A '79 Yamaha XS650 2FO . I have modified the rear to accept the KZ750B LTD M1 twin 18" disc brake hub . At the moment the front is stock with he the exception of the second brake . The rear is modified only by way of spacers to center the disc in the caliper and turning down the drive hub center to accept more common KZ650 #530 sprockets . The disc itself is a Honda CB200C turned down .200" to fit inside the caliper . The bearings in the rear had to be changed to accept the Yamaha axle .
I found a WM4 2.50" 40 hole rim attached to a Sportster hub and a WM3 2.15 19" 36 hole rim from some dirt bike for the front . Both rims are vintage Akront .The angle of the spoke holes is well within limits for adaptation to the Yamaha and Kawasaki hubs . All I have to do is polish replacement hubs and rims and deliver to the Wheelmaster .
The engine is at present a stock bore XS650 with a 277/83 crank . All else other than a stock XS2 left cylinder decompression valve remains either stock Yamaha or modified Yamaha parts .
That is the red bike as we know it at this time .
Last Edit: May 23, 2015 3:52:04 GMT -5 by kopcicle: If you're smart you will stop right here and not read any further , but how smart can you be ? You do own a XS , right ?
Thanks bubba , if you only knew how long it took to get this far ....
...and Dick , don't even start about the K&N's stuck on BS38's . They are there purely to keep the dirt out and a convenient place to store a set of carbs and otherwise useless K&N's . If anyone has been paying attention to me over the years this is NOT the way to do it . Constant velocity carburettors require an airbox , slide type carburetors can benefit from an airbox or use individual air cleaners .
The rear caliper is bone stock 2F0 . I was careful to leave as much of the conversion stock as possible . With the un-modified KZ750B LTD M1 twin 18" disc brake hub and rim the Honda disc centers in the caliper once .200" is taken off the diameter . Now one caution , the disc was "marked" CB200C but I did not take it off myself so I won't swear to it . I'm told that the KZ305 is very similar also so ya pays yer money and takes yer chances . I did turn down one side of the rear hub and I believe it was the sprocket side . I'll know more in a week or so . As the project stands the disc is centered in the caliper and the sprockets are so nearly in alignment that I may be able to let it go . I did have to futz with spacers for hours but it fits . I should say almost fits . I'll have to pull the wheel toward the drive side about .250" to put it on center line but with all else falling into place I'm far beyond complaining. I had considered the modification of the front hub to carry sprocket and disc but going without the dampener was more than I or the gearbox and transmission could tolerate .
I'm gonna need all the dampening I can get so the primary and clutch dampening stay also . Look at tit this way , more crap to replace when I finally get this thing to hook up .
"... solid blocks." I'll send you solid blocks ya ole horse thief . Better yet bottled dampening . Uncle Homer's private reserve . Pretty smooth over the bumps if ya don't mind a bit of temporary blindness .
Well, see how it works; you may get a bit more drive train lash than you bargained for, though. I always hated that cheesy sprung primary gear setup, but I've been too lazy to work out fitment of a rubber-damped hub and hunt down Vesconite rod stock. One of these days, maybe....
And no, I didn't figure you of all people would be hanging pods on vacuum carbies. But while we're on the subject, the OEM still air box is small and pretty restrictive. If you have a recipe for improvement, it would make a great fuel system thread.
Last Edit: May 13, 2012 15:49:53 GMT -5 by grizld1
I actually do have a somewhat butt fugerly remedy that I used for a road racing project . Even non CV carbs can benefit from a pressurized airbox but you would be surprised at the volume necessary . This got into experiments with pressurized float bowls by way of vent tubes in the intake airstream and what would otherwise be described as dangerously lean midrange leading into pressure fed fuel transitioning into WOT . I wasn't the first by a long shot but I was the only dolt that thought the twin could benefit . The largest impediment was the sheer volume necessary to achieve any gains due to the 360 degree crank . Some years previously I had tried this with a CB350 and a 180 degree crank with significantly smaller airbox volume even considering half the displacement .
If I go much further you're right , it needs it's own thread and I now have a CB650SC project on top of the two 1300 six's my 1000p the flh and the red bike . I doubt I'll be even vintage road racing soon if ever but there does seem to be some interest in the younger portion of the family so who knows ? I still have the Branch head and the molly frame ....
