Aunt Jonbretta's Tech Recipies for LI, TV, SX, Jet and maybe all the other LI variants except TV I, there's nothing about them here so far but some of this is still pertinent to them.

This page is about passing on information that will be useful to some folks and probably old hat to others in the doing of repairs or improvements to your Lambretta. Contributions are welcome, subject to the disclaimer that Aunt jonbretta endorses nothing that she hasn't tried herself and found useful, and even that doesn't mean that a given idea applied will work for everyone.Common sense and experience reign supreme, and by sharing the latter and trying our best to apply the former things usually improve. Send contributions to

Parts Substitutes

Does your round slide Lambretta die when you brake hard? *

Mine do, or did. LDs and Series I and II LI orTV Lambrettas were equipped with carbs which would sometimes cause the bike to die under hard braking. There is literature which describes how to fix this. It involves plugging one of the passages from the float bowl to the main jet/atomizer chamber. From what I remember seeing or reading, some of these carbs have one passage and others two. Supposedly when the extra one is plugged, the problem stops. I've never tried this, but rather tried the following fix. It's alot easier and seems to work fine.
Loosen the carb clamp and rotate it some so that the bottom of the carb, and more specifically the floatbowl, is swung forward. On LDs with the rightside mounted carb this means counterclockwise rotation and for LIs with the leftside mounted carb this means clockwise. Did I get that right? OK. Try it a little at first and test it to see if it fixes the problem. If not try it a little more. Obviously you can't go hog wild or the carb won't work, but I've had success at angles such as those implied in the pictures.


Aside from that it looks bad, the only thing that I can think of going wrong with this jimmy job is that it may make the bike run a little rich or lean, or it may cause the needle and seat to not seal as perfectly, which may mean that you need to remember to turn off the fuel when not riding so as to prevent flooding. Those are guesses though; my scoots suffered from neither malady as a result ot the tilt-job.
Make sure that the adjustment doesn't result in fuel hose or throttle cable crimping or stretching, and on MK III LDs see that the airhose still looks good or maybe change to a GP airhose, probably a good idea.
* By the way, if you have a pink wire Series II or you've done the pink wire conversion to your Series I or LD, the other reason for bike dying under braking is that your taillite bulb may be burnt out, check it out.

Lambretta toolkit
This is a good travel kit. For daily commuting you may not want to carry all of it, then again if you ride all the time you probably should. Send suggestions if you notice something missing or useless in this list.
  • ratchet handle w/13/16'' plug socket, for spark plug, front axle nuts.
  • 4-in-1 screwdriver.
  • 1/8'' straight blade little screwdriver
  • pliers w/cutters
  • 8,10,13,14,17mm 3/8'' drive sockets and ratchet extension.
  • 6,7,8,9,10,11,13,14 open end wrenches
  • flywheel puller
  • 3 or 3.5 allen wrench (cable trunnions)
  • 8mm allen wrench
  • 10mm allen wrench
  • jackstand
  • micro flashlite
  • 6ft. 16guage wire w/alligator clips
  • spares:
  • gapped sparkplug.
  • tyre mounted and inflated on rim
  • x-long throttle cable and barrel clamp
  • clutch inner cable
  • gear inner cable
  • tailite, pilot and speedo bulbs
  • fuel line
  • trans. oil level plug w/fibre washer
  • points with contact coating removed
  • condensor w/wire and connector

Subject: Mounting tubes into tyres onto Lambretta rims onto Lambretta hubs.

Dimensions of Lambretta standard, TDC semi-wide and TDC full wide rims


Innocenti standard rim 2.085'' 2.325'' 2.860''
TDC semi-wide rim 2.510'' 2.625'' 3.355''
TDC full wide rim 2.660'' 3.070'' 3.695''
Dimensions of clearance around rear tyre using different rim and tyre combinations. The 3.50-10 tyre is a Continental Zippy 3 and the 100/90 tyre is a Pirelli SL26. All measurements taken with tyres inflated to 35 lbs.


