This one does not have an ECU, the wires go straight to each coil pack.
ebay sells manuals for that engine. I have essentially the same 115, only a 2002 model. You covered everything that I would have suggested so I will suggest you get a manual and start rummaging through the trouble shooting section, or explanation area where they tell you how things work and compare what you read to what you have in front of you.
You don't have any mouse or rat droppings around the engine? If so, look for insulation chewed off wiring and wires touching that aren't supposed to be touching.
Go to an auto parts store and get a roll of 16 AWG wire and some alligator clips that will fit over the starting solenoid input 3/8" stud (battery + connection) and the black - wire from the battery that connects to the engine block. The battery needs to be fully charged and connected to the engine in the two spots mentioned like is the case during normal operation.
Remove the 8 pin remote control wiring harness plug from the engine compartment.
Remove the insulation from both ends of a suitable length of wire (3 each) and twist the wire on one end so that it will fit inside the sockets on that 8 pin plug and attach an alligator clip to the other end.
One wire goes in the Pin 2 (the color of the wire normally attached to Pin 2 is either Purple or Red with a Purple stripe. The alligator clip on the other end of this wire goes to the 3/8" stud on the starting solenoid where the battery red wire is connected.
The second wire is to be inserted in pin 6 identified by a yellow wire with a black stripe (don't confuse it with the black/yellow color code as that is the engine kill pin when grounded). This yel/blk wire is your fuel enhancement power.....the power you send to the engine when you are ready to start the engine and turn the key to on and PUSH in on the key. So, in operating the alligator clip on the other end of this wire, assume you are starting via the key as mentioned and touch the alligator clip to the same 12v 3/8" terminal mentioned above for as long as you normally "prime" your engine when attempting to start.
The third wire is to be inserted into Pin 7 which is identified by the yellow wire with a red stripe........this is the terminal that gets 12v when you want to start the engine so do not connect the alligator clip to anything until you are ready to attempt to start the engine.
Ensure that your fuel is hooked up and the carbs have been filled with fuel.....firm squeeze bulb on the input fuel line.
Activate the fuel enhancement for as long as you normally do, and then while keeping it activated, touch the alligator clip on wire 3 to the 3/8" stud mentioned and hold it there temporarily, which should cause the starter to start spinning.
If the engine starts or tries to start...meaning its getting fuel and ignition, then your problem is in the wiring harness to the control box or in the control box.
What you are doing here is simulating the voltage (signals) to the engine that normally come from the ignition key either on the dash or in the control box when you attempt to start your engine normally....nothing more, nothing less. The purpose is an attempt to locate the source of the problem.......with what you have changed in the engine it seems to me that the problem isn't in the engine proper.
