Probably the primer bulb is cracked leaking air in when you push it. Inspect it closely. Could also be fuel rubber hoses cracked all the way to the fuel in tank filter in the gas tank. last resort would be diaphramn in the carb. Either way your locate hardware store (that stocks mower parts)should have replacement primer bulbs and rubber hoses sold by the foot. IF not you will have to find SGE lawn equipment store for the parts or go on line.

I just experience the primer bulb issue on a 4 cycle Troy Built off the curb. It turned out as a vacuum issue X running at WOT and starting. From a search I saw the tip to crack/loosen the fuel cap and it went WOT. For some reason the Troy Built's low compression d/n feel good and I donated it and 4-5 others I experimented with. I'm sold on 2 Cycle Echo's quality for my small home use.

Primer/Purge Curiosity, if a vacuum is not the issue. Should the engine start if you by-pass the bulb by connecting the two lines together and manually prime the engine (with pre-mix)? If so, this might get your job finished vs having to stop for parts. I try to keep a spare bulb and spare generic fuel line at least for one repair vs having to go for parts then. Good recycled bulbs and lines are handy also and new in many cases. With different equipment the bulbs and lines can be a little challenging (at X dollars).

I hope this was not jumping a post vs adding a possibility.

Well I fianlly got the trimmer fixed. It was the diaphragm. I have a feeling a winter project will be taking the carburetor apart and giving it a good cleaning. Never worked on a 2 cycle carburetor before. Kind of makes me wish I could have taken vocational school classes and college prep classes in high school. Back then I was told you couldn't do both. I have used the college prep for my job but I would have liked the vocational classes for my life.

There are some youtub and good listed instructions on rebuilding carbs. Generic and specific, which I have found, close enough for most small 2-cycle carbs. The most challenging part I found was trying to replace the small fuel screen in the carb. This taught me to clean the screen w/o removing it with less psi from compressed carb cleaner or compressed air. I also find the fine screen being restricted and hard or cracked diaphragms as being common problems in the small carbs.

Below are 2& 4-cycle youtube and text examples different, which works similar enough. Digital Pics before pulling your fuel lined and in disassembly stages could save you from pulling your hair. LOL & Good Luck!

http://www.youtube.com/watch?v=VGq1wuBNM00

http://www.ereplacementparts.com/article/4582/How_to_Clean_a_2_Cycle_Engine_Carburetor.html

Why not try Votech school in your area! IMO never too late to take some classes. This benifits you and your local technical school system.

Good point rcmoser! I have been in Etc classes that would let you bring your small engine and later computers with needs that really made the classes worthwhile. I started in 1970 at some local High Schools and Junior Colleges (District Funded Extended Learning/Adult Ed/Etc). With today's traffic and etc, I hope that you could find a local class in your area (or see if interactive online classes are offered). Otherwise, will you be our instructor/advisor/troubleshooter? LOL!