Performance motor issues???

5 replies to this topic
  • Chazlom

Posted October 24, 2005 - 03:50 PM


I need help guys!

I'm going crazy trying to get my bike running again.

03 yz450, back in 03 I installed RPM's 469cc kit (12.5:1 piston) along with Engine Dynamics Valve and porting, and Edelbrock carb it ran great and raced it hard for a season.

In late 04 I installed Hot Cams, again ran great, no issues rode it hard another year.

Now late 05 I just installed a new 13.5:1 piston, and it won't run at all.
The installation went straight forward without problems, buttoned it up and it wouldn't fire. Went through everything, timing, valve lash, fuel, spark, everything look ok. I even rebuilt the carb, and recheck the timing, triple checked the valve lash. :banghead:
I did get it to fire a couple short times but it needed to have a 1/8+ twist holding open of the throttle the struggle to run for a minute or two, and it sounds like the timing is off, real rough.
Does the timing on the crank change due to the increased compression? could their be a timeimg issue with the Hot Cams and the increased compression? I'm just fustrated. Please help. :lol: :banghead: :busted:



  • SBRacing

Posted October 24, 2005 - 04:09 PM


sounds like timing ..something must be off?

  • Pincushion

Posted October 24, 2005 - 04:20 PM


You've timed it before with the Hotcams, so you should be familiar with the process as it differs from the stocker. Did you measure the ring gap on the piston before installing? How does the compression feel?

Visit the ThumperTalk Store for the lowest prices on motorcycle / ATV parts and accessories - Guaranteed
  • Fastest1

Posted October 24, 2005 - 06:00 PM


I am not sure about the Ebrock carb, but when you cleaned it did you adjust your idle back up? If the idle is set too low it wont start.

  • Chazlom

Posted October 24, 2005 - 06:32 PM


Hot Cams were installed as per instructions and as I installed them before. Ring gap needed to be filed to spec and compression is good kicking it through.

Idle is set @ 1.75 turns out, same as I had it before the piston.

I have crank timing set at woodruff key at 12:00, which also matches set mark on Trail Tech 12oz flywheel weight (that lines up with the crank straight up at TDC), with a visual looking down the the spark plug hole while moving the crank, so I can see exact TDC.
The cams are set at: Exhaust set at 9:00 and 12:00, Intake set at 12:00 and 3:00.

  • Ronin 26

Posted October 24, 2005 - 08:00 PM


did you check piston to valve clearance with the new 13.5:1 piston and the hotcams?

Related Content


Is it worth it? (Cam and High compression piston) by macgi77

Dirt Bike   Make / Model Specific   Honda   CRF 150/230 F/L
  • Hot  36 replies

yz250x vs 450 4t comparisons (preferably desert riding) needed by JakeNorthrupYZ450F

Dirt Bike   Make / Model Specific   Yamaha   Yamaha 2-Stroke
  • 9 replies

Is the 2016 GYTR Yamaha YZ450F too fast? by Fryboy

Dirt Bike   Special Interest Forums   Pro Racing
  • * - - - -
  • Hot  241 replies

YZ450F 03 Sparks driving me crazy by SirAttard

Dirt Bike   Make / Model Specific   Yamaha   YZ 400/426/450
  • 5 replies

2016 YZ450 by CaptainKnobby

Dirt Bike   Dirt Bike Technical Forums   Suspension
  • Hot  59 replies

Join Our Community!

Even if you don't want to post, registered members get access to tools that make finding & following the good stuff easier.

If you enjoyed reading about "" here in the ThumperTalk archive, you'll LOVE our community. Come join ThumperTalk today!

The views and opinions expressed on this page are strictly those of the author, and have not been reviewed or approved by ThumperTalk.