Thriller's (alfalfa's) 1973 Yamaha YB125

[alfalfa]

I recently got the urge to get a bike back in the garage and start enjoying that small bike life again. Was browsing up a storm on FB marketplace, trademe etc but everything seemed to be either too fucked, moonbeams or in the South Island. Sitting on the couch one night with the Mrs I got the notification that a 73' YB125 was closing soon. Had a few bids already but was still only $550 or so. Chucked a bid on, few back and forths with someones autobid "just to see how high it might go" and I ended up winning it for $590. Whoops . Supposedly a runner, but has been sitting for a while and the key is lost. Has been registered previously but lapsed.

Got in touch with old mate, bike was in Wellington so organised to go down easter friday and pick it up. Borrowed @anglia4's trailer and he decided to come along for the trip too, legend. Early morning hoon down to Welly, bike on the trailer, back to NP by mid afternoon.

 

Got it into the garage and started taking it apart to see what is lurking underneath.

Lots of surface rust

Grimey build up on autolube pump. Carb looks pretty good inside though?

Managed to get the exhaust header off without much trouble. Rings and piston looking good to me so I probably wont bother taking the head or jug off for now.

Things to do:

I have taken the ignition off and given it to the local locksmith to see if he can cut a new key that fits. The petrol cap has a lock on it too so I haven't been able to get inside that yet to see what state its in. I've taken the petcock off and there's no fuel in there so hopefully no holes. My big idea is that the fuel cap and steering lock and helmet lock were all keyed alike to the ignition but just used 2/3 of the 4 pins (or whatever) so if I can get the ignition key cut then I don't need to bang a screwdriver in and wreck the petrol cap. Worst case there seems to be NOS ignitions with keys and petrol caps on ebay indonesia for acceptable $$ so I will get one of them if no bueno with the locksmith. Fingers crossed he can because I don't really want to wait for Garuda Airmail to be able to ride it properly! 

I've got a new battery coming too. This model is electric start too which is lush/not in the spirit of old 2T at all .

Questions for the hive mind: unsure what I should do (if anything) about the rusty bits. My initial thinking was to do a quick wire brush of all the loose stuff that is out of sight on the frame under the tank, seat etc and then brush on some rust converter to try and slow down/stop whatever is left. Mixed reviews on effectiveness of that stuff though. Would that be worth it or a waste of effort? Better off hitting it with a wire wheel to properly get rid of it then spraycan/brush on some rustkill primer and closest colour matching topcoat?

[alfalfa]

Also, here's something weird. When it was last registered, it was as a "1999 YB125 Autolube" 

1999 is also the year that it was first registered (I think?) based on the little 12/99 on the registration tag.

It's definitely 'in the system' so I'm hoping re-reg shouldn't be too hard. It's got a vin tag and new font white plate.

Has anyone had a go at correcting an incorrect model year like this before? I've heard some chat that a while ago bikes used just be tagged with the year they were first registered rather than their manufacture year? I definitely want to get this on vintage reg if possible!

[tortron]

"When a vehicle's details are recorded incorrectly on the Motor Vehicle Register (MVR), these can be corrected by sending an Application to Change Vehicle Details (form MR16, available at any New Zealand Transport Agency agent) to the NZTA Most MR16 forms need to be sent with supporting documentation to prove that the information recorded on the MVR is incorrect i.e. if the vehicle model is recorded incorrectly we would require documents from the manufacturer to prove this before a change would be made."

[tortron]

You could probably show the frame number and supporting info from yamaha regarding deciphering year based on frame number. And of course that the vin is not tampered with/matches the frame number 

[peteretep]

for rust, this shit is seriously amazing, I used it on the inside of my new fuel tank and it came out amazing. also, its reusable

 

https://www.crc.co.nz/EvapoRust-Ready-to-Use/6895-3df38418-aaf1-46f9-abe2-534e825f0fae/

[alfalfa]

So I’ve been pottering away on this since rolling it into the garage. I'm rubbish at taking picture while working on stuff so this is mostly words sorry (not sorry).

