Manky's XS650 Yamaha

[Manky Monkey]

  Ha ha ha! Glad it's not just me who does stuff like that! Nope, no rags.
'ello Mr Toad, not heard from you in a while mate. Twin lead coil -both plugs hooked up to the same coil. So wouldn't make a difference would it?

[Dslam]

Hi Andy,
What ign system you using. I presume a boyer? If I remember rightly you set it up so the white dot lines up in the hole on full advance and the box retards the ign towards tdc at low revs so you may have set it to fire before the inlet valve has shut hence the spit back. Recheck the instructions for the ignition system you have regard advance.
Take the plugs out and shove your thumb over one plug hole and check for compression (stuck rings or valve not closing) do the same the other side, assuming all is ok on the compression front, drop half a teaspoon of fuel down each bore, plugs back in and kick it over, if it spits back out of the carb then the timing is out.

[Manky Monkey]

Yup, Boyer. White dot showing in the hole in the back plate.
Definitely got compression.
Looks like some fuel down the bores tomorrow then. 

[Manky Monkey]

So. Both pistons travel up & down together.
Both spark plugs are fed by the same coil.
So the 2 plugs fire at the same time, ("wasted spark").
It's just the camshaft set-up, opening the inlet valves at the appropriate times, that feeds the fuel/air mix in to one chamber then the other, that makes it fire on one cylinder then the other.

That means there's only one Top Dead Centre & one points opening, (or in my case electronic pick-up), firing position.
If I put fuel down both bores it'll presumably fire on both cylinders at the same time? But one will have the exhaust valve open when the other's shut?
If it fires like that, where do I go from there? At the moment the carb float bowls are flooding, (remember they're old mark 1 Amal British carbs) so there's definitely fuel flowing from the tank to the carbs.
If I'm getting a spark on both cylinders & it fires with fuel squirted down the cylinder, the carbs aren't feeding the cylinders? Lift the needles in the slides? Just trying to think ahead. I'm not a mechanic & although I've had half a dozen XSs over the years, I have a terrible memory & really can't remember the set-up from previous bikes.

[Olds]

Not having chokes will not help. Are the pilot jets and the two drillngs each carb clear ? Did you wash out the tank before filling with fuel ? Though the filters should stop gunk getting to the jets. Have you set the slide stops ?

[Dslam]

I am pretty sure you may have set the timing to fire at TDC. It should be X degrees before TDC.

http://www.650motorcycles.com/BoyerMicroPower.html

Check this out to make sure you have timed to the correct marks.

[Manky Monkey]

You're right Andy, it's set to the "F" mark. Just heading to the barn now, so will make that my first job.
Tell me about slide stops Dave.

[Olds]

Slide stop or idle adjustment screw. Not the mixture adjuster. 1 1/2 to 2 turns in after it starts to lift the slide.

[Manky Monkey]

O.K, first job was to re-set the timing to suit the Boyer electronic ignition. As Andy surmised, I had it set to the Haynes manual directions for points ignition. It's now at the Full Advanced setting.

The link Andy posted says:
Set the rotor TDC mark (#4) to line up with the line at # 3 in the photo. Number 3 is the total lead mark where the timing is set. All you do is turn the crank with a 17mm socket to line up #3 and #4 above, and set the white dot on either magnet in the timing index hole and that's it. Number 2 was used for setting the points, and number 1 indicates when the pistons are at top dead centre.

[Manky Monkey]

So here's mine.

[Manky Monkey]

Result: it fired -hurrah! Then it died -boo.

Spent the rest of the afternoon fiddling with it, but have reached the point where I'm going round in circles & confusing myself as to whether the changes I make are making it better or worse. The ignition seems O.K now. Think it's down to carburation -yeah, I know, self inflicted problems.