Front clearance
Side clearance
Inflated tyre width Inflated tyre height
standard rim,
3.50-10 tyre
.500'' .500''
semi-wide rim,
100/90 tyre
.500'' .220'' 3.950 17''
full wide rim,
100/90 tyre
.500'' .140'' 4.050'' 17''
Dimensions of 3.50x10 tires when put onto standard, semi-wide and full-wide rims. Two tires of different types were used to give more informative results; they are the Sava MC18, a radiused race tire, and the Continental Zippy 3, a blocky all-season street tire. All these measurements were done at 30 lbs.


Standard rim Semi-wide rim Full-wide rim Tire width on full-wide rim
Sava MC18 racing soft 3.50x10 16 7/8'' 16 7/8'' 16 3/4" 3 3/4''
Continental Zippy 3 3.50x10 16 25/32'' 16 25/32'' 16 11/16" 3 13/16''

Subject:You want your scooter bodywork to go together right.

This is about what to look at while assembling LD or LI bodywork onto the rolling chassis, typically after a re-paint, so that the bodywork fits well and the parts don't rub the paint off of each other. Attention to this issue will account for the important difference between a well and a poorly assembled Lambretta. These points of fit between the various body parts should be resolved and adjusted as necessary before any prep or painting is done, so that when you get back your shiny painted parts ready to assemble, you'll know that they are going to fit.
Now let's go. There are a number of separate body parts which fasten onto the frame. They're each supposed to mount up with a little distance between them and the part next to them so they don't rub against one another. On LI type Lambrettas, there are little rubber washers between the frame and footboards and between the frame and the floor portion of the legshield. On LD type Lambrettas there are no rubber washers. All of the different body parts are slightly adjustable as to their exact location on the frame EXCEPT FOR THE SIDEPANELS. Since you can't adjust the sidepanels to the rest of the bodywork, you have to adjust the rest of the bodywork to the sidepanels. This is most obvious on LDs and Series I/IIs because of how the sidepanels curve closely downwards around the rear end of the footboards.
1.First let's look at the various struts, that is the rear footboard supports, the main crossmembers which hold the centerstand on LIs or which hold up the front of the footboards on LDs, and the forward legshield supports. On the LD forward legshield supports, make sure that all the 4mm threaded holes are in good shape. You can do a pretty good job at ascertaining how straight everything is by using two different approaches .
First, with all bodywork removed and the bike standing there as a rolling frame, or with a bare frame on blocks, view the bike from the front so that you can sight back along all the crossmembers and see if ther're parallel with one another and perpendicular to the forktube of the frame. Adjust as necessary. Then view the bike from above and see if all the crossmembers are again parallel with one another and perpendicular to the frame. Adjust as necessary.
The second approach is to use a yardstick or whatever to see if you can identify a straight line along all the points that the footboards and legshield will mount to, so when viewed from the side it will be evident as to whether or not the surfaces of the legshield and footboards will be in the same plane.
Sometimes the feet of the rear footboard supports get bent downwards and this can make the footboard hang low in back. Bend it upwards till it's horizontal and parallel to the whole floor surface of the scoot.
Sometimes the whole rear footboard support can get bent inwards or outwards, causing the same problem. But also and more so this causes the footboard to swing inwards or outwards at the rear. This will be evidenced by a crooked or unparallel joint to the legshield at footboard front, and especially on LDs by the footboard not being parallel to the legshield along the outer skirt surface. It will also affect the gap between the footboard and sidepanel.
Sometimes the whole rear footboard support can get bent forwards or rearwards. This will be evidenced by the fact that the footboard mounting studs won't easily drop into their holes and rather the footboard has to be forced in and out of place. There should be a distance of approx. 11 5/8'' to 11 11/16'' between the front and rear footboard supports. Knock the rear strut forward or rearwards till the foorboard fits, then try the sidepanel for clearance with the footboard. In unusual circumstances, both front and rear footboard struts may have to move forward to clear the panel, but this would be rare. Sometimes the main crossmembers get twisted or bent up, especially on LIs. Since the footboard and legshield both rest and meet on this piece, it must be flat or the sheetmetal won't meet up co-planar. And while I'm at it, on LIs make sure that your stand mounting holes aren't mushroomed out, if they are then fix 'em and use stand re-inforcements when you mount your stand. Regarding stand reinforcements, denfinately call WCLW and ask to speak with Vince at 619 229 0201.
2. Put the footboards loosely on the frame. For SI/II and if you haven't done so, attach the righthand footboard support to the rearside of its mount on the frame and also put on loosely the footboard strips or use 5mm bolts to locate the footboards to the frame. Now put sidepanel beading on the frame, install the panel latches and put the panels on the scooter. You should have a minimum of 1/16'' clearance between the rear end of the footboards and the sidepanel where it curves down around the rear end of the footboard. That's where the footboards go. At the front end of the footboards you'll want about 1/8'' between them and the legshield. You may want to mark the location of the front of the footboards somehow for reference when placing the legshield.
3. Take off the sidepanels and footboards off and install the legshield. Now though it's easier said than done, I'm talking, not doing, so it's pretty easy for me. Fasten the legshield down with that 1/8'' clearance from where the footboards were supposed to go. To accomplish this, basically you fasten the top of the legshield first with the two little bolts from the front, usually so that it just clears below the chrome lock ring at the top of the fork column. Then you push, pull or lever the legshield forward from the rear edge till it's where you want it, getting it the same on both sides, then fasten it to the frame to keep it there. Now put the footboards and panels back on and see if everything clears. Once you have a tentative location for the legshield, fasten the horncasting on to make sure that it lines up with all its fastening holes. LI owners, try the footboard bridgepiece too with its rubber pieces.
The pictures below offer a tentative indication as to whether or not the legshield is in the right place. They show the same detail of the right side of two different scooters, at the rear edge of the legshield floor where it would meet the footboards.