Locksmith took aaaages to cut a new key so I couldn’t do much on the electrics/starting/running side while I was waiting for that to happen. In the meantime I pulled the carb off, stripped and cleaned it and reassembled. There was a bunch of varnish and crud in the bowl so gave that a good scrub out. Gasket still looked good so reused it. The main jet currently in it is a #190 which is 2 sizes smaller than the factory spec #210. I think I’ll get some extra jets to bring it back to stock so I can tune from there rather than have it be (potentially) too lean.

New AGM battery arrived. Connected up and slotted in nicely.

All of the control cables were either extremely stiff or completely seized up so I squirted some lube down them and worked back and forth until they were smooth(er). If these go bad again I'll look to replace.

Sprayed/brushed some phosphoric acid rust converter gel stuff on the header pipe and muffler which actually worked pretty well. The chrome is quite pitted but not too worried about that at this stage.

Finally got the ignition and new key back so it was time to fire it up. Connected everything and put some premix in a syringe connected to the carb (fuel tank still locked shut) and she fired up 3rd kick! Was a bit rough at first but settled down to idle pretty nicely. Stoked as, so good to hear it ring-a-dinging away. All lights and signals work. Charging system is putting out 13.5v at idle which is a little bit below the 14.0v @2000rpm spec but no worries?

 

The 2T oil tank had a bit of rust inside and around the outside seams. I wire brushed and scotched of the loose stuff from the outside. The oil that was left in there had gone real gross and started to separate with some big globs of gross suspended. Sloshed some petrol around to try and dissolve it and it cleaned up ok. Still some crud on the mesh filter around the outlet so I got in there with a very long toothbrush and some more petrol and got it pretty clean. Poured in some evapo rust to deal to the rust spots and left it for a few days. Cleaned up really good, that stuff is magic. Also threw miscellaneous rusty fasteners and other gubbins in a jar with evaporust to clean them up. I cleaned up the autolube pump and had to add quite a lot of shim washers to get the idle stroke set correctly. Bled the air out from the supply hose and checked it was pumping oil through into the case. All good!

Then I looked at the petrol tank again. The new ignition key didn’t fit in the tank lock (boo) so I had a go at making a tension wrench and lock pick from some old wiper blade spring steel but obviously I’m rubbish at lock picking  as this didn’t work. Screwdriver time. Put one in the keyway and started turning it with a spanner and the whole cap twisted open :o. Turns out I’m also rubbish at checking things properly and the cap was unlocked the whole time but seized up just enough to not open easily by hand when I first checked. Good news though, it’s mint inside so quick rinse out and chucked it back on. The chrome side panels came up pretty well with some autosol and elbow grease. I will redo the white lettering on the Yamaha badges at some point too.

 

[anglia4]

LOL at being unlocked the whole time.

This is somehow seeming like the easiest project on Oldschool. Its nearly finished!

[alfalfa]

Yeah pretty funny, I was so confused at first when it just turned and opened with no loud cracking or popping noises!

It's not all plain sailing, stay tuned for the next update...

[alfalfa]

I put everything back together, splashed some oil and petrol around the various tanks and wheeled it out of the garage to go for a first ride. Wouldn’t start :haha:

Checked spark (ok), fuel (flowing freely through line from tank), pulled carb and checked jets (all clear, fuel in bowl). Put everything back on again.

Lots of kicking, coughed a couple of times, some backfires and eventually it fired up and idled for not very long before dying. More kicking and got it started again, turned up the idle speed screw so it wouldn’t die. Jumped on, rode up the driveway and down the street for a few hundred metres and of course it died when I slowed down to turn around and come back home. Absolutely would not fire this time so I had to do the push of shame home.

I suspected electrical problems (likely condenser?) as fuel is there, carb is clean and set to factory specs and the electrics are 50 years old. It looked like quite a bit of pitting on the points surfaces so maybe the condenser wasn’t condensing properly and it was arcing across the points gap instead? I sanded the points smooth and reset the gap.There is f-all info on the YB125 on the internet for parts numbers etc so for anyone from the future looking for a YB125 condenser, the RD250/350/400 part 1A0-81625-10 is close enough to be correct. Capacitance, size, mounting and spade connector is identical, just the lead is a few cm shorter but still fits ok without stretching and too tight.. I got one from eBay from a seller in France. New plug, new condenser, fingers crossed?

