If your 2-stroke oil consumption seems to be excessive on and Oil Injection model even after correctly adjusting the oil pump cable, the plunger stroke setting may have been disturbed. The pump has to be removed from the engine and partially stripped to check and adjust this.
Remove the two screws holding the oil pump cable bracket to the transmission casing, and unhook the oil pump cable from the pump control lever. Pull off the inlet and outlet oil lines from the pump. (Remember you will have to clamp or plug the end of the inlet line to avoid draining the oil tank contents). Don't unscrew the oil union bolts at this stage - the bolts contain loose ball and spring check valves which are fiddly to refit and very easy to lose. Unscrew the two oil pump fitting screws and remove the pump from the engine. Be prepared for a small amount of oil to be spilt as the pump is lifted away.
Remove the three 4mm screws holding the two halves of the pump together and split the pump casing, being careful not to damage the thin paper gasket. Remove the spring from the end of the pump plunger gear and place it to one side to avoid loss or damage. The pump plunger gear can now be rotated by hand, and you should feel it lift slightly once per revolution under the action of a cam on its rear face - this provides the pumping action. At the opposite end of the pump, you will see a small grub screw and locknut in the centre of the pump end plate. Loosen the locknut and turn the grub screw slowly in while rotating the plunger gear, until you reach the point where the gear just fails to lift as it rotates. From this position, turn the screw back out by 3/4 of a turn and re-tighten the locknut. This will give the correct minimum plunger stroke of 0.45mm.
NOTE:- The locknut tightens against the pump end plate, and the endplate itself screws into the pump body on a left-hand thread. If you are not careful when tightening the locknut you may inadvertently loosen the end plate which will then unscrew itself as you are riding, drastically increasing the plunger stroke and oil delivery rate - the exact opposite of what you were trying to achieve. Hold the pump end plate with pliers and just nip the locknut with a spanner - it only needs to be tight enough to hold the grubscrew setting.
At this stage, the pump plunger gear and cam pushrod can be lifted out for inspection, and the pump end plate can be unscrewed (LEFT HAND thread, remember!) to release the pump control lever and its return spring. The inlet and outlet union bolts can also be removed to flush out the oilways in the pump body, but take care not to lose any check balls and springs inside the unions. (I think that the BS90 oil pumps only have a check valve in the outlet port only, other modesl have valves in both ports).
On assembly, the check valve components must be fitted in the right order, noting in particular that the two check valve springs are of different lengths and the two union bolts are different, the outlet bolt having an “O” mark stamped on its head. To assemble the outlet check valve, place a check ball into the pump outlet port (the lower of the two ports) and place the longer check valve spring into the union bolt. Then fit the union bolt along with its “banjo” union and sealing washers. For the inlet check valve, place the shorter spring into the pump inlet port, followed by a check ball. Then install the union bolt along with its “banjo” union and sealing washers, taking care not to dislodge the check ball.
NOTE:- If you come to refit the outlet union whilst the pump is fitted to the engine, the outlet port faces downwards and the check ball will simply drop out before the bolt and spring can be fitted. The trick here is to place a small magnet against the outlet bolt head, then put the spring into the union bolt and a check ball onto the end of the spring. The magnet holds everything together while you fit the whole thing to the pump.
Complete the pump assembly by following the reverse of the dismantling procedure, not forgetting to refit the spring in the end of the plunger gear. During assembly, ensure that all internal components are scrupulously clean and coated with fresh 2 T oil.
Once the assembly is complete, refit the pump to the engine and firmly tighten the fitting screws. On the drive and of the pump there is a 5mm screw or bolt with a fibre washer under its head. This is a combined filler and level plug for the pump gearcase. Remove the level plug, put a few squirts of oil into the pump gearcase through the screw hole, and then replace the plug.
If the level plug on your oil pump is a cross-head screw, it may be a good idea to replace it with a short 5mm bolt, as this screw is awkward to reach with a screwdriver once the pump is mounted on the engine. Remember, though, that the level plug is a pre-ISO thread (5 * 0.9 pitch), so don’t try using an ISO standard bolt or you’ll damage the thread in the pump.
Reconnect the oil inlet line to the pump after expelling any air bubbles and checking that oil flows freely from the line under gravity. Reconnect the outlet line between the pump and the Disc Valve Cover after priming it with oil from a pressure can. Refit the oil pump cable and adjust it to give 1mm of free play with the throttle closed.
Start the engine and warm it up at idle speed for a couple of minutes. Then with the engine still idling, raise the pump control lever by hand to the "full throttle" position and look for signs of oil and air bubbles moving in the transparent section of the outlet line. If no pumping action is apparent, stop the engine immediately and investigate the cause. Otherwise, continue to bleed the system by holding the pump control lever fully open with the engine running at a fast idle until the transparent section of the outlet line is free of air bubbles.
Once the system has been bled, take the machine for a short test run. After the initial run, inspect the oil pump for any obvious oil leaks and re-check the oil outlet line for air bubbles. Any air pockets remaining after the pump has been re assembled and bled should have cleared after a few miles of normal running. If air bubbles continue to appear in the outlet line, it is likely that you have an air leak in the system somewhere. A minor leak may not be enough to allow oil to escape, but it can allow air to be drawn into the system when the pump is operating. Remember that both the inlet and outlet oil lines are under suction when the engine is running - the inlet side is subject to suction from the pump, and the outlet side is subject to crankcase depression – so air can be drawn in if there are any bad joints. All oil union bolts should be firmly tightened - but take care not to overdo it and strip the threads in the pump body. If this doesn't cure the problem, carefully examine all the oil “banjo” unions, sealing washers and fitting bolts for cracks or other damage, and replace any that are suspect. The oil lines also need to be free from visible splits and be a good fit on the banjo union spigots. A careful smear of silicone gasket goo on the spigot can help to seal the joint - but make sure none can get into the oil lines or you may clog the oilways and wreck your engine. It may also be a good idea to wire the oil lines tightly onto the banjo unions at both pump and oil tank.
A properly set up "Jet-Lube" BS90 or BS100 should give at least 600 miles per litre of 2 stroke oil in normal use. If oil consumption is still excessive after carefully setting the pump plunger stroke and adjusting the oil pump cable, the plunger adjustment grubscrew may be turned in slightly to reduce the oil delivery rate.
Note, however that this is a last resort and you must first be certain that there are no other ignition or carburation faults making the engine run off-song, as this may result in larger than normal throttle openings and therefore increased oil consumption. If you do try altering the plunger adjustment, never move it by more than a quarter-turn from the factory setting described above, or you risk drastically reducing the oil supply on a closed throttle - a recipe for severe engine damage on the over-run - and be prepared to revert to the factory setting immediately if the engine shows any signs of distress.
