commander tickover adjustment

[cornishman]

I have just finished respraying my commander and thought that it would be a good idea to strip and clean carbs before refitting sidepanels etc ,all cleaned and set as per workshop manual jet height set by an engineer friend with access to measuring tools .now it wont tickover properly ,are there any base settings for the idle adjustment screws ? and can I use a morgan carbtune to synchronise the carbs ?.I have limited knowledge of the rotary, learning all the time but am pretty good mechanically any help would be appreciated as I want to ride it .fed up of tavistock

[Dell Boy]

My non technical but knowledge gained from experience, is run it around a bit ,especially at speed to let the carb settle down before you start fiddelling.When you do, do small adjustments.Also forget all your previous carb adjustment knowledge, it wont help. The best advice I received from the Norton factory in 1989 was that no matter what you did to the SU carb providing the engine was a good `un it would run reasonably well as the carb adjusts itself to suit the demands called on it.I have followed that advice for 30 years & countless thousands of miles & I DO NOT TOUCH MY CARBS, clean them or adjust them or even put oil in the damper pots except now & again if I think about it.My tickover on both bikes is 400 revs.I think you should look at the retard or lack of it with your ignition. This would cause it to have a fast tickover.I found the Grey commander was ticking over too fast due to me having, by accident, knocked the top of the thermistor. Put it back on & she now ticks over at 400 when hot enough [92 degrees] for it to retard the ignition.My problem is that both my Commanders run at about 82 degrees on a run & take a long time to get hot enough to retard the ignition say when stopped at traffic lights after a non stop run.Derek.

[Dell Boy]

P.S. Mixture screw heads should be flush with the carb body as a starting point. Then adjust by very small increments with test runs in between to clear out the engine.Derek.

[cornishman]

thanks for that info derek my problem is that it wont tickover it keeps stopping ,I fitted a digital ignition last year after starting problems, that made it run and start a lot better but the bike has never ticked over smoothly .the previous owner played with the carbs a bit apparently thats why I tried to put every thing back as per manual. really annoying at lights etc getting a bit fed up with it havent used it much since last summer because of this problem .I am getting so fed up with it I may consider selling the thing if I cant solve this problem dave

[Richard Negus]

Dave,There are two adjusters at each carburettor, either of which can screw up the idle if not set correctly.On the carburettor itself, and below the union where fuel enters, is the mixture adjuster - this has two screwdriver slots at 90 degrees, and is situated down a recess. This screw moves the jet in relation to the needle to make it richer or weaker over the whole range. Screw in is richer, screw out is weaker. This can only be set to the standard position by taking the vacuum chamber and piston off, allowing access to the top face of the jet, and using either a vernier depth gauge of dial gauge.The other adjuster is in the casting at the front of the carburettor and has a screw with a single screwdriver slot, the idle adjuster. This adjusts the volume of fuel/air mixture entering the engine at idle with the throttles closed. Screw in to reduce idle speed, screw out to make it faster.There is also an adjuster screw between the two throttle butterflies which affects how the engine pick up from idle. Almost impossible to access, but doesn't often need checking/adjusting.As your engine doesn't idle when hot, the first thing to try is the idle adjusters; screw both out equally, 1/4 turn at a time, until speed increases. You may find that the engine races after closing the throttle, so turn them in a little bit at a time until you reach a balance between idling and racing.If you can't get an idle, measure and, if necessary, re-set the jet position and try again.Still no idle when hot? The engine may be low on compression and need an overhaul. A bodge, sorry - short term measure, is to disconnect the temperature switch or thermister so it always runs at full advance and should then idle at about 1000 rpm.R.

[cornishman]

thanks for that richard you say that it may have low compression, the bike starts first time no noises from air intakes and it has only done 19448 miles could it still need rebuilding at this low mileage .many thanks dave

[Richard Negus]

Dave,I've known some that need a rebuild after 5,000 unkind miles in 20 years ! Cold starting isn't usually a problem with a low compression engine, but it becomes more difficult when re-starting a hot engine. If yours is ok in this respect, persevere with the carbs. There is an O-ring (55-1496, ANIL)in the cold-start mechanism that hardens with age and allows excess fuel into the airflow even when the choke is 'off'; this can give an irregular idle and even stalling. Carbs may be due for a complete clean and overhaul; viton-tipped float needles are available from Burlen.Silly thing really, but have a look at the vacuum pipe to the fuel tap. Rubber sleeves at each end of the plastic pipe have been known to perish and crack with age, letting air in and interrupting fuel supply.Take the fuel pipe off the tap; I've just had a Commander where the tap didn't shut off at all. Combine that with a leaking float needle and the result is excess fuel in the rotor housing.R.

[cornishman]

thanks once again richard as I write this carbs are on the bench been stripped completely all rubbers checked no problems as I replaced them as advised by pete morris when I bought the bike, new vacuum pipe and connectors fitted last week as the rubbers had cracked and a kit fitted to petrol tap as I had a chat to frank at the bristol show and he told me the story ref those, am now going to take them to an engineer friend to check and if necessary set the jet height will let you know if any improvment dave

[Richard Negus]

And when you're putting them back on the bike ......... check the smaller diameter pipes that go between the carburettor outlet casting and the rotor housing are fully engaged at both ends. They are soft metal and can concertina if not fitted correctly, allowing an air leak and loss of idle.R.