The actual bulbs all work the same way. Pressing the bulb produces small amount of pressure on one side, and a vacuum (or suction) on the other.

However, how the are designed to be used depends upon how manufacturer engineered the fuel system. Most "primers" are actually for "purging", where fuel is forced into the carb, but not to the engine. With fuel now in the carb chamber, the engine can draw the fuel and start. Engine with a purge bulb often also have a choke plate. There is a return line on the carb either going back to the tank, or in some older engines simply allows excess to dribble on the ground. Homelite used that system for years on their low-end weedeaters. Cheap but effective.

A primer bulb is set up to force fuel thru the carb and into the intake through an additional jet. This provides a rich mixture for starting. Usually a primer equipped engine doesn't have a choke plate, but this is not always the case. Briggs uses an actual primer on their vertical shaft engines, both with Pulsa-Jet carbs and with the Walbro float carbs. In both Briggs cases, there is no choke plate.

Thanks For The Good Reply! I agree my terminology should have been prime carb vs engine. I examined the Green Machine and experimented with it more this morning. I c/n find a model # on the trimmer and only info ("The Green Machine, Long Beach CA, Powered By Zenoah, Maid in Japan"). The Exam detected:

1. A leaking gas cap and line due to a bad gasket and cracks due to signs of loosing pressure as I pumped the bulb.

2. I switched ports at the primer bulb and there was only signs of pressure vs any priming but a small amount of gas was showing.

3. The machine runs fine after the "initial" start by pumping with my finger over the valve in the cap to hold pressure and gas to prime the carb. Manually priming starts faster.

4. The trimmer was given to me at least 20 years ago and I felt they used it at least 10 until having trouble getting it repaired which a carb kit fixed.

5. I use it as a hard blade trimmer only, with the split shaft it would do both, plus, I added a longer shaft.

6. The Power is the selling point, It Has Power To Spare At Half Throttle. loger

I just had a carb from a Mantis apart and couldn't figure out why pushing the primer bulb would not bring gas from the tank.

The primer bulb pushes air into the tank from the 90 degree elbow just below the bulb. The tank is pressurized and forces gas into the straight fitting at the bottom of the carb. There is also vacuum and pressure involved.

In my case, the primer bulb was pressurizing the tank, but no gas was entering the carb. The problem turned out to be the fuel inlet screen was blocked in the carb body. Cleaned the screen and everything worked well. First time I ever ran into this.

Thank Again For A Good Reply! Your post gave me a lot to look forward to experimenting with this morning. Your clogged screen is what got my attention since I probably had not been in the carb in over 10 years vs lines and etc..

1. The gray and old fuel line was hiding a lot of the fuel's action of pressurizing vs pumping.

2. I found the Green Machine's model # behind the gas cap on the body (# 030334B, 22.5cc).

3. A clogged screen w/n the problem vs old leaking lines and seals on the pressurized system.

4. The tanks 2 fuel line grommets might need fuel line connecting barbs in/by for tighter seals.

5. After replacing most line seals I could see/feel the pressure working as a prime each pump.

6. This old monster shows no signs of retiring. I c/n remember it's age related to needs vs mine.

LOL! loger

PS. Help Your Neighbor's screaming mower which took me back to the 70/80s before I remembered to put a drops of oil in the starter.

Baymee, I'm having the same problem as you did with my trimmer. I can prime the bulb, but I get no gas. The tank does get pressurized. Where do I find the fuel inlet screen in the carb? I've looked at the parts diagram, but I'm not having much luck finding it.

All of my fuel lines have been replaced. I did not replace the fuel filter. That may be next on my list. I've had my Echo GT-2000 for about 6 or 7 years. Cranks on the 2nd pull even after being up all winter so I want to get it up and running again.

Here is a link that might be useful: Parts Tree parts diagram

Baymee, would you agree the small screen is under the fuel inlet plate at the link below? It will come with a kit but I strongly recommend cleaning vs replacing. They sound easy to replace but that has not worked for me. To me it is easy to clean and check with compressed air or a can of carb cleaner with a stem. Old oil from evaporated fuel and old hard rubber was the problem I found once. Bad or contaminated fuel in one trimmer vs many is not bad compared to the neglected chainsaws. Good Luck Andrew! jow

http://footflyer.com/fix/motor/carburetor/walbro.htm

I remember being able to look thru the screen and see a small hole using a light. I had the needle out, so I was probably seeing through the seat. I would say the the screen is directly below the seat and I would clean the screen rather than replace it.