big gun over rev box

I have an 06yzf450. I have a full yosh exhaust hot cam and a 13.5 high compression piston. I notices when I put a big gun over rev box on it will not pull hard in third gear or under load. Take it off and the same thing. Need some help do i have somethng wrong in the motor or is the cdi boxes shot

Sounds like it could be jetting. Did you rejet when you added all of the mods? My experience is that when you add a pipe and hotcams you need to lean your jetting. When a fourstroke is running rich it feels like it won't pull hard.

I have rejetted, I have gone down to a 160 and it gets hot and I have also gone up to a 170. Feels like the same power through out.

Well then start with the real basics and work your way through. Make sure your CDI is plugged in all the way (since you were messing with it maybe it isn't plugged in right). Make sure your spark plug cap is pushed down all the way (Yamaha's have a nasty habbit of working their way up and losing spark). Try changing the spark plug. It doesn't sound like your timing is off, but you can check to be safe. Then you can start getting more technical. Check your clutch to see if it is slipping. This happened on my 250F when I did a bunch of mods like that the bike stopped pulling and it turned out that the clutch springs were not strong enough and the clutch was slipping (I wasn't getting extra enplay though which through me off). Then you could try a compression check.

Thanks for the info I took it a mechanic here the one that did the mods for me and he is baffelled to what to help me with it good to have another head in the game.

Keep us updated as to what you do and what you find.

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

  • Similar Content

    • By yz480doinwork
      Brand new, still in the packaging Lexx end cap fits the stock muffler of 2006 & 2007 YZ450f and 06-13 YZ250f. Comes with a forest service approved spark arrestor and two different size tips. Don't spend hundreds of dollars on a slip on, this tip can be quiet and forest legal or loud and make power! Also a note for WR450 guys: get this tip and find a used 06/07 YZ muffler, fits directly on 09-15 WR450. $80 shipped free to the lower 48. PM, call or text 406-223-8789
    • By Woody Oakson
      So I have a 2008 yz450f and I would like to add some LED lights to it to make it street legal. Mainly just a headlight and a tail light and turn signals if I need to (which where I live hand signals work).
      So where I need help is getting power from the stator to a battery. Wiring from a battery to anything else I got and understand and don't need help with (but recommendations are welcome). So my questions are.
      What type of power is coming from the stator. AC or DC? Will I need a regulator or rectifier? How do I wire something from the stator to charge a battery? What would that wiring look like? Would this stator work? Anything else I should know? Any help would be appreciated. Thank you.
    • By Samx22x
      Alright so I’m new to the site so maybe this question has already been asked. I have a 2002 Yz426f and I want a new exhaust, it has the stock header and silencer and sounds amazing but I’d like a little more from it, I know I want the fmf power bomb header and am kind of undecided on the silencer, I see on fmf’s website that their silencer will add low end and slightly take from top end and the other way around but I’m looking for increases throughout rpm range. I do a lot of trail, hill climbs, jumps, and wheelies so kind of need good performance everywhere in the rpms. My question is what silencer I should get and the jetting I should get for the carb. Thanks
    • By Zack Ailing
      hey guys just picked up a new project bike. Its a 2008 Yz450f with a big bore kit and a stroker crank. The total cc of the engine is now 499. It runs on race gas and will be an absolute monster when shes ready to rip. I will continue to make more videos on the bike so stay tuned Link to the video: 
    • By High On Octane
      2005 YZ450F, Athena Big Bore, Power Bomb, Q4.
      Ok.  Last fall after a decently hot day at the track, I noticed coolant leaking from the weep hole on my water pump after pulling into the pits.  Ordered an Athena re-seal kit, put it all back together and didn't really get a chance to ride it.  3 weeks ago, went out to the track, and after about 20 laps, it started leaking again.  Kept filling it with water to get thru the day, never ran anywhere close to dry or empty, jut a cup or 2 low.  Ordered a Hot Rods re-seal kit with bearing and also ordered a new w/p shaft.  Did it all again and got it back together, ran it, and as soon as it got to temp, it was leaking out of the weep hole again.
      So, what the heck am I missing?  I'm totally stumped on this one.  Is something wrong with my case cover?  Do I need to replace the w/p itself?  I'm feeling like I should've just ponied up for the Boysen in the first place, and now it's biting me in the butt.  Any help or suggestions is greatly appreciated.  Thanks!