Surging Commander

[Anthony Duffield]

I came back from the Shetland classic show with the left hand cylinder oiled up, two new plugs and all back to normal; however:At the same time I found that the left hand air control adjustment screw was different (3.5 turns) to the right hand screw (2 turns) I set both at 3 turns, i.e turn fully CW then CCW 3 turnsJust a few days ago I noticed that at 4000 revs the bike seems to surge, reading the posts on this subject I have returned the settings to as found with no difference, I have tried numerous settings but still with no joy, the settings effect the idle speed, to far our increases the speed so I have not tried to see if the surging goes away with the engine idling fast.Curent settings are 2.5 turns CCW on each screw, idle speed approx 800Yesterday I stopped to make an adjustment and noticed dirt in the fuel filter, when I got home I found a new filter in my box of bits, which I am now soaking in fuel to make sure it can stand ethanol, if it is OK I will try the new filter and see what happens.Otherwise the bike pulls hard and runs well.I really want to get it sorted before the International rally next month.If anyone has any ideas I would be grateful.ThanksTony

[gripper]

The air adjustment screws only control the mixture and flow at tick over because the throttle butterflies are supposed to be fully closed then. Once the throttle starts to open then the bypass bleed is redundant. The screws on the body of the carb control the height of the main jet and hence the mixture over the whole rev range. That needs setting with the carb tops off and a depth gauge, or the tail of a digital vernier calliper woks well.

[Anthony Duffield]

GripperThanks for the info.My new filter stood the test of ethanol and is now fitted but it was too late to get the bike out for a test run, once I get the chance to give it a run I will let you know what I find.ThanksTony

[Anthony Duffield]

I have tried, I think, just about everything:The bike pulls well and has no problem when the throttle is opening only when cruising at say 3k to 4k there is a misfire and a very occasional back fireChanged the plugs and checked the plug leadsGW recommended I clean the carbs (done), I will check the butterfles tonightChecked the trigger and reset the gapFound the regulator producing 17 volts, ran the bike with alternator disconnected, no change, earthed the regulator and output now normalChecked all the connections and changed back to the old ballast resistor, there was nothing wrong with the new one, I fitted two new 6 volt coils about three months agoChanged the fuel filterFound the fuel vacuum pipe split so renewed the whole of the pipe from engine to fuel tapChecked compression, there is no chuffing noisePerhaps my imagination but it seems to be drinking fuel but the plugs are the normal colourThe engine starts occasionally on one cylinder the left one but when only just a little bit warm ticks over nicely, pulls away cleanly, has plenty of speedNot having much experiance of SU carbs; I wonder if when using large throttle openings there is a jet for this purpose and when cruising there is another that takes over??I have booked to go to the International Rally next week, I dont want to miss it so any help and suggestions will be gratefully received.By the way I expect to take delivery of an electronic ignition supplied by Graham tomorrow, perhaps that is the answer??Tony

[Anthony Duffield]

i have sorted the misfire; last night I removed the right hand carb including the induction and idle tubes, stripped the carb 'again' made and fitted new joints cleaned both ends of the tube(s) checked the O ring which was luckily not hard boxed it all up cursing the clip that locates the fast idle rod and this evening took the bike out for a run; no misfire and smooth as silk.Why the right hand carb? it was this side that would not always fire up when coldI suspect I had an air leak probably where the induction tube fits into the rotor casing, anyway it is OK now and after a few more service type checks will be ready for Bremen.Tony

[graham]

Really pleased for you Tony,Our favoured mode of transport is quite old now! So almost any component can reach the end of it's fatigue life.Well done finding it, hope you have a safe ride to Germany,Graham.

[Anthony Duffield]

Graham,Many thanks for your advice on the phone, since first noticing the misfire some weeks ago and in the process of checking all possible causes I have learnt a lot about these bikes; still so much more to learn.I think my rotary is a great bike; it is interesting, challenging and can be a joy to own and ride.Tony