I believe I have pre detonation (spark knock)

[rysk29]

When I start getting at mid rpm I can hear a faint "tat tat tat" noise that gets faster and louder as I get to WOT.. When I get at top speed the noise will come and go and it surges.. When the noise happens it slows and it will go away for a second and it will speed up and start again.. My compression is at a good spot and I only use 93 gas.. I have heard those r main reasons for it. I don't know why it happens but I'm at a loss.. Any thoughts or has any1 had this b4?

 

[Frankenstein]

How long has this been happening for, what about vibration do you notice if it shakes a lot (like more than a lawnmower?)

 

[butre]

a lean condition or overly advanced ignition timing can cause knocking too. are you totally sure it's knocking? not just sloppy gears rattling or something?

 

[crassius]

It doesn't look new, but new motors can give out a noise like popcorn popping - I've always thought this to be ring-slap as it goes away as rings finally get seated. Other than that, an air leak can cause over heating and pre-detonation.

 

[gary55]

What you are describing with the speed up and slow down without no change in throttle position is common when engine mounts are becoming lose. The over vibration causes the fuel to foam in the bowl. The tat tat could be something else vibrating caused by the engine not being secure. Check your mounts then try it again. It could be something as silly as the exhaust tapping against the frame.

 

[rysk29]

the mounts are good.. i have dealt with the fuel foam before and its def not it.. the sound is def coming from engine.. it has done this since it was new.. it has over 400 miles on it..i have changed plug and put a new clutch assembly on it, but it still happens..i have also changed jets to a lower size and it still does it.. when it starts there isnt alot of vibration.. it does get worse but nothing crazy.. i have tested for air leaks and all is good.. i will try to get a vid with the noise later today.. its so aggravating lol is it possible to change timing without a new cdi

 

[gary55]

A lower size would increase the chances for detonation as leaner runs hotter. Have you done any mods to the engine like decking the jug of milling the head? Is the stock spark plug in it or did you change to a different type. The reason I ask is if you are using a plug that goes farther than the stock plug it could be slightly touching the the top of the piston and would be more pronounced at higher rpm and as the engine heats up.

 

[rysk29]

its the stock plug and i haven't modified anything.. i have raised and lowered the clip on needle and get no change

 

[crassius]

had an air leak last week so bad that bike would not stop running with plug cap completely removed from plug

 

[Deleted member 12676]

I believe there is a big variation in spark timing from one engine to the next. Sloppy manufacturing tolerances.
So the stock ignition timing is already close to being too advanced but maybe yours is past that and into the danger zone.
Either replace the engine or get an aftermarket CDI with retarded ignition.
Take the head off and see if there are any pock marks on the piston or the head. With detonation little bits come off.
see http://www.mikuni.com/tg_detonation.html