New Carb Question

[defrogi]

I got a new 23mm carb for my 4 stroke 50cc scoot. It has a 52mm big bore kit with performance head and cam, performance air filter, no rev limit CDI - high output coil, iridium plug, performance exhaust, performance variator and clutch, Dr. Pulley 6g sliders and a Bad Boy horn that is bad to the bone!

The new carb has a brass tube with a plastic cap that I can't figure out what it is for. There is a hose connected to the bowl drain port and a hose connected to the fuel line in. I got the carb from Scrappy Dog and have emailed them asking this same question but have not as yet received a response. I also posted this on two other scooter forums and no one seems to know the answer yet. Here are pics of the carb.

This is the tube in question.


Yellow outline is fuel line. Red outline is bowl drain line.

This is a pic of the bottom of the carb.

[Rebel]

Looks like just a vacuum port to me, it is plugged so I'd leave the plug on it if you don't need it.

You are running this carb and it is working well I assume.

[defrogi]

Haven't installed it yet. Waiting for the weather to warm up a little. It's COLD in my storage building ;-)

[Rebel]

Summer is coming!

[jmkjr72]

i will concure with rebel based on the location it appears to be a vacume port

[Rocketdog]

Your yellow circle in pic number two is a strange place for a fuel line. I would think the barb in question would be the fuel line. Why would a gravity fuel line feed up?

RD

[Rebel]

did it come with those two lines labeled? I'm referring to the two you have circled in red and yellow?

[defrogi]

I agree on the fuel line running uphill. The carb came with two hoses attached. The one is definitely the bowl drain line. I'm thinking that the other line that has a hose attached IS NOT the fuel in line, but what else could it be? I had a little time to tinker and put a heater in my storage building and I hooked up the new carb using the hoses as is. The scoot wouldn't start and gas was coming out of the air cleaner. I decided that until I know more I put things back the way they were with the old carb and everything works. I should have tried the fuel line attached to the "capped" brass line but it was taking way more time than I thought and decided to put things back the way I knew they would work until I find out more. It seems like every time I get something new for my scoot that really shouldn't be that big a deal it turns out to be way more than I planned on ;-)

[Rebel]

take the bowl off the carb.
hold the float up and blow through the line
if you can not blow through it with the float up but can with the float down, it is the fuel line.

[defrogi]

I finally got a response from tech at Scrappy Dog and the tube with the cap IS the fuel in line. He failed to mention what the other brass tube (with a hose attached to it) is for.

I may try it again today and put that cap on the "other" line that's use remains a mystery :-)

[Rebel]

looks like RD was right then.

[defrogi]

I got another response from Mo at Scrappy Dog.

"Unfortunately, I don't have this carb in front of me (it's on my wish
list). No instructions either. My first instinct was overflow/return
(for pumped bikes), bit it might also be some sort of vacuum hookup for
a fuel valve..."

I used the plastic cap that was on the fuel line on that second line and installed the carb. Everything is working great :-)

[Rocketdog]

Good news. I bet the yellow circle line with the hose on it is vacuum. For the fuel pump, or whatever.

RD