It really helps to spell out exactly what 'The Motor' is whenever you ask a question, there are a bunch and they differ.
I recommend that if you have a Skyhawk motor straight or slant head get yourself an NGK BPR
6HIX Iridium plug.
http://SickBikeParts.com has them for $8 and worth twice that, it is a performance boost you actually feel.
Note, the
6 is a temperature range.
The higher the number the more the plug dissipates heat.
It's summer in the dessert so I stock 7's here to dump as much heat as possibe, 6's are good all temp plugs, 5's are for really cold climates when you want to keep your motor warmed up.
CAUTION! The Iridium plugs can be too long for the cheaper motors!
Here is another tip, the 24G wiring in all these kits are junk from the motor mag to the CDI, especially those banana connectors.
I pop the mag cover and cut all 3 wires off the mag and run a round black 18G power cord type wire like a PC or your drill uses for a power cord soldered from the trimmed down CDI wires to the ground and top lug of the Mag on every build I do.
I leave the white wire snipped off at the mag lug since you can put your kill button across the two CDI wires to kill the motor too.
I actually take it farther on all my builds with my own black wire the size of a bike cable from the kill button to the CDI and epoxy on a spiffy box over the connections but that's not the important part.
The important part is to get every milivolt the mag puts out to the CDI and a good plug to spark the fuel mix.
With no pictures or even what motor make and type there is no telling, but if your gas line is next to your head that will cause your problem when the motor heats up and running wide open. The gas gets hots and you get a vapor lock in the gas line.
I hope that helps and good luck with it.