1981 Yamaha XS650S - Project Bike #5

I think you can just lump them in with all the other Chinese stainless brake lines. These were the first low cost China brake lines I discovered, and I bought a few. Then I found them for even a few dollars cheaper on eBay so have been getting them there now. So far, all have held up fine. The only "gotcha" with the eBay lines is most all seem to have the end fittings mounted in the same plane, parallel to one another. This works great if your MC has a front mounted line, not so good if the line mounts at the end like the stock MC. Banggood used to sell some lines that had the end fittings at about 90° to one another. They worked well on the stock MC.
Both of my 650’s have single, un drilled , but re surfaced discs, steel braid lines ( Banggood ), new EBC brake pads, new master cylinders, and rebuilt calipers. Both bikes have very firm lever feel and can be stopped hard with just one finger on the lever.
I should add that I also gave my rear brake a lot of attention, with new EBC shoes as well.
On some of the better brand name brake lines, you can rotate the end fitting to get the best angle for your application. These cheap China lines aren't like that though. They're crimped on solid so the way they come is what you're stuck with. I've often wondered why they don't build them with the ends offset maybe 45° or so, sort of a compromise between parallel and 90°. Something like that might work better in either scenario. As it stands now, a line with parallel ends mounted on a stock MC that has the line on the end puts quite a twist in it. I've done it, but I don't like it, lol.
Greetings! It's been awhile since I've posted in the forums.

This project bike was sold to a friend and we are scratching our heads on how to fix an issue that has plagued us for a couple of years. The engine starts, idles and runs well until you want to give it full throttle to pass, or accelerate quickly. Then it stutters, coughs, and just basically doesn't like that!

We've read through many of the forums here on solving that issue and have not found a solution for our problem yet. There is no change if we increase the mains to 142. If we set the floats in the 22-23 mm range, the bowls flood.

We have the Mikuni BS34's, currently with 137.5 mains, floats set at 27mm. As I said, the idle and midrange works great and we don't want to mess with that!

We are using pod filters, and the Delkevic 2 into 1 stainless exhaust system, which sounds great!

Has anyone had any experience like ours and found a solution?


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Yes, those pods gotta go. They check all the "bad" boxes. Besides being the pleated K&N style, which plain just doesn't work well on a CV carb, they're physically too small, and they're tapered (a CV carb doesn't like a tapered filter).

One more question though - are your floats brass or plastic? An '81 should have plastic floats and that 27mm setting you're running is the brass float spec. The plastic floats are set at 22mm. If the plastic floats are set to 27mm, that would be very lean, and that could explain why it's reluctant to take big handfuls of throttle. It's starving for fuel, lol. Also, you said the carbs flood out if set at 22 or 23mm. But where are you measuring to when you set them? If you're measuring to the flat part of the float up by the pivot, that explains it. That's the wrong spot and would make the setting richer (fuel level higher) .....


Thanks for these suggestions. We will definitely check it out with no pods and see what happens!

This is an 81 and it has BS34s with plastic floats. We tried setting the floats at 22, but the gas ran right through the carb bowls - overflowing. So, I assumed the spec was 27.3 mm based on the chart on https://www.xs650.com/threads/carbs-carburetors.43/ - measured as 5twins indicated.

The 2.5 inch speedo and tach came from Dime City Cycles.


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Seeing that small chrome speedometer there.
Is it accurate? Where did you find it?
Thanks, -R
Hey XST I noticed I have a set of those, excess to my needs in the bins.

I set the plastic float BS34's per the Yamaha factory manual, which is clear as mud about WHERE the vernier sets.
bs34 float height1.jpg

The floats LOOK right (about flat to the carb flange) using the metal plate as reference
bs34 float height5best.jpg

5twins could be right and the FUEL level is the gold standard. Be certain there are no bubbles in your tubing when setting, they fuggle the fuel height indication.
BS34 fuel level.jpg

So.... I'll respectfully disagree with 5T on this one and use the metal plate as my height reference. this allows me to sight across both sides using a mm gauge cut from an old metric tape measure.
I'm no expert but have set and run dunno 7 or 8 sets of BS34's this way.

(just checked a set this week) Bike runs great. (cough, stock airboxes and filters, commando mufflers)

just my opinion;
2 into one pipes are hard to tune? They'll draw so hard they'll over scavenge and pull raw mix straight into the exhaust. This can lead to going up to wildly big mains chasing a lean condition.
Thought experiment; With a two into one exhaust, might try larger valve lash settings, reducing the amount of time the valves are barely open on the ramps at overlap... dunno .005" and .010"?
If you have stock needles, the washer mod clears up a 4Kish hesitation, when all else is stock anyways. These early EPA carbs tend to have lean spot as the slides start to rise.
needle washer mod (3).jpg

Can you nurse the engine past 4-5K by feathering throttle a bit? that points to lean condition. If it goes through that range but sounds lubby dubby, burbly, that's rich.
bs34 float height6.jpg

The spec IS plus minus 1mm..............
If unsure a plugchop after a full throttle run will help you decide rich or lean.
Edit #15 be certain you are not getting fuel leaking past the float needle body o-rings a common problem.
Caps in place over the pilot jets, pilots removed and confirmed clear?
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Yes, the manuals are unclear on exactly where to measure the plastic floats to. There is also a discrepancy on exactly where the clear tube level should be .....

1981H-SH Fuel Level.JPG

1982SJ Fuel Level.jpg

I prefer the '82 spec as it puts the fuel level at or slightly below the top of the bowl. I've done several sets of BS34 plastic floats measuring as that Suzuki pic shows and they've all worked out well. Gary, your setting will result in a higher fuel level, and that may not be a bad thing seeing as how lean the BS34s are to begin with. As long as the bowls don't overflow, I guess you're good.
Thought you might reply back and good stuff! Yeah mine was the 82 and they changed the pic to below but NOT the TEXT lol
It's also completely unclear where on the carb body that line relates to.
In the interest of science I took ole paint out and after it was warmed up flogged it a bit. it's got a small stumble at 4K at full throttle, idles perfect, starts easy, is strong to redline everywhere else but that light stumble. Need to see what's in em I guess but For Allison's use they are perfect. cuz they are so forgiving, start with choke, push it in and it just sits and idles no throttle needed at 1200 while she helmet, jacket, gloves up. And it still idles nice, low n smooth when hot.
The number of times she'll go full throttle? ZERO.
If I get ambitious, I'll do a tube fuel level check.
As I said, I think the fuel level should be at (OK) or slightly below (better) the top of the bowl. If above that, the gasket is constantly soaking in gas and will leak, or at least "sweat" fuel eventually.