13.5 stock bore for 426 ?

2 replies to this topic
  • sidkeo

Posted July 10, 2002 - 10:55 AM


any advice on what to expect when replacing 12.5 stock bore w/ 13.5 piston. had to tear down top end-due to pea gravel inside the cylinder.......

how did i do it? well, hit a (1ft or so) vert jump and landed endo style in gravel at badlands.com (attica,in). proceeded to pickup the bike and start it. wouldn't start after a couple kicks. few minutes later, the kicking didn't need any decomp help. next day, kickstart wouldn't even move w/ or w/o the kickstart. tear proved the mess inside-have pics if anyone interested

Visit the ThumperTalk Store for the lowest prices on motorcycle / ATV parts and accessories - Guaranteed
  • thumper4life

Posted July 10, 2002 - 11:38 AM


im just guessing here, but do you mean 13.5 to 1 compression ratio instead of 12.5 to 1? :)

but if thats what you mean, then you can expect more power through out the range, most likely race gas (jetted properly) will be your best bet for fuel

[ July 10, 2002: Message edited by: thumper4life ]

[ July 10, 2002: Message edited by: thumper4life ]

  • Boit

Posted July 11, 2002 - 10:18 PM


Ditto on thumper4life's post. As an addendum, the race fuel will be needed to take advantage of the increase in power and more importantly, the increase in heat. As he stated, jet it correctly or you will be miserable. VP C-12 would ge a good choice and is easy to jet. VP MR2 or maybe even MR1 might give the best overall performance once jetted crisp.

Related Content


Wilson the Blue Privateer by jetfuel

Dirt Bike   Special Interest Forums   Pro Racing
  • Hot  50 replies

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


Dirt Bike   Make / Model Specific   Yamaha   YZ 400/426/450
  • Hot  30 replies

The "going back to the other darkside" adventure... by Monk

Dirt Bike   Make / Model Specific   KTM   250/350/450/505 SX-F & XC-F (4-Strokes)
  • Hot  113 replies
WR Camshaft Swap Info - last post by jamesm113

WR Camshaft Swap Info

  • 0 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.