Problems With Fuel Cap and Duckbill

[hotajax]

OK, here's what's up. I inherited a really worked over XL-12. As I think of it, I replace parts. One of the parts I attempted to replace was the duckbill check valve in the side of the fuel filler cap. Got the metal thing out, then ripped out the old duckbill with a paper clip. Reinstalled the new duckbill. Put the metal thing back in. Tried to run the saw, and it stalled out. Guessing it is not properly vented. So I took out the duckbill altogether. Can't really use the saw in any weird positions because fuel leaks out of the fuel cap. Yeah, I know you're laughing your butts off because I screwed up putting in a duckbill. So where did I go wrong? Once you stop laughing, I would appreciate comments. I doubt if I can buy a new fuel cap anywhere. Question: Does the vent in the side of the fuel filler cap have to be open before you put the duckbill in? Does the duckbill have some one way valve that lets air in and keeps fuel from flowing out? Thanks. Jake

[sweepleader]

The duckbill is designed to let air in and not let fuel out, so it has to be inserted the right way. That would be with the open end out, toward the metal filter. If it is in backwards it will not let air in, thus a stall when enough fuel had been used to cause a vacuum in the tank that the fuel pump in the carb cannot overcome. If it stalls right away, before much fuel has been used, there is likely some other cause. Might be a bad fuel line or carb kit.
Dan

[powerking]

My guess is a fuel line/filter issue and the fuel pump can't maintain good fuel pressure/delivery to the carb main chamber. It could be a leaky carb-to-reed valve block gasket affecting the pulse port. You could try a "test" gravity feed fuel tank & line to see if it makes any difference; or if you have a tool like a Mighty-Vac, then start checking the fuel line/system for leaks; etc. The duckbill valve ensures there is always neutral or positive pressure in the fuel tank.

Tom (PK)

[hotajax]

Jul 10, 2014 10:07:35 GMT -5 sweepleader said:

The duckbill is designed to let air in and not let fuel out, so it has to be inserted the right way. That would be with the open end out, toward the metal filter. If it is in backwards it will not let air in, thus a stall when enough fuel had been used to cause a vacuum in the tank that the fuel pump in the carb cannot overcome. If it stalls right away, before much fuel has been used, there is likely some other cause. Might be a bad fuel line or carb kit.
Dan

That was how I had it. Small end in first, then open end out, facing outwards. It stalled then. Is there a right way to insert the duckbill? I know the little end goes in first. But, how far in does it go, and what do you push it in with? Or, does the metal filter go inside the duckbill? There is no gasket around the filler cap, so I guess I can make one up out of cork and use a scalpel. Thanks again. Jake

[sweepleader]

Sounds like the duck bill is OK. It just goes in and the metal pushes up against it to hold it there. Without a gasket, the cap will leak but I doubt that would contribute to a stalling situation. Powerking's suggestion of checking the fuel line with a vacuum pump is a good one. Fuel lines often crack and leak air, then fuel will not pull. The line would not hold vacuum if it is cracked but you might not be able to see the problem otherwise. It could be just an adjustment problem too, you could try opening the idle screw a little till it starts to miss, then lean it slightly. It should be set somewhat rich in order to get good acceleration even if it is not the smoothest idle. The high speed should be toward the rich end too, so you get the rough top end, slightly below the fastest speed possible. That will help acceleration and keep the motor cooler under load. Check out the link below on carb setting, it is very good.

MCS did a great job on this one:
houseofhomelite.proboards.com/thread/2679/all-position-carburetors