Sparking problem

[Spark]

Hi all.
I have been ridding my 80cc bicycle since the start of the year. I always used the high oil that they specify but lately i tried lower oil and went from 91 octane fuel to 98. Straight away the motor started making a cracking noise and I went through 2 spark plug caps in a week. It blew the plastic part of the cap off the inner brass part.
I went back to 91 octane with 30 to 1 oil. The spark plug cap is lasting but now and then it still makes the cracking noise.
I've checked the plug and wiring but it all looks ok!
Any help appriciated
David

 

[HeadSmess]

cracking that could be called chirping or squeaking?

or cracking, metal on metal, bad sound? that, i cant help with.

the squeaking is usually the head gasket leaking. opinions vary on what to use...stock alloy, special copper, or plain teflon tape. dont use sealant, it doesnt last.
teflon tape is my personal choice.

use an NGK plug, B(R)5HS... the R is optional.

the standard plug cap is lousy, if it doesnt fall apart, it wears itself apart... again, NGK is the best.

 

[crassius]

vibration could cause cap failure - how are your motor mounts?