The floats were sticking & causing the carbs to flood. Took the float bowls off & there was a small amount of crud in the bottom of them -I rinsed the tank with a small amount of petrol before fitting. It's brand new, but has been sitting in a workshop full of grinding dust for quite a while. There's an inline filter on each fuel line. Each carb is fed by a separate fuel tap from the tank. No linking pipe between the float bowls, but there's a balance pipe between the 2 inlet manifolds. So I wiped out the bowls & cleaned the floats & float valves. That seemed to cure the flooding, so presumably just sticky valves through lack of use.

Put a gallon of fuel in the tank. The mixture screws are set to 1 1/2 turns out from the fully in position. The breather holes are clear Dave & the idle screws are set to 1 1/2 turns in after I could feel movement in the slides as I opened the throttle. A previous owner of the carbs has punched a couple of notches into the ali bodies, which seem to line up with the screw slots in these positions, so I guess they're more or less right.

After an awful lot of kicking, (what muppet decided to remove the electric start!), I had it running 3 or 4 times during the afternoon, but only for a few seconds before it died. The longest run was the first time, after I'd squirted fuel directly into the plug holes. Winding the mixture screws in or out didn't seem to make much difference. Blipping the throttle didn't seem to keep it running & winding the throttle cable adjusters in or out didn't seem to make any difference either. I've had a problem with fuel feed on a Triumph in the past which turned out to be my fault for blocking the fuel cap vent hole with chrome cleaner. So I left the cap off to see if it would keep running. No difference.

The carb tickler buttons are working, with fuel running out of the overflow holes underneath them when they're pushed down. So the float bowls are filling, but I'm guessing not enough fuel/air mix is reaching the cylinders?

So where do I go from here? The throttle slide needles have 3 positions & are currently in the middle one. Should I lift them up to the high position? Would that allow more fuel in? As stated earlier, I'm running the needle & jet sizes supplied by the guy who cast the inlet manifolds. They're the sizes he runs on his own XS, so should be about right. 

 

[Clive]

Can't quite see in the pic, but is there a gasket at the other end of the inlet, where it goes into the cylinder head? Could be air getting in from there weakening the mixture too much?

[Manky Monkey]

Yeah, there's a thick composite gasket at the carb end & a thinner one at the cylinder head end I think Clive -it was a long time ago that I fitted the manifolds. I can check if they're leaking , but pretty sure they're sealed.
Suffered a savage kickback at one point, which really bruised the muscle in my thigh, so I'm limping slightly now! When I was younger, this would be the point where I'd spend days fighting it, before giving up & selling it for a fraction of what it's cost me. Now I'll keep calm & persevere. It's curable, but I need advice on just what needs curing. I'm on holiday this week & have decided to take a day off tomorrow & enjoy the sunshine -taking the oft' repeated advice to walk away from it for a little while.
On the plus side, when it runs, it sounds like an old Brit twin -which is more or less what it is, (the XS was originally a BSA design). The pipes are loudish, but not excessive, (XS ive?). No nasty mechanical noises so hopefully all's well engine wise. Each time it's started, it's done so fairly easily -no Harley style, massive lunge on the kickstart required. Hopefully, once the carburation's sorted out -if that's what the problem is -it should be a nice, blat around the country lanes on sunny days type machine.

Any thoughts or suggestions?

[Manky Monkey]

Fuzzy photos, just to prove Nathan's wiring works. The lights are wired so that the side light & tail light are on all the time because I haven't got an on/off switch on the bars, just a high/low beam one. There are two key positions, the first is ignition + sidelight, then ignition + low beam. This is low beam. Indicators are LEDs & seem to flash at the right speed, (when bulbs are replaced with LEDs they often flash too fast, but can be fixed by fitting inline resistors). You can see the LED number plate light under the lip of the mudguard here as well. Horn works fine too but no photo of that 

[the coppersmith]

I'll probably get laughed at Andy, but ! do you own a blowlamp? warm up the engine gently, warm up the plugs 'til hot (ouch) screw them in and try, often once running they settle down. Bit of a set back, if it was easy you'd lose interest 
(PS if you do decide to sell it on at a fraction of the price, I'm yur man  )