Engine Knocking Upon Hard Deceleration

[Dutch-MI]

Well I took out the '88 KDX for the first time after break in of the new top end.

Everything ran great with the exception that when I would decelerate hard, I got a knocking / rapping noise from the engine. This wouldn't happen every time - mostly when I was in 4th or 5th at high speed and then decelerating or coming down a hill and downshifting.

I checked the rod for any up and down play when I had the head off and there didn't seem to be any.

Has anyone experience this before? If so, what did you find out was the reason?

Really appreciate any input.

[KDXGarage]

Did you have the clutch pulled in?

Which octane of gasoline do you run?

[Dutch-MI]

Only pulled the clutch in to shift gears but cant remember if i did that every time.

Used rec gas with 40:1 amsoil interceptor

[KDXGarage]

rec gas??

[targetman]

Rec gas= recreational gas (non-ethanol)

[KDXGarage]

What is the octane??

[Dutch-MI]

90 octane.

[ericr]

Could it be chain slap? Check the tension and condition of the sliders.

[KDXGarage]

That's not a lot of octane. Make sure it is not detonation.

[Dutch-MI]

Not chain slap.
Sounds like detonation. Any way i can determine if it is?
If 90 octane isn't enough, what else can i get?

[KDXGarage]

Do you not have higher octane in your area? Can you go to a marine gas station? I hear you all have a lake or two in Michigan. :-) A buddy here in AL (member here, treelimb) gets 93 octane non-ethanol at a marina.

[Dutch-MI]

Yeah - Ill get some racing fuel and see if that helps.

[Dutch-MI]

Well I mixed 50% 90 octane rec gas and 50% 110 octane race gas to get 100 octane. I only get slight knocking for about the first minute of gentling riding it around after it's warmed up. No knocking on hard deceleration anymore however my last ride was on a slow single track and not a big open loop like before.