Previous Previous Owner Claims; It's A Mystery

[turk]

I bought a new to me 1979 XS650 for my wife.
It looked good on Craigslist and in person,your basic 20 ft. semi-custom.

It came with a "build sheet from the PPO" that was tucked in with some paperwork that I got around to reading the next week.
The PO had mentioned having a build sheet over the phone,I really don't pay attention to those kind of things.
A bike is what it is.
I generally don't worry about claims of PO when buying a bike.
The first part of the Build sheet I dismissed as "11th grade automotive shop talk".
The second part which I could visually verify was accurate from what I know.
Dual front disc, Mikuni Vm carbs, extended swingarm,oil cooler,etc.

So yesterday I was following the excellent write-up on valve adj. form here and looked into the spark plug hole to see if I was at TDC.
I saw some "writing" on top of the left piston the was easily read.

80.95mm and S635

Are these 750cc pistons?

I did some research ,but, need some expert thoughts on this.

I was also able to verify the carbs are Mikuni VM38


The first paragraph of the build sheet went something like this:

it has a Bob Bertaut built 753cc engine with Web Cam #2and titanium valve kit and springs. Volkswagon valve adjusters and Mikuni round slide VM38 carbs, etc, etc, etc.


It is supposed to have been "Rodmans Special Roadster"


http://www.650motorcycles.com/rodman.html

My wife and are not "go fast" riders, really didn't need or want anything but a stock motor.
I do want a safe and reliable bike for my wife to ride.

I do need to know what I have so I can make it as good and reliable motor as I have the ability to.

Thanks for any advice or info you have!!.....Al

 

[turk]

here are some pics.

The piston on the left has the exact writing as mine.

 

[griinder]

If you don't want it anymore, I'll take it!!

 

[Tron]

Trade someone that has a rebuild stock motor!

 

[nj1639]

Nice surprise!

 

[5twins]

As far as VMs go, 38s are very big for this bike. Most run 34s, a few 36s, but I've rarely (if ever) heard 38s mentioned. Combined with all the other mods, I'm not so sure this is the best choice for the wife, lol. It may be modded to the point where it's finicky and not really a daily rider anymore.

I'm surprised you could read the numbers off the piston top. They usually carbon over pretty quickly. Has it just been gone through and freshly reassembled? If not, then there may be something else at play here, like those very large carbs throwing so much fuel in that it's washing the carbon off the piston tops and keeping them clean.

 

[turk]

I don't know if it has been gone through recently or not.

I hate to be this way ,but, if I called and asked the PO; I wouldn't believe him anyway.

I was Shocked at being able to see the writing myself, the piston is very clean almost like out of the box!, the right side is not as clean , but , you can see the writing thru a very thin film of black carbon!!

I wasn't going to post a thread about "all this" ,but, like I said I really need some advice before going much further.

I'm afraid that you may be correct about the carbs being WAY too rich and washing away the oil.

I was wondering if this really is a 750cc if the VM38 could work or am I better off trading or selling them and getting a pair of stock carbs?

My wife and I ride 7-8000 non-freeway miles a year ,so this is just a 200-300 mile a day runner on a weekend going camping and such.

We want it reliable more than fast, I just need to figure out how.

A lot of the external "custom stuff" I thought were useful improvements like the dual discs, martek ignition.,etc .,but this engine/carb stuff has me wondering what my next step should be.

5twins, I respect your opinion having read many of your posts ,so, any advice on my next step?

Thank-you for taking the time to respond.....Al

 

[5twins]

From all reports, stock carbs will work fine with a 750. At the very least, you might want smaller VMs. Have you positively I.D.ed those as 38mm VMs? They should have an I.D. # stamped on them somewhere. Here's a list .....

http://www.carbparts.com/mikuni/vm__round_slide_standard_specifi.htm

I have a pair of 32s, both lefts (idle adjust) and they're stamped with the I.D. # from the above list (32-33). I would think yours should be similarly marked, maybe with a 38-9 (if they are indeed 38s) .....

Maybe the P.O. just didn't know what carbs he had exactly, especially if he took over ownership from another P.O.

 

[turk]

That's the exact same picture I used to I.D. my carbs.

I got it from one of your posts!!

Here is a pic of my carb,the same view.


It says 38n 9 ...Al

 

[gggGary]

And this bike, big honking carbs and all, is now in gggGary's loving arms, Thanks Al!

 

[jsmith1107]

Hey congrats on the bike purchase!! Looks nice.

 

[nj1639]

And this bike is now in gggGary's loving arms, Thanks Al!

HAHAHAHAHA.....you dog! LOL.
Congrats! Whatcha gonna do with it?

 

[gggGary]

"Congrats! Whatcha gonna do with it?"

Here's the thread start.

http://www.xs650.com/forum/showthread.php?p=282742