primer bulb doesn't fill

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  #1  
Old 04-01-12, 03:19 PM
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primer bulb doesn't fill

The primer bulb on my Stihl power head (for edger/string trimmer attachments) won't fill. Of course the engine won't start as a result. What to check first?
 
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  #2  
Old 04-01-12, 05:00 PM
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Check to see if the bulb is cracked or the fuel lines. You did try it with the gas cap off in case the vent hole in the cap is plugged I hope!
 
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Old 04-01-12, 05:25 PM
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Bulb not cracked, yes I tried with cap off. With cap on I get bubbles in the fuel when I pump the primer.
 
  #4  
Old 04-01-12, 05:26 PM
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Assuming you have a KM 55 or 90 (something along those lines) checking that the fuel lines and vent lines are in good shape and of course the primer bulb isn't cracked is a good start, most newer stihl's use a vent line rather then a vented fuel cap. Next is this the first time the machine has been ran since last season? If so my suspicion would be the check ball in the primer base, primer bulb should be on the carb body. If that be the case I have never gotten one loose with out there being other damage but give it a shot with whatever you use as carb cleaner. Also if that is stuck the carb is probably plugged also. If that doesn't work replace the primer base or the complete carb, some of the stihl carbs retail for less the 40 bucks and that's a pretty easy repair.
 
  #5  
Old 04-03-12, 03:44 PM
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Yes, KM 55; yes, first start of year. I can't find diagrams anywhere - where is the "check ball in the primer base"? In the gas tank? Are you saying to spray carb cleaner into the gas tank??
 
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Old 04-03-12, 04:30 PM
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I'd start by taking the carb off, open it up, and clean it out with carburetor cleaner. This may be all that is necessary.
 
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Old 04-03-12, 04:59 PM
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I guess that's the next step. I tried squirting carb cleaner into the carb. For awhile the bulb sucked up a bit of cleaner, then it slurped up some black gunk and clogged and won't reinflate now. That can't be good.

I'm not real comfortable taking something apart without instructions or at least a diagram. For example the 2 nuts in plastic depression holding the air cleaner assembly to the carb - how to find a socket that thin? I must be missing something.
 
  #8  
Old 04-03-12, 05:20 PM
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a 1/4" drive 8mm socket should fit right in.
 
  #9  
Old 04-03-12, 05:29 PM
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Thanks Cheese, I'll stop making excuses and get on it tomorrow PM (ya right)!
 
  #10  
Old 04-05-12, 05:34 PM
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OK I have the carb apart and soaking. The bulb is in good shape. I still don't know what and where the " check ball in the primer base" is. Or when I should decide to buy a new carb.
 
  #11  
Old 04-05-12, 05:41 PM
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I said the bulb is OK, but when I seat it on top and compress, it doesn't reinflate. So it seems like one of the holes in the top of the carb that the bulb sucks through (the one with the semi-transparent diaphragm on it maybe?) is clogged or something.
 
  #12  
Old 04-05-12, 06:12 PM
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OK, I found a "repair manual" online but it's kind of vague. When I remove the bulb by unscrewing the "square end cover" that holds it on, there's a plastic "flange" under it between the bulb and the carb body. I assume the bulb has to suck fuel through one of the two tiny holes in the flange and that one of them connects to the brass fuel tube sticking out of the flange. When I seat the fuel bulb in the flange and squeeze, it does not reinflate so this seems to explain my original problem. When I remove it again it does inflate. So I assume that the hole it is sucking through (or the brass fuel tube) is clogged. I've tried spraying carb cleaner directly into the hole that has a metal ring around it, and into the brass tube, but no luck.

I guess the question now is: if I can't get it unclogged, whether I should try to buy the flange alone and how I find the oneI need - since Stihl seems to make finding parts as difficult as possible - can't find a parts diagram.
 
  #13  
Old 04-05-12, 07:34 PM
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Final report is now the bulb won't even compress when it's seated on the primer flange. So the fuel line in the flange is seriously clogged. Any ideas? If not, does anyone know how to find a part for Stihl? Because I'm not even finding the whole carb for KM 55 (Zama carb with brass fuel lines, no part number that I can find).
 
  #14  
Old 04-06-12, 12:13 AM
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You might want to just check on the price of a new carb. Some of these come so cheap that it's not even worth trying to fix them.
 
  #15  
Old 04-06-12, 05:40 AM
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Well the problem is finding a carb since there's no number on it. I have the bulb reinflating and there's nothing plugged in the 2 fuel lines (fuel flows out when I turn the fuel tank upside down). But I am still unable to suck fuel into the bulb although it reinflates now. Just a squeaking sound.

Is it possible the problem is the fuel pickup body, which has never been replaced (about 3 yrs old)?
 
  #16  
Old 04-06-12, 07:01 PM
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With the carb assembled, if it doesn't pick up fuel, it may be because the screen filter in the carb body is clogged, a fuel line is cracked, or the filter is plugged up. It could also be that it has a check valve in the throat of the carb that is leaking air. There is (should be anyway, I don't think I ever saw one that was unidentified) a number stamped into the side of the carb. It's small.
 
  #17  
Old 04-06-12, 07:16 PM
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I think the "black gunk" it slurped up is the check valve that has been destroyed by whatever, save some time and money just get a new carb, they are cheaper than they used to be. Have a good one. Geo
 
  #18  
Old 04-06-12, 07:29 PM
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If it has a C1Q-S71 or S66, which it should, the flange should be, 4228-120-2200. Have a good one. Geo
 
  #19  
Old 04-06-12, 10:45 PM
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Other than the word Zama, some tiny numbers off by themselves, and some illegible ink markings, "C1Q" is the only marking on the carb. I'll see if the dealer can ID it.
 
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