I need advice on putting performance into my XS 650 .

[URX111]

Hi: I have a 1971 XS 650 , and I want to put in a 750 Big Bore Kit. I only have one carburetor , so I'll need another one. I saw on ebay some PWK 40's should I get two or what ? Is there something else that is recommended ? I saw on the yahamaxs650.com site two Keihin PKW 32 for $250.00 , the ones on ebay are a lot cheaper. Any help is much appreciated .

Thanks Paul

 

[650Skull]

Hey Paul and welcome,

Some more information about your bike. I'm getting the bike may have one carb so it could be a hard-tail and not a Factory original.

XS1's has some changes done to the from the factory, The oil pump was enlarged, Carbs changed mid year.

The early 256 engines, (the 70-73 engines have longer con-rods), con-rod small end is 22mm. These do have a problem with stretching when worked hard, leading to the small end disintegrating and going through the cases. Hotting up an XS1 would be something i would do in small increments. A 706 kit, or even a 6th oversize about 680cc, coupled with a Larger diameter headers and some head work would give a nice bit of extra grunt. Keep the factory cam, going for a shell cam works on the upper rev range which isn't really what you want.

Another small change. A good electronic ignition with a good coil and spark plugs can make the bike more efficient and this does equate to a small increase in power.

EX500 carbs have been successfully incorporated on our XS650's. These are still CV cabs but from those who have done the swap they have found the bike is more responsive.

And Pics, Pics and more Pics.......................Don't get offended when others post and demand pics, pics and more pics............we have trouble understanding and reading and love comics that have pics, pics and more pics...............

 

[grizld1]

The long rod motor was preferred by for dirt track racing because of its softer power delivery, but as Skull notes, the stock rods are not up to taking what even the stock motor puts out if it's used aggressively. An XS1 performance build has to start with performance rods and a welded crank; it's not a cheap proposition.

The Keihin PWK40 is not a viable choice on any streetable 4-stroke motor anywhere near the maximum possible displacement of your motor. Even the "PWK32" (actually a bored out PWK28) presents problems due to the size of the atomizer/needle jet; Keihin produced only one NJ size per venturi diameter in the PWK series, on the assumption that the carbs would be used on 2-stroke engines. Keihin's 4-stroke carbs are the CR and FCR series, requiring deep to very deep pockets. Although Mikuni America doesn't think we need them, Mikuni makes 34 mm. 4-stroke flat slide pumpers that are sold spaced and set up for the XS650 by German and British vendors; have a look at www.mikuni-topham.de. A cheaper alternative is the round slide Mikuni VM34; reputable vendors are Michael Morse at 650 Central and Gary Hoos at Hoos Racing. Both of these guys are experienced racers and engine builders who can give you solid advice.

Welcome, and good luck.

 

[drgonzo]

I am very pleased with the VM34 set-up I got from Gary Hoos, plus you can't beat his service after the sale. I recommend Hoos Racing.

 

[MrBultaco]

He with the most money gets the most horsepower...

 

[grizld1]

Well, not always, Mr. B., but for sure he who tries to get horsepower cheap from a 256 motor gets a grenade!

 

[Raymond]

As all of the above. Performance costs, one way or another. Pictures, plus tell us a bit more about the bike, what you want to do with it, more about yourself, your experience & nouse with motorbikes & infernal combustion engines, plus as said pictures. Welcome to the forum!

 

[Downeaster]

Years ago - 1980's - I was building engines for other folks. Lot of 350 Chevys, a couple of BOP 455's and even a Ford 351. Nothing wild, just a good solid engine with somewhat improved performance. Cam/intake/carb/headers usually.

My local speed shop had a big sign behind the counter: "Speed Costs. How Fast Do You Want To Spend?"

 

[URX111]

I'm a little embarrassed to say , I'm recovering from a long illness and I don't have access to my vehicles . They're at my cousins garage , I hope to get to them soon. So now I spend my time in my room thinking about my trucks and motorcycles, that's what got me to this forum. That being said, I'll tell you how I got it.
A friend of mine got it and right off the bat he put in True Forged Pistons (very high compression) and a performance cam. On it's first voyage, it turn out that he left a bolt in the tool tray. I his haste to try it out he left off the air cleaners, and sucked the bolt in. That's what made him give it to me.
I got another True Furge Piston, got it running, and I could never get it to run right. I knew less then than what I know now. I figure now that it was carburation. So I eventually put it back to stock, it ran great.
I could put the True Forge Pistons back in and try to get more HP that way (with new carburation) but I figure I would have a hard time finding gas. I just saw the over bore kit yesterday when I was surfing and thought "here a way to get more HP". So that's where I'm at.

Paul

 

[Adamc]

I'm a little embarrassed to say , I'm recovering from a long illness and I don't have access to my vehicles . They're at my cousins garage , I hope to get to them soon. So now I spend my time in my room thinking about my trucks and motorcycles, that's what got me to this forum. That being said, I'll tell you how I got it.
A friend of mine got it and right off the bat he put in True Forged Pistons (very high compression) and a performance cam. On it's first voyage, it turn out that he left a bolt in the tool tray. I his haste to try it out he left off the air cleaners, and sucked the bolt in. That's what made him give it to me.
I got another True Furge Piston, got it running, and I could never get it to run right. I knew less then than what I know now. I figure now that it was carburation. So I eventually put it back to stock, it ran great.
I could put the True Forge Pistons back in and try to get more HP that way (with new carburation) but I figure I would have a hard time finding gas. I just saw the over bore kit yesterday when I was surfing and thought "here a way to get more HP". So that's where I'm at.

Paul

Hello Paul, my advice is to get what you have running well as a standard machine. Once you are satisfied you could look to improve both performance, braking and handling depending on budget. Where you live these bikes are pretty cheap to obtain (unlike the UK); so spending big bucks on big performance seems a bit silly to me. Just enjoy the bike to your budget.