Randy's Cycle Service Explains Carburetors, Choke & Cold Starting - vintage motorcycles. Randy's Cycle Service & Restoration in central Virginia USA. We service & restore all makes & models. We do not source or stock parts or sell vehicles. Technical advice starting at $25. Randy's Cycle Service & Restoration, www.rcycle.com
How to clean a carburetor in 15 minutes
These same instructions apply to most other slide throttle style carbs from
Mikuni, Keihin, etc
You can also take out the idle screw and spring while cleaning if you wish,
but typically that isn't required.
How Motorcycle Carburetors work and how to tune and clean them
Here's a link to the kind of carb cleaner I like best (it IS the best)
hey... awesome video..nicely explained !
just one question. Please do tel me wts AIR NEEDLE and LOW JET used for
again. ? i mean how and what do they work?
The air needle is like a transitional restriction to increase vacuum
pressure and tapered to prime the main jet flow gradually to ramp up fuel
flow from the idle/low circuit to the main circuit. Think of the circuits
like gears or stairs. The needle covers transition between 3rd gear to
about 5th gear on a six speed. It overlaps basically. Fuel is getting by
it from the idle/low- on through to where it's completely out of the way of
the main jet and the main jet fuel flow is roaring like the
Without the needle the carb would work, but not as smoothly through middle
throttle (where most people ride and have the most fine input or throttle
roll back and forth.
The low jet is like second gear on a transmission. You can shift from 1st
to 3rd, but again you risk stalling and it won't be as smooth. Also there
isn't really the mechanical inertia to carry the process on like you have
with a rolling vehicle with a flywheel on the engine and the wheels
turning. The pistons still create vacuum every other time they go down,
but air just doesn't have the punch that steel does when in motion.
The circuits in a carburetor have to be there or you would have a limit on
RPM range. An idle jet can't deliver enough fuel to really scream, and the
main jet couldn't go slow and would be VERY hard to start because the
engine would have to be spun up really fast. So you have usually four or
five circuits (I want to say jets, but their physically different) that get
air flow like stairs as the throttle opens. They are typically 1. Starting
circuit (choke on) 2. Idle circuit 3. low jet 4. Jet Needle 5. Main jet.
How Motorcycle Carburetors work and how to tune and clean them Check out
my other channel here http://www.youtube.com/watch?v=1KKvwMaIotA
How a carburetor works, schemes and explanations
This video explains, not in too much detail, how a 28mm Walbro diaphragm
carburetor works (using mainly schemes to point out what happens inside).
It explains what occurs at the venturi, what the butterfly valve is for,
how the needle doses the amount of fuel, and how does the diaphragm slide
How to diagnose carburetor vacuum leaks on your motorcycle
This is a simple video demonstrating the best method to detect vacuum leaks
around your carb boots. Vacuum leaks are a fairly common problem in older
bikes, and luckily they can usually be remedied quickly and easily, the
first step however is diagnosis.
If your bike is running rough, won't rev up or has an irregular idle,
before you take off the carbs and open them up, check for vacuum leaks. A
vacuum leak occurs when too much air is introduced into the combustion
chamber via a failure in one or more of the carburetor boots or other
rubber mating surface. When too much air is sucked in, then the bike cannot
combust the gasoline efficiently; there must be an optimal ratio. Therefore
it is up to you to detect these leaks, and either plug them up or replace
the carb boots.
In this particular bike, the engine was running VERY lean. Not only did we
have vacuum leaks, but the baffles were taken out of the engine, and the
previous owner had removed the air filter and neglected to install a new
one. This is not only dangerous by allowing foreign material to enter the
engine, but it also makes the engine run much hotter, as lean explosions
create more heat than regular ones (think about blowing on a fire in your
fire place: more air, hotter fire). This can be detrimental to a variety of
parts in the engine, and it is a good thing we didn't ride this bike around
too much before finding the problem.
If anyone has any questions as to why this is important or how to
find/repair these leaks, leave a comment and I will respond.
How to adjust the jets on motorcycle carburetors
This is a brief introduction to the fairly touchy process of re-jetting
your carbs. The techniques discussed here are fairly universal to most
carburated motorcycles, but not all, so your first step in performing carb
tuning should be to consult your repair manual and online forums. Hopefully
this video can demystify a lot of the process for you, so that you have the
courage and interest to do this yourself. Let me know if you have any