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Discussion Starter · #1 ·
Hi all.
Quick report on progress, (CB350K2 1970). Bought in November last year from a local (to me) importer of, mainly, US motorcycles, D+K. Saw it on their auction site, popped down for a closer look, decided there and then that I wouldn't find one in better condition unless it was a fully restored and horrendously priced example. One thing I must mention is that, over here, (UK) these are generally snapped up by the classic racing people so they are thin on the ground. This one had obviously lived a pampered life. No rust, chrome still very good, compression excellent, showing a very believable 9600 miles on the odo. It did have the usual rusted out silencers and the tank was badly dented. My check-list of replacements included replacing the cow horn style bars, mirrors that were faded, torn seat cover, tyres, brake shoes, some paintwork but, as I thought, that was about it.


Little did I know that decent condition tanks are like gold dust, and priced accordingly and that sourcing some original shape silencers would also be difficult. As luck would have it, Dave Silvers informed me, just before Christmas, that they had a newly delivered stock of pattern parts. I bit that, not excessive bullet and ordered them..... along with the chrome carb tops to replace the pockmarked originals, a seat cover and a throttle cable. I also came across a purported NOS tank in the correct greeny blue colour, but in California..... Price, horrendous, shipping even more so. I arranged for it to be shipped in the new year, rather than have it lost in the Christmas post.

I set too seeing exactly what I had got. Carbs were gummed up and needed a really thorough cleaning, but, once the new battery was hooked in, the motor spun up nicely. (after filling the bores with oil, squirting the cam box full and giving it a good spinning over with plugs removed on fresh oil). A new set of plugs fitted, dummy petrol bottle rigged up, fingers crossed and ignition on. Blow me, started right up, settled to a nice plodding tickover once warmed a little. No unusual noises, revved nice and clean. I breathed a slight sigh of relief, but there was no guarantee that the gear box was not a nest of vipers. With some trepidation, I whipped off the cam chain tensioner block to inspect the state of the roller. To my amazement, it looked, and felt, brand new. Still supple and unmarked on the chain run shoulders.


As the side engine cases were faded, I decided to remove them for cleaning and painting, gave me a chance to look at the centrifugal filter and the clutch. The filter was squeaky clean, clutch in good condition, plates separating nicely with no damage or wear evident.

There was a fair bit of remedial painting to do, basically the air filter covers, engine covers and some touch up to the frame. That will be done properly next winter.

The most vexed problem I had was the purported NOS tank, when it arrived in January. It was badly pin holed and had been re sprayed poorly. I had no option but to line it and make the orange peel lacquer finish good.
It looked to be sealed well enough that I tried filling it with a full tank of petrol. After a few hours standing, a tell tale bubble in the paint showed a weep.... Damn! I bit the bullet and cleaned the paint from the base of the tank, just the L/H side which is the weakest, bikes left for years on the side stand, water gathering along that side of the saddle tank. It had two areas of obvious weakness, but in general was not too bad. I cleaned up those areas to be left with two moderate sized holes. I needed to be mobile, if only to test the engine and running gear, so, more in hope than anger, I tried something a little different.
I bought a few tubes of Gorilla epoxy, the stuff with two tubes linked by a plunger. Dumped it all into a mixing tray, mixed the two parts thoroughly, and poured it into the L/H side of the tank. A little warmth to make it more liquid and left the tank propped up to allow the mix to settle in the bottom of the tank. After an hour, the epoxy had seeped through the weak spots and had hardened enough to smooth the outer surface flat. Thankfully, the white lower paint is easy to match so a quick spray later and it was ready for testing again.
Well, it holds fuel and seems sound enough, even after days of standing with a full tank of fuel. But, by good fortune a friend of a friend offered to straighten my dented, but sound, original tank.... and a damn good job he did of it too. I wound up repairing the amplifier in his Wurlitzer jukebox in repayment, an ancient bit of technology nearly as old as the Honda. BTW, that epoxied tank is still good, I have been using it while the repaired tank is painted and shows no signs of distress.... Worth a shot if your tank is bad, minimal cost if it doesn't work...

New tyres added to the spend, nice to be able to do them in the shed rather than traipsing off to a tyre fitters, and the price was a lot less shocking than the modern rubber on my Aprilia.

