The Trials of the Vintage Motorcycle Restorer - 2nd Edition.

[Tinkicker]

Well bike has been sat two days with a drip tray underneath. There is a thumbnail sized pool of blue oil in it...

Pump is still leaking.. Not much, but a single drip a day is too much. I hate oil leaks.

Plan B. I should have done this first. It is how I would have approached it if I saw the crack before putting it back together.
I have knocked all the epoxy putty off and removed the pump. It will be taken to work, the inners removed and the casing thoroughly degreased.
I have a bottle of thin viscosity superglue in my toolbox (useful for sticking flaps of skin back down when I lose a battle with a big bit of steel). I aim to rid the hairline crack of any trace of oil and fill it with superglue to seal it. I will then use a thin skin of epoxy putty or maybe even clearcoat applied by brush over the top to protect the cya from any future moisture.

If that fails, I will have to buy a secondhand pump for the casing and fit my innards into it.

It appears we have reached that depressing point in the build. The small stuff.
Rarely do the big lumps give problems. You fly through those whistling a merry tune.
It is the small stuff.
The carb, the coil, various small rubber parts that are after close scrutiny, perishing and need replacing. Not forgetting the bodges and feckups by previous owners. That special rubber grommet, spacer and bolt that was lost 40 years ago and replaced by a rusty roof bolt, square nut and repair washer sourced from a coffee can full of rusty widgets sat on a 1970s garage shelf.

That carb with the stripped thread. The replacement carb that will in all probability piss fuel out of the overflow on the first attempt to fill it.
The coil with the hard as a rock HT lead. The cheap unbranded points. New electrical gremlins that were working before.. The oil pump... The wrongly described and supplied aftermarket cables. Parts no longer available mean expensive gambles have to be taken sourcing genuine parts from other models that look the same.



At least nothing has been found to have been secured by woodscrews or bent nails on this build.. Yet.

We will overcome...

 

[Tinkicker]

Crack duly filled with several coats of superglue till it stopped wicking in to the crack, excess wire brushed off outside of pump and about a 2mm layer of 2 part epoxy resin applied over crack to stabilise it and protect the cyo from moisture.

Pump refitted and bled. 48 hours later and we have no sign of leaks. I will not be comfortable with it though until it has survived several hours of running.

Next is replacing the cheap points with the Daiichi set and trying the 175 coil to see if we get a spark. Then I will fit the tank and open the fuel tap waiting for the gusher out of the carb overflow.

The most distressing part at the moment is the fact that the blob of body snot on the rear fender keeps waving and shouting"Yoohoo, I am still here, I am still waiting to be sanded down and reshaped. I am not going anywhere. You cannot ignore me forever".

 

[Tinkicker]

Fitted the 175 coil to the bike and flicked it with current from battery positive. We have spark and a nice tick noise when the plug fires. Happy with that.
Reordered the exact same coil again for the 175. Happy with its performance on the 175.

Plugged in the black and white to the coil, ignition on and kicked it over. No spark.

Unplugged main multiplug and ran a wire directly from the black stator wire to the coil. Kicked it over. Nothing.
Almost certainly the problem is down in the stator.

Double checked the ignition and kill switches by checking connectivity across the black and white wire and ground.

Engine multiplug disconnected, ignition on, killswitch to run. No connectivity between black/ white and ground.

Ignition off or ignition on and killswitch to stop and we have connectivity. It is not the switches.

Ignition on, killswitch to run, multiplug reconnected. Connectivity to ground. I think the cheapo points are shorting to ground. I guess they did not enjoy their little bath in the sink.

Before I start to fit the new Daiichi points and time the spark, I need a good tidy up. It is like a hoarders junk pile in there. I hate it when you have to concentrate more on stuff going on around you than the job you are trying to do.

 

[Tinkicker]

New points checked against old. A bit of research gleaned a bit of info that despite having different part numbers, the points were interchangeable between the DT100 and the FS1. A bit more gleaned the info that the FS1 part number fitted everything from the TY80 to the TY175. We have the same points between many models, often with different part numbers.
Armed with a few part numbers, I went ferreting about on ebay. I had a hit on a set of Daiichi points listed for a Honda C70 step through but with a Yam part number on the box.
Likely because a step thru is far less "sexy" than a two stroke enduro, and not being a likely candidate for a restoration, they had not had the NOS " premium " added on to the price.
So there you have it, more leads to go on.