The muffler - header gasket was missing and the header/barrel gasket was pretty beat up. There was quite a bit of exhaust leaking out from the muffler joint. Again, nothing online that I could find for a “YB125 muffler gasket” and the part for its more common predecessor YA-6 is NLA everywhere. I did some measuring and trawling through other yamaha parts and the stock replacement for 70s XS500/XS650 371-14714-03 looks identical. These appear to be readily available which is nice. Order from PlenterNZ arrived with one of each, fitted the header pipe back on and tightened everything up.

The air cleaner foam has gone rank and started disintegrating. Again stock replacements don't exist online that I could find so rather than making the engine inhale chunks of foam I ordered a replacement sheet of filter foam and cut to size and glued together to fit the cleaner housing. Oiled up and reinstalled.

Everything back together and started up 3rd kick! Fiddled with the air screw and idle adjuster to get it sitting at 1200 rpm as per shop manual, checked with a cheap AliExpress hour meter/tacho. Its happy as.

Took it out for a decent ride around NP, went great. Brakes are quite rubbish but work, got up to 80kph on the flat without speedtuck. Neutral top gearbox is wack, I have to think about each shift but I'm sure I'll get used to it. Got props from an old lady walking her dog when I stopped for a photo "now that's a proper motorbike" 

Time for more riding to see what else breaks before I start the re-registration process.

[alfalfa]

I’ve been doing a bit of hooning recently, the weather and everything else has been lining up quite nicely. Goes hard (for what it is), and nothing major has broken or stopped working. On a big ride with @anglia4 @Itchybear and Bucket Barry we found a few kms of good gravel. The road tyres that came on it were fine but definitely left me wanting more. The forks also felt a bit shit. I’m not sure if this is because they just are (lol) or if they need some attention. I pulled them off and drained the oil out. Mmmm delicious smelly black fork oil.

The stanchions are mint which is great. I probably should have done seals at the same time but yolo will do them some other time. The service manual asks for SAE10W30. I had some 7.5W Motorex leftover from one of my mountainbikes so 165cc of in that went in each side. Found a steep speedbump and tried to do some jumps to give it a good test. Felt good, a noticeable improvement A+ would pest again.

 

In my quest for new tyres I discovered that 3.00-16 is not a common size and I had basically one (expensive!) option that was stocked locally. I emailed the NZ Shinko supplier and they told me if I want some SR241’s in 3.00-16 I would have to get my local store to order a minimum of 5, pay up front and wait 6 months for them to arrive. Thanks but no thanks. I got in touch with mxstore.com.au and they were more than happy to order a pair from their supplier and ship them express to NZ for free. The curse of rubbish NZ suppliers strikes again.

I fitted these myself - I’ve done plenty of MTB tyres but this was my first time on a motorbike. It’s a bit different with the long steel levers and not needing to worry so much about scratching or wrecking the steel rims. All went on ok, it’s much the same process just more aggressive. They look pretty good on there I reckon!

Took it out for a test hoon on some twisty roads close to home and did some skids in a gravel pit.

Now I just need to find a suitable rear rack or luggage carry system for some overnighters.

Bring on West-Pest ‘23!

[alfalfa]

Last ride ended with a few kilometres of state highway to get back into town after some twisties. I was all barred up from the prior hooning so once on the highway I just hit WOT and crouched down into a speed tuck. Coming up to a corner after a pretty long straight section I sat upright and rolled off the throttle to slow down and the little bugger nipped up! It started making a rank noise and rapidly dropping revs, lucky I was covering the clutch so whipped that in straight away and coasted to a stop. Gave it a few minutes to cool down and checked to see if it would turn over with the kickstart. Thankfully it had freed up so kicked it in the guts and rode home much more gingerly. Looking through the exhaust port and there is a definite gark on the piston that wasn’t there before. Guess I’m taking the head off after all…

[anglia4]

Bugger.

Hopefully nothing too nasty in there. 

[alfalfa]

Ok so I've got everything apart and am after some advice on next steps. 

Inlet side

Exhaust side

 

I can juuust feel those marks on the cylinder with a fingernail.

Hone cylinder, sand piston marks down and send it? New piston and rings? It's still factory size.

