There are Four areas of weakness.
1) the bendix.
a) If it gets worn or jammed up by swarf it may not engage. Normally one can hear the motor spinning but it never engages.
Clean or replace / repair the bendix.
b) I have known a badly worn ring gear to prevent the bendix from engaging. Normally this can be cured by moving the kart slightly so it engages on a clean tooth. Clean /file the tooth or replace the ring gear.
Worn or mashed ring gears can also hold the bendix engaged, in which case teh starter tries to do 100 to 200, 000 rpm. Normally ends up breaking the gear and possibly bending the crankshaft.
2) The Brushes.
The Brushes have a known problem where the brush leads break or detach. This is why you see people trying to bounce the kart into temporary contact long enough to get started.
a) the lead breaks where it is mounted to the connector.
Replace the connector and lead. Resoldering is possible but often gives a fragile joint.
Bed the lead in silicon to stop it vibrating and breaking.
Sometimes the lead is almost broken, with a few strands intact, and it just won't pass enough current to spin the engine up to speed.
b) The lead comes out of the brush itself. Replace the brush, lead and connector.
3) The battery.
a) the Battery is undercharged. It may register lots of volts on your meter, but any load drops off the voltage dramatically.
Recharge the battery. You need a constant voltage charge, not a trickle charger. Optimate seems to have a good reputation. Read the charging cycle guidelines on the Web.
b) The Battery is damaged. Again it seems fully charged but won't kick the starter over fast enough to engage the bendix. Replace the battery. You can get them for about £12 now instead of the £50 some people charged in the past.
4) The Loom.
You need a good earth to the engine. Relying on the electricity 'getting through' the paint on your chassis and back to the negative pole of the battery isn't enough. Some people bolt the earth leads to the engine, but the vibrations can break the earth wires. I prefer the earth bolted firmly to the chassis and secured with rubber snaps, then use a braid earth lead to connect to the earthed point.
You should check that all the wires are secure in their terminal. I had one that appeared 'right' but when I gave it a good pull, it just came right off.
The other favorite is Battery terminal connectors that have got 'loose' from being removed regularly.
The new digital looms have lots of connectors and points where the wires break, even Ron Shone gets frustrated with them sometimes.
HTH
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Formula Blue Starter by 'RevvedUp' (20 Aug 2011 @ 0:31)