£5.39 delivered to my door vs £12 for a set of unspecified make from aftermarket. Just because the pic showed points with a Daiichi trademark, the description did not specify the make they would send. Probably chinese tat like the ones I removed.


Honda C70 and DT100 points are the same. It pays to do ones homework. I love ferreting around. It is part of the fun.
cheap on top, Daiichi on bottom. I appear to have clipped the bottom of the pic. The heel was identical in size and angle.

Cleaned the preservative off the point faces, tested them for good contact, fitted them and did my due diligence testing before setting everything up. Hmm. Black wire was grounded whether points were open or closed. Disconnect condenser wire and put probe in its place. Points breaking contact.

The condenser has an internal short. I snipped the wires to test. It does not hold a charge.

So there we have it. Bad cap. It explains the odd readings I was getting.

 

[Tinkicker]

Rattling around the house with three dogs. It is home alone weekend.

The missus has gone to London for the weekend with her coven of witches to see Mama Mia in the west end. I pity London... A full coach of cackling women descending on it.

Anyhows, I digress. It seems like a two step forward and two step back kind of day.

A new Daiichi cap has been ordered and the ignition is on hold.

Meanwhile, the genuine Yam RT100 clutch cable has arrived. It fitted like a glove, unlike the chinese garbage the aftermarket boys tried to sell me.

Confirmed. RT100 clutch cable. Part Number 3M1-26335-10 is a direct replacement for the marked as no longer available DT100D, 1T9 cable that fits DT100 1977 - 1983.

 

[Tinkicker]

Thread is about a week behind so I will attempt to bring it up to date. Needs a few copy and paste jobs.







Soldered the condenser leads to the stator wire and to the flag terminal that goes to the points. Refitted the stator and put on the rotor finger tight. Set the points gap by mk1 mod 1 eyeball and checked they were opening and fully closing.

Kicked the motor over.... Nothing.

Had a quick look around. Put the killswitch to run ( it is a rotary with two outer stop positions and run in the middle)
Slapped myself around the head a little for being a dick and kicked it over.

Beautiful big fat blue white spark. Yey!

Because the conservatory is cold, cramped and with very little room to work in, that was enough of a result to call it a day.
I can only stand it an hour at a time in there, kneeling on cold floor tiles with typical heavy equipment engineer issued knees. They need a good greasing, but unfortunately did not come equipped with grease fittings. Sealed units and the grease within old, dry and contaminated with debris.
No choice but to creakily stand up, slowly get them moving again and get the hell out of there.

I will set the timing and button everything back up tomorrow.

 

[Tinkicker]

I had a final check behind the stator to ensure that none of the wires would be rubbing against the rotor or trapped. Spent a very frustrating half hour on my knees timing the ignition and fighting with screwdriver against magnet. Got the points opening at 1.85mm btdc, close enough for me, and nipped the rotor nut up.
Final check to make sure the points were opening and closing.

Plugged the stator harness back in and final check for spark..... Aaaargh.

Spark has vanished and I have no idea why. I wil look tomorrow, my knees hurt and I am out of patience.

The other task I set for today was to fit the chain.

Ordered the chain specifically for the DT100. 102 links.
Idiot aftermarket supplier thought it was ok to send one with 110 links... says 110L right there on the box.

Luckily I still have my professional Whale chain cutters sets from my motorcycle techie days, so it was a two minute job to cut it to size, took longer to dig them out of storage; but many customers will not have access to chaincutters. The aftermarket vendor has no excuse.

Those Whales have seen a LOT of chain cutting and rivetting action.

And chain fitted. It says 110 links right there on the box....

 

[Tinkicker]

Stopped sulking and went to have another look at the spark. Kicked it over, nothing. Put a cloth over the plug to shade it and wiggled the plug to ensure a good ground against a head bolt.

Kick. We have spark after all! Plug must have jiggled a bit and the ground was lost. It is very temperamental getting a good ground with all the fresh paint. Plug must be HARD up against a head bolt.

I put a couple of drops of premix down the plug hole and screwed down the plug.

Ignition on and kick. She popped off immediately for a half a second. Yippee.

Encouraged I loosely plonked on the fuel tank, cut a fuel hose and put the tap on reserve, watching the float chamber overflow tube closely. No drips.
Nah, never happens. I suspiciously pull off the fuel hose to see if it is getting fuel. It was.

Well I never. I finally had a bit of luck.

