Stihl fs400

[aquatoo]

I have a Stihl FS400 clearance saw, which when I pump the bulb to try and start it the carb leaks fuel through the front of the carb barrel, Is this normal and if not what might be wrong?

 

Help please

[TreeswingerPerth]

Have you checked the fuel line aint split ?

[aquatoo]

It's not the fuel line. I took the filter off and the plate behind it and can see the fuel running out of the barrel

[GardenKit]

Has this problem just occurred, or is it after the carb and fuel pipes have been off and refitted?

[aquatoo]

I don't know whether it is an old problem as I have just acquired this brushcutter. The screws were loose in the carb so I took it off, checked that it looked clean inside, tightened the screws and put it back again.

 

The brushcutter has at some stage lost a piston ring which has trashed the piston and barrel - but I can deal with that. There were quite a few other things like missing screws and jammed starter pawl. All simple stuff apart from the carb. I'll take it off and check the pipes again but it seems strange that with the front cover of the carb off and I push the bulb, fuel appears to flow out of the main bore of the carb. Does this suggest a failed diaphragm? I looked at those and they seemed okay.

 

Any suggestions welcome

[GardenKit]

I was just wondering if the little pipes on the primer had been put on the wrong way round. If so, and if the return pipe to the tank is too long and can act as a pickup pipe then the primer wil act as a fuel pump (which it is not) and pump fuel under pressure to the metering chamber. This could cause your problem. (I guess it is currently a non runner)

 

In normal action the primer creates a vacuum in the metering chamber which pulls the fuel up the rubber pipe, through the carb and back to the tank via the primer. In this scenario there is no pressure within the carb to cause a leak.

 

Just a thought.

[aquatoo]

Sounds good. I will look at that later on today and let you know. It may be that I put them the wrong way around on the bulb. I didn't know that it made any difference.

[aquatoo]

I remember, having thought for a bit, that I was careful to put them back where they were when I took them off. They were probably on the wrong way around when I got it, because, as I said, it had been dismantled at some stage. I'm sure you must be right.

 

Many thanks

[aquatoo]

I now know that they were on the wrong way round. Unfortunately it still won't run as at some time it has broken a piston ring which has then made a really neat groove up the wall of the barrel. I assume that it had seized.

New barrel and new piston and rings.

 

Not the bargain I had been led to believe!