1980 Build for Dad

We can't move our needles on the U.S. spec carbs, they're "fixed" (only one clip slot). But, I really haven't found this a hindrance when tuning them. Normally, as you increase the main and pilot jet sizes, they bleed over into the midrange and eventually make it too rich. Then you would lean the needle clip setting a step to fix that. But with our U.S. spec BS34s coming so lean from the factory, this richening of the midrange from the bleed-over just seems to make it right.
 
We can't move our needles on the U.S. spec carbs, they're "fixed" (only one clip slot). But, I really haven't found this a hindrance when tuning them. Normally, as you increase the main and pilot jet sizes, they bleed over into the midrange and eventually make it too rich. Then you would lean the needle clip setting a step to fix that. But with our U.S. spec BS34s coming so lean from the factory, this richening of the midrange from the bleed-over just seems to make it right.

Yes Sir
Impressing Knowledge. As usual
That bleeding over between different jets and settings I do believe is what makes people
Gets lost.
I Know of one who had a California model emission restricted he claimed ...who never managed to get it right.
He was experienced ..Many years from many bikes
But ended up getting the mixture to lean .And overheated .. Engine damage
 
It's been awhile since I posted in this thread, but I thought it was about time for an update. First of all, I re-jetted the carbs per @5twins recommendations and it is running great! From what I have read online this spark plug is about where it needs to be at in terms of mixture, right?

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I have been riding it quite a bit and have since learned that my forks are in desperate need of repair. The seals are leaking oil and they easily bottom out when braking. I have also noticed that my front brakes were not performing all that well. When I tore down the frontend I rebuilt the master cylinder, but only cleaned out the caliper (and it was in pretty rough shape). Having learned a good bit more since then, I decided to rebuild a caliper I found in Dad's shop. It was in much better condition than the original on the bike and after new seals and boots I am hopeful that it will perform better. Would like to add a second caliper, but don't want to drop the hundred bucks on a LH caliper right now. I also upgraded to a one-piece braided stainless steel brake line and drilled out the rotor, which looks awesome!

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Had a hell of a time getting the forks apart. That allen head on the bottom of the fork is a bear... had to use an impact to get it off. Once apart, I felt even better about deciding to rebuild these. I changed the fork oil only a few months ago, but it was already fouled and blackened.

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Got the new parts in the mail, so I just need to get them back together now! @Jim also kindly provided me with these 1" spacers:

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I plan to add the spacers, perform the Minton Mods and experiment with the oil level and adjusters. Will try and shoot some more fork videos for comparison.
 
Would like to add a second caliper, but don't want to drop the hundred bucks on a LH caliper right now.
FWIW, XS650 brakes are a significant amount of unsprung weight. It's something for consideration before doubling up on that. A stock brake rotor and caliper is approximately ten pounds.
 
Yep! Rotors are available down to two pounds! Brembo caliper adapters are also off the shelf. That, and a little more oil in the forks to control the last 15% of travel will have this thing stopping and going almost like a modern motorcycle.
 
There's a lot to be said for not bothering with a second disc. A physicist told me you don't get any more braking force - won't go into his arguments here. The advantages of a second disc on a race bike are things like better cooling and symmetrical braking force/less fork twist. With the drilled disc - yes, looks awesome - one-piece braided line and rebuilt caliper you will see a big improvement. And as Brassneck says, a smaller bore caliper will greatly aid the 'feel'.
 
Thanks all for the feedback! Glad I didn't jump into a second caliper... these are all good arguments worth considering. A smaller bore master cylinder sounds like a great idea and is fairly economical, as well. By smaller are we talking like 13mm or 11mm? Any suggestions?

Have been considering drilling the disc out for some time. Did you use a drill press?
I did and it was a fairly nasty affair. Big surprise... but the brake disc was quite hard. I would strongly recommend a cobalt bit and some cutting fluid. I don't think you would get very far with HSS. I also just barely touched them with a chamfer/countersink bit, I read that you want the holes to have fairly sharp edges.
 
I used an 11mm master cylinder from a Honda VT750 and a blue spot caliper from an R6 with an FZR600 disk and am very happy with the combination. Two finger braking is no problem.

I also used an XJ750 front rotor on the back to lose some weight as the Maxim disk is 5mm thick (IIRC) vs the stock 7mm and slotted. I think I have about $140 total in brake upgrades, including the braided stainless lines front and back from ANplumbing.com (the old Earl's), the rest came from eBay.

1980 SG Back From The Dead – AKA Dad’s bike | Page 2 | Yamaha XS650 Forum
 
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The master cylinder from an XV 250, (Route 66, V Star) are 12.5 mm Nissins that fit the XS. They are suited to a sloped handlebar arrangement but there have not been any reports of leaks due to the way they sit. At a smaller diameter they apparently provide a better feel. I got this one off a 2009 XV 250 for about $50 (AUD) I think. Cleaned it up and it has functioned perfectly. It's a Yamaha original so no Chinese substitute.
 

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The advantages of a second disc on a race bike are things like better cooling and symmetrical braking force/less fork twist.
Either of those reasons will do for me.
Sure, the ultimate limit on braking is the tyre adhesion, but up to that point as much braking as possible, thanks.
 
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