if they are pressed too many times.  The primer base has two check valves in it that keep fuel moving in one direction only, and the device is meant to suck fuel up the fuel line from the tank, fill the metering chamber in the carb and then dump any excess fuel back into the tank.  In operation, the bulb should be pressed until you can feel fuel being squished through it, then you know the fuel line and carb are full and the engine should start on full choke with a couple of pulls.  When replacing these things, it is important that the suction port of the primer be connected to the carb and the other one goes back to the tank.  You can easily find the suction port by hooking a short fuel line from a container of fuel to each port in turn and squeezing the bulb to see which one sucks.  If it is hooked up backwards, it could either suck fuel out of the tank and flood the engine by forcing fuel through the carb, or depending where the tank fuel level is with respect to the primer return line, could seriously lean out the air/fuel mix.
A side advantage of a primer is it makes it easy to drain all the fuel out of a saw.  Just drain the tank, pump the primer until it is just sucking air, then drain the tank again.  The carb and fuel line is now empty but if you are really fussy, it might start up on choke and run for a short while to get rid of any residual fuel or fumes.

[Al_Smith]

Weedwackers and blowers seem to be the main types that use primer bulbs .As it seems more often than not it becomes a problem when they go bad and a fact often over looked .

They are inexpensive often you can buy them by the dozen on flea bay for a couple of bucks.

[CR888]

I have found a few different designs and mounting frames. Would buying them by the dozen be OK for multiple brands of ope? Are they different in size? I also notice the Chinese ones are harder and not as soft as OEM ones, is their better quality types available like walbro or something? I like the air purge primer, I wish some of my bigger saws had them.

[old2stroke]

They all function the same way so any that you can fit to the saw should work as long as it is hooked up right.  There are differences in size and mounting methods so if you don't get the right one, there could be mounting problems. The main culprit in longevity appears to be alcohol in the fuel that causes the bulb to harden and then split.  Bulbs made of better material should last longer, anyone have any brands that are better?

[CR888]

I often see just the plastic bulbs for sale online without the base that has the check valves. Generally are ALL the bulbs the same size between models. Its just usually it's just the plastic bulb that fails/cracks, not the base. I want to order a dozen online and just want to be sure they fit. Also are they all serviceable as far as just replacing the plastic bulb and not the whole assembly? Thanks

[Al_Smith]

There are different sizes and styles .Generally speaking most on line suppliers will list what they fit .If not they show a picture .