OutdoorKing Repair Forum Forums Repairs and Maintenance Questions on Trimmers and Brushcutters Two Stroke Trimmers & Brushcutters Mcculloch trim mac 240

Hi I am new to this forum.i have been given a mcculloch trim mac 240 as the person I got it off could not get it to run.when you first start it after you have primed it it will run for about 5 seconds then cut out.i have stripped it all down cleaned every bit of it even took the carb to bits and give it a good clean all the gaskets are all ok looks like it has had a kit fitted.put it all back together and it still does the same thing prime it and it runs for about 5seconds.has anyone got a clue what I should try next I have just found out that he was only using unleaded petrol instead of putting oil in with it could it be that any help please.

Hi Eddie. I see that this is your first post, so welcome to Outdoorking. You have posted in the correct section for members to be able to help you fix your problem. Here at Outdoorking, there are many knowledgable members that are always willing to share information. I may not be an expert but may be able to help you somewhat nonetheless.

I found an owners manual: http://www.mcculloch.com/ddoc/MCCO/MCCO2007_EUenAPen/MCCO2007_EUenAPen__530163965.pdf

On any 2 stroke, when a machine comes in for a service, a good first step is to examine the condition of the engine. Scoring, piston or cylinder wear, rings stuck, bearing play are usually what I check for.

Now, you mentioned that someone had previously run the machine with straight petrol. I think that a good first step is to verify that it has done any damage to the piston/cylinder. I say this because when someone says they have run a 2 stroke with no oil, I get a bit worried and 9/10 the piston is extremely scored. I see this a lot on chainsaws, more then trimmers because chainsaws are always running at maximum rpm, whereas trimmers are not. But anyway it's always a good first step.

To do this, remove the muffler from the engine and shine a torch through the port. While turning the engine over look at the skirt of the piston and rings. Look for any deep scoring. Now turn the engine until the piston is all the way at the bottom and look at the cylinder wall (bore). This will be harder to see so look carefully.

If the previous owner had run straight petrol through the trimmer even for not long, then the piston will be severely scored on the exhaust side. Just a suggestion, try this before you go any further with it. I am now curious to see how long the straight petrol was in there for.

That is spot on advice, any 2 sroke I trade / buy etc, I remove the muffler and take a look, It takes minimal effort and can save considerable time in the long run.

Thanks for your reply I will have a look on Sunday and let you know.

Have not had time to check the piston or cylinder wall.can anyone tell me does the carb work by vaccume if so how is it created is it through the diaphragm only trying to figure out how it works and how the petrol gets from the petrol bottle up to the carb.thanks

I'll try my best to explain it:

A 2 stroke carburetor (zama, walbro etc) has the same principle of a 4 stroke carburetor but uses different methods to draw fuel into engine. I'll try to explain its different parts.

Fuel pump diaphram:
This carburetor uses vacuum and pressure pulses from the crankcase that moves the fuel pump diaphram up and down. When the pump diaphram moves up it expands the area in the pump chamber and creates a vacuum and sucks fuel into the chamber through a check valve. When the pump diaphram moves down it compresses the area in the pump chamber and fuel is then forced through a check valve into the inlet needle.

Metering diaphram:
The normal float and needle and bowl system on a 4 stroke carburetor is the same principle here. On a two stroke carburetor you cannot use a float and bowl because you need to rotate the machine on extreme angles, which would cause the float to fall and shut off the fuel.
On this carburetor it uses a needle, metering lever, spring and metering diaphram. The spring closes the needle which is connected to the metering lever and keeps fuel from entering the chamber. As the engine runs fuel is being drawn from the metering chamber and into the carburetor. This makes the metering diaphram push against the metering lever. The fuel pressure from the pump is great enough to overcome the spring pressure, and thus opens the needle which lets fuel into the chamber.

Hope that explains the roles of the diaphrams in the carburetor. As for the primer, it has a major role in getting fuel into the carburetor for cold starts. If you ever take a primer bulb off, you will notice two check valves, one inlet and one outlet. When you press the bulb, the outlet check valve opens which forces fuel/air into the fuel tank. When you release the bulb, the outlets check valve closes, and a vacuum is created. This vacuum that is created in the metering chamber, pulls the metering diaphram onto the lever and pulls the needle off its seat. The open needle now causes a vacuum to draw the fuel from the fuel tank, through the carburetor and back to the primer bulb.

Thanks for your reply I understand how it works know.i think it mite need a gasket kit putting in the carb I have looked for a name and all I can se is Mexico and a code w230 but can not find with that name or code on

Here is the illustrated parts list for your trimmer:
http://www.klippo.com/ddoc/MCCI/MCCI2002_AAaa/MCCI2002_AAaa__530087918.pdf

The carburetor is a Walbro WA 226. Here is the workshop manual for the carburetor:
http://www.walbro.com/media/21895/WAseries.pdf

Eddie, A carburetor kit might seem a logical step to fix your problem, but I am curious, have you checked the piston for scoring yet? As stated above I thought that this was a good first step, as you said the previous owner ran straight petrol through the machine.

Yes checked for scoring had a good look the piston is ok and the walls on the bore are clear of any scoring.rebuilt it and same problem only run for a few seconds after you prime it.thanks

Hi again Eddie, thanks for verifying you did that, now a couple of quick things you can try just to determine where to go. Just before we go any further, I know you probably did but did you flush the fuel tank out and put new mixed fuel in? If yes then continue on... When you prime the machine and attempt to start it, while its running, apply the choke. If you find that you can get the machine to run on the choke ( even poorly) I would start by turning the mixture screw OUT slowly. This will richer up the mixture. If this doesn't help turn the idle speed screw (not the mixture screw, the one connected to the throttle plate)all the way IN until it stops and see if it will run, Don't worry if it runs very high, you can adjust it.

Hi James changed petrol I have stripped every part of the strimmer cleaned it and put it all back together but still will not run.the wife is winding me up she says I can take a car engine take it to bits renew parts and rebuild it then put it in a car and it starts.but you can't fix a strimmer she is trying to wind me up.i will try what you said and let you know thanks j