170cc Athena Kit wont rev Past 9500RPM

[vtrtomuk]

HI Chaps,

Advice on my predicement please,

Built a 2003 DT125R last year, with an athena 170cc kit and Full athena exhaust.. life gets in the way and its only this year iv got it out and ran it in, this is a full nut and bolt rebuild, new crank and internals etc..

specs 2003 DT125R 3RM with a 3RM-20 CDI, Athena 170cc Kit Full athena Exhaust, standard 28MM Carby with 290 Main and 25 Pilot. Inlet reeds are carbon fibre Yambits Jobby.

under load or with no load it will not rev past 9500rpm like its hitting a rpm govener like a chainsaw....

iv upjetted and down jetted 270,280,290,300,310,320,330,340 all the same blocked off powerjet and with powerjet etc...

powervalve is visually aligned up the exhaust port and functioning, but have all so tryed pinning it open, visually confirmed. same thing....

The Baiscs, new plug, new ht lead,coil and cap, jets as above, snorkle in snorkle off, powervalve pinned and with YPVS. Reed switch behind clocks is out and tucked away out the housing.

my only other thought is to reduce the plug Gap, but seeing if anyone else has seen this or had exprence with the 170 kit

any advice aprecated, Cheers

[Calum]

Hi there,

You're literally describing the characteristics of the big bore engine. It's not going to rev like the OEM setup, a big bore kit will drop over revs and this sounds like it's in the right ball park figure.

I'm not saying 9500 is the limit, but this is definitely past its peak power and I wouldn't expect any power gains past here.

The next step for retaining revvibility will involve more drastic tuning.

• Zeeltronic CDI Ignition System
  • Allows you to have a fully derestricted ignition system
  • Customise powervalve for the Athena kit
  • Squeeze out a few more RPMs
• Cylinder porting
  • Greater volumetric airflow through the cylinder
  • Allowing it to breathe easier
• Transfer window porting
  • The transfer windows most likely need porting due to the larger bore
  • Gasket match the cylinder to the cases
• Porting the cylinder base removing the obstruction to airflow from the reedvalve
  • Air flow is greatly disturbed by the cylinder spigot protruding into the intake
• Fit VForce4 Reed Block from Blaster
  • Proven to increase mid-range and overrev performance
  • Boyseen dual stage reeds can also help but seeing as your requirement is literally at the top end of the powercurve then you don't want dual stage
    

Just bear in mind, you're now demanding a lot more from the engine than stock and seeing as you're seeking peak power you're going to want supporting mods.

• Uprated clutch springs to avoid clutch slipping
• Forged connect rod to resist rod stretch/fatigue
• Forged light weight piston to withstand the demands