Nope, optimal air box volume wouldn't surprise me at all; my other ride is a 2003 Zook SV650 with a hugeass air box over downdraft throttle bodies. But what I was agitating you for (on behalf of members; I run a pair of TM36/68's with pods, haven't used vacuum carbies for years) was suggestions on how breathing for the still air box could be improved by the street rider who wants to retain the OEM carbs and get more out of them, rather than suggestions for the ball-to-the-wall race builder (who's gonna be inspired by his own brand of firewater anyway).
So I take apart a XS650 crank and find this . The one with the slugs in it is the early "256" crank from about '72 an '81 is on the left for comparison . I guess I don't know everything about these engines . The crank shows no evidence of having been apart before . New one on me .
Last Edit: May 23, 2015 3:49:15 GMT -5 by kopcicle: A bit more than a screw loose here don't you think !
I'm leaning more towards 110-145 , Trick , VP 110 . When I can't find "good" fuel E85 is a good substitute without a jet change . Without something like Blendzall (castor plus long chain octane boosters and a methanol carrier) I'd have to change jets for straight Methanol . I don't have to tell any long time tuner of the XS that compression isn't the best direction to go in finding more area under the curve .
The cure to the self created symptom is three sets of carbs . One set for pump 92 , one for the race fuel and E85 and one for straight methanol . The rubber in the stock BS38's has enough issues with 10% let alone E85 . The Methanol just trashes everything unless dry (near zero water content) and the E85 works with nearly the same jetting with just a change in timing .
The real advantage to E85 if properly set up is cooling through latent heat of evaporation and easier starting than straight ethanol or methanol . E85 is a little easier to tune to because its rich symptoms are a bit more evident than straight ethanol or methanol . When using straight methanol additives need to be added to the fuel in order get any visual indicators on the plug .
The compression increase came by way of the bore increase and a significant dome on the Kawasaki (MTC K1327H)as well as careful adjustment of assembled height . With less than .050" piston to head clearance a substantial quench/squish area is gained along with the compression increase . You can always loose compression with the addition of base gasket and a cam adjustment within reason . I've run as little as .037" piston to head clearance on a fresh engine with only incidental contact with carbon deposits and saw evidence of the quench effect disappear around .055" . The final numbers aren't in yet but 12:1 plus or minus is the expected .
Keep in mind that this is an aberration , not a motorcycle . This is a hooligan , outlaw , full silly , nut case , animal in animal clothing . It is not practical transportation in any sense of the term . Its meant to shatter ear drums , make the eyes water , scare dogs , cats , children , and old ladies. "I want to kill. I want to kill! I want to see Blood and gore and guts and veins in my teeth! Eat dead, burnt bodies! IMean: Kill. Kill!"
get the picture ?
Last Edit: May 23, 2015 3:48:14 GMT -5 by kopcicle: Credit to Arlo Guthrie for the quote from the "Alice's Restraunt Anti Massacree" and the single malt scotch
so ... 8.1" = 205.740 mm half the stroke = 37mm Cr 500 rod = 144mm MTC-K1327H compression height = 24.8793 205.740 mm deck -205.8793 assembled height +0.1393 mm or 0.0054" Think I'm close enough to worry it into spec with head and base gaskets ? :-) 8.1" is the distance from crank center line to top of the XS650 cylinder The 1/2 kit price is $255.73 as these pistons were originally meant for a big arsed 1300+cc over bore of the Z1/KZ 903/1015 I think that beats the hell out of $400/pr don't you ? Then again it took me countless hours to track down the information on the interwebz and on the phone I am not soon going to forget that brain dead 20's something at Wiseco that told me the compression height was "proprietary" Or Ross and J&E both wanting minimum orders of 8 Or the nameless ID10T that kept telling me " they have different pin diameters it won't work " no matter how many times I told him it was a CR500 rod with a different small end diameter " That's a two stroke rod " , well yeah , sooooo ... So my machinist answers the email with the dimensions with " And what was so hard about that ?" I get him on the phone and the voice of reason tells me " Dennis , not a whole lot of people think like you do . You're just going to have to accept that fact and learn to live with it . I have "
Get it from Mike or do it yourself the price difference isn't enough to quibble about . Any real savings will be from your machine shop of choice and or your assembling the pieces . I will stress for the novice that these discussions are all hypothetical until the assembly is trial fitted and the dimensions/clearances verified . many thanks to Brett ,Greg , Dick , Bubba , LarryC , APE , Cliff @ MTC , Jack and Google Calc for the conversions . xs650temp.proboards.com/index.cgi?action=display&board=EngineModified&thread=17014&page=1for the original thread .
