OutdoorKing Repair Forum Forums Repairs and Maintenance Questions on Trimmers and Brushcutters McCulloch Trimmers & Brushcutters Trim Mac 240 priming query.

My neighbour asked me to fix his 240 strimmer. Generally in good order and little used. Stored over winter with fuel in (oh yes!) Wouldn't start. Emptied old fuel out of tank. Out came bits of disintegrated fuel line. Had broken into many pieces and crumbled to touch. Tank off and swilled out. Retrieved the loose fuel filter/sinker and bits of dead tubing.

Ordered and received the fuel line kit - basically a short length of both dia. pipes. Simple job - cut pipes to correct lengths, connect filter, fit pipes to correct locations on pump assy. New fuel. When depressing/releasing primer bulb - NOTHING ! No fuel in pipework. Carefully took off bulb/valve assy. All appeared to be "as new". Didn't poke any further. Bulb is is good order and all seems airtight with gaskets in good condition.

Apols for long-winded post (it's my first). It's probably something simple - but what ?? Help would be very much appreciated. Thanks.

Mike.

Hi Mike, welcome to Outdoorking.

That machine seems to have an ordinary Walbro WA carburetor, so you should not have too many problems sorting this out. The most common reason for a primer system not to fill with fuel after replacing the tubes, is because the tubes have been connected backwards at the carburetor. One is a suction hose, with a weighted intake filter inside the tank. The other is a fuel return line, which just enters the tank but is probably above the level of the fuel. If they are connected the wrong way around, the priming system will suck air from above the fuel, and blow bubbles below the fuel. You might begin by seeing whether bubbles are being generated in the fuel when you operate the priming bulb.

If the hoses are the right way around, and there is no suction air leak in the intake hose, the next question will be whether the primer pump is actually creating suction in the intake hose. If it does not, there will be a fault in the pump. You should be able to check this by putting a finger over the end of the suction hose or suction fitting, pressing and releasing the bulb, and seeing whether your finger is sucked against the hose or fitting. The bulb should not be able to return to its normal full-inflated shape when you do this.

Hi Grumpy. Many thanks for the welcome and for the suggestions. The problem may be with the pump. With both hoses off, I tried to see if there was any vacuum at all on either of the brass inlets/outlets. Zilch! I took the bulb off again and checked that. Visually ok and it sticks to a glass plate like a limpet on steriods when squeezed and released. Soooooo do I assume that the problem could be with the valve assy. dooferiser thingy that lurks below the bulb? I'm a little wary of poking at it too much to see what moves and what doesn't. Would soaking it in neat petrol for a while to dissolve any crud that may be in its guts be advisable or is it easily stripable for closer examination? Thanks again. Mike.

Mike, I suggest you begin by downloading (free) the carburetor manufacturer's general service manual:

http://www.walbro.com/media/21936/SERVICEMANUAL.pdf

Note that in general the WA model does not have an air purge pump, but yours does. It is not especially unusual for those pumps to stop working, though more often than not it is the bulb that fails, which is not the case with your carburetor. Here is the schematic of the carburetor, showing the detail of the air purge system pump, from the front cover of the manual:



You will see that for illustration purposes, a generic carburetor is shown: it happens to be a barrel-valve type which is quite different from yours internally. However we are only concerned with the air purge system pump, in the lower part of the carburetor. The purge system takes in fuel through the intake port on the right. This intake of fuel is sucked through the pumping and metering chambers, then is pushed out through the return hose on the left side of the pump, back to the fuel tank. It sounds as if one of the purge pump's check valves may be stuck open, but any other source of air leakage into the bulb would have the same effect. The manual refers particularly to the check valve below the fuel jets:


If you go to Page 25 of the manual (it will show as 27 on the Acrobat page counter), this is the beginning of the section on the air purge system. You can find there all of the nauseating detail on how it works and how to overhaul it. Please come back when you have read this, and we can go into detail.

Thanks for that Grumpy. I will read through the manual and maybe investigate the outlet valve situation. Something ain't sealing somewhere for sure! Mike.