Scooter 50cc carb question-- what is this part on the carb? what does it do?

Question

I don't know how to put a link to this picture, so I'll type it out.

www.scootusa.com/4_engine_parts/448.jp...

This is the bottom half of the carb.

what is the part that has the black rubber piece on it-- you know... the little island that kinda extends from the carb. Better yet what is the whole island anyway? Also, there is a flap(not shown) that pushes that pin(the pin that the black piece mostly covers) down when i pull the throttle. What is that flap called? This is a 50cc scooter carb. I need to know what these all are cuz it seems like the flap may or may not be pushing the pin in enough. THANKS, and for some reason it wont let me put a "g" at the end of the above address. It should end with 448.jpg

Answer 1

The first part that you describe appears to be the "O" ring which seals the top half of the carb with the bottom half.  This is important because if any leakage here will result in poor economy and a messy engine bay.

The second use of rubber in the carb is the "Float Pin"  This is a conical shaped rubber that is attached to the top of a small cylindrical metal shaped like a tiny pencil.   This piece fits on top of the float.  When the bottom half of the carb gets filled with fuel, the float (which is made of plastic) rises and then the "float pin" mounted on it, goes and forms a seal with the brass s***w (jet) mounted on the upper half of the carb.  This stops the flow of fuel, till such time as the fuel is utilized and the float gently comes down again.

Answer 2

That Thinga-ma-jig is what's called "Acellerator Pump"

Any time you open the throttle a bit,,,it squirts an extra shot of fuel into the engine.

It does that  in order to compenstate for the Intake Vaccum Drop  caused by sudden throttle opening which "drops" the normal suctioned fuel rate.

The "Pin" looking thing is the Pump Rod/Plunger,,,it's connected to a Diaphragm piston.

It's held "UP" by a coil spring under the black,rubber bellows.

The FLAP you describe is the Pump Lever,,,it pushes DOWN on the Pump Plunger to push Out the Fuel into the engine.

It's all like a Glorified Turkey Baster,,Toilet Punger,or Hypodermic Syringe.

The important thing is to Realize that it's FUNCTION is Strictly MOMENTARY.

One Single Small ,short Squirt of EXTRA fuel delivered at the instant the Throttle is Opened.

Then it's job is Done till Next  time throttle is Popped open.

So it has NO Effect on steady throttle running.

In fact,You could Disable it or even Remove it.

The Difference  You'd notice would be Flat,Sluggish,"Boggy" THROTTLE RESPONSE----especially at Lower RPMS

.........................................

Your Loss of Speed / Power going down the road could be a variety of  of different things.

Most LIKELY suspect would be a Fuel Starvation issue.

The Carb holds "X" amount of Fuel in the Bowl.

That's an EXCESS amount--a Reserve---for the Running Engine to draw from.

The Float Valve system allows that Fuel Volume to be Replenished and Held in reserve,On Standby,,,,BEFORE the engine Needs it.

Anything which Restricts  the Fuel Flow ,,,CAN allow the engine to Intermittently Run out of IMMEDIATELY available fuel in the Bowl.

Example: a Partially Blocked Fuel Filter,,or Fuel Valve Screen,,,,or even a Crimped Fuel Hose or Plugged-up Tank Vent.

Engine may run Fine & Normal at 30 mph,,,under LOW Fuel Consumption conditions.

Delivery Rate can keep up w/ demand

At 45~50,,,it May approach equilibrium,,,and begin to run peculiar cuz it's BORDERING on  "running Out of Fuel" momentarily.

Fuel Delivery Rate is just beginning to be overcome by demand.

"Semi-Starvation"

Then maybe at 70mph,,,,DEMAND overwhelms Delivery rate.

Bike will Consume all the Bowl Contents very quickly,,,Faster than it's coming INTO the Carb Bowl.

Power Drops,,,RPMS  Drop,,,,and thats a "Trick" because it gives Extra Time to refill the bowl.

Soon as Fuel level "catches up",,,,bike runs fine again for a short while,,,,then the Cycle Repeats.

Realize that Gas always Is entering carb,,,,and just the FUMES will indeed support SOME LEVEL of engine Running.

Makes for a variety of interesting Run/Surge/Get Weak/Regain Power scenarios

Very Erratic running,,,and almost always  with Loss of Power & Speed.

But Only down to a certain level,,,,where it seems fine.

Go Faster,,and the misbehaviour resumes.

I would not Swear thats your problem,,,,but Fuel Blockages are common problems.

Worth verifying that everything is clear and in order.

A REALLY dirty air filter can also do that.

At Low Flow Rates it can Pass enough Air to run right.

As ya go faster,,,,,it's Not Only the Restricted Total Flow Volume....

It's Possible that the Bulk Airflow Thru the Filter can cause the Filter Material to be "Sucked Closed".

Thus,,,for a Given amount of airflow restriction,,,at Much  Higher Flow Rates the Restriction can INCREASE.

So the AirFlow Debt increases Exponentially,,,it Sorta Snowballs.

Clogged up exhausts can experience a similar type effect.

Ignition faults,,,such as Bad Spark Plugs,,or Failing Coil or CDI components,,,will USUALLY cause a real distinct tantrum of running----misfire,spitting,sputtering,,... erratic,"noisy" misbehaviour.

Very Seldom does Ignition probs cause a Soft,Quiet,Smooth decline in Power/Speed.

That's more typical of a FUEL fault.

Hopefully that gives you some ideas of things to check out

Good Luck