Benefits and/or Drawbacks to going with an Over-Bored Cylinder?

[Et2rnal Smoker]

I have had many MX motors over the years but have ever had any need or desire to have them bored out to a larger diameter. I am curious about it with my blaster for two reasons. (1) I bought an 04' from the original owner in great shape....only to find out later that he had Never even opened the airbox lid, let alone serviced the filter, it literally deteriorated into my hand. It still runs well enough, but I'm going to install a fresh Wiseco Pro-Lite and rings and will be sending the head to Ken O'Conner for milling and re-shaping as well as the jug for honing (if the cylinder can still be within std. specs) and am considering a bore job and hone to .20 or.40 over (if not able to hold std. specs) or possibly anyway, (2) if I can figure on what difference that would make with regards to power charactaristics and/or jetting changes. I am also going to be adding a DMC Alien exhaust and am planning on going with the DMC jetting specs as well. 260 Main, 5th groove on stock needle and stock 32.5 pilot, Airbox lid removed. Any feedback, suggestions or testimonials appreciated.

 

[89blaster89]

over boring the stock blaster cylinder to the max .90 over will make no noticeable power increase

 

[Motocrossguy17]

from what i believe they don't make it go faster or anything think its just easier if you can get away with the standard bore as the over bore pistons i believe are more expensive.

 

[Awk08]

boring a stock cylinder even to it's max adds negligible power, only go as much as needed, if even needed.
ken will steer you straight, i'd allow him to inspect/measure it and he'll then tell you, or sale you, what piston is needed,
then bore/hone it to that exact piston.

no jetting changes are needed for bore/piston,
buy a few sizes main jets in the 290-260 range for those other mods, plug chops will tell you what jet is correct.
the stock pilot and needle will be fine.

 

[blasterBruce]

If Found that my Mods like the Needle clip on Middle Or Stock Position with my DMC And K&N Air Filter With no Lid , I have a 290 Main Which Is about one Size too Big , To deal with weather changes and Less plug chops and Main jet changes .

 

[joeak47]

I'm going to install a fresh Wiseco Pro-Lite and rings .

Be sure to religiously warm up that engine before use,or you could have trouble.

 

[blasterdemon7]

Like said. Boring larger then you need is just. Waste of service life of the jug.

 

[heatlbj6]

If your bring it to ken and want some power you might as well just have him port and polish the top end you'll see a big difference there

 

[Et2rnal Smoker]

Thanks for the heads up fellas, I appreciate it.

 

[blasterdemon7]

If your bring it to ken and want some power you might as well just have him port and polish the top end you'll see a big difference there

That's for sure. Even porting by itself with no other work done will give you a nice power increase. The cool part of porting is that as you do Add one like. Better pipe and larger carb. The more power you will get from the porting.

 

[Blaaster]

DMC needs a #260 main with needle on 5th clip, richest.

Air box lid off +2 sizes.

32:1 mix + 1 size.

One more to be on the safe side for cold weather #300 main should be fine.

Plug chop to confirm.

I run #320 main with similar setup other than I use 25:1.