So the included valve angle of the Kawasaki 900-1100 up to 83 was 63 degrees . The included valve angle of the XS was 76 degrees for all but the OW72 head . This results in a 6.5 degree difference . The relative importance of this is that it allows for a continuous increase leading from the limited squish area into the combustion chamber . With the bore increase more area is exposed for modification . One of the things the Stock 650 lacked was little if any squish/quench area .
Just a little information on squish/quench area . It has been said that squish/quench area is a band-aid for poor combustion chamber design . On the other hand moderate but effective squish/quench area increases flame front turbulence during ignition cycle turn around through TDC and promotes slightly better scavenging during exhaust cycle turn around tdc at the expense of a short sharp pressure rise as the intake valve is opening . Originally thought to be an impediment to low lift intake flow further experimentation fount that the resistance to the inertia of the the resonant intake charge tended to compress the charge prior to entry into the combustion chamber . This eventually leads to a discussion in inlet valve/seat venturi/geometry at low lift and does not pertain to the present thought . I just wanted to include that little bit of information as I'm sure most are aware that the intake valve is open a significant amount as the piston turns around during overlap .
The combination of roller bearing main and rod as well as the bending loads on the crank won't let you inside of .037" piston to head unless it is a fresh set of bearings and you are inspecting every few hours of running time .
The combination of a three angle valve grind with out blending the angles , no back cut on the intake , no front cut on the intake , minor short turn radius work and filling in the far side of the bowl went a long way toward promoting effective combustion chamber turbulence and actually reduced the ignition lead necessary for peak power .
A cam profile that buries the intake valve head in the valve pocket of the piston for as long as possible also contributes to improved flow . I'll leave that as a rate of angular change extrapolated as a non linear output for your experimentation . Suffice to say that when you get the valve started is as important as how fast you accelerate it off the seat . There all sorts of arguments for and against long rods specifically in the XS that I don't care about . The major reason I installed the long rods and light valves is that I'm able to "dwell" the intake valve head in the piston relief for a considerably longer period of time without unobtainium valve components . The whole point is that after low lift flow , mean average initial flow into the cylinder , across the back of the valve needs to transition onto the surface of the piston and in our case piston dome , without encountering significant impediment . Only when the piston finally retreats from the valve and flow transitions into gross mean flow does the port itself really start to work and become the ultimate obstruction to flow. Jack's thread from '04 when coupled with pics saved elsewhere is a very good guide of what NOT to do more than what to do . Not that Jack did it wrong by any stretch but he does go into great detail what NOT to do .
Opening up the bore 5mm gives you a 2.5mm ring all the way around the outside of the combustion chamber that can be made larger if the head is decked a moderate amount . A constant wedge of between 5 and 7.5 degrees is what I've used for ages . It shouldn't surprise you that the 5 degree was mostly for heads like the Small block Chevrolet and the 7.5 degree was more effective in hemispherical chambers .
So if you are to weld on the heads the obvious would be the intake port floor and the short turn radius . What isn't so obvious is reducing the bowl volume to the point that the majority of the volume under the seat is venturi .
I've only approached 42 degrees total lead in the alcoholic because that's just the nature of the beast . More often maximum power would come well before detonation and generally prior to 38 degrees total lead . On pump gas maximum power should usually be found before 36 degrees and as little as 30 degrees if the above information is applied .
I'll only add a little food for thought here as an advanced exercise . The exhaust port can in some cases benefit from sinking the valve into the head slightly if it is done specifically to raise average flow velocity . That whole can of worms for another time .
I'm a little frustrated today because I didn't get nearly the time to work on the beast as I wanted and most of the issue was outside my control so I took it out on the keyboard instead .
By the way I've said before , I'm here to make your head hurt and your eyes bleed . How am I doing ?
...I reposted part of the aussie sight somewhere else and it was ready to paste
The late Phil Irving could hardly have wished for a more loyal disciple than Ron Valentine, best known in motorcycling circles as designer of the highly successful Westlake racing engines. More than 30 years ago nobody was quicker than Valentine to recognize the merit of Irving's proposed cure for the engine vibration that, in varying severity, had long plagued Britain's big four-stroke parallel twins, condemning their riders to mobile vibro-massage without the option.
The essence of Irving's brainwave was to replace the standard crankshaft with its crankpins in line, by a shaft with its pins staggered so that when either piston is at top dead centre (where it primary inertia force is greatest) the other is approximately at midstroke and generating no primary force. This arrangement considerably reduces the engine's maximum inertia force, and thus vibration - though not by so much as the 50% one might suppose, as we shall see later.
