Removing airbox restrictor


I'm planning on removing the airbox "restrictor" on my Euro-model 99 WR. I guess this will lean the jetting. Do I therefore have to counteract this by riching the jetting? Is it a simple case of raising the needle, or do I have to change jets? I normally run at nowhere higher than a 1000ft altitude, and mainly at sea level. Any ideas on jets? Your help would be appreciated!


I have a Euro 98 WR, In standard form from new it would barely run and was aweful at starting. Once run in, I fitted a White Bros E Series S Bend can (not header), removed airbox lid, and advanced can to YZ settings. It now runs very cleanly and seems perfectly set up - with not jetting changes. Do not be worried about possible airbox flooding with no lid as all has been OK throughout this winter.

Only possible down side of the above is the aggression. For trail riding its a hooligans dream. For dry or wet enduros its also good. But for any kind of technical enduros or lots of off camber rooty hill climbs its a git. The power comes in too quickly and violently. If this is your main kind of riding, then just stick with the standard cam timing. Theres no need to change the jetting.


Many thanks. So, I guess I can remove the airbox lid, and leave everything else.

FYI, the e-series header pipe is a worthwhile investment because it allows complete free access to the oil filter. Why oh why Yamaha made the pipe cover the oil filter, I've no idea!

Thanks again.


Sea level set up. Standard WR exhaust timing

pilot 48 needle standard main 178 (standard pipe)or 180 (performance pipe)with airbox open. Fine tune with fuel screw -start about1.5 turns out.

Will run well enough on standard jetting with lid removed, larger pilot if it seems lean for starting. Larger main if it will run on choke when open. There is some gain with the richer jetting but it generally needs less restrictive exhaust for best effect. I prefer WR exhaust timing as do other Australians, better in the technical, more forgiving and gives away very little in mid range. I believe that the YZ timing requires an aftermarket exhaust.

There is an aftermarket airbox called the Vortex made for the YZ and WR now. It has a tuned plenum chamber and will be better than removing the lid for that reason. The Thumper Racing team is running one on their WR, they left their carbon fiber unit behind at the Vortex factory and never asked for it back -- I guess they like their Vortex. You can see some pictures of the bike and the airbox info at

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