Question about a New carb

[MadPC]

Hi all, I am wondering if it take a while for the fuel to get into a new carb for a gravity feed system.

like say u get a new engine or exchange a new carb for the engine, you connect you fuel line and then open the fuel value... do you usually get the fuel into the carb immediately? or you have to wait for hours, and even days?...

I know there is an Atmosphere vent for letting the air inside the carb out... but I wonder how long does it take...?

 

[Papasaun]

If all is working properly, the fuel should be in the carb almost instantly. Fuel valve open? No problem with the vent in the tank cap? If you open the fuel shut off valve while the float bowl is off the carb, you should see gas trickle or flow out the carb as soon as the valve is opened. I think your problem is possibly with your low oil shut down circuit on your motor. I posted a reply to your question in General. Hope this helps,

Papa

 

[rcjunkie]

No, fuel won't usually flow into the carb to fully fill the carb float bowl. The reason why is that the fuel must displace the air in the carb. Pushing the primer button can help immensely while throttle is fully open. An open throttle pullsneedle valve out of the main jet which allows air to escape. I often prime a new carb but opening up the drain plug on the bottom of the float.

 

[MadPC]

Hey rcjunkie, you said "the fuel must displace the air in the carb",

that's exactly what I thought. But for my case, I am using a 4stroke honda engine(GXH50), and it does have a primer button on the carb.

Also, you said"An open throttle pullsneedle valve out of the main jet which allows air to escape"

well, I opened the carb and there is no needle on the main gas nozzle. Just a round shaped metal piece that control the air flow... (I guess more air flow will suck more gas from the carb bowl)... in the other word, the gas nozzle is always open...(It just that the hole maybe really small)

In fact, I believe the Atmosphere vent will also let some of the air out right? Right now.... I just let my bike sit for 2 days and hopefully the gas will slowly "soak" into the carb bowl...

oh Thanks for you reply btw!

 

[MadPC]

Ok, so if you look at the picture I drew, u will quick notice that the air is trapped inside the carb once the fuel level pass the "main nozzle hole" on the bottom. The air have no where to escape...

so... my question.. how do u get the air(grey) out from the crab?

 

[MadPC]

ok... just as I thought... problem solved.

So what I did is to drill a hole on the carb bowl @ the position between the top n the bottom of the floating pastic. then I opened the fuel valve to let the fuel flooding the bowl... now of course the air pressure isn't regular inside the bowl so the fuel would spill from the hole.

Then I close the fuel valve, and I angle out the bike a bit so that the fuel would stay away from the hole for a while. Then I used some black sillcon to seal the hole... wait for 4 hrs or so( supposedly it's 24hrs ) and I fired up this baby! Everything works now! amazing!

I will post some pic soon