does silencer affect jetting?

I've noticed several people experiencing problems with the 426 missing at 1/4 to 1/2 throttle, including myself. I'm just wondering what effect removing the silencer and putting in a YZ throttle stop has on the stock settings. To be more direct, does removing the plug make the bike run richer, or is that problem a function of the other 101 variables that affect the way this bike runs? I've also been told the idle speed setting can affect how the bike runs at lower speeds. I turned mine up a bit, and it doesn't backfire as much when shutting down at half throttle after a hard hit. Coincidence?

I'm waiting to do some serious adjusting until I get a good moderate temp day and a spot to ride around 3000 feet, but I want to try to avoid monkeying with adjustments that don't need fixing. Any helpful advice for the best place to start and what changes to expect would be appreciated.

I also asked earlier if putting the silencer back in after changing the throttle stop causes excessive exhaust pressure problems at ludicrous speeds. I haven't seen any problems mentioned yet.


Changing the exhaust alters the jetting but so do other factors like temp & altitude. When opening things up on the exhaust you may find it lean whereas YZ cam timing seems to go the other way. This can vary at different throttle positions. The stock DRR/DRS needles start increasing fuel early and sometimes need a leaner clip position. Adjust the pilot screw or needle clip first to make the most of the stock jetting. If you search on needles DVP and EKP you will find overwhelming amounts of discussion. Check the latest post "... the honorable DR J, Taffy, Andrew.." for a quick look.

The stock jetting and needle are chosen with the baffle in mind whereas what you will find posted in TTalk is mostly for more free flowing exhausts and airbox cover removed. There is much more potential begging to be tapped in there. :)


[This message has been edited by James Dean (edited 03-27-2001).]

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