Engine overheating (Honda Africa Twin 750, 1989-2003) [Information for owner: Troubleshooting]

Engine overheats

Coolant level low. Check and add coolant (Chapter 1).
Leak in cooling system. Check cooling system hoses and radiator for leaks and other damage. Repair or replace parts as necessary (Chapter 3).
Thermostat sticking closed. Check and replace as described in Chapter 3.
Faulty radiator cap. Remove the cap and have it pressure tested.
Coolant passages clogged. Have the entire system drained and flushed, then refill with fresh coolant.
Water pump defective. Remove the pump and check the components (Chapter 3).
Clogged radiator fins. Clean them by blowing compressed air through the fins from the backside, and straighten any bent fins that restrict air flow.
Cooling fan or fan switch fault (Chapter 3).

Spark plugs fouled, defective or worn out. See Chapter 1 for spark plug maintenance.
Incorrect spark plugs.
Ignition control unit defective (Chapter 5).
Faulty ignition HT coils (Chapter 5).

Main jet clogged. Dirt, water or other contaminants can clog the main jets. Clean the fuel tap filter, the in-line filter (XRV models), the float chamber area, and the jets and carburettor orifices (Chapter 4).
Main jet wrong size. Check the jet sizes according to the Specifications in Chapter 4. The standard jetting is for sea level atmospheric pressure and oxygen content - if you are constantly running at high altitude (where the oxygen content of the air is reduced), the mixture will be affected.
Throttle shaft-to-carburettor body clearance excessive. Refer to Chapter 4 for inspection and part replacement procedures.
Air bleed holes clogged. Remove and overhaul carburettors (Chapter 4).
Air filter clogged, poorly sealed, or missing (Chapter 1).
Air filter housing poorly sealed. Look for cracks, holes or loose clamps, and replace or repair defective parts.
Fuel level too high or too low. Check the float height (Chapter 4).
Fuel tank breather hose obstructed. If the breather hose is blocked a vacuum can form in the tank which will restrict flow.
Carburettor intake manifolds loose. Check for cracks, breaks, tears or loose clamps. Replace the rubber intake manifolds if they are split or perished (Chapter 4).

Carbon build-up in combustion chamber. Use of a fuel additive that will dissolve the adhesive bonding the carbon particles to the piston crown and chamber is the easiest way to remove the buildup. Otherwise, the cylinder heads will have to be removed and decarbonised (Chapter 2).
Improperly machined head surface or installation of incorrect gasket during engine assembly.

Clutch slipping. Can be caused by damaged, loose or worn clutch components. Refer to Chapter 2 for overhaul procedures.
Engine oil level too high. The addition of too much oil will cause pressurisation of the crankcase and inefficient engine operation. Check Specifications and drain to proper level (Chapter 1).
Engine oil viscosity too high. Using a heavier oil than the one recommended in Chapter 1 can damage the oil pump or lubrication system as well as cause drag on the engine.
Brakes dragging. On disc brakes this is usually caused by debris which has entered the brake piston seals, or from a warped disc or bent axle. On a drum brake this is usually caused by a seized brake operating mechanism.

Engine oil level too low. Friction caused by intermittent lack of lubrication or from oil that is overworked can cause overheating. The oil provides a definite cooling function in the engine. Check the oil level (Chapter 1).
Poor quality engine oil or incorrect viscosity or type. Oil is rated not only according to viscosity but also according to type. Some oils are not rated high enough for use in this engine. Check the Specifications section and change to the correct oil (Chapter 1).
Faulty oil pump causing reduced pressure in system. Check the pump for wear (see Chapter 2).

Modification to exhaust system. Most aftermarket exhaust systems cause the engine to run leaner, which make them run hotter. When installing an accessory exhaust system, always check whether differeni carburettor jet sizes are needed and rejet the carburettors accordingly, if necessary (see Chapter 4). Often the best way to determine this is by running the bike on a Dyno.