750 big bore maybe?

[lightningronnie]

Just wondering if there is any way to visually tell if an xs650 motor has a 750 big bore kit, maybe markings externally. I have a guy telling me he thinks the P/O had one installed. Before I go look, I thought I would apply for an education. Thanks.

 

[jay760]

The only way to tell is by shining a light down the spark plug hole and looking at the edge of the piston, if you se a flat ridge around the edge then it is over size.

 

[PickleSlice]

Unless he can prove it, go on the assumption that it's a stock 650. Saying "I think maybe someone I don't know did something" is not a valid selling point.

 

[lightningronnie]

Thanks for the response.

 

[grizld1]

A few years ago a guy in my area picked up mutilated F-model, bragged about how fast it was, and swore up and down that the PO had put a 750 kit in it. He holed a piston and called on me for help. To make a long story short, I put a caliper to the holed piston he showed me--74.9xx mm., bone stock. He honed the cylinder, stuck another stock piston in, and kept bragging that the bone stock motor (no port work, stock cam, stock carbs, choked-up baffled straight pipes) would push his POS to 140 mph.

Unless the price is dirt cheap, I'd walk away from that.

 

[lakeview]

You probably already know that the commercial big bore has big fins as well, the only external sign.

Any time I look at one, I always look at the cast in size on the bottom of the barrels, just in case it is a real rare early stock 750. Haven't been disappointed in not finding one yet!

 

[grizld1]

Lakeview, that's only true of the Mike's XS/Heiden Tuning kit, and there are far fewer of those around than 750 conversions that involve removing OE sleeves, boring the barrels, and inserting 80 mm. sleeves. Good luck finding one of those factory XS750 twins! And yes, folks, there is such a beast--just enough made to comply with old AMA rules, which required that race machines, to be legal, had to be based on bikes produced in a stated minimum number.

 

[lightningronnie]

I appreciate the advice.

 

[XSnin0]

Thats a pretty crazy thought.

Whats even crazier is that there's probably very few of them still in existence and even on the road... in hands of people who will probably never know

 

[CDNTX650]

Those factory 750 are pretty neat. One on ebay a few years ago. Only way to tell is serial number and the bores say 740 something cc. They were sold without warranty I believe also.