OutdoorKing Repair Forum Forums Repairs and Maintenance Questions On Hand Held Blowers/Vacuums Petrol Blowers & Vac's Stihl BG56 dying

Folks I picked up a Stihl BG56 in excellent cosmetic condition which caused the previous owner some issues. He said problems started with a split primer bulb and he replaced it and it never ran well again which is when I got it.

It will not fill the primer bulb which sits on top of the carby. It fill it perhaps a few mm then you press it again and you can see bubbles coming from the hole where fuel comes into the bulb.

I replaced both the fuel lines and checked the in tank line for splitting. The new fuel line I used is see through which helps with seeing what's happening. When you press the bulb fuel is drawn from the tank. The bulb partially fills then fuel returns to the tank in dribs and drabs via the return line.

I put a carby kit through it which was gaskets only no needle.

Bulb function didn't improve at all.

Machine starts and runs but is erratic. Sometimes it runs well other times it is difficult to start. Other times it will only stay running through constant revving. Motor is not noisy.

I checked the compression and it came in at 110psi. I'm wondering if this is the culprit although the bubbles through the primer base concern me

Hi Aldot, i was going to suggest the diaphragm but you've changed it so that eliminates that.
If it's got a remote primer, did you try reversing the fuel lines on the primer bulb end or if its got the primer mounted directly to the carb try switching the inlet and return lines and see if that helps. Beyond that mate i'm stuck and hopefully someone else will jump in and shed some more light on the problem.

Hi Aldot and bigted,
I'll fess up and say I really haven't got a clue with these things, but sometimes the simplest things can be the answer...if its got a vented fuel tank cap....is the vent blocked or obstructed?

Hi Aldo, here is the owner manual for that blower:
http://www.stihlusa.com/WebContent/CMSFileLibrary/instructionmanuals/BG_56_66_86_SH_56_86_Manual.pdf

Here is the workshop manual:
http://www.google.com.au/url?sa=t&rct=j&q=&esrc=s&source=web&cd=5&cad=rja&uact=8&ved=0CEYQFjAE&url=http%3A%2F%2Fwww.planetuniverse.org%2FviewUnlockedDocument.cfm%3Ffid%3DAE9EAF4A066983B7FEB34B5C56BA885A&ei=MRHgU4urCYzc8AWa1oLICA&usg=AFQjCNGwdHhxAso3IwYkHfr4iQzt8eoszw&sig2=unnZyN4SPpCsWvsvMBIJEg&bvm=bv.72197243,d.dGc
(I can only get it to open in Internet Explorer, not Firefox. I haven't been having a lot of happy outcomes from Firefox lately.)

It sounds as if the manual fuel pump has a stuck valve or another form of suction leak, probably due to something that happened when the previous tenant took it to pieces. If the pump is properly sealed and the valves work, the bulb should just stay collapsed when you press it, if the intake is blocked. Incidentally you should always recheck the pump with the suction pipe removed and your thumb over the intake port: if the bulb does not stay collapsed after you press it, you then know you have an air leakage problem inside the bulb-pump or carburetor. Remember, an air-purge starting system draws fuel through both chambers of the carburetor, as well as through the bulb-pump. If it leaks air anywhere (suction pipe, either chamber, or the pump) you will get what you've got. You'll also get what you've got if the pump has a stuck output valve, but in that instance, it will draw fuel if you put your finger over the output port.

You seem to need Section 10.4.1 of the workshop manual (page 63 onward). As far as I can make out the carburetor is a Zama C1Q.

Thanks for the information Grumpy.

I will try and get some info and pictures up when I have a chance to fiddle next week. Interestingly whilst contacting Stihl for a price on a new primer base block, which has the valves for fuel flow whilst priming, they said it should not cause running issues unless the bulb is split and causes an air leak.

They say the carby is faulty.

I think most of the places an air leak could occur are in the remainder of the carburetor rather than the primer base, but since it happened when somebody made an amateur repair of the primer, I'd begin by inspecting that. However I wouldn't replace it without testing it in detail. Here is the Zama workshop manual that covers your carburetor:
http://www.zamacarb.com/pdfs/TechGuide_2007.pdf

Here is the primer pump:


As you can see, if the outlet check valve (C) is stuck open, pushing and releasing the bulb will just push air out through the return hose, then suck the same air back in. This is my favourite explanation in this case because the pump was worked on immediately before the problem arose. However, a largish air leak into either of the carburetor chambers would also produce more or less what is happening: air would be sucked into the pump through its inlet check valve (B) and pumped into the fuel tank through the fuel return line.

Why not just remove the bulb, then try to blow into the primer pump through the fuel return line? If you can, valve (C) is stuck open. If you can't, it's not.

I patiently waited for the right price on a complete new carby from the US. The blower now runs like new. I have yet to suss out the old one. I will one day try the new primer on the old body to see if something is worth keeping.

Thanks for reporting back, Aldo. I'll close this thread.