So, as a tribute to Derek from vice grip garage, a few drops of premix straight down the carb throat for good measure, waaaaay too much. Perfect.
Choke on, ignition on and kick...

Second kick and away she goes! Yippee.

Making smoke and generator rotor doing rotary things.

First check, set throttle stop screw to allow a fast tickover.

Second. Does the clutch work and do we have five in the box? It does and we do.

Third, pull off the oil line, pull back the pulley to get max pump stroke, get it bled, get the measuring cylinder under the end of the oil injection pipe and count 200 pump strokes. Do we have the required 5ml?

We do have the 5ml. Pump is good. Still no sign of oil leaks or bad check valve. I can fill her up with normal fuel now.

 

[Tinkicker]

Thread up to date as of this morning.

Wiring routed and clipped. Airbox refitted, chainguard refitted, chain tensioned, gear lever fitted, generator and sprocket covers back on.
Tank back on. Disappointngly, there is no room between fuel tap and carb to fit an inline filter. I ordered the smallest paper centered one I could find, but sadly no room even for that.

Set carb airscrew to.2 turns out as per spec, but it would not run. It would fire and run for a second or so before cutting out.
Turned it in by a half turn and it runs like a champ.

Checked clutch action. Just fine and even neutral is easy to find once the engine warmed up. A bit recalcitrant until then.
I suspect when the frictions bed in, it will be fine.

Had it idling for around half an hour had did a few more tests.

Horn does not work. Not looked into it yet. I have AC voltage up to the headlamp terminals and the instrument lights work.

Thats about it for now. Another requires my attention.
Need to fire up the VFR and get her thoroughly warmed up. They are famously warm blooded and hate cold weather. The need to keep fresh fuel in the carbs is critical. Once the fuel starts losing freshness, you are in a world of pain. The cold starting circuit is extremely lean and is barely adequate even if run daily in cold weather.
She will fire on one, number two will chime in and allow it to run without starter assistance.
It can be a couple of minutes until three and four decide to put in an appearance. Touch the throttle or choke at all until then at your peril.


Instrument illumination lights up, we have main beam lit and the low oil light goes out when in gear as it should.

 

[That hurts]

Getting there slowly TK

 

[Tinkicker]

We appear to have gotten a page or two behind the original thread again. Not missed much though. It is all about the thing not wanting to start......




Well. The bike continues to make a Chimpanzee out of me.

Got the kickstart blasted, painted and refitted during the week, put the oil pump cover back on and gave it a kick over.

Conservatory temp around minus 1c. It fired and ran for a second, then cut. Kick, kick, it fired for a second, then cut.
Rinse and repeat for five minutes before abandoning the bike to its freezing cold fate.

Time for a ponder. It ran fine for over half an hour last time it ran.... All I have done is fit a cover and a kickstart. The kickstart was fitted previously and has no bearing on the issue. The oil pump cover is not an issue...

What has gone wrong....?

Ponder 1. It is getting fuel but losing spark. But new plug, points and condenser fitted. Timed up. Running just fine with no hint of a problem before.

Ponder 2. It has spark but is not getting fuel. A check of the plug showed wet with fuel.

So number 1. I fitted the rotor and tightened it with the tools I had available at the time. My home tools are a motley collection of old cast offs and bargain basket buys.
I have tools valued in the tens of thousands of pounds at work and this makes for little enthusiasm for buying good tools for home use. They are completely inadequate for anything but the simplest tasks which is why many of the tasks are done at work during lunchtime.

So has the rotor come loose and sheared the crank key? It would account for the symptoms.
I finally remembered to bring home my sheave holder and removed the rotor. Nut was tight and key intact.
At least with the correct tools, now I KNOW the rotor is fitted correctly. Points were opening and closing as they should.

I dried off the plug with a blowtorch and refitted it, managing to leave a shiny smooth spot on my fingertips as I removed my fingerprints on the getting ever hotter ceramic as I did so. Great.

Kick. Start, run for a second, die. Buggerynation.

Carb? With no reliable source of float height info, I just made sure the float arms were straight. Was the starter circuit not dipping into the fuel? Just as I was contemplating pulling the carb, I spied a brand new plug, loosely screwed into the head of the 175 to keep moisture out until.I replace the piston.

It can't be the plug because it is brand new. However, it is only a couple of seconds to try.

