rattle under load

[Barton]

Been out today to try the 42 pilot jet.
The needle is standard on 2nd position and got 178 main jet.
off road ok but on the tarmac sections at around 35 - 40 mph it surges if you get into top gear and on an up hill when you open the throttle there's a noise like a small end rattle, don't think its detonation as plug color is good and no oil dripping from exhaust.
Any ideas

[john r b]

Check the power valve. It may need adjustment.

[iconic]

Top gear, high load, low speed....chain slap? Try tweaking the chain up as tight as safe and then try it again.

Cheers

[bowhunter007]

My vote goes to power valve. First time I heard it on my 300...I thought I was having catastrophic engine failure

[Jakobi]

Powervalve slop, chain slap, pipe springs vibing against pipe, pipe vibing against header, the nut on the front of the brake rotor touching the fork guard. So many sources of noise which are generally most audible at lower throttle openings and higher speeds.

[Barton]

my thoughts were chain slap or the power valve. Pulled the power valve cover off the primary side of the cylinder and the mechanism is on the stop but there is very little spring tension to hold it closed so it may be fluttering and causing the noise.

[Coop]

Pipe o-rings. I know I sound like a broken record lately but I was surprised how loud the rattle was from worn o-rings lol. Mine is nice and quiet now.

[motopsycho87]

Could well be detonation, just try raising the needle 1 to see if it goes away.

[Jakobi]

Originally Posted by Coop

Pipe o-rings. I know I sound like a broken record lately but I was surprised how loud the rattle was from worn o-rings lol. Mine is nice and quiet now.

They make a racket! And they don't last long until you get a good set of viton ones in there. The stock lower pipe mount is weak as and starts to allow movement as it flogs out pretty soon too allowing more movement and associated vibrations. I notice this noise most on the stand/during deceleration rather than on the throttle though.

[Coop]

Mine was deceleration and early throttle under load, such as getting on the gas after s sharp turn on an incline.