[Bdk438]

At about half throttle the detonation is pretty bad ... seems to run great. I’m using e-free 91 octane and also added octane boost. No change... Any ideas?

 

[Nanook12]

Why would you add octane boost to a 91 octane fuel? Is your timing off?

 

[Bdk438]

Trying to remove the detonation... if timing is off I have a light to check for the F mark but if it’s off how do I change the timing?

 

[Bdk438]

You can’t.

 

[shadetree]

yes you can !, you replace the cam chain..with it being a 2007 ?, its prob over due for a new cam chain !.

 

[Bdk438]

Guess that is a split the cases job. I believe the cam is buried. The engine has only 700 miles, 180 hours...

 

[shadetree]

Guess that is a split the cases job. I believe the cam is buried. The engine has only 700 miles, 180 hours...

the cases do not have to be split. the cam chain is either behind the front cover ?, or rear cover ? ( sorry...its been a few, and I have not worked on a 420 lately ). but I do know the main cases do not have to be split. hours and miles dont mean a lot to me ?, its how it was treated in those miles and hours that counts !.

 

[Rocketman5144]

Front cover, both clutch assemblies have to be removed

But first I'd check a few other things. Is it getting hot? Does your fan ever come on?
What heat range spark plug do you have in it?