May 2020

The main task for the Suzuki would be to fit some new handlebars. The low bars it featured had the annoying habit of trapping the riders knees against the fuel tank on anything more than modest lock, which could easily end badly. Most of these bikes were originally fitted with dirt stlye braced bars, probably for this very reason.

I had found a pair but was not sure if I would find enough length in the wiring and control cables to allow their use. Fortunately everything was designed to cater for them, so they did not put up too much of a fight. Just lots of rerouting until the best combinations were found.

Because of having to mess with the throttle cable I found that one carb slide was jammed partially open. The led to removing the right carb to free it up, and the inevitable cleaning of old fuel residue from the float bowl and all the bits inside it. Obviously the same situation would exist in the left carb, so that got cleaned up too.

The bike had arrived with the fuel tap removed as it had been leaking. I stripped and cleaned it and found it to be working as designed. There is a vacuum line from the left carb which operates a diaphragm in the tap body, so the fuel shuts itself off when the engine stops. There is a priming position which bypasses the vacuum control so the carbs can be filled should the bike have been sitting for a long time and the fuel evaporated from the float bowls. As it had. When I refitted it all to the tank and put some fuel in, I found that there was a split in one of the feed hoses, so I replaced the hose. Presumably that explained the leak.

The 6 volt battery was history, so while waiting for another I was preparing the bike for what would be its first run in a long while. Kickstart lever is on the left side which feels odd, but the lack of serious compression from such small cylinders means it is not a problem.

Well. Shall we say it is not usually a problem. On about the third kick the engine locked solid. Would not move. It felt like a hydraulic, so I removed the spark plugs, and sure enough, the right spark plug was doused in oil. I kicked it over with the plug out and was rewarded with a gout of oil which ran down the front mudguard. I cleaned it all up and tried again, with exactly the same result. So I cleaned it again. It seemed there was a lot of oil in the right side of the crankcase. By searching online I happened to find some photos of a complete set of crankcases for one of these motos, and noted that there were two drain plugs underneath the cases - one for each side of the crankcase. I removed these and drained oil from both sides, but mostly from the right.

Perhaps the long period of sitting had allowed oil to drain down from the oil tank which is mounted quite high under the seat. This motor has pump fed positive crankcase oiling, whose supply is controlled by a third throttle cable. Perhaps with one slide jammed open the pump control had been partially open and encouraged this. The oil tank has a sight glass which was well covered, and removing the filler cap showed it was still a bit over half full.

A couple more trial kicks and the engine locked again. Dang. It would seem that the oil pump may be over delivering. The pump is conveniently located under a small cover above the right footpeg, and only two screws retain it. Popped that off for a look see. The cable operated lever which controls the delivery was all intact, and there are markings for setting it up when the throttle cable is at rest. All appeared to be normal, and the oil lines were all clear type, so by kicking the motor over several times with the spark plugs out I could see that there was virtually no oil moving, and certainly not enough to explain the volume that the piston was sucking into the cylinder.

And then the obvious came to mind.

I got a piece of rubber hose the right size and tried blowing gently down the exhaust pipe from the tail end. Sure enough some oil shot out of the cylinder. I took the bike outside and gave it a real good blow, which resulted in a small Torry Canyon like affair and oil all over the cylinder head, so then it got a degrease and hose down. That exhaust design is perfectly placed for excess oil to neatly fill, and it had. Being a 2 stroke the piston sucks both from the crankcase and also the exhaust, at least until the motor is running, so it was simply sucking the oil back up the pipe and into the combustion chamber. Sheesh.

Happily that provided the cure, and now it kicked over with seemingly equal compression on both pots, so it boded well for a successful start. The new battery duly arrived and was fitted, so outside we went and proceeded to prime the carbs. All good and no leaks. There now ensued a dozen kicks with no signs of life, although the ignition light was glowing with some enthusiasm. Then I remembered there was a choke lever, but it would not stay on by itself, so adopting a contortionist pose I held the choke lever while kicking, and after a while it fired up. It then stopped as I let go of the choke lever, but several more brief starts got us to the point where the motor kept going, even though I did need to keep the choke on. Some tuning obviously required methinks.

Then I noticed a slowly spreading pool of fuel beneath the bike so switched everything off. Fuel was dripping from the vacuum chamber of the fuel tap where its two halves screw together. As the engine had now stopped running, the leak stopped of its own accord, but would of course begin again if I resumed. Looks like the fuel tap will be coming apart again.

Well - good progress none the less. It now runs at least, but the tank will need removing to allow removal of the tap without losing the rest of the fuel. I consoled myself by taking some photos while the rain held off. That fuel tank looks as good as new. Perhaps it was restored at some previous time.

The seat also looks far too pristine to have been there since 1971, even if it had been in a dark room, but it certainly looks like the genuine article.

I do not recall having seen one of these bikes looking this good even in the mid 70's...

Fortunately the bike is so incredibly short that the rider is virtually sitting with their head directly above the steering head, so the pretty little clocks are not obscured by the brace on the new bars.

Hard to imagine it has covered that many miles, although when you look closely at the engine cases and the cycle parts the signs are there.

Though they are not my usual fare, Japanese bikes are an interesting deviation from British ones. The degree of quality control made them stand apart from the outset, but now that they have aged, some very quirky issues can arise, such as those just described. Having less experience on the type means this can take some time to resolve.

What a cool little learner bike this must have been all the same. Looks like a transistorised real bike.

There is now one more possible serious complication, and it is once again a 2 stroke thing. Left sitting for long periods of time, some of the engine seals can harden up and cease doing their job. One symptom of this happening is that the engine may suck oil from the gearbox into the right side crankcase past a seal which is fitted to the crankshaft, inside of the outer main bearing. I imagine a total engine strip would be involved in its replacement, and I would not be up for that. I shall drain and refill the gearbox to ensure it has its correct 850ml of oil. If it does not, then that is likely where the oil came from. However, some running may get the seal coping again as it gets hot and oiled, so only time will tell what the prognosis is even if it turns out that it was gearbox oil.

Well, a second strip of the fuel tap disclosed that the outer edges of the diaphragm of the vacuum control were beginning to disintegrate, and not only were parts not forthcoming, I found a new old stock example of this Mikuni fuet tap being sold on eBay UK for 200 poonds. No thank you. Reassembled it with blue hermetite which is reliably fuel resistant, and when reinstated in the tank and a few kicks applied to create vacuum, we seem to be leak-free. Good-oh then.

Next thing was to drain the gearbox oil. Reassuring to find it contained the correct 850ml, so the excess oil has simply drained down into crankcase/exhaust via the oil pump over an extended period of time. Perhaps the stuck throttle cable did play a part, but more frequent starts in future would probably avoid a repeat of both these scenarios.

I started the bike for the second time in order to begin tuning it, but it was unhappy running, and while there was a good plume of 2-stroke smoke from the left pipe there was none from the right. I have never experienced a 2-stroke seizure, and am not about to do so now, so I shut it down. A quick inspection revealed that the right plug had not been firing, although you would not have known from the exhaust nore, which was still busy enough to sound like a twin. The spark plug had obviously not enjoyed being force-fed several good servings of old oil. I bought a new pair of plugs and fitted one to the right cylinder, so that when the rain finally stops I may be able to tune the beast.

Or not...

Progress to 29 June 2020.