Fitted the new plug loosely and off she popped on the second kick. Feck it, faulty plug. It is not the first of the batch I bought. I reckon three out of five used failed. That is in around 200 miles.

I buy my plugs from reputable places like amazon, but there are a lot of chinese knockoffs out there. I am viewing this packet of plugs I have with considerable suspicion now. If they are knockoffs, could they have contributed to my 175 demise?

I will refrain from commenting on what I would like to do to chinese knockoff artists with no regard to the end user. It would not be pleasant reading.

 

[Tinkicker]

We jump forward a page. It may be odd reading at times because there are a lot of contributors comments that I am not including because I do not have permission to do so. The other thread is currently running at over 18 pages and 8000 views.
If I include any material from this site on other forums I do the same. Only copy and paste my own contributions. To do anything different would not be fair to the other contributors.

May be a little out of context....


>>>>Just ordered a couple of Denso W24es-u plugs to try. I have no faith in those NGKs anymore.

Happily, same plug in both DTs.

Went to try the 100 again. Seems the new plug has gone the same way as the previous one. One easy start and warm up to operating temp run, allow to go cold, then the same 1 second run shennanigans.

We have air. We have fuel. We have spark and fire with brand shiny new plug. We have intermittent or no spark with a heat cycled plug....

 

[Tinkicker]

Well. Here I am. The one armed paper hanger...

To cut a long story short. Smacking the gear carrier pins out of the reduction hub of a kessler axle on monday.
They are TIGHT and flush to the outside of the hub so you need a short drift to get them moving.

I found an old two inch diameter drain plug. Perfect. Proceded to swing the 16lb hammer and on the third pin, the drift proceded to fly out at great speed, hit my right hand before flying across the workshop.
Hospital says poss hairline fracture but because of the swelling they could not be sure as xray was not clear enough.

Minutes before it happened i was moaning and groaning because I have man flu and was feeling sorry for myself.

So now right paw in a brace, two fingers taped together... And man flu..

Have I ever mentioned my luck?

Anyway I took the opportunity to do a little lefty, one handed work on the 100. Checked spark with new denso plug. Fat spark. Checked it with the old NGK. Fatter spark. Presumably because the denso has the U electrode that lets the spark grow inside.

Kicked bike over. Ran briefly but stopped. Plug wet. Crankcases flooded? Dried plug, kicked bike over with fuel off and plug out, but no real sign of flooding.

Plug in. Ran for a second but stopped. Plug still dry. Could it be the starter circuit?

Removed airfilter and dribbed a little brake cleaner down the carb throat. Kicked and she popped off second kick. Set a fast idle.

Ran it for five minutes and turned off the fuel to scour the crankcases and combustion chamber clean of any excess fuel.
Yup, rpms rose as she went lean and carb emptied.

Fuel on and tried again. Second kick and she was away, sounding crisp off the throttle. I ran the carb dry again to preclude any flooding issues and will resume tomorrow when she is cold.

Also checked fuel tap to make sure it shut off and opened correctly. It did. I did not want it allowing the crankcases to slowly flood overnight if faulty.

So we have always had a fat spark at the right time.
We have always had air.
We have always had fuel.
We have had no running from cold with heat cycled plug.... But it should.
once running it sounds crisp off the throttle and has a nice smooth idle.

I am thinking either cold start plunger or fuel lost just enough zing for a reliable winter cold start, but it came from a sealed container.
Around 50% of the fuel content in the tank was premix at 32:1 and the oil pump is conected. It does white smoke quite heavily, but I recall RT100s being similar heavy smokers until the exhaust got hot.

Any other ideas? It is plain weird. I know for a fact the reeds are in very good condition and the crank seals are new genuine. The problem is not mechanical.

Bad hand is a bloody nuisance.

 

[Tinkicker]

Hand a bit better this morning. Kept brace off last night and probaby rolled around on it during the night. Must have been rolled back into the correct position. Hurty but moves. I can use it lightly. Don't think it is broken after all.
Time to see if the bike would start.


Choke on, ignition on. Kick. Nothing but a feeble fart then nothing.

I resolved to brace myself today for a little more stringent outing in the freezing conservatory than my usual of late, run in, kick, swap the plug, get it running and retreat asap until the next test tactic.

Found the original carb and traced through the enrichment circuit inlet tube in the float bowl right to the plunger housing.
I got out my trusty welding torch cleaners and ascertained I could not clean out the drillings in their entirity. Too many dog legs blocked off by ballbearings. It had several 90 degree bends.

