The blue '76

If you don't know the maintenance history on your points (when they were installed), it's best you get some back-up sets. The points are a wear item and should be replaced about every 10 to 15K miles. In that time, they open and close literally millions of times and the spring steel strap that snaps them closed can start to weaken. Even if the points faces still look good (not pitted), that spring strap could still be getting weak. It's good to see you are using a dwell meter. That's the most accurate way to set the points gaps and the only accurate way to set used points. I shoot for the lower end of the spec range on the dwell meter. This gives the largest still in-spec gap.

Besides guarding against over-advancing and pinging, there's another benefit to retarding the timing a couple of degrees. I think the bike runs better and stronger at high speeds and RPMs like that. As you probably noticed from just setting it, there's a range provided to set the idle timing in. The spec is 13°-17° BTDC. The actual "F" mark is in the middle of that range at 15° BTDC. I set my timing over around the right slash mark, or at about 12° or 13° BTDC.

Many thanks 5twins, I will have a closer look at the points and timing, and will follow your advice on the idle setting. I did get a spare set of points just in case, I am somewhat used to working with points ignitions from having worked a lot on older cars. I also know the benefits of converting to electronic can bring, but I would like to see if I can keep it running well, just with the original parts.

That said, I also just ordered a Stebel horn, from their USA 'scratch and dent sale' website page - about $12 including shipping, seemed like a very good deal.
It may seem odd that retarded timing runs better but if you learn the model history of these bikes, you'll discover we're really not running the timing retarded at all. When these came out, they had a slightly different timing spec. It was 10°-15° for idle and 38° for full advance. So, retarding the new spec by a couple of degrees puts you smack dab in the middle of the old spec, the spec this motor was originally designed to use. When Yamaha updated it, they said it was to smooth out the low speed running and idle, which it does, but I think it may also kill off a little power. The early bikes did make a few more HP and , granted, there were a different cam and pistons at play here, but the timing spec may also have had something to do with it.
It may seem odd that retarded timing runs better.....
If we look back to older car distributors, it makes sense. They had a centrifugal advance (like our XS's) and a vacuum advance. When you put your foot into it hard, manifold pressure increased or...vacuum dropped if you will. That drop in vacuum retarded the ignition. Typically, low speed mixtures were leaner and had a slower flame front. That required more advance. Higher power settings typically were richer and have a faster flame front... requiring less advance.

On the balance, being retarded under load is much more important than being advanced at low power settings. Pistons hole at high power... not low.

I've often wondered if it would be worth the bother to try and adapt a vacuum advance to an XS.....
Yesterday I replaced three light bulbs in the gauges that had failed, only one was still working. A fiddly job but now the gauges emit a cozy-looking light and I can see how fast I'm going again.

Today or tomorrow I just may tackle the carbs. I ordered rebuild kits from MikesXs that came in (Made in Japan so hopefully good quality) and also the NOS horn arrived -much beefier than the (what looks like an after market) horn that's on there now, and I can just barely hear myself.

The engine runs very good, but it does emit a pretty strong 'old car smell' so after checking ignition, replacing the plugs with Iridium ones (7, I may swap today with 6-es since I only ride in the city) and valve clearances, I think the carbs deserve some attention. I do still need to check the spark plug wires and condensors/coils and see if the engine uses any oil, although there's no hint of blue smoke and the engine supposedly has onky 5K miles on it.

Other things I may get to this weekend are replacing the horn button, narrowing the handlebars a bit, replacing the clutch cable and some polishing.
Beware of the jet sizes included in those rebuild kits, they are often incorrect. The '76-'77 kits in particular often include the larger jet sizes used in the '78-'79 carb sets (#27.5 pilots, #135 mains), not the correct '76-'77 carb set sizes (#25 pilot, #122.5 main). The kits may also contain a generic needle. Don't use that either. There's only one o-ring in your carbs, on the needle jet, but the kits don't include it. It may need replacing though. Check to see if the needle jet is a snug fit into the carb body. If it's loose, the o-ring has perished. A 1mm x 4mm size can be used.
You guys know everything! To my rescue again.

I checked the kit and sure enough it has the larger jets. Oh well. I did also order those tiny o-rings so I should be ok on those. If the mileage (5,000) is correct, which I believe it is, then the needles and jets should still be fine anyway, but the o-rings maybe not. Plus there could be crud in the carbs as there was a bit in the petcocks. So I plan on going ahead and taking the carbs apart, clean, replace the o-rings and do a general inspection, I hope the rubber manifolds and the slide diaphragms are still ok.

