XS Horsepower changes through the years.

[Orion61]

I was reading up on the xs650 and I found references pertaining horsepower changes in the 650.
the early 70 and 71 were rated 53hp @7000 rpm and the 72-74 were lowered to 48? and the 1975 XS650B and up were raised again to 50hp. All the following were at 6000 RPM. I thought I had heard the last year or two were raised again to 54 but I cannot find that reference.
Can anybody straighten this out? Also what exactly what did they do to the Engine to make these changes? Compression carbs cam lift/duration?
I have owned 4 or 5 of these beautiful bikes, I have an XS 650B right now that is by far the best out of all of them.
I also had a 71, the beautiful yellow flake xs but It didn't have the low end take off power all the rest of them did. It was tuned fine, started fine and ran great on the highway, It was probably the smoothest running of the bunch.
Signed.....
I lost my Horses, then found half of them...

 

[grizld1]

Don't believe much that you read in regard to old hp claims by motorcycle factories, enthusiasts, or most journalists! The engines from 1970-73 were essentially the same with the exception of the electric starter and a minor change in head design in 72-73. (Jack likes the 70-71 heads best for performance port work, but in stock form there's not enough difference to account for a loss of 5 hp.) In 74 valve timing was changed with a milder cam; that reduced max output and produced the greater low rpm grunt that you refer to. Other changes included shorter rods and smaller wristpins. Engines from 74 through end of production were essentially the same; the change to 34 mm. carburetors in 1980 had little if any effect on max output. There was absolutely no change to the 82-83 motors that would have resulted in any measurable power increase. Any changes in measured output from 74 through end of production will be a matter of variations in individual motors (some come off the assembly line faster than others) or test conditions: altitude, accuracy of equipment, pretest tuning, etc.

 

[BigJohnParts]

Most HP claims were made on the certificate of origin. A document the factory sends to the dealer making it possible to register the new M/C in whatever state the dealer happens to occupy..The HP is measure at the crank, not at the rear wheel..

 

[jetmechmarty]

My father-in-law was a Yammie dealer in the day. He had a few of them. He told me the bikes at this price point had variable performance out of the crate. Some had a whole lot of go, others, not so much.

The dealer just prepped them and set them on the floor. We all know the variables that can hinder or improve performance.

 

[hooser]

Look at the listing it was bhp, meaning brake hp at the crank not at the rear wheel. Yamaha did that on all there bikes. The were rated at 43hp at the rear wheel.

 

[TwoManyXS1Bs]

More food for thought:

http://www.xs650.com/threads/top-speed.30903/page-3#post-311967
http://www.xs650.com/threads/any-of-you-guys-had-your-xss-down-the-1-4.31566/

 

[weaselbeak]

I owned both early and late models, never felt a dime's worth of difference.

 

[jetmechmarty]

I once did a drag race with a buddy. We're roughly the same weight. Him on a XS-2, me on a XS650SK. It was pretty much a toss up. Not that that really means anything.

 

[BenVoiles]

The later models ran real lean stock.