Removed the choke plunger and got a length of windscreen washer tubing to blow down the plunger orifice to see if I could feel air coming out the inlet tube. I could.

All righty. So if i did the same on the bike carb I should hear bubbles and the bowl vents venting air.

Removed plunger and blew down the plunger orifice. No restriction evident. Same as the other carb and air was coming out the vent tube. No bubbles though, does this mean the float height is too low?
Another thing to worry about and add to the mix. My head is akin to a bingo machine full of floats, carbs, jets, sparkplugs, points and coils all whirling around and intermixing like a madmans kaleidoscope.
Which is going to pop out next?

Before I refitted the plunger I gave it a good polish with some grey scotchbrite and a good squirt of GT85.

Pull out plunger, fuel on, ignition on. Kick. Away she went first kick.
To coin a phrase from Dereck at VGG. " Well I'll be dipped".

I have absolutely no idea what I did, but whatever it was, it seems to have worked. I will try again tomorrow to see if it is cured, or is still toying with me. No point in hiring the mariachi band until then.

I guess I can take those poor, maligned NGK plugs out of my conservatory bin bag now. They are probably still good.

 

[Readie]

Nice one , I was going to suggest polishing the plunger….…

ooohhh, that sounds like a euphemism…and with a bad hand…..

 

[That hurts]

Hand a bit better this morning. Kept brace off last night and probaby rolled around on it during the night. Must have been rolled back into the correct position. Hurty but moves. I can use it lightly. Don't think it is broken after all.
Time to see if the bike would start.


Choke on, ignition on. Kick. Nothing but a feeble fart then nothing.

I resolved to brace myself today for a little more stringent outing in the freezing conservatory than my usual of late, run in, kick, swap the plug, get it running and retreat asap until the next test tactic.

Found the original carb and traced through the enrichment circuit inlet tube in the float bowl right to the plunger housing.
I got out my trusty welding torch cleaners and ascertained I could not clean out the drillings in their entirity. Too many dog legs blocked off by ballbearings. It had several 90 degree bends.

Removed the choke plunger and got a length of windscreen washer tubing to blow down the plunger orifice to see if I could feel air coming out the inlet tube. I could.

All righty. So if i did the same on the bike carb I should hear bubbles and the bowl vents venting air.

Removed plunger and blew down the plunger orifice. No restriction evident. Same as the other carb and air was coming out the vent tube. No bubbles though, does this mean the float height is too low?
Another thing to worry about and add to the mix. My head is akin to a bingo machine full of floats, carbs, jets, sparkplugs, points and coils all whirling around and intermixing like a madmans kaleidoscope.
Which is going to pop out next?

Before I refitted the plunger I gave it a good polish with some grey scotchbrite and a good squirt of GT85.

Pull out plunger, fuel on, ignition on. Kick. Away she went first kick.
To coin a phrase from Dereck at VGG. " Well I'll be dipped".

I have absolutely no idea what I did, but whatever it was, it seems to have worked. I will try again tomorrow to see if it is cured, or is still toying with me. No point in hiring the mariachi band until then.

I guess I can take those poor, maligned NGK plugs out of my conservatory bin bag now. They are probably still good.

Hope the hand continues to improve TK ... can't be far off now, but don't ride it if there's even the remotest chance of ice.

With you luck and all that ...

 

[Shadowryder]

Thread is about a week behind so I will attempt to bring it up to date. Needs a few copy and paste jobs.







Soldered the condenser leads to the stator wire and to the flag terminal that goes to the points. Refitted the stator and put on the rotor finger tight. Set the points gap by mk1 mod 1 eyeball and checked they were opening and fully closing.

Kicked the motor over.... Nothing.

Had a quick look around. Put the killswitch to run ( it is a rotary with two outer stop positions and run in the middle)
Slapped myself around the head a little for being a dick and kicked it over.

Beautiful big fat blue white spark. Yey!

Because the conservatory is cold, cramped and with very little room to work in, that was enough of a result to call it a day.
I can only stand it an hour at a time in there, kneeling on cold floor tiles with typical heavy equipment engineer issued knees. They need a good greasing, but unfortunately did not come equipped with grease fittings. Sealed units and the grease within old, dry and contaminated with debris.
No choice but to creakily stand up, slowly get them moving again and get the hell out of there.

I will set the timing and button everything back up tomorrow.

those knees sound like mine.

