Motor rebuild options

Timmahh

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Pictured is my 83 xs. It started out riding it 7 years ago as pictured fully assembled. then 5 years ago I decided to take it apart and rebuild it right to my liking. It wouldn’t go over 50mph before guessing because it had stock jets with pods and straight pipes. It was on pause because of life in general. But now I’ve been working on it. Repainted everything. Rewired the whole bike. Now I’m at the point of rebuilding the motor. I’m stuck on the idea if I should order the 750 kit from mikesxs or just rebuilding it as the 650. I’m already set on carb kits from reading the posts on here and knowing who I’m going to get them from. The motor now is bone stock. Never been bored. But the pistons definitely look like it had a long life in this motor. So what are your guys opinion on what route I should take with this engine rebuild?
 

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IllusiveJack

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I never understand why you'd want to bore it out to a 750 because you still have the same rpm at 60mph with standard pistons but use more fuel with a 750, is it because you want to get to higher speeds quicker, what is it that makes you want to turn your 650 into a 750? I would understand if you had the other half on the back and she weighed more than the bike and a little more pulling power was needed.

Don't forget all the re-jetting the carbs headache that follows the big bore kit and as you all know every XS responds differently so its all trial and error. I have rebuilt a few engines and more or less all of them have just had a re-bore and they all run great.

If you want a great sounding 750, by a Triumph.
 

teamWicked

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I never understand why you'd want to bore it out to a 750 because you still have the same rpm at 60mph with standard pistons but use more fuel with a 750, is it because you want to get to higher speeds quicker, what is it that makes you want to turn your 650 into a 750? I would understand if you had the other half on the back and she weighed more than the bike and a little more pulling power was needed.

Don't forget all the re-jetting the carbs headache that follows the big bore kit and as you all know every XS responds differently so its all trial and error. I have rebuilt a few engines and more or less all of them have just had a re-bore and they all run great.

If you want a great sounding 750, by a Triumph.
I bought a bike with BBK installed and did indeed have to go through the rejetting process. Not a real big deal even for an amature like me. The bike has a very impressive midrange pull with 18/34 gearing. We don't own these old bikes for their sheer power, I may go 18/32 some day as an experiment and drop the 60mph revs another 100-200. My son rode it and instantly start planning on how he would do a BBK on his 80 Special. Another local friend 650 guy rode it and said "it's better than ice cream, like Christmas came early". I have an 81 winter project that will not get a BBK if I like it's all around goodness when finished. If I find the bores worn (it runs good on the centerstand) I would really have to balance the cost of rebore and BBK. Seems a 2nd over gives 700cc. I haven't ridden the 81 yet, it had little brakes and horrible tires when I picked it up. The BBK is an attractive option if during rebuild you find that a rebore and new pistons and rings are needed anyway.

It is different stroke for different folks.
 

Jim

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I never understand why you'd want to bore it out to a 750 because you still have the same rpm at 60mph with standard pistons but use more fuel with a 750, is it because you want to get to higher speeds quicker, what is it that makes you want to turn your 650 into a 750? I would understand if you had the other half on the back and she weighed more than the bike and a little more pulling power was needed.

Don't forget all the re-jetting the carbs headache that follows the big bore kit and as you all know every XS responds differently so its all trial and error. I have rebuilt a few engines and more or less all of them have just had a re-bore and they all run great.

If you want a great sounding 750, by a Triumph.
By all accounts from those here on the forum that have done it, the 750 offers a good, noticeable increase in power. Enough so that re-gearing for a lower rpm at cruising speed still gives good acceleration.
I bought the 750 kit when it was offered for $350. Re-bore, pistons, rings and gaskets will come close to that.
Haven't installed it yet, but I expect it will be money well spent.
 

jetmechmarty

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Meanwhile, I did a top end last year and another in work. Both just got rings, no bore. I’m content with the 650 and I ride it often. If I want to go fast, I have an XS11 that’s pretty quick and has an old bike charm of its own.
 

5twins

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Yes, I'm happy with a "fresh" 650's performance as well. And now with the low cost (but good by all reports so far) oversize piston kits from Cruzinimage, you can easily do this for under $200.
 

WideAWAKE

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I never understand why you'd want to bore it out to a 750 because you still have the same rpm at 60mph with standard pistons but use more fuel with a 750, is it because you want to get to higher speeds quicker, what is it that makes you want to turn your 650 into a 750? I would understand if you had the other half on the back and she weighed more than the bike and a little more pulling power was needed.

Don't forget all the re-jetting the carbs headache that follows the big bore kit and as you all know every XS responds differently so its all trial and error. I have rebuilt a few engines and more or less all of them have just had a re-bore and they all run great.

If you want a great sounding 750, by a Triumph.

Ride one and you’ll get it. Mine out does a later stock 650 in almost every way possible. The later XS is kind of a boring ride in my opinion. My 750 with Mikunis and open pipes runs much more like my xs2 does past 5k rpm but it does it all the time. Much more aggressive and while the xs2 wants to cruise at 55-60 the 750 is fine cruising at 75 without the shakes haha.

A nice triumph is gonna set you back 10-20k depending on the bike. And an xs will out due one in every area but style - at a fraction of the price.

Jetting isn’t much of an issue. Baselines are well established and just need a little patients to tweak and dial in.

Atleast that’s been my experience with em. Be hard to go back to a later stock bike.
 

Timmahh

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Thanks guys for your inputs on the bbk. I came to the conclusion that I’m just going to rebuild it to stock size. Probably buy another motor to do the bbk along with performance cam, valves and anything else anyone offers. Now where can I get the best quality piston and ring sets for the 650? I’m looking at yamahaxs650.com kit and tried to find wiseco set but didn’t have luck
 

5twins

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I see that YamahaXS650.com has their oversize piston kits on sale for about $75 at the moment so that would be the best deal. The Cruzinimage kits are $80 + shipping. You'll need to do some inspecting and measuring to see if a 1st (.25mm) or 2nd (.50mm) oversize kit is needed. Many times you need to skip right to a 2nd oversize piston if the wear and/or cylinder scoring is excessive. The 1st oversize (.25mm) may not be enough to clean the damage/wear out of the cylinders.
 
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