A second benefit stems from the fact that when either piston is stationary at tdc, the other is moving at or near its maximum speed and thus contributing to the flywheel effect, so that the flywheels themselves can be a bit lighter for the required level of smoothness. It was this consideration that dictated Irving's original choice of 76° for the spacing of the crankpins. For with that angle - given that the centre length of most connecting rods is near enough four times the crank radius - when either piston is at tdc, the "big-end" angle (con-rod to crank) in the other cylinder is a right angle, hence piston speed highest.
To their shame - and perhaps because of an irrational horror of uneven firing intervals? - the manufacturers of even the most vibratory parallel twins showed not the slightest interest in Irving's proposal despite the relative ease with which they could have converted an engine for test by twisting the crankshaft and camshaft, adjusting the spark timing and fitting a second carburetor where necessary to obviate a mixture bias from overlapping induction phases.
Following the demise of the British industry, it eventually fell to Ron Valentine (and his assistants, including mathematician Tom Oliver) to prove the soundness of Irving's scheme when (three or four years ago) they completed their second 76° crankshaft for Steve McFarlane's 952cc (80.5mm x 93.5mm) BSA parallel twin classic racing sidecar outfit. Stretching both bore and stroke of the original A65 engine had aggravated its vibration to the point where the crankcase was in danger of disintegration.
Machined from a solid bar by Dave Nourish, Nourish Racing Engines (NRE), in his Oakham workshop, the new shaft proved to require balancing (to a factor of 50%) as if it were two separate flywheel assemblies joined together. Once that was done, the engines character was transformed. Gone were the frantic shakes. Instead, said McFarlane, there was a slow and lazy throbbing sensation as - to the accompaniment of a pleasant off -beat exhaust lilt, reflecting the 436°/284° firing intervals - the revs soared to 7,000 RPM and the more powerful 1000cc - 1200cc Imp engined outfits were humbled as the BSA won its heat in the Snetterton Race of the Year meeting in 1990.
Encouraged that his and Nourish's sacrifice of valuable time and effort had proved worthwhile, Valentine decided to follow his hunch that a 90° pin spacing would give even better results. True, the instantaneous contribution of the descending piston to flywheel effect, while the other was at tdc, would be slightly reduced because it would be just past its maximum - speed position (big-end angle only76°, not 90°) but there would be two overriding benefits - one to mechanical balance, the other to the smoothness of the flywheel effect.
Balance would be enhanced because the top and bottom dead - centre positions of either piston (where the secondary inertia forces act upward) would coincide with the midstroke positions of the other, where the secondaries act downward. Thus those forces would counterbalance one another at the cost of a small rocking couple.
As to the moving piston's contribution to the flywheel effect, this would be the same whether the stationary piston was at tdc or bdc (the big-end angle being 76° in both cases). With the earlier 76° pin spacing the ideal "big-end" angle of 90° was achieved only when the stationary piston was at tdc. When it was at bdc and the moving piston was rising, not descending, the angle was only 62°, so the effect was not constant but fluctuated at high frequency. Of these two benefits in favour of 90° pin spacing, the absence of unbalanced secondary forces is clearly the more significant.
When the subject of "cranky cranks" was discussed in Motorcycle Sport three years ago Charles Bulmer suggested that a 180° crankshaft would be even better provided its primary rocking couple were eliminated by means of a crankshaft-driven contra-rotating balance shaft. Quite so, for an engine so designed from scratch by a manufacturer, as with some Hondas.
But what Phil Irving was proposing was the least possible alteration to already established mass-production lines to overcome a serious deficiency in British parallel twins. Given a clean sheet of paper, he had long since shown his own preferences for twin cylinder four strokes: designed just before the second world war, his 600cc Velocette Model 0 vertical twin was a model of smoothness; like its racing stable mate, Harold Willis' 500cc super-charged "Roarer", it had contra-rotating geared crankshafts and shaft drive. Later, his postwar 50° V-twin Vincent Rapide ranks as one of the industries greatest designs.