Earlier today I did swap out the plugs for the '6' ones. I also replaced the header and silencer gaskets on the righg exhaust, since there was some leakage. The bike seems to run a bit stronger now and also smells less. I spent about an hour tooling around LA running errands, it was great (and HOT today, felt like mid-eighties). On my last stop, a grocery store, an older gentleman started talking to me about 'that old Yamaha', he spotted me on the road and followed me into the store, just to chat.

The left '7 iridium' plug was not looking that great when I swapped it for the '6' one , a bit sooty, while the right one was nice and grey-ish. So I do suspect the (left) carb, although I suppose it could still also be the condensor, wire, or coil. Those are still on the to-check list. Next weekend, when I should have my new master brake cylinder and progressive fork springs in. It keeps getting better and better.
On your forks, adding a bit more oil helps. I use the 6 inches down method. To dothe6 inch down, remove the fork caps, let the forks totally collapse
Use a piece of clear tubing. Put a zip tie snuggly o the tubing. Slide the zip tie so it is 6 inches from one end. Pour a few extra ounces of oil into fork.
Slide the six inch end of tubing down into the fork. Suck on the tubing, this will draw the oil above six inches down out. You won't draw any more than the six inches down.
If you have a vacuum tool you can use that to. Oil don't taste to good.
This extra oil leaves a smaller air space above the oil. this decreases the fork dive on braking.
On the front brake, the stock mater cylinder was a 16 mm bore size. Using one from a later bike with a 14 mm bore size will greatly improve your brake. It won't feel quite as wooden. It will feel much stronger.
I don't know why the '76-'77 rebuild kits are like that, they've been that way pretty much forever, lol. Someone, or maybe a bunch of someones, needs to tell the kit maker about it. But, over the last 30 or 40 years, I'm sure someone has. Maybe the maker just doesn't care.
Yesterday I finally got around to replacing the clutch, tach and speedo cables with new ones from Motion Pro. The clutch was the most pressing, as the original cable required so much force that, after just 7 miles of LA city streets commuting, I typically would have enough. After lubing and installing the new cable, cleaning and greasing the 'pivot-widget' and the first of the two through-block push rods (that one had a LOT of gunk built up) I am pleased to report that the clutch is now quite do-able. Still heavy, but just not as heavy as before. Also it seems that there's more clutch 'action', before it felt as if half my effort went into just stretching the inner cable rather than actually moving the clutch. So now, for example, it's easier to get the bike into neutral when standing at a light.
I also lubed the throttle cable which didn't seem to really need it, but now is as light as a feather to move. All in all the bike is now that much easier, literally, to ride. Next job is to change the oil and filters, and the fork springs. Maybe next weekend.
Yes, keeping the cables well lubed, especially the clutch cable, is very important. I try to lube my clutch cable once a season. I combine that with cleaning out under that left side cover and re-greasing the worm assembly.
Thanks gggGary, I did change the cable routing somewhat from the factory schematic which helped as well, but now I see there's more to be done there. I know from experience the routing can make a big difference.
The lever has a bronze (or copper) bushing in there already, and seemed to be in good shape (this bike only has 5,000 original miles on it). Will keep at it but am already very pleased with the result so far.
Yes, keep the lever pivot greased as well. Every little bit helps. I find plain motor oil works better at lubing the cables than that spray cable lube. That spray stuff may be easy to use but I don't think it lasts very long.
Well I had a challenge yesterday with the carburetors.
Last week, when I replaced the clutch cable, I had to remove the tank and to do that, of course I had to undo the fuel hoses to the petcocks. Those fuel hoses were beefy aftermarkets and they had hardened quite a bit over the years. When I went to re-attach the right one to the petcock, I struggled quite a bit to get it on, and in the process, I was concerned some old rubber pieces might have gotten into the fuel hose. Nothing bad happened during my test drive though, so I figured all was good.
Then, one day during the week, I left for work (at 5:30 AM, nice and quiet on the LA roads) and after about a mile, the engine started to hesitate badly. I only made it back home with the choke pulled out. I figured I was right after all, and debris from the hose had gotten into the carburetor.
Luckily, the new Yamaha fuel hose I had ordered with Partzilla had finally arrived, so yesterday I set to finally taking off the carburetors, figuring I would test the slide diaphragms, given them a good cleaning and replace some of the parts from the rebuild kits I had gotten from MikesXS a while back. I studied the carb how-to here on the site.
So I did find the two small pieces of old rubber in the right carburetor. The slide diaphragms were in A-ok shape, fortunately. With the bowls off, I figured the only pieces I would replace were the ' valves' - the widgets that close off the fuel suplly when ordered to do so by the floats. Since the bike has only 5,300 miles on it, I am assuming that the needles, springs, jets and everything else that wears, should all be as good as new still. There was no dirt or varnish in the float bowls and I decided not to take off the side covers and leave well enoug alone.
One of the bowl gaskets I replaced, the other one was still in good shape so I left that one in place. The new gasket was quite a bit thinner than the old one but I figured that would not make any noticeable difference. I re-assembled the whole lot, with the new fuel hoses, which went ok. I did get very dirty hands so I decided that, next time, I would make sure to wear some of those latex/nitrile whatever gloves.
I forgot to mention that a previous owner / their mechanic had at some point put 1 inch sections of rubber hose into the breather pipes on the cylinder head, thereby restricting the unburnt air/fuel mixture flow back into the air boxes and back into the engine. I knew these were not stock, as one was longer than the other and they were sort of raggedy-cut. I imagine this was done as a 'tuning' measure, back in the day? The most interesting part about this discovery though, was that one of the hoses had gone soft and had swelled up so much over time (from those unburnt fumes no doubt) that I was barely able to blow any air through it! I had noticed the bike would smell a bit when sitting at a traffic light for example, like an old Beetle without pollution control, and now I was hoping that by removing the blockage, the engine would ' breathe' better and the smell might get less.