Picture 1 shows the rear edge of the legshield too far rearwards in relation to the rear edge of the sidepanel channel.
Picture 2 shows the rear edge of the legshield more properly related to the sidepanel channel.

So in a nutshell: first the footboards locate according to where the panels go, then the legshield locates according to where the footboards go, giving everything a little space in between.

Here's an addition. If you need to move the crossmembers or footboard supports on an LD, You can do it with a piece of 3/4'' steel bar about 2 feet long as a lever. Slide it inside them and have a go at it. Usually you'll have to round-file out some chunk of paint or weld from the inside of the tube. For the footboard supports you'll have to lie the bike down on its side



Subject: Jetting.

If you want to learn about jetting, this is a great site so click on this:

Subject: lightbulb blowing on A.C. lighting system Lambrettas.

It's probably your stator, or more exactly the lighting coil thereon. If you think about it there's really not much to those systems. A magneto, some wires and some bulbs. That's it. What else could it be? This was my thought process as I tried to figure out why my Series II was having this problem. It's an occasionally encountered problem with A.C. Lambrettas, though usually on 6-poles. One popular repair is to tell the customer: 'Sorry, we don't know what the hell's going on here so we put in a bunch of 12 volt bulbs, try that for a while, see ya' Another popular cure is to install a 6v. 'zener' or 'clipper' diode (if you can find one). I'm told it works well, as it grounds off voltage in excess of 6 or whatever its cutoff is. Not wanting to have to hunt one down and unwilling to send myself down-the-road in the dark with some hope-this-works lighting scheme, I opted for actually repairing the problem. So I got another stator and swapped it in; and as it turns out, BINGO! Before I swapped, I put in all new bulbs, started the bike and warmed it up till it would sit and idle happily for an indeterminate length of time. Then I got an AC voltmeter, turned on the lights, and tested the brown wire output while everything was on and hooked up. I was getting 5 - 5.5 volts at a nice 'taillight' IDLE! Well what do you think THAT stator's going to put out at 3 or 4 thousand RPM? Too much. So then I changed stators and took another reading and read about 3.5 volts at the same idle, which is about what you want to see from the brown wire. That's more like it, so I went out over the next few days on some long high speed stretches, lights on, and they were all still on and doing fine when I finished. End of problem. I think you can buy new 6-pole AC lighting coils but for 4-poles you may have to rewind yours. It's not hard, just time-consuming, but it beats not being able to ride just because the sun went down and your lights blew up by about the time you shifted into third.
By the way, 'taillight idle' is the concept, again for 6VAC bikes, of setting your idle speed up high enough so that your taillight is adaquately visable when idleing (at a stop light for instance) at night. Safety First.

