Turbo YZ


350 replies to this topic
  • yz480doinwork

Posted April 27, 2009 - 08:22 PM


the scilencer is already hooked up. why cut if off and have an annoying bike when its already on? the bike is not tuned correctly yet so i have to take the load off the engine to get it past its blubbery stage. and it has the stock clutch

  • qwik12beat

Posted April 28, 2009 - 09:31 AM


Does it stutter when it begins to build boost?? When you get it to hold 8 pounds does it creep or spike at all, and what does the boost fall to at redline? You would be surprised at how it would sound without the muffler. If done correctly you should end up with somehting similar to the sound of a F-16:) I would also run a dumptube, and an external gate:)happy boosting

  • yz480doinwork

Posted April 28, 2009 - 04:50 PM


yes its studdering badly. i have been playing with tuning and i have gottin it better on low-mid but it wont build boost like it was before. past half throttle or once most of the load is takin of the engine it starts to studder badly. tryed almost everthing idk what to try next. the engine is running so badly it wont redline. its building about 2 pounds low-mid range.

  • finthat

Posted April 29, 2009 - 02:31 PM


Good job 480 keep chipping away at it, you'll find the tune yet. You may have to play the sacrifice game.....give up a tuned idle for a better running bike at full boost. Or find the middle ground somewhere.

Fun and frustrating all at once.

  • TIG88

Posted April 29, 2009 - 03:29 PM


Take it to a dyno, or get a wideband O2 sensor. This will tell you where its running badly, and why, assuming its fuel related.

Also, dont take the muffler off. Its straight through anyway, and since its already on, it wouldnt make sense otherwise. If it had baffles or something, I would take it off.

  • Dirtymutt9

Posted April 29, 2009 - 03:39 PM


that is really cool, how much money have you spent on this project?

  • qwik12beat

Posted April 29, 2009 - 03:46 PM


If you havent checked for boost leaks i would definetely start there. If all checks out i would close the gap on the spark plug a little. What psi does the wastegate open at?? Check those leaks man. Sounds like it was boostin good, and you created your first boost leak:smirk: Check it out. lemme know what you find

  • yz480doinwork

Posted April 29, 2009 - 07:10 PM


the waste gate is tighten way up for my testing. it wont pull boost its tuned so poorly. i tryed a bunch of diffent jetting/ needle settings again tonight and it still wont run. ill check for leaks but i dont think there is any. i have spend just around $1000

  • x2468

Posted April 30, 2009 - 09:45 AM


the scilencer is already hooked up. why cut if off and have an annoying bike when its already on? the bike is not tuned correctly yet so i have to take the load off the engine to get it past its blubbery stage. and it has the stock clutch


save weight? :banghead: thats all i was thinking

  • TIG88

Posted April 30, 2009 - 01:52 PM


Do you still have the 12.5:1 stock piston, and the same CDI?

Are you sure its just not pinging/detonating when you start to add boost?

Hows your plug look?

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  • JamesNad

Posted April 30, 2009 - 02:14 PM


i forgot all about pre-detonation with boost, that could be causing it to run kinda crappy under boost but it would have to be a major case of detonation.

and idk how long the piston would last if it was detonating so bad to cause it to run bad.

  • grayracer513

Posted April 30, 2009 - 02:40 PM


There is no such thing as pre-detonation.

One of the things that results from a turbo being too large, or being slow to spin up for any other reason is that the compressor speed lags back enough to become a choke point in the intake tract. If the compressor speed rises too slowly to allow air to freely flow through to the carb without interference, it causes a vacuum to form in front of the carb, in effect, becoming a choke. A compound vacuum/pressure gauge tapped into the intake between the carb and engine will find this problem. Under normal circumstances, the pressure at this point should never be lower than -1 in/hg under any circumstance, and ideally not as low as that.

  • TIG88

Posted April 30, 2009 - 03:04 PM


Gray that makes complete and utter sense. That would explain why he keeps leaning down the main jet.

So... a smaller turbo, or...?

  • yz480doinwork

Posted April 30, 2009 - 07:22 PM


i dont believe that is the problem because its building about 2 pounds of boost when/while it is studdering. and when i let off my blow off valve is functional, which means there is boost after the carb. also it runs good of the line (building boost) and while still underboost it starts to studder. i took the carb off and we have an idea. gonna try somethin, i think it will clear up the studder.

  • yz480doinwork

Posted April 30, 2009 - 07:26 PM


Do you still have the 12.5:1 stock piston, and the same CDI?

Are you sure its just not pinging/detonating when you start to add boost?

Hows your plug look?



i have an athena 478 kit. their piston is slightly lower compression than stock i belive. but if i get the studdoring takin care of i will get a low comp piston. i know for sure its not detonating on 2 pounds of boost with 110 octane. its not even making any power, its rich, the plug is black as 2 in the morning. i got an idea tho.

  • grayracer513

Posted April 30, 2009 - 08:21 PM


Gray that makes complete and utter sense. That would explain why he keeps leaning down the main jet.

So... a smaller turbo, or...?

If that happens, and it appears not to in this case, the cure is a tighter exhaust scroll, and/or turbine fan.

  • yz480doinwork

Posted May 02, 2009 - 06:08 AM


If that happens, and it appears not to in this case, the cure is a tighter exhaust scroll, and/or turbine fan.


in other words would a smaller diameter header pipe work? like one off a 250? im not gonna do that just wondering. im headed out to try my little trick on my carb right now. hope it works. guess ill find out!

  • grayracer513

Posted May 02, 2009 - 07:24 AM


in other words would a smaller diameter header pipe work? like one off a 250?

No, that would work against you, most likely. Anyway, if it's created any boost, the compressor is running faster than the normal speed of the incoming air.

  • TIG88

Posted May 02, 2009 - 09:24 AM


What is this little carb trick you keep talking about yz480?

  • yz480doinwork

Posted May 03, 2009 - 05:24 AM


i tryed pluging up the accelirator jet to prevent fuel from blowing through there, when the float bowl is pressurized i think it was blowing fuel throught the accel. pump and right into the engine. i tryed it, it helped a little but i still have the studdoring problem. i got an idea im gonna try with some of the vent lines.. idk what to think





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