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Knock / Rattle when putting on power

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i have recently fitted a 290 kit (3.6 hrs to be precise)

the problem i have is a knock/rattle when giving the engine loads of gas at low revs. if i turn on the power slowly it doesn't occur. i can rev the bike freely when stood still and it doesn't happen.

i have checked the chain and that is fine.

does anybody have any ideas please.

this has only become apparent since fitting the kit,

thanks:banghead:

ps one thought could it be the camchain guide blade rattling (ie slight up and down movement) in the new barrel. the camchain was fine???

Edited by feckless
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Bad gas? Low Octane gas?

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Different years had different advance curves programed in the CDI. (My '09 with 290 will detonate at low RPM with full throttle where the same piston did not when on my '05) The low rpm tourqe of the 290cc encourages grabing lots of throttle at low RPM, so you might need a bit more octane. I try to ensure fresh high octane gas and avoid low RPM lugging and avoid the detonation.

The standard Athena compression ratio piston didn't detonate, but the higher compression piston(J.E. I think?) from Lukes Racing will detonate when lugged at very low RPM.

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thanks for the replies. the fuel i use is 95 octane. highest i can get is 98 so may try that and see if any difference

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How did you rule out the chain slap? Even with a good fit, the chain still slaps at low rpm's and heavy throttle.

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there is a bit of slap on the drive chain. but i do not believe that is the problem as the rattle has a more mettalic sound. have put some higher octane fuel in and problem still there.

will have to delve deeper i think

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UPDATE

it turns out the problem was the rear sprocket i had fitted (50T with 14T front)

i put my 52T sprocket and the problem went completely.

strange how noise travels.

i can only think the rear sprocket was maybe slightly eccentric which was causing the chain to whip and snatch on the front sprocket.

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