Subject: Lambretta Jet 200 or other LI type comes out of 4th gear when it shouldn't.

There are a few things which can contribute to and/or cause this. It's probably not the cursor, though this part is often changed out as an attempt to fix this problem. If you cursor is in reasonable shape with just a little rounding/polishing on the corners of the tips that bear on the insides of the gears, and the inside corners of the gears themselves are nice and square and free of wear, then they are probably not the problem and the following procedures and examinations should be performed. First let's start with what's supposed to happen down in there. The cursor is moved to within a given gear by the shifting fork which has little bearing pads in its upper and lower arms. These ride in the round track around the outside of the cursor as it spins along with the axle (or 'layshaft'). Now the motor drives the clutch, the clutch drives, and is mounted on, the primary gear cluster, and each gear on the cluster drives and is in constant engagement with its corresponding secondary gear, all four of which are free-spinning on the axle. The cursor has six parallel arms which slide in the six grooves back and forth along the axle. At the end of these arms a little nub sticks up above the width of the axle and fit into notches cut into the inside of each of the axle gears. So whichever gear the cursor is placed within, that gear, already driven by the primary cluster, will drive the cursor, which in turn drives the axle and moves the Lambretta. So that's how the trans works.

1. The hub bearing's bearing on the issue:
Now there's a certain amount of space that all of this fits into. on the left it begins at the landing machined into the case which the hub bearing comes to rest upon. On the right, it ends at the landing machined into the case which the cast iron endplate comes to rest upon. First the hub bearing gets installed, then the axle / cursor assembly is engaged with the shift fork and into the bearing. Well, the axle is located against the bearing, so the bearing is what determines the location of the axle. When you then tighten on the rear hub, that is what finally and exactly locates the axle. So the bearing must be right. There are out there in the world at least two versions of defectively produced bearings. The width of the bearing is 18mm/.708 in. and some of the outside diameter is machined down small enough to fit into the hoke in the case, leaving a lip or flange of the bearing which rests on the landing machined into the case. the thickness of this lip should be .237 in. If it wasn't machined down to that dimension as sometimes happens, then the bearing will not fit as far into the case as it should. The second bearing defect is that sometimes the ball tracks in the races are machined out of alignment so that the inner race resides outwards of being in plane with the outer race. Either of these defects can cause the axle to install too far out towards the wheel, making for some extreme endfloat shim requirements. It can also contribute to the next issue.