The next battle was the registration process, packages of special delivery envelopes bouncing back and forth to Swansea. At last, a full month and a half after starting the process, a brand new log book dropped through my letterbox. And then another one dropped through the day after.....
Hopefully, the last spend was on a brand new, period correct numberplate. That duly arrived to be fitted with alacrity, I was gagging to take it out on the road.

It did run, quite nicely, but the gear lever was fouling the exhaust and the mirrors pointing skywards. A few swift adjustments later and I could take it for a more extended run.
I'd like to report a serene passage with the birds tweeting and a smile on my face, but, no.
It ran fine, but once hot, would die as soon as I came to a stop, like a gradual fading away rather than a dead stop. Its performance was less than I remembered, or expected, seeming to be very sluggish. A more intimate inspection showed that the R/H points gap had almost closed up, L/H were fine. I reset them, noting that the holding screws on the points backplate were the only ones on the whole machine showing any sign of being touched.... Hmmmm.......

Longish story cut short. She would run fine from cold, carb adjustments normal enough, air screw and throttle stops well within spec, but once properly warmed up it began to cough and spit, dying at tickover. Now, I had not inspected the carb mounting rubbers too closely. They looked to be in good condition, as in, no cracks, still shiny black, supple enough to allow carb removal and fitting with ease. But, with the engine running, a spray of WD40 told a different story. Sure enough, once removed, there was obvious oil ingress inside the rubber bore. Seems that the junction between rubber and metal mounting plate was separating, probably with the weight of the carbs, the jouncing out on the road adding to the effect. New mountings ordered, Dave Silvers will never be poor with people like me around.

As I wait for them to arrive, I would like to add to the build story so far.

As a matter of course, I replaced the ancient 2 phase, selenium rectifier and 'regulator' unit with a modern combined reg/rec unit. (my spare from the Aprilia). Way over specced but bombproof in this application. Its a large unit, but slotted in nicely behind the battery box and rear mudguard. This is, of course, a three phase device, so all three alternator outputs are connected directly. The positive output from the reg/rec fed directly to the battery, the earth lead to the battery earth. This way there are no voltage losses by using chassis earths and old loom wiring. The alternator output is less than stellar, so every volt and amp preserved is welcome. It also obviates the need for the yellow, yellow-white leads to the handlebar switch, handy when I came to fitting my new, UK style handlebars.

I obtained a set of the lower, UK/euro style bars, the American cow horns it came with not to my liking, at all. They didn't come drilled for the cables to run internally, so that had to be done and the switch units wiring fed through. Not too difficult and, as mentioned, deleting the yellow leads made the job easier.

During this period, I was also rubbing down my repaired tank, filling in the little ripples and dings, priming, then finding even more little dings to fill. A local paint shop managed to get a very close match to the original paint, finally I could begin to finish that long drawn out job.
I am indebted to the guy who suggested a painless way of removing the Honda wing badge. This involves gently easing a fork behind the badge and using the tangs to ease the mounting stubs from the plastic grippers on the tank. Makes it a painless undertaking with no damage to paint or badge.

New tyres fitted, along with new brake shoes. BTW, anyone who decries drum brakes should take a ride on one of these. They work remarkably well, hauling me down from speed with good feel and enough power to lock the wheels on slightly greasy roads, don't ask how I know..... I know that, back in the day, I have no memories of the brakes being inadequate and we used our bikes to the max, usually two up if we could persuade the local young girls along for a ride out..... (Probably not politically correct these days, ho hum....).

To continue. Carb mounting stubs arrived, fitted... and made not a scrap of difference. (Actually, that's not quite true). All jets clean as a whistle, what the hell could it be? I checked valve clearances, timing, points gaps, again. Then, as I mused over a cup of tea, the penny dropped. The idle mixture jet is hidden beneath a plastic insert in the bottom of the carb body. Why I kept overlooking it I can only put down to my advancing years...well, I am getting on a bit. Sure enough, a bit of judicious cleaning and poking through with some fine strands of wire and we were back in business again. (Its the only jet that actually unscrews BTW). As I mentioned, I thought the inlet stubs had been a waste of money, but, since fitted, I have found the airscrew settings to be a full turn less than before and it starts, on choke, but immediately ticks over, rather than having to be cajoled. No doubt about it, that the old stubs were porous to some degree.