Again drawn by Ron Valentine and machined by Dave Nourish, the 90° crankshaft has four flywheel discs and is a replacement for the conventional (360°) shaft in one of Nourish's Westlake powered classic racing 500cc NRE Triumph based pushrod parallel twins. Since the total upward inertia force with the standard crankshaft occurs when both pistons are at tdc together, it might be supposed that separating the tdc positions by means of staggered crankpins would halve the force and double its frequency, regardless of whether the stagger is 76° or 90°. Not so as Mr. A Archdale was at pains to confirm in the original "cranky cranks" discussion, although the individual tdc forces in each cylinder remain one half of the total for the 360° shaft, the total upward force occurs when both pistons are level and their cranks equally disposed each side of tdc, i.e., 38° before and after tdc for the 76° stagger and 45° for the other. The point one must grasp here is that - although one piston is moving upward and the other downward when they are level - their inertia forces are both upward, as can be seen in the accompanying curves, where both points are above the base line. Note too that the 45° points are slightly lower on the curves than the 38s, indicating a slightly lower force in favour of the 90° pin spacing.
Last Edit: Oct 11, 2020 12:36:40 GMT -5 by kopcicle: fix broken links
buell88: Anybody have any idea who built the xs650 tracker used in the Draggin Jeans Ad on Pipeburn?
May 16, 2017 16:24:09 GMT -5
joshua: The regulator/rectifier unit I got from Mikes PMA has closer hole spacing than original. Are we supposed to mill the holes to fit?
Jun 7, 2017 19:25:58 GMT -5
joshua: My bad. I found the bracket they supplied to mount the rectifier/regulator... Uh oh. How is this meant to work? Which way is it meant to mount? Looks like I have to use some spacers or something. Good instructions would be nice.
Jun 7, 2017 22:09:52 GMT -5
craig8johnson: Not sure if this is the right spot or not but oh well...
Jul 11, 2017 18:04:15 GMT -5
craig8johnson: I'm checking the charging system. I'm afraid I might have fried the last battery. With the solid state regulator (after market) what should it be charging at. The book says, I think, 15 volts. I'm hitting 17 when revved. Is that too high?
Jul 11, 2017 18:06:19 GMT -5
gggGary: Yes 17 volts is too high, about 14 volts is max, sounds like you don't have the right regulator or it's wired wrong.
Jul 13, 2017 6:54:33 GMT -5
dean: Just saying Hello, new member who is going to fix up a 79 XS650 that has seen its better days. I will definitely have lots of questions coming up.
Jun 23, 2018 16:45:32 GMT -5
tt650: Trying to breathe life into a 1980 that's been stored (indoors) for 25 yrs. Air filters are dry rotted. Have cleaned carbs but she only runs briefly on choke then stops. Need jet setting info and other ideas that might help her idle and rev.
Jul 3, 2018 19:15:19 GMT -5
trix13: Hey everyone! New to the forum and am fighting those gremlins!! New charging system, ignition switch, coil and fuse box. Resistance is higher than normal on the ignition pick up so I'm trying to find one. No such luck yet.
Aug 16, 2018 8:50:48 GMT -5
trix13: Also, even though all of my connections are clean, I cannot seem to find out why , when at higher rpms, I hit the signals and the rpms pulse with the signals...hahah. same with the brake light. I appreciate all input!!
Aug 16, 2018 8:55:08 GMT -5
bob99: how do I post a question. I am new to the forum
Jun 6, 2019 10:52:10 GMT -5
adlpc: Hello all! Been enjoying your edifying posts and discussions - and as a fan of the XS650 since my early teenage years happy that I now own a 1980 Special which I plan to turn into a vintage half faired racer. Thank you all for being here!
Oct 1, 2019 0:58:56 GMT -5
jimothyj: Hello everyone, I just joined & wish would have known about this site in 2014 when I brought my 1974 TX650A back from the grave. I have spent a good deal of $$ and alot of time on it. Just painted it and working on electrical, I will post pics soon,
Apr 10, 2021 2:14:13 GMT -5
louisvan: trix13 - I had a problem with my 1975 SX650. When I got to highway speeds, the engine lost power. The problem was in the connectors. At a certain vibration and the wind pushing on the wiring loom, the connector lost continuity. A bad crimp to the wire.
May 20, 2021 1:19:09 GMT -5
deadlykittin: Hey guys,. i have a 82 xs650 special, super new rider, with almost no knowledge on bikes. So was just riding it, getting used to the clutch and all that. But i was noticed its really hard to get the bike to start, using electric start. And the kick pump---
Aug 4, 2022 17:09:55 GMT -5
deadlykittin: loses compression after the first kick. Ontop of that, i noticed it 1, wont go into neutral when sitting still. and now it dies after getting it started in neutral and going into gear
Aug 4, 2022 17:11:01 GMT -5
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Sept 24, 2023 5:07:09 GMT -5