2. Range of travel of the cursor:
The bearing, as well as being the stop for the installation of the axle, is also the stop for the cursor when it falls into 4th gear position. If the bearing's inner race is too far outboard for any reason, then the cursor may be prevented from reaching its stopping point at the bearing because the shifting fork may be running into the inside of the engine case before it can carry the cursor all the way to the bearing. This produces two problems. Firstly, the nubs or fingers of the cursor don't go all the way within the gear, making it easier to slip out of gear. Secondly, The cursor doesn't travel far enough to allow the locating balls to come out of the axle far enough to solidly locate the cursor in place, making it easy for the cursor to slide back over them and out of gear. The forces that actually cause the cursor to come out of gear are a mystery to me. Maybe it's something like squirting a cherry pit out from between your thumb and finger.
Another cause of limited cursor travel can be the shift fork itself. If the holes for the shift pads are drilled too far on the right side (as it's in the motor) of the ends of the fork, then there'll be too much meat on the left or inboard side and may be hitting the case before sufficient travel is achieved. Even if well drilled, the ends of the fork might still be just plain too wide. Look for telltale shiny marks in the engine case where the fork comes up to it. If so, there will probably be corresponding shiny corners on the fork where it's hitting. You can prove if it's hitting. With the axle, cursor and fork in place and with the gears removed, move the cursor to 3rd gear position. Hold a strip of paper behind the upper fork end and shift into 4th. Repeat for the lower. If either end of the fork captures the paper against the inside of the case, then it's hitting. If you're satisfied that you have a proper bearing and there is no problem with the shift shaft and linkage as will be discussed next, then the solution could be to simply grind off the excess thickness of the fork ends. After doing so, re-test with the paper. You could also do the paper test between the heels of the cursor and the bearing inner race to confirm that the cursor is getting all the way there in 4th as it should.
Check the fit of the fork pads in their holes n the fork. Any appreciable looseness or wobble will only detract from the fork's ability to put the cursor where you want it to go. If there's practically any visible tiltability to them, replace them. They do wear out and almost every example I've seen merited replacement. Be sure to also get new and extra 5mm circlips for the installation in case you lose or bend them up; they're TINY.

3. Shift shaft splineing and linkage travel:
Once the bearing and cursor travel issues are resolved, then make sure that the external linkage ain't doin'ya wrong. On the shift shaft there are two sets of splines: the lower internal ones for the fork and the upper external ones for the shift lever. The lowers and uppers are of the same number and diameter. Typically, the upper and lower splines exactly line up with each other and this can be seen by carefully looking along the length of the shaft. Occasionally, they don't. If you're going through this procedure with your transmission and are now satisfied regarding issues 1 and 2, then maybe it's time to tentatively or finally re-assemble the trans. Install bearing, install axle/cursor ass'y into fork/shaft ass'y and fully home to bearing, install all gears, shims and rest of bearings and just snug down endplate with nuts and FLATWASHERS. Now put on the shift lever and while rotating the axle shift through the gears. When you snap into 4th, you should hear a solid sounding 'clank' as the cursor hits the bearing. You may need to re-position the lever so it has room to travel far enough rearwards to get into 4th. Now here's where the spline issue comes into play. When in 4th, the lever should have a little room between it and the rear dampener support, enough in fact to also allow room for the flat shift rod and it's rubber cover to also travel to 4th without hitting the support. Now with these things assembled and also with the flat rod hooked up in front with a trunnion to the double-ended cable lever, go through the gears on up to 1st. You should be able to shift fully into 1st without causing that cable lever to hit the forward bolt head of the cable lever support. In other words, you should be able to find a spline position for the shift lever which allows the entire linkage system to travel fully from 1st to 4th without running into anything at either end. If you can't get this done, then you need to get a shaft with a slightly different relationship between the two sets of splines. It seems that Italian shafts usually have aligned splines, whereas Spanish shafts often times have off-aligned spline sets. Ther may also be some variation in the splines of the forks and of the levers. West Coast Lambretta Works has both types of shafts and you could send them yours so that they could find the correct other kind that you need.

4. Cursor spring and balls:
Put in new 5/16 in. balls, enough said on that. Now regarding the spring, I've seen all the above mentioned procedure followed and still had hopping out of 4th. Those springs for the balls in the layshaft can become tired and should well be replaced while you're in there considering the cost of the spring and magnitude of the job. However, a stiffer spring will also make for somewhat more difficult shifting, so you may want to test ride the bike (perform #5-Final re-assembly/shimming) for as long as it takes to determine success to-date in curing the problem. If it still slips out, then put in a stiffer spring, which happens to be the spring used in the business end of the kickstart shaft to push out the plunger. So order a k/s plunger spring and try that. Stiff shifting can be eased to a degree by polishing the inner notched tracks of the cursor so that the balls move more easily over them. But at this point you might not want to polish the 4th gear slopes out at the ends for the sake of keeping that friction.