 

[Tinkicker]

Well it starts. Not as crisply as I would have liked, but it runs. It sputtered and died on the first few kicks, gradually getting a little better each time. By maybe the 5th or 6th kick she was running. After that, she is first kick reliable.

I don't suppose that is too bad considering the winter temps.

We turn to the headlamp. Does a conventional 5 and 3/4" car sealed beam fit in the headlight rim?

Reason I ask is because a retailer is selling 5 3/4" sealed beam direct replacements intended for classic cars and comes fitted with a 6v Halogen bulb for a 3 pin H4 type connector. I guess this means I do not have to tamper with the original connector and the light will be brighter.

Alternatively I can just buy an aftermarket reflector and american prefocus 35/35 bulb holder suitable for DT175MX. I know the headlamp bucket is the same on both bikes but I will have to rewire the connector.
Obviously the sealed beam replacement is the preferred option. Monetarily, there is very little difference between the two options.

I have a new 300 x 16 Kenda K262 rear tyre and new tube coming from Germany. It was oddly cheaper to buy from a German retailer and pay for shipping than it was to spend more time trying to source one in the UK.

Depending on the state of my hand, I may wait till the holidays to fit it. That makes the rear end complete.

I have ordered the front tyre and tube also, along with new rim tapes front and rear. I made the decision to swap out the wheelbearings while I have the wheel out. Nothing wrong with the originals, but no point having one set of old bearings when every other one is new.

That rear fender is still taunting me...

Outstanding items are the tyres, headlamp as mentioned, exhaust outlet ( still available from yamaha), a set of indicators, the annoying fender, a pair of mirrors and she is pretty much complete. The tailamp is ready to bolt straight back on the fender.

 

[Captain_Saxa]

This has been a fantastic morning read

 

[Tinkicker]

Well. Since I hurt my hand, apart from attending to one handed stuff, I have been pretty stuffed where work on the bike goes.
Saw the quack yesterday and he advises I may be good for light duties next week. Light duties in my job? Yeah ok.

Anyway, I can use a screwdriver without too much discomfort now, saw I thought I would have half an hour on the bike.

The lay up has meant I have had a lot of time to stare at it and ponder.... Why does it start once OK, run fine, then refuse to run more than a second the next time.

One of those problems that strongly pointed to a malfunction on any of the systems. Fuel, air, spark or compression.

Carb was cleaned, all passageways and jets I could get into scrubbed and it had a half hour in the ultrasound bath, then everything checked by blowing through.
Ignition system is all new quality aftermarket with a fat spark.
I know know it is not an issue with the plug after trying 3 or 4 with the same result.
Dropping fuel into the carb or cylinder resulted in a strong start.
I strongly suspected a weak condition from cold. I knew the pilot jet was not plugged because it runs ok when warmed up a few seconds.
This meant the enrichment circuit. After stripping the plunger out and blowing down the plunger drilling into the float bowl, it started on second kick and picked up strongly within seconds . Yippee
Time after and subsequently attempts since, it once again became difficult to start. Why!

Now able to at least hold a screwdriver in one hand and steady a part in the other, I could look a bit deeper.

I think God loves a tryer because by jove, I think I found the answer.

Strongly suspecting the float level because I do not have reliable info , I thought it may be too low causing the weakness. I never head of it affecting the starter circuit though, but everything else checked out. I had already ensured the starter circuit drillings to the plunger was clear.

I removed the carb with a bit of difficulty, very little room around the carb area to get in on the 100. Airbox has to be removed because it surrounds the carb on one side, and exhaust is very close on the other. To remove the airbox, the chainguard has to come off. A bit more work than my hand needed, but best foot forward.

I pulled off the floatbowl and looked down the starter jet. Nothing. I blew down it. Nothing blocked. I poked a torch nozzle cleaner into the starter jet tube intake. It was clear. Hmm why start, then cut after a second..

Ping. If there was some loose debris or fluff in there, in between the tiny intake to the tube and the bottom of the tiny jet, it may allow fuel into the tube, and on kicking the bike over, float up to the underside of the jet, partially blocking it.
The bike starts, quickly uses the fuel above the jet and cuts.

To cut a long story short, I swapped the float bowl from my other carb to try.

Tank back on, fuel on. Ignition on. First kick. Light off and an extremely strong start indeed. Better than it has ever done.

I will retest tomorrw to see if I cured it or not, then button everything back up.