General information
1. To reduce the amount of unburned hydrocarbons released in the exhaust gases, a pulse secondary air (PAIR) system is fitted. The system consists of the control valve (mounted behind the right-hand radiator), the reed valves (fitted in the valve covers) and the hoses linking them (see illustration). The control valve is linked by hose to the front cylinder intake duct and actuated by the vacuum created therein.
17.1. PAIR system control valve -XL650V models
2. Under certain operating conditions, the vacuum in the front cylinder intake duct opens up the PAIR control valve which then allows filtered air to be drawn through the reed valves and cylinder head passages and into the exhaust ports. The air mixes with the exhaust gases, causing any unburned particles of the fuel in the mixture to be burnt in the exhaust port/pipes. This process changes a considerable amount of hydrocarbons and carbon monoxide into relatively harmless carbon dioxide and water. The reed valves in the valve cover are fitted to prevent the flow of exhaust gases back up the cylinder head passages and into the air filter housing.
Testing
Control valve
3. Remove the valve from the motorcycle (see below).
4. Check the operation of the control valve by blowing through the air filter housing hose union; air should flow freely through the reed valve hose unions. Now apply a vacuum to the vacuum hose union and repeat the check: no air should now flow through the valve if it is functioning correctly.
Reed valves
5. Disconnect the reed valve hoses from the control valve (see below).
6. Check each valve by blowing and sucking on the hose end. Air should flow through the hose only when blown down it and not when sucked back up. If this is not the case the reed valve is faulty.
Component renewal
Control valve
7. Remove the fairing (see Chapter 8).
8. Disconnect the vacuum hose from the lop of the valve (see illustration 17.1).
9. Release the clamps securing the reed valve hoses and the air filter hose and disconnect them, then remove the control valve from the motorcycle.
10. Installation is the reverse of removal.
Reed valves
11. Remove the fuel tank and the air filter housing (see Sections 2 and 4).
12. To remove either valve, first release the clamp and detach the air hose from its union (see illustration). Unscrew the bolts securing the reed valve cover and remove the cover. Remove the reed valve and the base plate, noting which way around they are fitted.
17.12. Release the clamp (A) and detach the hose, then unscrew the cover bolts (B)
13. Installation is the reverse of removal. Clean off any carbon deposits and make sure the reed valve components are correctly fitted.