So, that's just about it for now. She'll be ridden in the summer, any niggles noted and then a full strip next winter, powdercoat the frame, source a rear mudguard as the one I have has some small splits from the rear light mounting bracket bolt holes. I will get round to rubbing down the front forks alloy lowers as they have faded and lost some lacquer and a thorough clean and polish should keep me busy enough.

I'll report more on the actual riding experience as I get some road time on her, but I think the major snags have been addressed. Fingers crossed.



As a footnote..... Yes, at urban speeds it all seemed fine. But as soon as I ventured out onto the more open roads and started taking her through 70 mph, she would run up fine, but then almost stall, one cylinder (R/H) miss-firing badly and generally not happy. I had noticed a touch of this earlier, but it seemed to clear so I just kept it in the back of my mind.
Either electrical or fuel, 50/50 as to where to start. As a quick check, once limped home, I opened the R/H carb drain screw, just to eliminate fuel starvation. A few dribbles oozed out into my cup. So, fuel supply. Turned out that the gallery between fuel inlet and the needle valve was almost completely blocked. It allowed a dribble through, just enough to sustain low revs, but not the higher fuel demand of high revs. Blew it through with the airline, it took 30 psi before whatever had solidified in there finally let go, went of like a shotgun!

Last thing on the (present) list is a 17 tooth front sprocket. Just to calm thing down a little at the higher cruising speeds of motorways and fast A roads.
 

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Discussion Starter · #2 ·
Time to update the story.
I fitted the 17 tooth front sprocket and that certainly gives it more legs, quite relaxed at 60mph and pulls through to 80 mph easily, so its by no means overgeared for top end. I see that an 18 tooth sprocket is available, but have been advised there might not be enough clearance in the available space. It will be with me shortly and we will see. Probably have to fit a longer chain so this might not be a budget upgrade.....
So, where were we.
I thought I had solved the fuel delivery problem, she was quite happy now holding 60mph for the twenty or so motorway miles up to a friends house. On the way back I decided to gentle her up to top speed. As I have said, 80mph no problem.... Then, the dreaded splutter as one cylinder began to cut out, again.
I had thought I had completely cleaned out the fuel system, but checked it all again. Fuel bowl filter clean as a whistle, no debris in the bottom. I tried blowing down the main fuel inlet pipe and, whilst I could feel air exiting the fuel tap to carb pipes, it didnt seem to be particularly strong. Strip off the tap from the body and... yes, the channels that carry the fuel from tank to the tap were full of powdery residue, including the the half moon channel in the tap handle itself. Now a good blow through gives a strong gust of my nicotine stained breath, hopefully, that is that laid to rest. Worthwhile checking all of the fuel tap on a bike laid up for the many years that this one obviously has.
 

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Nice write up mate, I've got a '72 K4 model so just a little later.

One very worthwhile upgrade I've found helped was the fitting of electronic ignition, I went for the Boyer Bransden kit (293) which also comes with new coils, leads and caps.

It also does away with the mechanical advance/retard so pretty much fit and forget, I binned those big 'bars off as well and fitted 400 four ones.

I also got a UK spec rear light from an old CB500 from the same era, these are a direct replacement for ours but half the size, the wiring is even the same colour.

Regarding the 17 tooth front sprocket, is the standard chain still long enough?

Cheers.
 

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Discussion Starter · #4 ·
Hi Shep... and everyone else.
Boyer ignition high on the list, funds a little strained at the moment, I'm awaiting the outcome of a speeding ticket for... Ahem, unruly speeds on the Aprilia. At 71 I really should know better!
Anyways, that was the first mod on my CB72 so I am a complete convert.
So, I left the story having cleaned out the fuel tap and that was it, (halleluja). Fitting the 17 tooth sprocket should not need a new chain, but it will pull the wheel up quite near the front of the adjustment slot in the swinging arm. There is lots of clearance between sprocket and clutch pushrod, not sure why Honda chose such a frantic final drive ratio.
But, the 18 tooth sprocket arrived this week, Now things do get a bit crowded behind the sprocket cover, especially since I have fitted a DID o ring chain of chunkier dimensions than the non o ring that came on the bike.
It still pulls right up to 80, still accelerates smartly, but drops the revs about 800rpm lower in top gear. For relaxed motorway cruising I give this my hearty recomendation, with a caveat. I am a 12 stone, skinny 5' 9''. If you are.... heavier, or, how to be polite, of a more ample girth, this might need a little lower gearing. But I still recomend going to 17 teeth.
 

