Starting tips for your motorcycle – Part 2
If initial troubleshooting is not successful and your motorcycle still refuses to start, you will need to apply your technical knowledge: In order to carry out the work described here, a basic understanding of vehicle mechanics is required. If you are in any doubt, you should probably have your bike repaired by your local motorcycle workshop!
Advanced troubleshooting for motorcycles
Cold start spray
If you haven't used your bike for a while and you're having problems starting it, spraying a little Procycle Motor-Start-Fix into the intake manifold of the air filter may help (see Fig.1). This provides the rich air/fuel mixture required to start a cold engine. When using the electric starter, don't press it too long, as this draws heavily on the battery and will quickly drain it. If the cold start spray doesn't help, don't just carry on operating the starter motor – follow our troubleshooting guide.
Testing ignition voltage
Is the battery ok? If the starter motor has difficulty turning over, it's possible that the power supply is too weak to produce a strong spark. Try charging the battery first. If an acid battery begins to "bubble" after just a short period of charging, then it no longer has sufficient capacity and you need a new one. If you have a maintenance-free battery, you will have to rely on the indicator function of the charger or have the battery checked by an authorised motorcycle workshop.
If a fully charged battery does not solve your problem, the next step is to check the ignition. If you own a sport motorcycle, this can be a real hassle, as it often involves removing the seat, tank, airbox and at least one side of the fairing. Attach each spark plug connector in turn to an ignition voltage tester and hold the tester against the engine block (earth) (see Fig.2). The voltage tester protects the ignition electronics against voltage peaks and may only be dispensed with on motorcycles with conventional ignition (vintage motorcycles) – if you have one of these, you can hold the bare end of the spark plug cable around 5 mm away from the engine block (you will need to wear gloves).
Contacts and cables
When you attempt to start the bike, the spark must jump across an air gap of at least 5 mm to earth – if it can do this it is strong enough for good ignition of the fuel-air mixture. If the spark is too weak, check the connections of the ignition coils. Defective connection? Spark plug cable too old? Is the entire wiring harness too old? (this would be indicated by greenish cable cores) (see Fig.3+4)? In the case of conventional ignition systems (with contact breakers): Can you see strong sparks at the contact (then replace the condenser and points)? This requires resetting the ignition, so this is not a job for beginners! Spark plug cables, condensers and spark plug connectors are all cheap spare parts, so you should replace them every now and then as a preventive measure. In the case of multi-cylinder engines, always make sure you assign the right spark plug cables to the right cylinders. Failure to do so will result in loud backfiring. On four-cylinder engines, the first ignition coil generally supplies the 1st and 4th cylinders and the second supplies the 2nd and the 3rd cylinders:
Adjusting conventional ignition
In the case of conventional ignition systems: Check the ignition timing using a timing light, which is placed between the positive of the contact and earth. Switch on the ignition and turn the crankshaft slowly and evenly with the wrench. When the "F" marking aligns with the marking on the housing, the lamp must light up – and precision is important here (see Fig.5+6). If this is not the case, you will need to reset the ignition. To do this, first adjust the points gap with a feeler gauge (gap 0.3-0.4 mm). It is very important to work precisely to avoid damaging the engine (e.g. due to too much spark advance). Another potential cause of a weak or non-existent spark is a defective ignition coil. If you suspect this to be the case, have a Bosch service centre or a motorbike workshop check the components.
Important: Ignition coils often go on strike when they heat up and work again after cooling down. In the case of electronic ignition systems (breakerless), failure to spark may also be due to a defective ignition box. In this case you will need to get your bike checked over by an authorised dealer for your make of motorbike (or a specialist workshop).
Checking the appearance of the spark plug
Remove the spark plugs, check for any signs of damage and rectify where possible:
Spark plug totally dry and pale whitish (see Fig.7): Ignition is working but no, or too little, fuel is reaching the cylinder. Check if sufficient fuel is reaching the carburettor. Is the fuel tap clogged? Is there a kink in the hose? Is a large air bubble blocking an external fuel filter? Is the choke working? It must be possible to reach the maximum position.
If the choke and fuel supply are working properly, you will need to remove the carburettor and dismantle and clean it, as it would appear to be clogged with resin or otherwise contaminated. Use air pressure and Procycle Carburettor Cleaner for this task. You can use a thin, soft wire to clean the channels, but this must not be used on the jets. Ultrasound is a particularly effective way of cleaning the carburettor. Ask your local dealer if they have an ultrasonic bath. If you have a multi-cylinder engine: Once you have replaced the cleaned carburettors, you will need to synchronise them again (you will find further details in our DIY tips "carburettor")
Spark plug is sooty black and very wet (see Fig.8): The cylinder is running too rich; it is probably flooded due to the fuel tap and/or float needle valve in the carburettor failing to close properly. If the bike is not used for a prolonged period, this may even allow fuel to leak into the engine oil. If you suspect this is the case, it is essential to change the oil! The float needle valve is located in the float chamber of the carburettor. You can check with a finger nail: If you can feel a step (recessed "ring"), it needs replacing (see Fig.12). Check the fuel tap for leakage by removing the hose overnight and leaving a container underneath. You will find float needle valves and fuel tap seal kits for a range of models in our catalogue. You can either clean the soiled spark plugs using a brass wire brush and check that the gap is the standard 0.7-0.8 mm or, better still, replace them with new ones.
Spark plug sooty black but not unduly wet (see Fig.9): The cylinder is running too rich. Clean or change the spark plug. If you often have problems starting your bike due to sooty black spark plugs, you should check the carburettor setting, or there may be another problem with your carburettor. If you frequently ride at low speeds in city traffic and have to start the engine repeatedly, it may be better to use iridium spark plugs, as these have significantly better self-cleaning properties. Iridium spark plugs are also ideal for vintage motorcycles because they deliver a strong spark even at a lower voltage. However, they should not be used to "gloss over" other defects!
If the cylinder is performing well, the spark plug should be a light brownish colour and dry (see Fig 11). However, because the choke causes the engine to run rich, you're not likely to find a light brown spark plug after trying to start your bike. If the spark plug is a normal brownish colour but damp from unburned fuel, then it has not sparked (see Fig.10). Try replacing the spark plug. If that doesn't help, go back to Item 2 and check the ignition of the respective cylinder.
Download this tip
For the garage: Simply download, print out and take it with you.
The Louis Technical Centre
Problems getting spare parts? Or maybe you've got a technical question about your motorcycle or an accessory The Louis Technical Centre can help! Remember to quote all the necessary details of your vehicle – better still, send us a copy of your registration document.
We will get back to you as quickly as possible!
So: send us your technical problem!
- by e-mail to email@example.com
- or by letter to Louis Technical Centre, 21027 Hamburg
These tips for DIY mechanics contain general recommendations that may not apply to all vehicles or all individual components. As local conditions may vary considerably, we are unable to guarantee the correctness of information in these tips for DIY mechanics.
Thank you for your understanding.
Louis DIY Mechanic Manual
The printed version
The big Louis DIY mechanic manual available in a printed version: in color and practical A4 format at cost price.