1984 Kawasaki Z1100R
Q: My problem is that after around eight to 12 miles the engine starts to go off one cylinder at a time until the engine finally stops as though I had run out of fuel. I then wait about 15 minutes and I can then start the engine and it does the same. I have changed the plugs, plug leads, plug caps and coils, stripped and cleaned the carbs and carb filters, set float heights, removed the petrol tap, cleaned the filter and changed the fuel pipe. I have checked fuel flow from the tank through the three-way tap and in the gravity feed position the flow is good. I have tried running with the petrol tank cap cracked open in case the small air vent may have been partially blocked, as this might have caused a vacuum on the tank and at the same time ran it with the petrol tap in the gravity position and still it stopped. The tank has been relined and I thought this might been part of the problem but checking inside the tank everything appears okay. As you can see, I have checked fuel should be getting to the carbs so I may be on the wrong track: the only thing left is the ignition pick-ups and the ignition coils igniter box – they might be heating up then cooling down. Help! Bill Brown A: Well I must say you seem to have covered pretty much everything in your investigations to eliminate problems with the fuel supply and have gone a good way with the ignition system. As you suggest, there are only three further areas to cover: ignition coils, pulser coils and the ignitor. I suspect you are right that whatever is the dodgy part is working okay until it heats up then maybe a coil or component fails, or maybe some insulation breaks down and the unit stops working. The difficulty here is that it would be difficult to find a way to test the units yourself to find out which is defective. You could test by substitution but this could turn out to be quite an expensive method, as you would possibly end up replacing parts which were working okay. Thinking about it though, everything works and then the failure spreads until nothing works. You have two ignition coils and two pulser coils, but only one ignitor so… that would suggest the ignitor is the dodgy component. It is obsolete now but you might get a secondhand one or you could try Electrex on (01491) 682369.
another diagram I have, there are black and white wires coming directly from the pickup, and these are connected to black/white and black/yellow wires respectively, and these connect to the white/purple and white/orange wires respectively on the AB11. But yours are green/white and green/ yellow. Has the black colour in the wires’ insulation turned green over the years or something? Anyway, the rational answer would be for you to connect green/white to white/purple and green/yellow to white/ orange and see if it works. Incidentally, you are meant to have a 5PU pickup. Is yours identified as such? You can test it by checking the resistance between the wires, which should be between 600 and 700 ohms.
1980 Honda CB250N Superdream
Q:I hope you can help with a carb problem on my Superdream. The bike is a 1980 250 fitted with Keihin VB 30B 5LN carbs. I have stripped and cleaned them, fitted new O-rings on the inlet manifolds, ensured the fuel height is equal in both carbs (see further comment below), have ensured that the diaphragms slide easily and the butterflies close etc. The problem is that although the bike starts and runs fine if I pull the clutch in with the throttle closed when travelling, the revs hang at 4/5000 revs and reduce only gradually to a normal tick-over. I have looked at a lot of forums, which incidentally all show a diaphragm rubber not the metal assembly that I have on mine, but can find no answer. Another carb problem is that of the height of fuel in the float bowl. The non-adjustable plastic float assembly coupled with the revised float needles do not seem to match the float height measurement in the book and clear pipes coupled to the carbs showed different heights. I have adjusted this to equalise them but don’t know how far up the float bowl the fuel should be. Finally which way should the air screw be turned to richen or weaken the mixture at tick over?
Paul Skinns
A:First I just need to clarify some carburettor terminology: your carbs have metal pistons rather than rubberized fabric diaphragms, so they resemble SU rather than Stromberg carbs from the car world. These work in the same way and rely on the balance between air pressure (or lack of, as in the creation of a partial vacuum) and the force from a compressed spring to set the position of the throttle slide. The usual cause of a reluctance of the engine to slow down, as you describe, is an air leak in the carburettor mounting but another possibility might be that someone has substituted the wrong springs above the pistons. The strength of these springs is crucial to the correct operation of the carbs. You are quite right that the plastic floats you have are not adjustable. These replaced an earlier design which had plastic floats attached to a brass tang which could be bent to adjust the float height, but perhaps Honda/keihin thought that this was never done correctly by mechanics anyway. I do not have a copy of the genuine Honda manual but the diagram in the Haynes Superdream manual showing how to check the float height looks wrong to me. I shall be exploring this in a separate article soon. For the moment though, the reading you should hope to measure is 15.5mm. On your carbs, you are adjusting the quantity of air in the pilot mixture and hence screwing in will richen the mixture. Again, I shall discuss that topic separately.
Tank trouble
Q:I am just starting work to renovate my bike. It was pointed out to me that ethanol in modern petrol will dissolve the resin in the glass fibre of the tank and gum up carburettors. I did a bit of research, read as viewed on Norton and Greeves websites, it certainly confirmed what I was told. Only Caswell’s GTS1750 was mentioned on the Norton site for sealing of tanks. Further research revealed several options, but many like Petseal (one I’ve heard of) seems to be for metal tanks. Can you offer any guidance as to products and pitfalls? Paul Rackett
A:Yes, you do need to do something about that tank straight away. The resin is not proof against ethanol and it will start to dissolve, with the gummy residue being carried into the carburettors causing blockages. To be honest, glass fibre tanks were a bit dodgy in the first place, with stories of them splitting open in a crash and certainly a knock would make them leak, so if you have a choice it might be best to replace your tank with a metal one. A number of products are available but the primary point to appreciate is that you need to ensure that whatever you choose is suitable for glass fibre rather than metal. Among the easily available products, Wylde’s in Leeds sells Flowliner, which costs £40, while Caswell Europe offers GTS1750 for a slightly surprising £60 (though most of their products do seem to be expensive compared with their competitors.) Whatever you choose, make sure you follow the instructions carefully as messing it up will make the situation worse, rather than better. I shall be covering the subject of tank liners in a Workshop article soon.