See if you can figure this one out!

[Boris]

That one bit me a long time ago on a 550 KAWI,since then thats the first thing I do is swap out the plugs,I have also had new plugs that did not fire correctly or at all.the next thing is to cut the plug wires back and install new boots if the plugs don't fix the problem,Always and I mean always follow the KISS rule,Keep It Simple Stupid!

I'm with you there but before I cut the leads back I check the start/stop switch.
KISS

 

[john zigler]

Yeah, brand new plugs out of the box! Who would of thunk it!
What made that plug do that? How did it get retarded at the NGK factory?

could have been dropped at some point. internal crack.

zig

 

[PWCdoc]

I just logged on today and saw this...I'd have guessed a bad spark plug immediately. I had one on a Yami motor rebuild as well and each time I saw the rear cylinder backfire (looking thru carbs) and each time it blew the rear crank seal out. After replacing the seal for the 3rd time, it then began backfiring in #1...then knew exactly what it was. Pissed me off big time and I labeled it my $1000 spark plug for each additional time I tore the motor back down to replace the crank seal.

 

[BBYamaha]

:fest30: DING DING DING!!:fest30: We have a winner!!!!

They were brand spankin new plugs and one of them was a bad egg!
I put a old set in and it purred like a kitten.
I can believe it was that simple!:Eyecrazy:

I've never seen that before ever! What got f'ed up at the factory to make that new plug do that??
It was a NGK BR8HS

I spent way to much time trying to figure this out and even swapped complete electrical systems to test and it still constantly back fired.
Good Guess Terry! I dont really have a prize for you though... :smile:

I wouldnt have guess it but have seen it, but we spent 51$ on 3 spark plugs and 79 miles to lake to test only to feel one cool cylinder, one 17$ spark plug later it ran great (after a rebuild) wish it were a 3 dollar plug..