So on to the test ride. Idle was greatly improved, super smooth. It was good before, but now clearly better. However, on the road I had a big problem: anything over 3,500 RPMs the bike would hesitate very badly, and refuse to rev much higher. It ran awful.
Oh boy, what have I done?

So this morning, I took everything apart again (went a LOT quicker this second time), and I decided to do two things: (1) swap the old valves I had saved back in, and (2) replace the one old gasket with the new one I still had. I had read the float bowls had to be at the same height, and the slightly thicker old gasket would interfere with that. Although I could not imagine the half millimiter difference would have that much of an impact, I figured that, and the new valves, were the only things I had changed, so that was all I could come up with to try and remedy this newly created problem. I measured the float height with the new valves (24 mm), and then with the old valves re-installed (23mm). Both within spec for these 38s (24 +/- 1 mm).

Everything back together, my hopes were not high, but onto the test ride and boy, what an improvement! The hesitation was completely gone, and the enginge pulled a lot stronger through the entire rev range than before, when it would hit just a bit of a flat spot, around 4,000 RPMs. Now it pulls evenly and strongly, all the way to 7,000. It's a lot faster now, really noticeable.

So moral of the story, for me, is that either the half millimeter difference between the old and new gasket, OR the new valves were not up to the task. Or perhaps I had somehow goofed up on one of the many other small steps in putting things back together, I don't know, but I am not touching the carbs again until I really, really have to.
The rubber restriction plugs in the breather housing outlet tubes was actually stock starting about with your model. But maybe someone lost one or both of yours and made substitutes out of rubber that wasn't compatible. I've had mine in there for many years and they are probably the originals, which means they've been in there since '78, and they've never deformed. Running without them may allow excess oil vapor to get sucked into the airboxes. Unfortunately, you can't get replacement restriction plugs, but all is not lost. In 1980, the breather box was redesigned with a single outlet and had the smaller opening cast right into it. This later model breather will bolt right on your motor .....


The float setting spec for your '76 carbs is actually 25mm ± 1mm, not 24mm. Matching float bowl gaskets is a good idea. I'd keep an eye on eBay for some N.O.S. originals. They come up at a good price from time to time. They're still available from Yamaha but they're a bit spendy, too rich for me, lol ......
I recently had been away on business for 3 weeks and upon return found the clutch almost impossible to operate. This was with a brand new Motionpro cable, properly lubed (Motionpro luber and lube). After some 'exercise' and re-lubing it was ok again, but I was not happy about this. So I decided to look for a NOS nylon worm-actuator-thing and a NOS Yamaha cable. Found both, installed them today and now the clutch is really quite easy to operate, never been better, almost as light as my 2018 little 310R BMW. I did have to lube the cable to get it to be this light so I hope it will last for at least 6 months before requiring re-lubing.
And last weekend I finally got around to changing the oil and both filters. She seems to leak a bit now, maybe the oil I got is a bit thinner. I put in new gaskets but perhaps I need to add some permatex-type sealant, will have to see where it's coming from.
Anyway she purrs like a kitten, so much fun to ride. I actually like the mild vibration.
By the way I have noticed that everything I do on the bike takes twice as long as on my other bikes. Because I work in the street, people passing by keep wanting to chat about this wonderful classic machine and share their bike stories. A bonus.