Performance motor issues???

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:



sounds like timing ..something must be off?

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?

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.

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.

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

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