Here's how to find and adjust the mixture screws on your carburetor.
Note that metering-block style carbs such as Holley and Demon more often have one or 2 mixture screws in each metering block depending on the number of venturi. Also those may not be located at the bottom of the carb as in factory carburetors.
DIY Carburetor Synchronize / Balance Tool
This is a homemade bottle style carburetor synchronization tool ( homemade
manometer ) and balancing tool. If you are going to attempt to, or want to
know how to sync your carburetors, there are a few things to know first.
1. Carburetor Synchronization = Adjusting your carburetor throttle plates
or throttle slides so they move from your carburetors idle setting to wide
open throttle simultaneously, or in sync with each other.
2. Balancing Carburetors = Adjusting your carburetors so they allow each
cylinder to flow or pull the same amount of air and fuel at your desired
idle speed. Carburetor sync and carburetor balancing go hand in hand.
3. Idle speed screw adjustments must be made at normal operation
4. Air fuel mixture screw adjustments must be made at normal operating
5. Air fuel mixture adjustments only affect your carburetors pilot circuit,
which means from idle to part throttle. Air fuel mixture screw adjustments
have zero effect on wide open throttle.
6. Carburetor running rich = Too much gas not enough air.
Carburetor running lean = Too much air not enough gas.
7. Wide open throttle rich or lean conditions are adjusted two ways:
A. Carburetors with throttle slides have a clip on the carburetor main
jet needle. Raising the main jet needle clip drops the needle deeper into
the main jet and will lean the carburetor out. Lowering the main jet needle
clip will raise the needle and enrich your carburetors mix.
B. Carburetors with throttle plates (butterfly style) need to have the
carburetors main jet changed to a larger diameter jet to richen the mix or
a smaller diameter jet to lean your mix.
8. If your engine will not idle correctly or your air fuel mixture screws
seem to have no affect on the engine at idle, then most likely your pilot
jet circuit is clogged and you should clean it.
The snowmobile in the video is a 1986 Arctic cat cougar 500 fan cooled, it
has Mikuni vm34 roundslide carburetors which have a primer nipple on the
engine side of the throttle slide. Perfect place to attach a homemade
manometer to balance everything. These mikuni vm34 roundslide carburetors
were common on many motorcycles, snowmobiles and atv's. Suzuki, yamaha,
polaris, arctic cat, all used them at one time or another, they are good
carburetors when they are dialed in.
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
Setting the timing and adjusting the carb
Set the timing by ear, and got the idle slowed down so I could do a little
adjusting on the carb. I'll do more when it's cold, so I can set the
choke and all. Love the way it's sounding..
How To Find A Vacuum Leak - EricTheCarGuy
Vacuum leaks are one of the biggest causes of engine performance problems.
This video is pretty straight forward in it's approach to finding a vacuum
leak. On thing I might mention is that not all vacuum leaks are at the
engine. Some HVAC systems run on engine vacuum and can cause a leak under
the dash in some cases. I've even seen vacuum operated door locks. Just be
sure to be careful spraying flammable stuff on a hot engine, you don't want
to take one problem and make it a whole lot worse. You can also use a spray
bottle with water to do this same test. It may not be as effective, but you
don't have to worry about spraying a flammable substance on a hot engine.
For more information on diagnosing engine performance issues, check out
this article I wrote.
The best place for answers to your automotive questions:
Information on Premium Membership:
Due to factors beyond the control of EricTheCarGuy, it cannot guarantee
against unauthorized modifications of this information, or improper use of
this information. EricTheCarGuy assumes no liability for property damage
or injury incurred as a result of any of the information contained in this
video. EricTheCarGuy recommends safe practices when working with power
tools, automotive lifts, lifting tools, jack stands, electrical equipment,
blunt instruments, chemicals, lubricants, or any other tools or equipment
seen or implied in this video. Due to factors beyond the control of
EricTheCarGuy, no information contained in this video shall create any
express or implied warranty or guarantee of any particular result. Any
injury, damage or loss that may result from improper use of these tools,
equipment, or the information contained in this video is the sole
responsibility of the user and not EricTheCarGuy.
How to adjust Quadrajet/Dualjet fast idle
Quadrajet/Dualjet Rochesters have a fast idle adjustment screw that is
separate from the base idle screw.Here's how to locate it.
NOTE THAT THE CHOKE ITSELF MUST BE WORKING IN ORDER FOR THE FAST IDLE TO
How to debog your Quadrajet part 3
In the first two videos we looked at operational theory of the Quadrajet.
In this episode we'll explore a couple mistakes the home mechanic often
makes in an effort to improve the performance of this unit.