Fuel squirting of tank vent one purge bulb pressed.

[peatff]

45 minutes ago, adw said:

With a purge carb you normally do not have a full choke flap as it is not needed because the carb is fuelled ready, all reduces emissions. 

 

I've not seen any differences in choke flaps for purge and non purge on any I've done. Pre-fuelling the carb doesn't eliminate the need for choke it just primes the pump chamber so it doesn't have to suck a charge through. You still need a rich mix from cold don't you ?

[adw]

Yes you still need a choke quite correct, I need to look at the carb for these saws, I was going from the power cutter carbs  that only have half a choke flap compared with a complete flap for the non purge carb, I will try it get some pics to how this.

[Hunter]

 

Thank you for every body who tried to help me.

 

I have taken carb out and connected and tested it with small container with fuel in it. When purge bulb pressed it doesn’t suck fuel and bulb remain empty however it push air in return line hence it was building positive pressure on fuel tank which lead to fuel squirting out of vent hole.

 

I have pulled identical carb from another working saw and connected to same purge bulb and it worked at should.

So I confirmed that the issue is with carb.

I then checked the carb kit which i have replaced and it is in correct order, I also checked metering needle and in seems fine.

At this stage I become desperate to find out what is the problem so I pulled all removable parts like metering needed, diaphragms and gasket from the working carb to the non working  cab and tested it again and it does not suck any fuel!

So problem most be with carb body itself.

I have cleaned it again with carb cleaner and no joy.

Aldo tried lifting metering needle but nothing worked.

I guess I need new carb.

I see there are Chinese one on eBay for £16 but do they work?

 

[openspaceman]

Firstly that air is getting in somwhere around the purge bulb because there is no air in the line from the carb.

 

Secondly if it is not sucking fuel into the carb are you sure you have not blocked the small hole between the metering diaphragm and the return nipple/pipe on the carb? The gasket may be upside down and 180 degrees out. Have you checked Spud's suggestion of the gauze filter between the pump and the inlet needle valve?

[Hunter]

3 minutes ago, openspaceman said:

Firstly that air is getting in somwhere around the purge bulb because there is no air in the line from the carb.

 

Secondly if it is not sucking fuel into the carb are you sure you have not blocked the small hole between the metering diaphragm and the return nipple/pipe on the carb? The gasket may be upside down and 180 degrees out. Have you checked Spud's suggestion of the gauze filter between the pump and the inlet needle valve?

Hi

problem seems with carb body itself. There must be blockage in Fuel  inlet pathway.

as stated,  I have exchanged all removable parts from another working carb and it did not suck any fuel.

[spudulike]

I had a 525XPT  in over the weekend and the purge bulb would depress but was having trouble pulling fuel through and it turned out to be crap in the gauze strainer.

I would try to work out the passage of fuel through the carb when the purge is pressed and find out what is stopping the fuel flowing.

A blocked gauze strainer, needle/metering arm issue or a gasket sealing the purge channel is the most likely fault but you will only get there with inspecting the thing. No idea if the AM carbs are any good. Worth a try if very cheap.

[openspaceman]

1 minute ago, spudulike said:

I had a 525XPT  in over the weekend and the purge bulb would depress but was having trouble pulling fuel through and it turned out to be crap in the gauze strainer.

I would try to work out the passage of fuel through the carb when the purge is pressed and find out what is stopping the fuel flowing.

A blocked gauze strainer, needle/metering arm issue or a gasket sealing the purge channel is the most likely fault but you will only get there with inspecting the thing. No idea if the AM carbs are any good. Worth a try if very cheap.

I know nothing about this saw or its carb but it occurs to be that if the metering arm is low then the needle valve will not let fuel past, on older saws it was possible to depress the centre of the diaphragm through the hole to atmosphere. with this depressed and a clean gauze filter there is no obstruction between tank and purge bulb.

 

Mind adw still doesn't think it is a carb problem.

[adw]

Can you just humor us, depress the purge bulb, whilst depressed blank the shorter of the two connections off with you finger, now let the purge bulb out with finger still over the short connection, does the bulb readily come out, or does it stay compressed?

[Hunter]

3 minutes ago, adw said:

Can you just humor us, depress the purge bulb, whilst depressed blank the shorter of the two connections off with you finger, now let the purge bulb out with finger still over the short connection, does the bulb readily come out, or does it stay compressed?

Done this already and it stayed depressed

[adw]

So the check valve in the center section of the carb is stuck ( the part with the outlet purge pipe connect ) this part seems to be available as a spare part.