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Previously I posted that I could get my B&S 550 engine to start for a few seconds after priming, then it stalled out. It was suggested that I (a) clean the carb out thoroughly and (b) check the diaphragm. I did both. I also accidentally pulled out the coil/rope on the starter. The diaphragm had 2 tears in it, both on the little 0 shaped wholes. I put everything back together and the primer still pumps gas, but now I can't get it to even start for a few seconds. I also put in a new spark plug. Now doesn't start at all - nothing. Currently rope only pulls out and rewinds about 90%. Could it be the diaphragm that's causing it not to start or do I need the full 100% pull of the starter rope?

Since you're savvy enough to check out the diaphragm, I would suggest replacing it. I recently bought one for a B&S 550 engine I came across. If you do any carb work, it's cheap insurance to replace the diaphragm, the one I got was $3.90 shipped and it's an OEM part, not aftermarket. Since yours has tears, I would start there. If that doesn't solve anything, you spent $3.90 to totally eliminate the diaphragm from the equation. Before you install the new one, take a can of carb cleaner and squirt through ALL the holes in the carb until you clearly see the liquid come out another hole. If this is the same engine I worked on, there's no adjustment on the carb so there's more guesswork eliminated right there.

Aside from that, does the engine run on starter fluid? I wouldn't worry too much about the rope. I had a 6HP engine that only had half it's pull rope and I used it like that until I could get new rope. Didn't have a problem because the engine ran fine. It's just difficult on the shoulder Once you get the engine running, you can fix up the rope.

*EDIT*
For reference, here's the diaphragm I bought for the work I did:
http://www.ebay.com/itm/25085935168...NX:IT&_trksid=p3984.m1439.l2649#ht_500wt_1180

Great seller, fast shipping and, most importantly, OEM. You should double check that the part # matches the one required for your engine.

I'm not familiar with engine starter fluid, but it does have the red ball you squeeze to prime the engine with gasoline.

I will get a new diaphragm on asap. My only concern: before I took off the carb to clean it out, the mower would start and run for maybe 20 seconds(I'm guessing that's probably off the gas squirted from the primer pump?). Since I reassembled everything, the squeezing the red ball still pumps gas into the engine, but the engine won't start at all - no life, just as if there were no gas or the spark plug was unplugged. Could taking off the already ripped diaphragm when I cleaned the car possibly damaged it further so now nothing works?

That's why I was saying to give it a squirt or two of starter fluid to see if it's the carb or something else that's not making your engine run. If it runs on starter fluid then you know the carb is having an issue somewhere. If it doesn't run then you need to check for spark, timing and valve clearances.