Do the initial troubleshooting procedure rather than play expensive guessing games.

Check the compression... what are the individual psi readings of all cylinders?

Check the spark (all s/plugs removed) which should jump a 7/16" gap with a strong blue lightning like flame... a real SNAP!

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(Spark Tester - Home Made)
(J. Reeves)

You can use a medium size philips screwdriver (#2 I believe) inserted into the spark plug boot spring connector, then hold the screwdriver shank approximately 7/16" away from the block to check the spark or build the following:

A spark tester can be made with a piece of 1x4 or 1x6, drive a few finishing nails through it, then bend the pointed ends at a right angle. You can then adjust the gap by simply twisting the nail(s). Solder a spark plug wire to one which you can connect to the spark plug boots, and a ground wire of some kind to the other to connect to the powerhead somewhere. Use small alligator clips on the other end of the wires to connect to ground and to the spark plug connector that exists inside of the rubber plug boot.

Using the above, one could easily build a spark tester whereas they could connect 2, 4, 6, or 8 cylinders all at one time. The ground nail being straight up, the others being bent, aimed at the ground nail. A typical 4 cylinder tester follows:

..........X1..........X2

.................X..(grd)

..........X3..........X4

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The stator under the flywheel can be checked visually for a meltdown. Look closely at it. If there is any cracks and/or a sticky substance dripping down on the timer base and powerhead area, that would result in a AC voltage drop to the powerpack. Should this condition exist, replace the stator. This condition, when it begins, may result in perfect spark when the engine is cold...BUT... after it warms up, then shut down to fish a bit or whatever and all that engine heat rises to the flywheel and stator area, that stator fails, resulting in weak, erratic, and eventually no spark! A stator in this meltdown condition requires replacing regardless of whatever reading one may get out of it.
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Voltage To Powerpack Failures
(Magneto Capacitance Discharge Systems)
(J. Reeves)

The usual cause of having those type powerpacks fail repeatedly is having a very small of voltage applied to the Black/Yellow wire (Kill Circuit) at the pack. Test as follows.
Disconnect the Black/Yellow wire at the powerpack.

Insert either a ampere meter or a volt meter set to its lowest DC voltage reading between that Black Yellow wire on the wiring harness side, NOT the powerpack side and ground.

With the ignition key in the OFF position, observe the meter reading. Now turn the ignition key to the ON position and again observe the meter reading.

Any reading, movement of the meter needle, even a microvolt, would indicate that battery voltage is being applied to that Black/Yellow wire. If a reading is present, remove the other end of that Black/Yellow from the raised terminal of the ignition switch.

If the reading ceases to exist when the Black/Yellow wire is removed from the ignition switch, replace the switch. If the reading continues to exist, there would be a short of some kind in either the engine or instrument wiring harness.... to determine which, simply unplug the large electrical plug(s) at the engine which would eliminate the instrument cable.

Note that the black/yellow wire must not have any other wire attached to it for the following reason!

Keep in mind that any accessory that has 12 volts running to it, especially when turned on, will have voltage flowing thru it and trailering out thru its black ground wire to complete the circuit. If that accessory has it's black ground wire attached to the "M" terminal that the black/yellow wire is attached to.... you will have voltage flowing directly to the powerpack.

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(Possible Ignition Switch Short)
(J. Reeves)

This is assuming that there is absolutely no spark on any cylinder.

To test the ignition switch for shorts, remove all of the spark plugs, then disconnect the black/yellow (kill circuit) wire from the ignition switch, then crank the engine, testing for spark via a 7/16" gap as mentioned in other suggestions above. If you now have spark, the problem is usually a intermittent short in ignition switch.
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Let us know what you find.

Thankyou for the reply , as soon as I get home I will look into everything that you have mentioned . So in your opinion it is most likely electrical and not a fuel issue (carbies)