norton commando carbs

I JUST ADJUSTED THE ORIGINAL AMAL CARBS ON MY 74 MODEL. IT WILL IDLE VERY NICELY AT 900 RPM. THE PROBLEM IS THAT IT TAKES 30 OR 40 SECONDS FOR THE RPMS TO FALL BACK TO IDLE AFTER I BLIP THE THROTTLE. IT SEEMS TO FALL PRETTY QUICKLY TO 2000RPM THEN SLOWLY EASE DOWN TO 900 RPM WHERE IT WILL STAY. THIS BIKE IS NEW TO ME AND THE FIRST NORTON I HAVE OWNED. BEEN SITTING 25 YEARS WITH 3000 ORIGINAL MILES. YES I REBUILT AND CLEANED CARBS. RUNS GREAT OTHER THAN THE IDLING PROBLEM. ANY HELP WOULD BE APPRECIATED

Welcome! Got any pics of the bike? A sticking auto-advance or unbalanced carbs can cause that symptom.

Could be cables or the throttle hanging up a bit. I pulled the cables off of mine, hung them up in the shop and made a funnel shape out of tape and plastic, then sprayed Corrosion Block in there and let it hang until it came out the other end. It made a big difference in the amount of drag on the cables.

There are cable lubing tools made specificaly to push lube through a cable housing. I have never used one, but the idea appeals.

Russ

It could be an air leak in the intake somewhere. Possibly the o ring on the mixture screw ( they get worn ) or somewhere on the carb mounting.

Could be one or both of two things:

The cables are not fully extended as has been mentioned, take the air cleaner off and turn the throttle with engine off and hear the slides "slam" down.

Or, it could be your fuel mixture screws are set too lean. Turn them in until fully seated and then back out one and a quarter turns for a pretty close setting.
Too lean will cause the motor to run on and not settle down fast.

Maybe your threaded adjusters at the top of your carbs need looking at, no kinks in cables, etc?

Also check/replace balance hose between the carbs.

G'day Ken,... Sticky throttle piece, old cables, worn slides, even the springs can get a little weak right at the end of their travel. It's all good fun, do the slides snap shut o.k. ? Clean revving but slow to return to idle can mean a Lean mixture at 1/4-1/3 throttle opening, then as the bike settles, the Idle jets take over. Do a plug chop at 1/4 or so throttle on the road. Read up on the Amal threads...AC.

first check is an easy one. with engine off does throttle snap back to the idle stop's?? if it does and still has the point's the MOST likely culprit is a sticky auto advance unit. the best thing you can do is to covert to an electronic ignition as the auto advance unit is a lot of trouble to keep working properly.

I've had my Norton a month, new to Nortons. Tried to set up carbs but no great success.

bought carb kit and three new cables.
Striped and fitted new gaskets and o rings
joint sealer on the manifold gaskets...after making special tool fro removing manifolds...er shortening down allen key.

lubed and fitted cables....
visually set up the slides with one turn on each and set up adjusters for even pull
1 1/2 turns out on the idle mix

adjusted tappets, changed oil, cleaned plugs.

oh well start it up and spend the rest of the afternoon on it....
fired up and idled nicely.....took it for a spin and dropped the idle.... that was worth doing.
Rode it yesterday and very smooth.
PS my slides are alloy with brass sleeves.
can't beat new bits...and they are not very expensive either.
have fun.

No need to shout Kens74, we can hear you just fine.

Well KEN ? How did you go ?

Thanks for all the help for a NORTON newbie. The timing advance was the problem, 30 year old oil is a poor lubricant.