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...not sure why Honda chose such a frantic final drive ratio.
Simple... back then, all of Honda's Japanese competition were 2 stroke bikes and Honda wanted the 350 to have strong acceleration. Even at that, most Hondas were geared high enough that they couldn't pull redline (or power peak) in 5th gear anyway
 

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Thanks for the reply, hope I'm still getting speeding tickets at 71! I'm a sprightly 53 so a bit to go.

I'm 12st as well so 18 might be ok but think I'll try the 17 tooth first, good insight to why a they chose such low gearing.
 

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Discussion Starter · #7 ·
An update. (coming thick and fast lately!)
Took her for the first real extended run yesterday, 150 miles, mixed motorway and A roads. At last all the niggles seem to have been sorted, she ran well, holding 70 on the Mways, easily keeping up with A road traffic.
Now, one favourite stretch of road is a long uphill drag, with an equally long downhill stretch. She held on to 60 - 70 on the uphill in top, but there was no acceleration in her, that would need a drop to fourth and some pretty heavyweight revving. On the downhill stretch she whizzed right round to fairly illegal speeds, so, given the right conditions it will rev out in top. Conditions were cool temps and a light breeze. The problems come with any sustained speed over 60. Its been a long time since I've ridden and unfaired, upright bike. I am finding that air resistsance is really noticable, I am having to hunch down to minimise the drag on both me and the bikes performance, it makes making progress quite tiring. I am starting to consider a period type fairing and lower bars, but, I suppose I should treat her as a 50 year old lady and ride her accordingly..... but adressing the airodynamics of a brick would give us both an easier time out on the road.... To be decided.
 

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Discussion Starter · #8 ·
Well, here we are again with an update, actually, a 500 mile update. It would appear that all the earlier little problems have been resolved, she is now the bike I remember from 1969. The authorities relieved me of a hefty sum of money for my indescretions on the Aprilia and my licence is also a little shredded, but, hey ho, lesson learnt. However, what the Lord taketh away, he also giveth. Our banks had a nice little con going on called PPI, a charge on credit cards and loans. Deemed illegal, we, the poor people, have been able to claim back these charges. Sure enough, I had been mis-charged to the tune of £6500.... First thing I did was contact Boyer Bransden for one of their excellent electronic ignition kits. It finally arrived after being on back order for a month to be fitted with alacrity.
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This is a comprehensive kit. Everything you need for the conversion including coils, HT leads and plug caps, all wiring and a good fitment guide written in English(!).
It is a true fully electronic unit, the mechanical advance unit is removed and the magnetic pulse rotor fitted. The PCB 'points' baseplate carries two fairly hefty coils that are the firing point triggers. All very robust and well made. Total fitting time including tank removal, 30 mins, but I do have an electronics background and have fitted other such kits before. Timing is carried out the same way as with points fitted, I use a strobe gun to set the advance up, matter of a few minutes.
The results are very satisfying, best demonstrated by the rock steady tickover without the ocasional stumble from a sparking contact breaker. At £180 I heartily recomend this package.

The only other major job has been to fit a rear carrier. I was underwhelmed by the racks that are on offer. I really need the modern convenience of the Givi type top box, somewhere to store wet weather gear and helmet, some tools and a dry place for my tobacco.
I settled on modifying some Givi arms I had lying around, from a Kawasaki ZZR600 if you are interested. Far more discreet than the tubular errections and far stronger. A fair bit of modification was involved but nothing that would require the services of NASA. I think you will agree that it looks neat and quite in keeping with the appearance of the bike.
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As I have said, I have put the first 500 miles up in my ownership, despite the pretty horrendous weather we have been suffering lately. Some vintage Jap bike shows and runs up to Skipton and Settle.
During this period I have been slowly increasing its cruise speed. I am quite confident in holding 70 - 80 mph on the motorway stretches that are the quickest way to get out to the good riding roads. It hums along in the 7 - 8000 rpm range quite happily and is in no way a hinderance to other traffic. What I have noticed, with some amazement, is just how frugal these things are in comparison to the big modern bikes. Easily reaching 60 MPG even at these highish sustained speeds. (Just as I remember). Its also very satisfying to have gentlemen of a certain age stop in the street to come and look her over, do a bit of reminiscing and complimenting. All in all, a very satisfying build and one I am enjoying immensly.
 

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