5. Final re-assembly/shimming/cables:
Assemble the trans, bolt down in the proper position your shift lever and re-attach the flat shift rod and sheath, put the brakes back on if missing, torque the hub on to 110 ft./lbs., put on the endplate and tighten it with new nuts and FLAT WASHERS, and check the end play between the endplate and shim. You should go for between .003 and .011 in. play. If you don't find that gap, then put in a larger or smaller shim as necessary til you get it. When right, replace the flat washers with new lock washers and lock 'er down. As long as you're in there, check and adjust as necessary your kickstart and your chain tension. Put on the sidecase and re-fill with oil before you forget it. Now shift into neutral where the rear wheel will spin without it turning the motor. Re-attach the cables if necessary. Especially if the cables have been detached, make sure that the gear cable housings are fully in their receptacles in the fork clamp before tightening the trunnions at the rear. With the cables hooked up and adjusted, the little pointer on the headset should point exactly to the '0' or neutral mark on the shift control when the transmission is in neutral. If the cables are too tight, shifting will be difficult.

Epilogue. Layshaft to cursor fitment:
This whole discussion is based on one particularily difficult 4th gear slipping problem incountered on a Jet. The final solution turned out to be the exchange of an Italian layshaft for the Spanish one. I didn't do this final thing, but apparently it goes thusly: The diameter of the Italian layshaft is of a much greater diameter than the Spanish part for a certain portion of it's length, and that portion has the grooves which the legs of the cursor slide within. This additional groove depth more exactly controls wobble or general sideways deflection and digression from perfect axial positioning of the cursor. So probably the cursor was flailing around so much that it would lose sufficient location within the gear, or the cursor feet refused to stay sufficiently square to the gear dogs, and the cursor was probably pushed out by force being applied to surfaces out of square because of excessive slop in the cursor's location. Anyway, that fixed it. So if you have another layshaft, preferably Italian, to compare the amount of slop in cursor fit, it might make that final difference, or at least will probably improve this aspect of shift location.

Subject: Soldering on a small ball end for the throttle or choke cable.

Buy a foot of 1/16" brass tubing at the hobby or hardware store; call first to confirm their selection of little hobby-grade brass.
Buy some Tinners Fluid from the plumbers store, and some silver braise or silver solder from the hardware/auto parts/hobby store. You also need a propane or some little torch.
Cut about a 3/32" long piece of the brass and square and clean up the cut end.
Make sure to hook up the other end of the cable with the throttle or choke in the closed position for accurate location of the ball end when you solder it into position.
Slide your little brass piece onto the cable and mock it up in position at the carb or choke plunger. Make sure to close the cable adjuster on the carburetor all the way down, and then back out about 1/8" to allow for final adjustment as necessary.
When positioned, make a little mark right next to the tube with a fine black marker (Sharpie) so you then know where to solder it.
Bring the cable back out of its location. Making sure to keep the brass end exactly where it will go, clip off your excess new cable length a little bit further out than the end of the brass. Spread out the strands of this extra little length of cable so that they make sort of a cone or funnel shaped fan as wide or a little wider than the O.D. of the brass. This will prevent the brass from coming off, now and after you've soldered it.
Now it's time to solder. Put the cable so you have room to comfortably AND SAFELY solder it. Clamp or somehow hold the cable so that it is horizontal and pointing outwards away from the bike and AWAY FROM THE GAS TANK. As necessary make sure that the brass is slid back to exactly where you marked it to go.
Drip some tinners fluid onto your brass and cable so that it runs all through the joint. Heat the work with the torch and then while heating, feed in the solder. Don't breath the smoke. The first time, the solder may not spread, so wipe off any black residue on the work and re-apply tinners fluid and re-solder the work. Don't go overboard with flame size, not much is needed. This time you shoild get a nice little ball of solder over the brass and cable. Make it so that it's a nice chubby size, and that it still fits through the cable adjuster or into the choke plunger. You might need to file down a side of it to fit. There you go.

