Amals again

I finally got my '72 norton to idle as smooth as can be but when I twist the hand grip quickly the motor stalls. It has to be quit fast and I don't notice it when riding "normally". Also I've noticed the acceleration isn't what it used to be.
Carbs appear clean and I rechecked the timing.
Any ideas?
Katzboo

Try screwing the idle air mixture screws in a little at a time and blip the throttle again. My 850 will stumble that way if the idle mix is too lean.

Thanks Dave I'll try that to see if I'm on the right track. I didn't want to sacrifice the smooth idling but getting off the dime is what makes it all work

Katzboo

By getting that nice idle you have got the carbs synced on the throttle stops, but if the slides aren't synced then you get a hesitation on initial opening as the cylinders fight each other. There are various ways of syncing the slides but a rough and ready way is to remove the float bowels and the needles will be exposed, you can watch them as you open the throttle and adjust the cables using the carb top adjusters to get them to start moving together. Don't use the throttle stops to adjust the slide sync, sounds like you have the idle spot on so leave well alone.

what I do is start by removing the air filter, screw in both idle screws to the bottom (all the way in) and screw out 1 & 1/2 turns (wright down what the original setting was for ref). Make sure you have play in both throttle cables and set the slide height position equal using the throttle stop screws. You can do this with a drill bit a a comparison gauge.
Now here is the important bit...stick a piece of tiewrap in both carbs so that the tiewrap rests against the underside of the slide and pivots on the carb body inlet hole. You have to put a slight bend in the tiewrap to do this..You now have two horizontal sticks poking out of the inlet of your carbs, which if you gently twist the throttle twistgrip on your bars, will move down as the slides move up. These two sticks should start to move at exactly the same time....if they dont then make an adjustment to the cable at the carb top until they do.
Once you have that right, put the filter back on and fire up the bike. Make minor adjustments to each carb throttle stop screw, the one on the body that holds the slide from dropping further, untill you have the idle speed right. (Adjust both carbs the same amount). Now adjust the pilot screw by small amounts in or out until you hear that carb running a bit faster. Once you have that point screw in about 1/8 of a turn.

Can I make one further point....When you pull those amals apart you quite often loose the tapered needle position on its grooves, and end up putting it back in a different groove. The way you describe your lack of accelleration as compared to previous I suspect these needles may need moving 'up', so the clip wants to be in a groove lower down the needle.

Good luck, let us know how you go on.
Stu

Thanks for that Bigstu. After 37 years with my Commando that is the clearest explanation I've ever seen on how to do the synchronizing. I'm an electrical guy so there are a lot of ty-wraps around here. That is a great method. I know what I'll be doing this weekend.

Russ

I sync mine with a carb stick - vacuum gauge.

I bought mine almost 30 years ago, and can synchronize up to four caburettors. Of course with the Norton I only need two of the hoses.

Mine looks different from this one, but is the same type (hoses connected to mercury columns)



Basically, set the air mixture and idle speed as you normally would, and also make sure the vacuum reading is identical on both carbs. Once balanced, crack the throttle and you'll see the mercury move. If both columns don't move together, adjust one cable, no more than a 1/2 turn at a time, until the columns are synchronized.
Once balanced and synchronized, the mercury columns will move in unison throughout the rev range. I put mine on the carb stick each time I change the oil, just to make sure everything's still good.

Since everything in my garage is a twin, I use a TwinMax http://www.casporttouring.com/thestore/prods/24002.html
No hazardous mercury to deal with and you can lay it in a tankbag and actually check balance under load. I find it as accurate as the manometer (I still have one for the occasional 4-cylinder I get asked to work on) but much easier to use.
Ron

Ron L said:

Since everything in my garage is a twin, I use a TwinMax http://www.casporttouring.com/thestore/prods/24002.html
No hazardous mercury to deal with and you can lay it in a tankbag and actually check balance under load. I find it as accurate as the manometer (I still have one for the occasional 4-cylinder I get asked to work on) but much easier to use.
Ron

Click to expand...

That's pretty cool.



Under $100 too.

Thanks for the tiewrap technique. I have my carbs synced to near pefection, however that didn't cure my problem. I pulled the plugs and found they were sooty so I'm looking at trying to lean everything a bit. I rechecked my floats and I'm confident they are at the proper level although confident is a relative term. My needles are on the center position, moving them down may help being to rich. I had new rings put in this spring but I can't imagine that would have this effect.

katzboo

I'm still learning the fine art of carb tuning especially at idle.......but alas, the 71 (former) basketcase has only been in service not quite a month:

there are 2 one points that I'm confused about ;

the mixture valve on the side of the carb: does this control the mixture only at idle or throughout the rpm range?

secondly.... I screw that IN to lean the mixture?...... (o.k., now that I think of it, that makes sense)

thanks:

kfh

Hi Katzboo
Maybe worth checking the connections to your coils, and the ones to and from your ign system. Maybe the quality of the spark is your problem.
Stu.

I'm still unclear: does the mixture screw setting affect the entire rpm range or just during idle and low rpm's?

hi 71,the mixture screw only governs idle and overlaps slightly onto the cutaway, i believe its an air screw so meters air and not fuel,lab posted good info on amal carbs on the other index (anything else motor cycle related)

71basketcase said:

I screw that IN to lean the mixture?...... (o.k., now that I think of it, that makes sense)

thanks:

kfh

Click to expand...

I believe you actually screw OUT to lean the mixture. The pilot jet meters air, not fuel. Screwing the mixture screw in cuts air flow, richening the mixture. The pilot jet only controls to about 1/8 throttle, when the throttle cut-away takes over.

As the throttle slides wear, you'll have to screw the pilot screws in to compensate for air leaking around the slides.

as always, thanks loads, folks

Karl

here's why this site is great:

so I was cruising around the tech site here and FINALLY realized that on the 71, the needle is attached in the MIDDLE groove, not the last one.

I changed it and voila! it idles like a dream!

thanks for a great site!


Karl

Always nice to get a bike running sweet again, well done. I suspected the tapered needle position.
Carbs go like this, but with quite big overlaps....
Full bore = main jet
1/2 to 3/4 bore = tapered needle position
1/4 to 1/2 bore = type of slide...the shape of the cutaway (ignore this one unless you really keen)
0 to 1/4 bore = polot jet and idle screw.

You should tune your carbs in this order by doing 'plug snaps'...ie running for 30 secs on the road at full bore, hitting the kill switch...coasting down with engine dead and checking plug colour ...white=lean, black(soot) = rich
then 1/2 bore for tapered needle
then get it idling on air screw
do again from top
done.
Stu