Stihl HL75 Carb issue

[wicklamulla]

Hello, basically my hedge trimmer stalled abruptly and wouldn't restart unless it had full choke and when the choke was turned off it stalled out again. Anyway on stripping the carb i found this small rubber disc (lower RHS of pic) inside the primer bulb. The circular alloy part with the hole thru it (on LHS of pic) was partially dislodged with a tiny spring beneath it, i pushed the spring and alloy part back in situ and the machine now runs but not as crisp as it did. Now i wonder if that rubber disc is meant to be installed benath the circular alloy bit ? Thanks Ken.

 

[spudulike]

Not sure TBH, stihl list the whole assembly as one part so I guess it isn't meant to be taken apart....Mmmmmm and I would:lol:

 

These are valves, one allows fuel to be pulled in to the primer bulb, the other one allows fuel to be pushed in to the actual carb.

 

One valve will seal under vacuum and open under pressure with the other one doing the complete opposite.

 

I guess you could use a bit of soft fuel hose on the right holes and work out what needs to be done?

[wicklamulla]

Thank yew Spud. If anyone happens to have a parts schematic/diagram for a Stihl HL75 that would be gr8. Thanks all, Wicklam.

[GardenKit]

TBH, I don't think this was your problem, as the purge bulb is redundant once the machine has started. It actually works by creating a vacuum in the metering chamber which is then filled by fuel being pushed by air pressure through the carb. Any further pumping merely pumps fuel back to the tank via the return pipe.

So your problem would cause poor starting, but once started it should run fine.

Maybe you partly cleared something else when you stripped the carb.

[wicklamulla]

TBH, I don't think this was your problem, as the purge bulb is redundant once the machine has started. It actually works by creating a vacuum in the metering chamber which is then filled by fuel being pushed by air pressure through the carb. Any further pumping merely pumps fuel back to the tank via the return pipe.

So your problem would cause poor starting, but once started it should run fine.

Maybe you partly cleared something else when you stripped the carb.

 

 

 

Cheers Barry, Yes i did completely strip the carb 'whilst i was in there' and cleaned it and carefully blew it out with the airline. Must pop down to see you as me mate needs a carb ferrra Mantis rotavator. Tanks, W:thumbup1:

[ashtree]

I'm pretty sure this is a Zama carb and if you Google it there is a very informative set of service notes from Zama.

 

The litle black disc is a one way check valve (there are others) and I think should go one side or the other of the little spring under the alloy cover you pushed back in. A bit of sucking and blowing with a suitable bit of rubber pipe should help ypu to work out which way round it should be.

 

Zama stress that under no circumstances should you blow this type of carburettor out with an airline for fear of dislodging the various check valves. I went gung ho with the airline the other day and now I've got a little black disc too..........don't know where the hell it came from.

 

The good news is that a new carb can be had for just a few quid, so don't struggle too long.

[wicklamulla]

I'm pretty sure this is a Zama carb and if you Google it there is a very informative set of service notes from Zama.

 

The litle black disc is a one way check valve (there are others) and I think should go one side or the other of the little spring under the alloy cover you pushed back in. A bit of sucking and blowing with a suitable bit of rubber pipe should help ypu to work out which way round it should be.

 

Zama stress that under no circumstances should you blow this type of carburettor out with an airline for fear of dislodging the various check valves. I went gung ho with the airline the other day and now I've got a little black disc too..........don't know where the hell it came from.

 

The good news is that a new carb can be had for just a few quid, so don't struggle too long.

 

Cheers Ashtree, I've put the little black disc somewhere safe fer de moment and i won't bodder refitting it unless the hedge trimmer becomes difficult to start. As is without the disc in situ the machines runs fine. Regards, W.

[GardenKit]

Cheers Barry, Yes i did completely strip the carb 'whilst i was in there' and cleaned it and carefully blew it out with the airline. Must pop down to see you as me mate needs a carb ferrra Mantis rotavator. Tanks, W:thumbup1:

 

I wont have one in stock, so get the numbers off the carb and let me know.

Got a very nice, pre-owned, Mantis with Honda 4 stroke for sale though!

[arbormonkey]

I had murder with mine turned out it was a sticking needle but got feed up with it in the end chopped it in

[openspaceman]

On 08/11/2015 at 18:35, ashtree said:

I'm pretty sure this is a Zama carb and if you Google it there is a very informative set of service notes from Zama.

 

The litle black disc is a one way check valve (there are others) and I think should go one side or the other of the little spring under the alloy cover you pushed back in. A bit of sucking and blowing with a suitable bit of rubber pipe should help ypu to work out which way round it should be.

 

Zama stress that under no circumstances should you blow this type of carburettor out with an airline for fear of dislodging the various check valves. I went gung ho with the airline the other day and now I've got a little black disc too..........don't know where the hell it came from.

 

The good news is that a new carb can be had for just a few quid, so don't struggle too long.

An old thread but I have a problem with my HL75, it's old but not a lot of work and on the original blades.

 

Problem is it has sat with aspen in it for 2 years and now I cannot start it.

 

I suspect an electrical fault but just a question about the carb; it has never had the mixture screws altered from factory setting, indeed I don't have a tool to alter them.

 

It fires up once from cold every time with the choke and then never fires again. I have stripped the carb and nothing visible (I was half expecting to find a little globule of water somewhere). I'm a bit loathe to undo the mixture screws and flush the jets out with carb cleaner so can they be altered to just take a screwdriver? Is there anything else different about the Zama carb, I'm assuming the check valves diiscussed earlier in the thread are just in the purge bulb part of the carb?

 

In the meanwhile I'll buy a new plug and research a replacement coil and work off a ladder 😞