idle speed varies

Hi,
I rebuilt my amal mk1's ran about 1,000 miles so far.
Now at traffic lights w/ engne warm/hot the idle will climb about 200 rpms.
A brap of the throttle can bring it down to proper idle again.
All cables new from Barnett made to exact length as take offs.
Just curious whats going on as I have not encountered this before?
Thanks in advance :shock:
MarshalNorton

Might be worth checking for air leaks between carbs and head.

Could be many things; an easy one is to check there's at least 12 volts at tickover, 'cause if you've fitted a Boyer a lower voltage at tickover would start to advance the ignition and a brap ( I like that) would bring the voltage up getting the ignition back under control.

When you check the voltage load up the battery the same as you would when the problem starts ie brake light on etc.

Cash

I have had similar problems. It was a small vacuum leak in the 2 to 1 manifold and with a tighten
and a couple adjustments of the air screw she was runs at 950 all day....

But at night, With the lights on, Brake on etc. it still sits at 950 but will die occasionally at a long light.
Im thinking about upgrading the alternator. With the boyer & brake lights it may just be to much.

Thanks for the replies.
I'm still running points and therefore I'll check that the manifolds have not work loose to create a leak.
I'm still running stock dual Amal's.
They run great off the line and will wisk you up to 6,000 rpms no problem.
Just hot a a traffic light did I notice the varied idle?
MarshalNorton :?:

My bike (a '73 850) did exactly the same thing, i.e. erratic idle and fast idle that could be cured temporarily by blipping the throttle. I am running new Amals and Boyer ignition. Because of my work schedule my bike sits for about five weeks between uses. I always drained the carbs before I leave it. Nevertheless, evetually it stopped idling at all. I remedied that with the wire-pokey method. I also used a 1/64" drill, which is a smidgeon smaller than a #78. All was OK for a bit, but now it is starting to become difficult to idle again.

So, I think my problem was/is a progressively clogging idle circuit due to either gunky gasoline or debris. Maybe you're experiencing jet-plugging too.

I am considering drilling out the Amal pressed-in pilot jets and installing screw-in pilot jets that would be easier to clean, but haven't done it yet so I cannot say whether that will remedy the problem. My plan is to fight it a bit longer and then, if I can't get it sorted, to go to a Mikuni as I have the carb already.

Could be tired auto advance springs.