Thoughts on Thumper Racing XR660 kit

Specifically the "Baja" XR660 kit with the 9:1 compression. I don't want to fuss with race gas and in the Idaho hinterlands sometimes the only gas I can get is 85 or 87 octane.

My melted down 1991 XR600 needs a new piston and bored out to the next size. I think it's 1.0mm or more over already so a re-sleeve may be in order anyway.

Oh yeah, I'm on a budget for this bike and would like to have most of the rebuild parts ready when I box it up in Dec.

In other news, I have a brand new Wiseco piston (0.076/0.0030 over) piston/pin/rings/clips that I don't need. Any takers?

"O"

Specifically the "Baja" XR660 kit with the 9:1 compression. I don't want to fuss with race gas and in the Idaho hinterlands sometimes the only gas I can get is 85 or 87 octane.

My melted down 1991 XR600 needs a new piston and bored out to the next size. I think it's 1.0mm or more over already so a re-sleeve may be in order anyway.

Oh yeah, I'm on a budget for this bike and would like to have most of the rebuild parts ready when I box it up in Dec.

In other news, I have a brand new Wiseco piston (0.076/0.0030 over) piston/pin/rings/clips that I don't need. Any takers?

"O"

9:1 compression on 85 or 87 octane prob. be ok. not much more though.

on my XRL with 8.3:1 comp. almost feels like its unhappy with the fuel. could be me though feeling guilty about not feeding her the best!LOL

Specifically the "Baja" XR660 kit with the 9:1 compression. I don't want to fuss with race gas and in the Idaho hinterlands sometimes the only gas I can get is 85 or 87 octane.

My melted down 1991 XR600 needs a new piston and bored out to the next size. I think it's 1.0mm or more over already so a re-sleeve may be in order anyway.

Oh yeah, I'm on a budget for this bike and would like to have most of the rebuild parts ready when I box it up in Dec.

In other news, I have a brand new Wiseco piston (0.076/0.0030 over) piston/pin/rings/clips that I don't need. Any takers?

"O"

I run a XRL with a Wiesco 10.25:1 piston with Hotcam and have no problems with pump 93 octane. I would guess 9:1 and pump gas would be fine.

My 9:1 comment was in reference to Thumper Racing's two XR660 kits, one is 9:1 (for Baja and other places with poor fuel) and a 10.5:1 compression kit:

Our basic high compression 660cc big bore kit with a 10.5:1 compression ratio has been the anchor for all our XR600 modifications. Its reliability has now been field-tested by our customers--with excellent results. This basic kit delivers a strong straight line power curve, making the XR600 even easier to ride. The only drawback to this kit is that it requires good gas to ensure against detonation. We recommend 100 octane or better. Feed her a steady diet of good gas to our C-5 octane booster and she will give you years and thousands of miles' worth of sheer pleasure.

Both kits have a price tag of about $250 (piston and sleeve) before gaskets.

My 1999 XR600 with the stock 9:1 compression runs well with 85 octane at higher altitude and 87 octane down lower.

Any thoughts on the kit?

"O"

If you are on a budget you can just go to a 100mm bore without a resleeve. That gives you 628cc. Wiseco makes a 100mm 9:1 piston for the XR600.

If you are on a budget you can just go to a 100mm bore without a resleeve. That gives you 628cc. Wiseco makes a 100mm 9:1 piston for the XR600.

I have a feeling that the bore is already a 100mm and I'm not 100% sure the bore is usable right now (bike ran with a busted oil pump for a very long time and fried two top ends). The new piston that came with the bike is much too small, enough that it is visible by just looking at the pistons. The piston that came with it is either a 97.5 or a 98.

I may have it mic'ed today to see exactly what I'm up against. Thanks!

"O"

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