Workshop session Saturday September 21st 2024
Dnieper 650...
This on-going project belonged to our club member Annabelle. Shed loads of work had already been done on the bike but it was still suffering from rough running. One idea to help try and tune the carburettors was to employ a Gunson's colour tune. A colour tune is a device that allows the mechanic to actually see the fuel burning in the combustion chamber. Most noteably and orange tint to the flames shows that the fuel mixture is too rich and this is what was happening in the bike's right hand cylinder when the throttle was opened with any enthusiasm. Annabelle tried raising the needle clip to lower the needle and reduce the amount of fuel that could flow past it for any given throttle opening. However this did not appear to alter the smain symptom ,which was mainly the fact that the right hand cylinder started to intermittently misfire when the throttle was opened. Some work had already been done to try and address a poorly seated valve but the consensus was that the valves were still behind the problem and needed further work.
Worthy of note was the fact that club member (and ace fabricator) Phil James had been kind enough to fabricate an adaptor to fit the available 12mm Colourtune into a 14mm spark plug hole. He had made the adapter from an old 14mm sparkplug welded to a nut and cut with an internal 12mm thread and it worked a treat.
Kawasaki KZ550 Limited
In order to get the engine started Graham and first time visitor Mark worked together to trace what was preventing the starter motor from actuating. Eventually, with the aid of a wring Graham found a wire in the starter motor circuit disconnected at the back of the headlight. Once the engine was running Graham and Mark worked together to try and get the bike's carbuettors balanced. Eventually all four of Graham's 40 plus year old genuine Suzuki carb balancer gave the same reading. Despite this, the engine sounded rough until the revs were raised. The cause of the noise would have to be investigated before the any thought is given to riding the bike on the road. In another development Club Mechanic Phil bought the bike's newly recovered seat into the workshop session. Local trades person Stan Leather had recovered it with leather, giving a very professional look to it.
Kawasaki Z250A (Scorpion)
With the help of 1st time attendee Mark and club member Don, Graham installed two size 88 main jets in the carb urettors. This was roughly a 10% increase on the orginal fitment and was intended to take account of the air filter box having been removed and replaced with two pod type filters. These filters offered a lot less restriction to the air flow though the carburettors. Increasing the airflow meant that the amount fuel that could be drawn through the jets needed to be increased to try and match it. Whilst work was being done on the carbs both carburettors flooded to a lesser or greater degree. Graham found that a piece of debris had become trapped in the needle valve of he left hand carburettor stopping it from closing fully. Don spotted the fact that the float heights of the two carburettors were significantly different. This also lead to the discovery that Graham had managed to fit one pair of floats upside down! However despite correcting this the float heights were still significantly different. Graham put this right by bending the 'tongues' of the floats and then using a vernier gauge to check the floats were the same height when they closed the float valves. Because Kawasaki only provide a measurement for the 'fuel level' and not the float height itself, the fuel level would have to be checked before the bike could be used in anger. Althugh the bike ticked over smoothly, the engine raced for a while before dropping to its idle speed. One possible cause of this issue that Graham had encountered several times in the past, was that the springs in the ignition's advance and retard mechanism had weakened and stretched. This would allow the weights in the mechanism to stay partially out, leaving the ignition partially advanced until they finally returned to their resting place. The mechanism on the Z250 relied on a pair of weights being flung outwards by centrifugal force as the engine sped up, causing the ignition timing to advance. The springs should return the wights to their resting position causing it to retard to its idling position. Upon takng the unit apart Graham found that dried up grease meant that that the points cam was reluctant to return to its idling position and that weakend springs would have allowed the ignition timing to flutter. Graham cleaned and greased the mechanism and slightly reduced the length of the springs. Finding out whether this helped to stop the engine from racing before ticking over would have to wait until another session.
Jailing 125 trials bike project
Don had now finished spraying the fuel tank so work could now be done to re-spray various other components in order to start the process of reassembling the bike to be used as a trials bike