For more on this Tech Tips Vol. 4, text or call Bob at 214-636-7368 or email at • visit at
Suggestions and opinions presented in "Tech Tips" are provided for the benefit of clubmembers and guests. If you're not completely comfortable with performing your own mechanicing please hire a qualified shop or independent mechanic. Bob Cox/Custom Classic Cycles and the NTNOA are not responsible for accidents, property damage, injury or fatalities resulting from any information contained in "Tech Tips." • Unless otherwise stated, all graphics, photos, illustrations and copy in "Tech Tips" are the exclusive property of Bob Cox/Custom Classic Cycles • Copyright © 2017
Tech Tips Vol 2 Top
You’ll need to know which handlebars you’re using such as UK/European, Western or Hi Rider. Custom bars may require a custom-made initial cable. Let your supplier know exactly what you’re trying to fit. Bars are measured by overall width, rise and
pull back.
Use new plastic banjo filters and fiber float bowl plugs (not shown) as they are prone to leaking.
A balance tube links the two
manifolds together. Automotive vacuum rubber hose works fine.
2 INITIAL CABLE - If the standard cable is used on the quick action version it will not let the carb slides drop fully. Conversely if you use the QA cable on a standard throttle you will not be able to adjust out all the slack. I prefer the
quick action over
the standard.
3 JUNCTION BOX - Unless you’re using a dual cable Amal throttle, you’ll need a one-into-two junction box. These come new with the nylon “piston” that the cables slot into. Do not be tempted to grease or oil the piston or the cables.
1 THROTTLE - You may or may not have your original Amal throttle and if you want to use stock, readily available throttle cables then this is the way to go. Minor variations aside, Commandos used two different versions of the Amal throttle - standard and “quick action.” The latter introduced on the 850’s provides more throttle with less twist and requires a different longer initial cable.
064600 - Standard
062032 - Quick Action
061451 - Western/Standard
064137 - Euro/Standard
064602 - Western/Quick
064601 - Euro/Quick
064638 - Hi Rider
019824 (air throttle or choke, if used)
033144 (takes 2)
065192 Twin Taps & Twin Amals
061440 Early
376093 Filter for banjo fittings
622151 Float plug fiber washer
062819 - 30mm Mk 1 Carb
065196 - 30mm to 32mm*
062711 - 32mm Mk 1 Carb
*RH10 Heads
033281 - O ring carb flange
NM23358 Tuffnol 30mm
063458 Tuffnol 32mm
R-0990 K&N Universal air filter for twin Amal Commandos
PART NUMBERS - Numbers shown are from Andover Norton and may vary from one supplier to another. "NM" prefix numbers are old and may be superseded.
065749 - Carb 850 Mk2A/Mk3 Left
065750 - Carb 850 Mk2A/Mk3 Right
062359 - Carb 750 30mm Left
062360 - Carb 750 30mm Right
062709 - Carb 750 32mm Left
063710 - Carb 750 32mm Right
Note: Specify Premier Carbs for the best. Check with your supplier for the correct carb for your exact model and altitude.
If you’re running without an air filter and/or open
pipes then you may need a different main jet, needle
jet and needle or even a different slide cutaway. Check and set the float bowl height even on new carbs - easy with “Stay Up” floats with bendable steel tabs, not so with original plastic ones which require brass seat adjustment.
NOTE: Chokes are not addressed because they are so seldom needed and best removed. Be sure to plug the hole with the correct plug which screws in from the top in place of the choke cable adjuster.
4 SHORT CABLES - These go from junction box to carbs and are the same length. Be careful routing them as they need to pull the same. If one goes under and the other goes over an obstruction(s) they won’t pull evenly coming off idle. These cables take a beating where they make a sharp turn down into the carb tops.
5 CARBURETORS - Most Commando’s use 32mm Amal Mk 1 Concentrics but they are different inside depending on the model. We all know the shortcomings of Amals and if you’re reviving old ones give them a thorough examination before you start ordering parts. Typically the slides and slide bores will be worn even to the point of being out of round. The needle jet and its accompanying needle will be worn meaning an overly rich mixture. The old bowl floats will not like our modern gasoline/ethanol fuel so new “Stay Up” floats are in order. My recommendation is to start with a brand new pair of Amal Premier Carbs. Let your supplier know your model, where you live and any special tuning so they arrive with the correct jetting.
6 FUEL LINES - You’re gonna want new ones for sure just don’t expect them to stay clear and flexible too long. Modern fuel makes them yellow quickly and become hard - not good for keeping the engine movement isolated from the tank and petcocks. I rebuild mine using 5/16" spring clamps in place of the crimpings and 1/4" ID braided fuel line which I buy at length (Dime City Cycles). The original line fittings and the short crimped section that joins the two lines together are all that I retain. While you’re dealing with fueling it’s a good time to inspect the petcocks for leaks. Again they don’t like the ethanol gas either and pack it in quickly if not using ethanol resistant materials.
7 MANIFOLDS - These are not handed but it’s very important to get the right ones for the head port size on your Commando. Some are 32mm at the carbs and 30mm where they join the head. Others are 32mm at both ends (’73 850 for example). Don’t overlook the tuffnol heat insulators, the “O” rings that go between the manifolds and the carbs, and the allen bolts with (my preference) split locking washers. Normal split washers are too wide so source the correct narrow width ones from your supplier.
When assembling manifolds to carbs do not overtighten the nuts as it will distort the manifold flanges. Ditto when tightening the manifolds to the head. Also be careful not to drop the allen bolts or lock washers into the intake ports especially if using stainless. I plug the intakes with wads of paper towel and then remove them only when that particular carb goes back on.
8 AIR FILTER - If you’re willing to put up with the original “ham can” air filter arrangement then more power to you. Do your fine carb synchronizing before you install it and be sure the doors are shut to your workshop so your neighbors don’t hear you cussing when you try and install the rubber carb gaiters. Someone at Norton made the space about 3/8” too narrow. A better option is the K&N air filter for Commandos. Not original but so much easier to remove and reinstall, remove and reinstall, remove and reinstall...
To remove the inner allen bolts which hold
the manifolds to the head requires dexterity
and shortened allen wrenches. The original
carb bolts use a smaller wrench than the
stainless steel replacements (the latter
being smaller). I cut the wrenches down
using a Dremel tool with a cutoff wheel. The
steel is a bit hard for a hacksaw but can be
cut that way with persistency. Trim on the
long side and then grind down to these OD’s. File bevel edges in the flats on both cut ends so they’ll find the bolt holes easily.