I've got some richer main jets coming. The current main is a #190 and the factory size in the manual is a #210. I had that on the list to change but hadn't quite gotten around to ordering it 

I also need to find a timing dial gauge to check that's in spec. On the last ride I'm sure I heard a rattle at higher rpms in 1st gear that was different to the normal 50 year old 2 stroke noises. Maybe detonating? I haven't touched the timing at all though but I guess it could be,

There are some timing gauges on aliexpress for pretty cheap ($60 or so) - has anyone had any experience with them?   https://www.aliexpress.com/item/1005004098969689.htm

[Goat]

That doesnt look too bad at all,

I'd just hone the cylinder and biff some new rings at it. If you can get a new piston for not much more, than do that too. I've seen alot worse running fine.

I'd say alot of 2 strokes would look like that if you pulled them down. 

I've heat seized a few bikes before, and just kept riding them with no problems after they had cooled down.
High RPM and closed throttle positions are not ideal for 2 strokes. Best to feather throttle down etc. But yeah, long periods of WOT are also a bit scary. Could be a bit lean and getting a bit hot, but then again, how much WOT are you intending to do. 

Lean condition could be crank seals too? 

[GregT]

I'd just replace rings as they look like they've lost tension. Hone bore and wet and dry on piston. Do a crosshatch pattern on the piston skirts as it helps retain oil. Also take the carbon buildup off the top of the exhaust port.

Top of piston does look a tad lean. Oil your filter element which will richen it up quite a bit. Timing you should be able to check with a strobe light.

[alfalfa]

Cool cool thanks chaps, that's kinda what I was thinking. New piston and rings are only a little bit more expensive than a ring set on ebay so I'll have a look again if there are any better prices otherwise go for that.

Aware of the closed throttle high rpm issues - I always try to roll off slowly and not close all the way. I had also adjusted the autolube pump stroke to deliver a bit more oil than stock at the closed throttle position to keep a bit of extra lube flowing through when it's in that condition.

I might try and make a leakdown tester to check seals.

38 minutes ago, GregT said:

Top of piston does look a tad lean. Oil your filter element which will richen it up quite a bit. Timing you should be able to check with a strobe light.

I had scraped quite a bit of carbon off the top of the piston before I took those photos - it was fairly dark when it came out.

Will also get in and clean out that port before putting it back together.

[alfalfa]

So now that I had the top end apart I figured I might as well get some of the bits tidied up. Took the head, barrel and air cleaner cover pieces to the local vapour blaster to get cleaned up. He did a great job and they came back looking super tidy. My first time having alloy parts vapour blasted and I was really impressed, the finish is ideal for half-assed restos like this where a super shiny or polished finish would look out of place. 

I took the barrel up to the local kart shop and they spun it up on the hone and cleaned up all the garks. I tidied up the piston myself with sandpaper and got some nice crosshatching back on the skirt so hopefully it holds a bit more of an oil film. Put it all back together with a set of new rings. I also increases the main jet size back to a factory #210 from the #190 that was in there. I have a #200 that I might test out if it's a bit rich but it will probably stay in there forever...

Followed a progressive warm up engine break-in schedule from somewhere online and it seems to be running mint. All ready for 600km of mixed gravel as a shakedown run .

Next on the list was to figure out how I'm gonna carry extra fuel, spares and gear etc on the rapidly approaching Taranaki Tunnel Hunt. I had a blue plastic crate lying around that seemed like a good idea so I fiddled with some cardboard-aided-design to make a rack for it to mount on. Final version feels fairly solid but I'm only like 60% confident it will last the whole ride . The rack is ok but the crate is quite flexy...

 

[GregT]

Mate used to carry a dog in one of those crates on his bike. Make it weatherproof with a cover and you're set.

[Berlina96]

I have one the same, what road speed are you able to maintain?

[alfalfa]

@Berlina96 It's comfortable at 80-85 indicated. I can get it to 95 km/h on the flat if I tuck a bit and really wring its neck.

I think I'm still one size too rich on the main jet as it would previously get to 100 indicated before it seized.

Those speeds are all straight off the speedo - I haven't checked accuracy with a GPS yet.