Cagiva mito 125 for sale here on Ebay UK
Cagiva mito 125 parts for sale here on Ebay UK
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Safety Message: Working with fuel systems carries a risk of fire risk.
Cagiva Mito 125 Carburetor Jetting & Tuning Guide
Getting the jetting right on your Cagiva Mito 125 is the difference between a high-revving masterpiece and a seized engine. The carburetor’s job is to provide the perfect ratio of air and fuel. If you are running Lean (too much air), the engine runs hot and can melt a piston. If you are running Rich (too much fuel), the bike will be sluggish and smoky.
This guide helps you identify the correct jets for the standard Dellorto PHBH 28mm carb and how to "read" your engine's performance.
Standard vs. Derestricted Jetting (28mm Dellorto)
Standard (Restricted): 115 Main Jet, 55 Idle Jet, 55 Diffuser Jet.
Full Power (Derestricted): 120 Main Jet, 60 Idle Jet, 60 Diffuser Jet.
Note: If you have a sports air filter or performance exhaust, it is usually advisable to increase the main jet size by another 5 points to prevent leaning out.
The "Plug Chop" Test: How to Check Your Jetting
The most accurate way to see if your jetting is correct is by checking the spark plug color after a high-speed run.
Warm the bike up to operating temperature.
Ride in 2nd or 3rd gear at full throttle for several seconds.
Simultaneously pull the clutch and hit the kill switch (do not let it idle).
Remove the spark plug and check the porcelain color:
White/Grey: Too Lean (Danger! Increase main jet size).
Mocha/Chocolate Brown: Perfect!
Black/Oily: Too Rich (Decrease main jet size).
The Jetting Equation
A simple rule of thumb for figuring out your starting main jet:
Equation: (Carb Diameter x 5) x Modification Factor.
Stock: 28 x 5 x 0.85
Sports Filter: 28 x 5 x 0.90
Full Exhaust & Filter: 28 x 5 x 0.95
jets are M6 on the dellorto 28mm
A simple equation for figuring you main jet is to multiply dia of carb by 5
and then multiply buy 0.85 for stock 0.9 for bike with sports air filter fitted
0.95 for air filter and exhaust .
28 x 5 x any of 0.85 - 0.90 - 0.95
cagiva mito 125 PHBH 28mm bd card
standard
115 main jet
55 idle jet
55 diffuser jet
rejet to these after you derestrict
120 main jet
60 idle jet
60 diffuser jet
its always advisable after any change to do a plug chop test (see below) to test combustion conditions , this will give a clear indication of the jetting state , also its recommended to increase jets size 5 points for any sports airfilter or exhaust fitted again do the plug chop test to ensure correct running conditions
the purpose of the carburettor is to provide your engine with the correct ratio of fuel and air. Although the carburettor can’t provide the ideal mixture at all loads, the different parts of the carburettor work to try and create this ideal mixture for proper combustion.
The cagiva mito 125 carburettor consists of the following parts:
- Fuel bowl
- Shut-off needle
- Floats
- Main jet (provides mixing above 1/2 throttle)
- Pilot jet (provides mixing from idle to 1/4 throttle)
- Jet needle (regulates flow of the main jet as the throttle is opened; 1/4 to 3/4 throttle)
- Needle jet (passage to which the jet needle resides)
- Air screw (adjusts the amount of air from idle to 1/4 throttle)
- Idle screw (adjust the idle speed)
How does the carburettor mix air and fuel?
Fuel from the tank enters the bowl through a small passage until the floats rise up enough to force the shut-off needle into the passage (prohibiting any more fuel from entering the fuel bowl). The main jet is usually found near the bottom of the fuel bowl. As the piston moves down, it draws air into the cylinder. This air flows through the throat of the carburettor and creates a vacuum which sucks fuel into the cylinder via the main jet.
The mixture screw is able to adjust the air in small amounts in order to fine tune the mixture (usually at idle). Most carburettors require adjustment of this screw and a jet change. When you change a jet, you are simply giving the fuel a smaller or bigger hole to flow through, thus changing the amount of fuel that reaches the cylinder.
What is meant by running rich or running lean?
These terms refer to the amount of petrol being delivered to the engine. If you are running lean, then the ratio of fuel to air is too low, that is, there isn’t enough fuel reaching your engine for the amount of air that is reaching the engine. This can cause the engine to run hotter and leave you with a seized piston. Running rich means that there is too much fuel reaching the engine for the amount of air that is reaching the engine. Running slightly rich is generally acceptable and protects the engine as the excess fuel helps to carry heat out of the engine. If you are running very rich, you will have a very smokey exhaust and performance will suffer.
The ideal ratio of air to fuel is called the stoichiometric ratio.
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other jetting articles
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How to check Jetting
Mark your throttle housing and grip in 1/4 turn increments. Use a marker
Now get the motor to operating temperature by riding around.
Once the motor is warm, ride in 2nd and 3rd gear from the low RPM to high RPM. This puts a good load on the motor and is an accurate test of performance. Try to notice if the problem gets worse or better as the motor heats up.
Now try to locate the throttle opening at which the problem exist.
plug chops are the key to fine tuning the main jet once the other circuits are set:
White to Porcelain / Chocolate / Mocha Brown to Black-Wet
A plug chop simply means looking at the sparkplug to determine how you are jetted at a particular throttle stage. The only tricky part is in isolating the throttle stage. Before starting, clean your sparkplug and filter and warm the bike up.
To check the main jet, which operates from 1/2 to full throttle, get the bike up to a steady full throttle or near to it for a good few seconds, then simultaneously pull in the clutch and kill the engine. Don't let the motor drag you to a stop, or fall to an idle, because you want to isolate the plug colour at full throttle.
Get off and check the sparkplug colour It should be a light chocolate colour. If it's white, the air/fuel mixture is too lean and you need a bigger main jet. If it's black or really dark brown, the air/fuel mixture is too rich and a smaller main jet is needed. If you need to change jets, change by one size, and do another run.
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