Subject: Fixing stripped choke threads on your Lambretta carburetor.

This job takes a lathe, good condition drill press, and a hydraulic press to do well, and a 9mm x 1.0 tap to do at all, so get those things or take the job to someone who has them and will do the job for you. I currently have access to them so I might do it for you for a fee, probably about $40.00.
Now I've done this a few times on SH carbs so this procedure will be for them. I'm sure that one would use the same procedure on MA/MB carbs as well, making adjustments if needed regarding drill diameter, insert depth, or anything else.

Part 1: Drilling out the bad threads and beyond.
Disassemble the carb completely.Get two pieces of 1'' square or rectangular tubing, (cut a longer one in half!) or any pair of things that are exactly the same height and a minimum of about 4 inches long. Drill and tap to 5 mm a hole along close to the edge and about half way along the length of each of the two pieces. Clean off any drill or tap welting around the holes. Mount the carb on these blocks using the float bowl screws or M5x30 bolts with flat washers. Set this on the table of your Drill Press.
Set the drill press for about 300 r.p.m. I suggest drilling out the choke bore in two stages in order to minimize the chance of the bit grabbing the part or of the bit not starting concentrically to the bore. First use an 11/16 bit. chuck the bit tightly, then set the depth stop for .840" from the top of the bore, +/- .015''. That depth stops just short of the horizontal bore for choke air intake, which can be seen from the front of the carb. Set the depth by marking the depth on the outside of the part of the carb you're drilling. Then set it on the press just off to the side of the bit and lower the bit to the mark and tighten your depth stop. Test-lower the bit outside of the carb to see if it stops where your mark is. OK, so drill it out, holding the carb firmly with one hand while you drill with the other. Feed slowly, and clear it frequently 'til you're there. Dump the junk out of the carb.
Now put in a 25/64 bit, which equates to .394''. Double-check your depth; you'll probably need to reset for the new bit (the bits are new, aren't they?). Drill out to this final size and depth. Blow out and clean out the carb.

Part 2: Make the insert.
Assuming that you don't have some lying around, go buy some 7/16 brass round rod, 1/2 inch if you can't find the smaller. Cut a few 1 1/2'' pieces in case you screw one up. Put one in the lathe and get an 8mm drill bit and drill all the way through that puppy. (NOTE: a 5/16 bit didn't work for me even though they're supposedly the same as an 8mm, I had to drill the insert out later with an 8mm for the choke plunger to fit into the carb.) If it went off crooked through the brass, try another one and go slower or get another lathe. If it drilled true down the whole length of the rod then you're in. Now set up a bit to cut down the outside diameter of the rod. Hold the piece by about 1/2 inch, thereby leaving an inch available to be turned down. You're going to turn about .900'' down to final diameter, so that leaves you with about .100'' safety margin to avoid hitting the chuck with your tool (Did I mention SAFETY GLASSES?). That 25/64 bit is around .394'' in diameter, so when you get .010 or .020 close to arriving at that diameter, stop the lathe, back away the tool and try to fit the carb onto the insert. You're looking for a light snug fit, and you should be able to push the carb on a small part of the way by hand before it becomes too tight to continue. Various factors make it too difficult to specify here a certain dimension, so it's a judgment call. If you think that the piece will press in the rest of the way without being too tight and splitting the carb out, then you're done on the lathe.

Part 3: Prepare and install the insert.
Get a hammer and a sharp small chisel. put the 8mm drill bit in the insert for support and lie the turned-down part of the insert on an anvil with the unturned part hanging off the edge so it allows the turned part to lie flat. With the tools, put some light burrs lengthwise here and there around the insert to give it grip when it's pressed in. Don't hit it too hard or you'll expand the diameter of the insert.
Get some bearing lock goo such as Loctite 660 or some other stuff like that's designed to fit bearings which have become worn or loose in their landings. Smear it around on the insert. Install the insert into the carb. tap in lightly with a hammer 'til you're sure that it's going in straight, then continue installation with a press or maybe in a big vice. If the turned length of the insert is greater then the depth drilled into the carb such as will be the case by having followed the dimensions suggested above, then the insert will stop in the carb with just a 16th or so of the turned length still showing at the top. Put the job away for as long as it takes for the bearing lock goo to dry.

