proper way to raise the idle

MikeM · May 20, 2016

I need to raise the tick over slightly. What is the proper way to sync the carbs?
At tick over its very slow and the orange charge light is on. Slight increase on the the throttle puts the light out and smooths the tick over.
Its tick over at about 800 RPM and seems to smooth at about 1000.
I assume there are screws on both carbs?
Suggestions?

htown16 · May 20, 2016

On the side of the carbs are screws that angle up. Mark where the slot of the screw is on the carb body with a magic marker. Turn each screw in the same amount until you get an even tickover. Shoot for around 1000 to 1100 rpm on a hot engine. About a quarter of a turn should do it.

MikeM · May 20, 2016

Thats what I need.
Thanks for that.

montelatici · May 20, 2016

Come on. Let's give the guy the correct answer. First, synch the carbs. Unscrew the idle screws (the one that is angled upward) so that they don't touch the slides. Stick a finger into each carb inlets and turn the throttle adjusters so that you feel both slides moving at the same time. You have to remove the air cleaner obviously. Once both slides move exactly at the same time you can set the idle. Close the air screw in to full stop, not too tight mind you, but full stop. Then, set both air screws at one and one half turns out. Then start the bike and adjust the angled screws a little bit at a time to get close to the idle you want. Once that's done, feel the exhaust pulses coming out of the exhaust and try to set those angled screws so the pulses from both exhaust pipes are about equal at the rpm you want your idle at.

Danno · May 20, 2016

What about leaning out the idle air screws a quarter turn at a time until the rpm goes up and then dropping it back with the throttle stop (angle) screws? The one-and-a-quarter or one-and-a-half turn settings are just a starting point.

montelatici · May 20, 2016

Why would you want to over complicate a relatively simple process to achieve an idle you are comfortable with? Set the air screws at 1 and 1/2 turns and then set the idle after synching the carbs. Sheesh. I have owned Commandos since 1971, and have raced them, every guy that tuned these bikes did it that way from when I was 18 years old, I learned the process from those guys, all dead by now. Why try to re-invent how to boil water?

bluto · May 20, 2016

The drill bit method is a very easy and accurate way to sync the throttle cables before adjusting the idle speed and mixture screws (and having the cables adjusted properly makes a BIG difference in how the bike runs off idle)...details are in the link below along with a lot of good rebuild and tuning info.

http://www.jba.bc.ca/Bushmans%20Carb%20Tuning.html

montelatici · May 20, 2016

Driil bit? What a silly concept. Your fingers can feel the movement of the slides much more accurately. Unbelievable these youngsters.

kommando · May 21, 2016

No method is silly, I back off the throttle stops and allow the carbs to snap shut and adjust the carb top adjusters until I hear one click not 2 clicks. Read all the variations and pick the one that suits. I prefer my version as I have the black plastic air filter housing making access to the carb entries difficult.

Danno · May 21, 2016

Also, synchronizing the throttles properly involves removing the balance tube between the manifolds and attaching a pair of vacuum gauges or carb stix (whateve) to assure the throttles are operating together. The visual or drill bit method is just another starting point. Kinda like using the mark on the alternator rotor to set ignition timing.

ashman · May 21, 2016

montelatici said:
Driil bit? What a silly concept. Your fingers can feel the movement of the slides much more accurately. Unbelievable these youngsters.

That's the way I do mine using my fingers to feel the slides, have been doing this for 40 years now and my Norton is still running great.

Ashley

grandpaul · May 21, 2016

montelatici said:
Set the air screws at 1 and 1/2 turns and then set the idle after synching the carbs.

The chance of getting a perfectly matched pair of carbs that will each respond exactly the same to the same number of turns on the low speed mixture screw is relatively low.

Danno said:
What about leaning out the idle air screws a quarter turn at a time until the rpm goes up and then dropping it back with the throttle stop (angle) screws? The one-and-a-quarter or one-and-a-half turn settings are just a starting point.

THAT is the correct method.

MikeM said:
Its tick over at about 800 RPM and seems to smooth at about 1000.

Yes, 1000 RPM is the correct idle speed. 800 is too low.

montelatici · May 21, 2016

Well, go ahead and over complicate the process for the guy. I have been tuning Nortons for street and track since 1970 . For a guy that just wants to get his idle at an RPM he is comfortable at, you are throwing in adjusting the air screw to compensate for minute differences in mixture at idle. This results in too many variables and will guarantee that he will have a difficult time getting to the idle he wants with both cylinders doing the same amount of work. Remember, the last part of the job is feeling the exhaust pulses from both cylinders and making sure they are equal.

Danno · May 21, 2016

It is what it is and if it's over-complicated, that's why little children don't mess with old motorcycles needing arcane methods.

htown16 · May 21, 2016

I find that I have to adjust the idle both up and down slightly on all my bikes on a fairly regular basis and carry a screw driver in my riding jacket. Could be how long the gas has sat in the tank, the temperature, ambient air pressure or even the phase of the moon. That why I told the original poster to just turn the slide screws up slightly. I always feel the exhaust pulses to determine if the cylinders are pulling evenly, forgot to mention that.
With that said I do know how to do a proper full readjustment. Theres a number of different methods that probably all work about equally well with vacuum gauges being the ultimate answer. I use basically the Bushman method with a few tweaks and that gets done fairly regularly but you shouldn't have to go through the entire proceedure everytime the bike decides it needs an eighth turn on the idle screws to run a little better on any given day. If a simple slight adjustment of the slide screws isn't making it happy by all means do the full adjustment proceedure.
See the section on synchronizing the carbs for idle and slow speed running in this link for the method I use.
http://www.jba.bc.ca/Bushmans%20Carb%20Tuning.html

B+Bogus · May 22, 2016

kommando said:
No method is silly, I back off the throttle stops and allow the carbs to snap shut and adjust the carb top adjusters until I hear one click not 2 clicks. Read all the variations and pick the one that suits. I prefer my version as I have the black plastic air filter housing making access to the carb entries difficult.

This is what I do too.
Works fine for me.

Danno · May 22, 2016

I assume the clicks you refer to are the slides hitting the stops? Seems like you could have one held high by the cable/carb top ferrule adjustment and run the stop up to meet to get both to click simultaneously and still not be the same height.

Fast Eddie · May 22, 2016

Danno said:
I assume the clicks you refer to are the slides hitting the stops? Seems like you could have one held high by the cable/carb top ferrule adjustment and run the stop up to meet to get both to click simultaneously and still not be the same height.

To avoid against that, simply checking for slack in the cable outer, where the cable enters the carb, when the throttle is closed. No slack = slide is not seated.

You can actually get the slides very close like this. Listening for the 'click' when snnapping shut is then a final confirmation.

montelatici · May 22, 2016

That defeats the purpose. You want to check the movement of the slides when they are being lifted. Sure, they might snap back and hit the bottom at the same time when the cable adjustment is slack (with different slackness for both carbs, so they won't necessarily lift the slides in unison. The whole idea is to set the cable adjustment so they lift the two slides in unison.

Biscuit · May 23, 2016

montelatici said:
That defeats the purpose. You want to check the movement of the slides when they are being lifted. Sure, they might snap back and hit the bottom at the same time when the cable adjustment is slack (with different slackness for both carbs, so they won't necessarily lift the slides in unison.
.

Yes they will. Because the slides are spring loaded, if the are sync'd to lift at the same time, only one click will be heard when they snap closed. If one is pulling first, the other one will be "clicking" back first, you'll hear two clicks.

This should the last check though, after assuring the throttle slides are sync'd initially, and are resting on the also sync'd stop screws.

proper way to raise the idle

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