fuel supply problems - and fuel line confusion

[sfinnie]

Hello all, first post. Please be gentle!

I'm trying to restore a friend's McCulloch 3500 chainsaw. It's mid 1990s so getting on a bit. But seems in reasonable condition... other than fuel supply. It starts up & runs fine if I put fuel straight into the top of the carb, but stops when that's used up. So it's not drawing fuel from the tank. I've replaced the fuel lines & filter, cleaned the carb out & replaced the gaskets, diaphragms & needle. I have two questions:

1. Does anyone know what the fuel supply line connections should be? I'm not 100% sure that the lines, as I found them, are correct (see below)
2. Notwithstanding above, any suggestions on how to resolve it?

Fuel Supply
When I first removed the cover, the fuel supply lines were as follows:

1. Line 1 from tank to carb (with fuel filter in tank). Carb is a Tillotson HU-57A and only has one fuel port.
2. Line 2 from tank, connected to an in-line brass ferrule, then onto a rectangular piece of laminated soft material that has a plastic connector in it that the line terminates on. The material sits between the carb and the cylinder block.

That's it. Lines 1 & 2 are not connected in any way. There's no purge/primer bulb present even though the saw has a hole for one. Given the carb only has one fuel port, I'm not sure how a bulb would connect even if there was one.

I'm guessing line 2 is a breather for the fuel tank, and the brass ferrule is a one way valve to stop fuel escaping. But that means there's no way to prime the carb on startup. Maybe that's right? But then, why would the saw have an aperture for a primer bulb?

Silly question as a bonus: assuming the brass ferrule is a one-way valve, I presume I can test it just by passing fuel in? Should pass one way and not the other?

Many thanks for any suggestions.

 

[Bob Hedgecutter]

Watch this- its on a 3200 but should be similar I think.

It shows where the lines should go in relation to carb, tank and purge valve (which I suggest you add seeing as how the saw has provisions, but it is missing) a DANG sight easier than I can type it all out and still leave you confused.
When someone tinkers, it can lead you astray as you put it back together the way it arrived.
Has a Stihl MS 230 show up here recently in a very similar condition, busted purge valve bulb, so was "altered" to delete the tank breather and the busted purge valve became the breather!

 

[sfinnie]

Watch this- its on a 3200 but should be similar I think.

Thanks, had a look.

It shows where the lines should go in relation to carb, tank and purge valve (which I suggest you add seeing as how the saw has provisions, but it is missing) a DANG sight easier than I can type it all out and still leave you confused.

My problem / question is that the carb on my machine only has one port for connecting a fuel line to. So I can't figure out how to "wire in" the bulb. The one in the video has two fuel ports on the carb: one connected to the tank, the other to the bulb. As I understand things, the bulb pulls fuel through the carb from the tank, through the bulb, and then back into the tank. That relies on there being two fuel connections on the carb.

But if the carb only has one fuel port, I can't do that - unless I'm missing something?

When someone tinkers, it can lead you astray as you put it back together the way it arrived.
Has a Stihl MS 230 show up here recently in a very similar condition, busted purge valve bulb, so was "altered" to delete the tank breather and the busted purge valve became the breather!

Yeah, I'm wondering if I'm misunderstanding something with the breather (assuming that's what the other fuel line is). But I keep coming back to the carb only having 1 fuel port, and hitting a brick wall as to how the bulb would be connected.

Thanks very much for your help, really appreciate it.

 

[Bob Hedgecutter]

Could be someone has owned the saw previously. had problems with it and replaced with parts from an older similar model (pre purge valve). I would imagine a 3500 to have one and the two port carb to support it.

An ideal set of circumstances would be, you would find another one someone had straight gassed and burned up the piston/cylinder- that you could pick up for free and swap the carb and purge valve from onto your own.

 

[sfinnie]

Time for an ebay visit...

Thanks again for your help Bob, very grateful.