Part 4: Tapping and finishing the insert; whew!
Now clean it up real well and try to drop your choke plunger down the hole. if it goes all the way down then you're done. If not, put the 8mm bit back in the drill press and run the drill all the way down until it just starts to touch the bottom of the bore, where the choke jet sticks up through. Withdraw drill, clean carb, try plunger. You may need to file the new bore out with a fine round file,run the 8mm drill in it some more, finely sand your plunger, or get one that's worn smaller. The plunger should slide all the way down by itself so you can see it blocking the air intake hole in the front. Then while it's in there, screw in the choke jet from below. You should see the plunger slowly rise as the jet screws home and lifts the plunger.
Put carb in a PADDED vice so that you can hacksaw off most of the excess insert, but leave it about 1/8 inch taller than the casting around it. now put your 9mm tap tightened into the drill press. Put the carb under it. While applying slight pressure with the drill press of the tap into the insert, HAND TURN (no motor) the chuck with the tap in it into the insert and start cutting threads. Using the drill press will guarantee that your threads are straight in the carb. Tap down about 5/16 inch deep, clearing the tap frequently for nice clean threads. Now machine the insert down to final level, flush with the carb. Do this preferably by milling it, or if not, then put it in a vice, hacksaw it off very close to flush, and finish with a file. Next, run the tap back through your new threads to clean up the beginning where you just milled or filed. Try the plunger again, if it goes, you're done. Remove blocks, clean, re-build, and install carb.

Substitute Series I and II Steering Lock

As a satisfied Series II rider I represent probably a good number of others who are missing that hard-to-get and expensive steering lock, the one with the cool little flip-up cover that's worth about it's weight in gold, or at least silver. Well, the other day it occured to me that a Series III one may work, and they only cost $12.95 or something.
Though it's not the correct part, thieves may not notice the inaccuracy and probably won't stay long enoughto critique the bike anyway, so you should be OK with it.
Except for the flip-up cover, the lock itself and all the other lock system parts (pin, spring, locating screw and welch plug) are the same for and interchangeable amongst Series I, II, and III. In a nutshell, INSTALL IT.
Here are some notes about installation
My install was on a TVII so dis-assembly included removing the ignition switch. LI owners will probably have to remove the kill switch. If the pin and spring are in place, push on the pin from the top to see if it operates well and freely. If the welch plug is in place, operate the pin with a little screwdriver horizontally through the lock body hole. While holdling the pin down, try the headset to see if the pin is doing it's job. If not, your headset may be clamped too high up on the fork for the pin to reach the frame lock ring. If those things aren't in place or working then you'll need to get that in order.
Make sure that the horizontal hole for the lock body is free of paint; the lock is precisely sized to the hole and much paint in there will prevent the lock from going in.
Put some grease on the lock cam, then slide the lock into place with the locating hole up; line up the locating hole under the locating screw hole so that you can see them lined up with each other. As you slide the lock in you'll have to push the pin down to allow the lock cam to pass over it. Screw in the locating screw to locate the lock. Test-operate. if it works then you're good to go. Fit the welch plug if not already done into it's recess in the headset around where you dropped the pin through. Re-assemble the headset and go field-test it, like at the liquor store or the mall. Make sure to own spare keys. Lock it when you park it for the night, then go out in the morning to ride and remember that you locked it, and now you have to go back in and get the key. See how many days it takes to adopt your new routine. Fun. (Grrrrrr)
If the headset isn't down at least this close to the chrome lock ring, then the pin may not reach down far enough to lock the steering. That's what happened when I first tried to get this lock working. I had to remove the headset and file down lower the notch in the back of the fork where the clamp bolt passes by to allow the headset to slide down far enough on the fork. I still don't know why this was necessary.