Carburator "needle" torn

My motorbike was jerking when I traveled half way at the middle of the
highway. Fuel did not seem to flow smoothly and continously when throttle is
opened while traveling but I managed to drag to a nearby workshop.

The technician has checked that the "needle" in the carburator was torn.

Out of curiousity, what can be the reasons that cause the needle torn?

Thanks in advance.

 

Before this happened, I was asked to fill up 4 small holes at the exhaust by
the inspector from the inspection center.

Could this be the problem that casued the carburator needle to break?

Note:
Face the rear of the motorbike directly, the exhuast hole is at the center
of the exhuast pipe and 4 small holes besides this center hole.

Bike Brand: Suzuki Maruader
Bike model: GZ125

 

Needles don't tear. Diaphragms do, but that wouldn't provide the
symptoms you describe.

My suggestion - a useless mechanic is trying to bullshit you.

 

There are TWO things in a carburetor that are called a "needle".

The jet needle is a long round piece of aluminum that is tapered. It's
about 50 millimeters long and 3 millimeters in diameter.

It goes up and down in the brass tube which is called a "needle jet".
Engine vibration will cause the jet needle to hit the needle jet and
the jet needle can become worn in the area where it hits the needle
jet.

The needle jet will become worn to an oval shape. The jet needle/needle
jet combination will not work properly when the parts are worn out, the
engine will get too much fuel at small throttle openings.

The OTHER part that is sometimes called a "needle" is the float valve.
It is in the float bowl and it is about 10 millimeters long and is
square or triangular shaped to guide it up and down in the brass float
valve seat.

The float valve has a conical rubber seal on the end to stop fuel
flowing into the float bowl when the fuel level is high. That rubber
seal can stick to the float valve seat and the rubber can tear. This
can happen if the motorbike isn't ridden very often and all the fuel is
allowed to evaporate out of the float bowl.

 

Bureaucrats will walk all over you, if you let them.

The four small holes are probably for style. Do any exhaust fumes
actually come out of those four holes?

Some rider like more noise from their exhaust system. They drill extra
holes in the end of the muffler. But it's easy to see that somebody
drilled extra holes. The extra holes look crudely drilled.

You should have contacted the inspector's supervisor and told him that
your muffler is stock and the holes were for styling purposes, and that
you did not drill any holes in your stock muffler to make more noise.
If the inspector's supervisor didn't correct his subordinate, you
should have contacted the supervisor's supervisor. You have to fight
the bureaucrats or they will walk all over you.

 

The float valve has a conical rubber seal on the end to stop fuel

The technician also told me that the "head" (made of rubber) which the
needle is inside that moving up and down was harden. He replaced the harden
"head" and now the bike is back to normal.

There is one set back now that the bike can't go faster than 70km/hr.
Previously (before this problem) it can go up to 90km/hr.

 

I am still not sure what part was replaced, but it sounds like the
large rubber diaphragm
is what he called a "head". If you look at the carburetor parts
diagrams you won't find anything that is called a "head" in English.

Maybe that's because the inspector made you weld up some of the holes
in your muffler. The engine can't breathe in fresh mixture if it cannot
get rid of the exhaust!

 

My guess is

You have what's know as a "constant velocity" carburetor.

The rubber diaphragm holding a slide an needle was torn.

When he replaced the diaphragm, he may not have gotten
the needle set right.

You should probably find another mechanic.

If you had to fill in holes in the muffler, you may need a new
muffler.

Anybody with this many strange problems is likely a troll.

 

I don't think so. I suspect he's just not very mechanical, compared to
us. He's apparently in Singapore (or Malaysia, posting to a NG via a
host with a .edu suffix, so he may be a student whose native language
isn't English. Maybe "NewBie" <> speaks Cantonese or
Mandarin.