cause of deonation or possible pre ignition?

[jetlag]

yes i blew the crown of my piston near the exhaust port and a small dent on top, just wondering what could have caused it?
ran 92 octane with a 120psi compression
list of mods:
malossi bore,crank,pulley n fly clutch, scorpion pipe ct chrome w/28oko black to uni filter.

it was running all good with 55pilot 135main with clip in the middle air screw i believe was at 1 1/2-2 then one day i decided to experiment with the needle so i raised the clip and raised my pilot to a 58. so i rode pretty far untill i notice my 1/4 throttle would lag and i would have to give it more gas to clear it out about 1/2 to full throttle. so my instinct thought it was lean so i pulled over and drop the clip to the middle with the same pilot and rode home and i think i must of left the a/f screw in at 3/4 turns out by accident and it would run the same as if the c-clip didnt make a difference and it was getting worse until i got home and took apart and piston was f***d but bore was all good. idk if too much unburnt gasses could of cause this problem or maybe ignition timing? any help would be appreciated cause i replaced the piston and dont want it to happen again.

[Bear45-70]

Too lean a fuel to air mixture. Did you rejet the carb and do plug chops to check the mixture?

[kingkamehameha]

Possible air leaks

[jetlag]

Too lean a fuel to air mixture. Did you rejet the carb and do plug chops to check the mixture?

well when i pulled over to the side to drop my clip i took off the plug to look and it was a powdery black but i know its not a legit way of telling. before the upjet in pilot n clip raised it was reading a perfect brown on wot plug chops. i can get the main jet down im would like to know how to check mid range throttle. would it be the same as a plug chop at wot except doing a chop at half throttle or would it have to be by the response. one thing im missing in my tuning is a cht gauge.

[jetlag]

Possible air leaks

what is a proper way of doing a leak down test? before taking the bore apart i seen no signs of leakage or oils.

[Bear45-70]

Possible air leaks

what is a proper way of doing a leak down test? before taking the bore apart i seen no signs of leakage or oils.

Not likely a crankcase leak. An intake leak is 100 times more likely. Oh and a lean condition will always melt the piston regardless of fuel octane.

[kingkamehameha]

Too lean a fuel to air mixture. Did you rejet the carb and do plug chops to check the mixture?

well when i pulled over to the side to drop my clip i took off the plug to look and it was a powdery black but i know its not a legit way of telling. before the upjet in pilot n clip raised it was reading a perfect brown on wot plug chops. i can get the main jet down im would like to know how to check mid range throttle. would it be the same as a plug chop at wot except doing a chop at half throttle or would it have to be by the response. one thing im missing in my tuning is a cht gauge.

Cht gauge is the best way to tune your midrange

[jetlag]

does anyone know the stock slide number on the 28 okos "silver". im starting to think the black okos has a leaner slide than the 28 keihin pwk which is 3.5 and the blacks is stamped with 5. i notice my hardest position to tune to was 1/4 and the rest would be fine and i like to cruise at the 1/4.

[Bear45-70]

does anyone know the stock slide number on the 28 okos "silver". im starting to think the black okos has a leaner slide than the 28 keihin pwk which is 3.5 and the blacks is stamped with 5. i notice my hardest position to tune to was 1/4 and the rest would be fine and i like to cruise at the 1/4.

[jetlag]

sorry bear but the picture don't show for me? all i see is the photobucket icon.

[Dio89Elite]

sorry bear but the picture don't show for me? all i see is the photobucket icon.

It's the same for me, all I see is the icon too. o.O

[bakaracer]

the slide itself will not cause that. with the size jets you were using, most likely there is a leak somewhere. what plug are you using?

[jetlag]

the slide itself will not cause that. with the size jets you were using, most likely there is a leak somewhere. what plug are you using?

b8hs gap to 0.25... can someone tell me how to check for leaks? all gaskets were new and put sealant only on exhuast side "ulrta copper i believe". new hoses all with clamps to ensure a good seal and bought nipples to close all holes. oil pump plugged with a oil plug with ultra grey to make sure no leaks there with a makeshift bolt holder so it doesnt go flying out. this whole motor is fresh. broke in bore to 300miles with my 55pilot to 135 but just that one time with clip up one and 58 pilot then brought back down clip to middle is when the detonation accrued.

[jetlag]

just more info on my setup, 32:1 ratio "4oz" castor 927 mix in a gallon jug to precise mixing and i put one gallon of 92 in my truck before putting into my canister.

[bakaracer]

if the leak is on the intake side, you wont see any oil leak as its sucking in air only and on the down stroke the reed closes. check the manifold or spigot for cracks. to do a leak down test you need a plug for the exhaust. you can use a boat plug. a low pressure hand pump or bike pump that has a pressure gauge that can read down to 1 psi. a plug witha nipple to hook up the pump to that goes into the intake spigot your only pumping it to 6-7psi and thats it. it should hold that pressure or drop just a little no more than 1 psi.