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2.1 Carburetor diagram and principal parts
1 - air intake
2.2 Operating ranges. Scheme of phases while running
Figure 2 shows the section of a venturi according to the operating periods regulated by the throttle valve opening. In every phase of operation, it is possible to vary and select the optimum setting.
2.3 Installation angles
The tapered-needle-type Carburetor s with concentric, central float chambers have a horizontal main barrel and can be mounted up to a maximum inclination of 40 degrees from the horizontal (figure 3).
2.4 Engine connections
The Carburetor is usually connected to the engine with one of the following:
2.5 Air intakes
Different air intake arrangements are possible for each type of Carburetor :
As far as the lengths of the trumpets is concerned, remember that short trumpets are usually used on Carburetor s for two-stroke engines and longer ones on Carburetor s for four-stroke engines.
For particular requirements, such as on some racing engines, Carburetor s with air intakes having a special shape are available eg PHBE H and PHM H models.
On motorcycles with simple aircleaners or air filter-silencers, it is extremely important to check on the efficiency of the filter and for perfect sealing of the filter box to prevent damage to the engine and to the Carburetor .
Any change in the filter-silencer may produce a change in the carburation and consequently fresh adjustment and tuning of the Carburetor may then become necessary.
Remember also that replacing the filter or silencer with a trumpet usually results in an increase in the amount of air drawn into the engine and consequently there should also be a suitable increase in the size of the main jet fitted.
2.6 Construction materials
The Carburetor bodies are diecast in aluminium or zamak alloys.
For special weight-conscious requirements, there are some small-volume Carburetor s in elektron magnesium alloy.
All the setting parts such as the jets, atomisers, needle-valve seats, etc are made of brass.
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