Geting small engines running smoothly again. Bolt on units. Mottor scooters. Gokarts. Marine outbouards.

The first thing we all tend to is check the spark of the spark plug. I guess that's as good a any place to start.  Before you start safety first. Don't take any risks. Clear away all flammable material well out of the way. Check there is no leaking fuel dripping over the engine.

Once the plug is removed examine the tip. The electrode tell us a lot. They can be bone dry indicating fuel starvation , bone dry and sooty a sign of a far to rich fuel or wet and oily a sign of excessive crank case oil. With experience you'll learn to recognize those signs to a normal condition.

Reconnect the high tension cap shorting the plug electrode onto any part of the metal. The cylinder head fins are typical electrical.

Crank over the engine.

If no spark test a couple of known good spares to illuminates a faulty plug.

If there is still no spark or not happy with a week and spindly looking one check electrical terminals are not on there way out. Check the cap inside and out connections. Check wiring and electrical plug in connectors. Broken contacts rotting and cracked insulation can leak some electrical current away from the plug to earth likely the cause of the week looking spark. Shrivelled up and old looking insulation can do it. If by any chance previously worked on check fibre, rubber and plastic washers that should not have been there causing improper insulation. Check for improper electrical contacts that should not be there too. Check loose terminal and frayed wires. Overall if brand new looking wiring  is anything to go by, is a good yard stick to the condition of what good wiring should be. A good tidy up won't do any harm.

If there is a strong spark the next step is to check fuel. Load some fuel into a empty oil can and squirt a generous amount into the spark plug hole. Keep vagrant with potential inflammable liquids well away from your work area. Replace the plug and cap and start the engine.

The engine should attempt to run. Any problems it shouldn't run properly petering out to a stop in a few seconds. There is a good chance if you have a four stroke engine there is some mechanical problems with valves not working properly. Spiting back as if  electrical misfire is a sign of a inlet value burnt out. Burnt out exhaust values can do it. Don't take that for granted just yet though at lest until you complete the fuel tests to be sure it's only fuel problems.

The next step is to recheck the condition of the plug again. Remove it. if it's bone dry tells you to investigate a fuel line problem. Safety first disconnect the plug from the cap and make sure the fuel tap is turn off. Don't take any risks with the spark plug cap dangling anywhere near the fuel line parts.

Disconnect the fuel line and turn on the tap and observe if fuel pours out. If it doesn't don't take any risks immediately close. If a traditional carburetor there is a good chance it is just the float needle valve reassembled upside down from previous work on it chocking off the fuel supply.

Again safety first by keeping the fuel cock is turned off. If the engine design allow it remove the bottom of the float bowel. When you turn on the fuel cock fuel will attempt to pure out of the float needle hole. Don't take any risks immediately shutting off the fuel tap again.

Testing and finding out which way it goes back replace the float needle holding up with a finger and turn on the tap. Very gently let it drop a bit. If it doesn't leek fuel repeat the experiment the float needle the opposite way. It should leek fuel. Observing the contours of the needle helps determine which way it goes back in.