Vintage J-Model Whizzer

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Carter "N" Carburetor

Back in March I wrote that I was keeping my eyes open for a Carter Model N carburetor. When I bought this bike it had a Tillotson MT8A, which works fine, but it's not a correct Whizzer carb. The engine runs well with it, but it's a glaring incongruity on a J-model engine. The majority of Carter N's that I've seen for sale are either the wrong type, or non-repairable parts carbs, often showing signs of damage or abuse, or missing key components. Back in June, a New-Old-Stock 703S came up for sale on eBay. It was beautiful, but the price went sky-high, and I was really looking for something I could restore (and also, I prefer the brass bowl over the aluminum one.)

Finally, early this month, a 703S came up on eBay. It seemed to be just what I was looking for: correct, complete, and unmolested. Plus, it had the brass bowl, apparently fully intact. There appeared to be a lot of corrosion, but no serious issues. Of course, there's no way to be sure until the carb is disassembled and examined. I decided to go for it. When the bidding ended, I was the proud owner at a price of $54.00!

Here are some of the pictures included in the auction (dig the lush, mauve carpeting!):







The seller shipped quickly, and I couldn't wait to tear into the thing. I was anxious to see if the carb looked as good on the inside as it appeared to be on the outside. I had already ordered a repair kit (needle, seat, float lever pin, and some gaskets), and was hoping that I would be able to make any other parts that need replacement. Click here for an exploded view of the 703S carburetor.

(to be continued)
 
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Sure seems to be quiet around here lately.


Like me, a lot of folks are probably preparing for the holidays. I've been struggling to find the time to finish this write-up on my new carburetor, so I took a "snow day" today to try and catch up on a few things. Back to the "N"...

On receiving the new (old) carb, I was pleased that it looked complete and all-original. Very few signs of actual abuse or mishandling -- it just appeared to have sat around for many years, accumulating a modest amount of dirt and corrosion. The brass bowl showed no sign of cracking around the rim, and only a couple of very small dents. So far so good.

Removing the bowl revealed an intact float, but with a very slightly collapsed top:



Another view:



I don't think that this is due to any kind of physical smashage (is that a word?), but more likely an irregularity in the manufacturing process, where the soldered assembly was not sufficiently cooled prior to sealing, and the top caved in slightly due to the inside pressure dropping as it cooled. I don't think that it affects the operation of the float at all. I leak-tested the float, and it passed with flying colors.

The needle and seat looked ok, but I'm replacing them with updated versions from the kit. This applies also to the float lever pin (#24-23). The original float needle was made from brass, sealing against a brass seat. The modern replacement needles have a non-metallic tip (probably nitrile) at the sealing end, presumably for more reliable sealing action.

With our attention still in the bowl area, a potential problem with these die-cast carb bodies bears some discussion. The hemispherical bowl of this model carburetor is held in place with a 5/16-24 male-threaded brass "bowl nut" at the extreme lower end of the carb body. Moisture-induced erosion of the female thread can destroy the holding-ability of the bowl nut (it's actually more like a bolt than a "nut",) leading to a chronic gas leak. I have seen at least one extreme cases, where it was necessary to tap the 5/16-24 thread out to 3/8-24, and installing a larger bowl nut and sealing washer. Some of this erosion is evident on my carb, but thankfully not to any great extent:



Apparently, the problem stems from moisture condensing in the fuel bowl. Being heavier than gasoline, the moisture gathers at the bottom of the bowl, enabling and accelerating natural corrosive processes. Therefore, it's a good idea to drain and clean the fuel bowl from time to time, and leave it drained during long periods of inactivity.

With the bowl removed from the carb, I was able to make a more thorough inspection. I verified that there no signs of cracking, and I was able to tap out the two minor dents with little effort. I gave the bowl a good going-over with some scotch-brite, and then began a wet-sanding process. I started with 400 grit silicon carbide wet-or-dry paper, and proceeded in steps through 1200 grit, using WD-40 as the "water". Here's how it looked after the first stage of sanding:



Final polishing will be done with powered buffing wheels, using Tripoli, and then White Rouge, followed by several applications of paste wax.

I'm getting a bit ahead of myself here. Back to the dis-assembly process...

Most of the rest of the carburetor came apart fairly easily. One note of caution: when removing the choke shaft assembly (14-368S), be sure and place something (a finger, a popsicle stick, etc.) over the 8-32 threaded hole on the side opposite the choke lever before pulling the shaft out. There is a spring-loaded detent ball (116-16) that will come shooting out, if you're not careful.

Also, use caution when removing the small, round-head screws holding the choke and throttle plates to their shafts. Use a well-fitting screwdriver, and a careful, firm twisting action. It's also a good idea to spray a bit of solvent on the threads (PB Blaster is my favorite) prior to attempting removal. A careful, delicate approach is called for. A previous individual apparently did not follow this procedure, and stripped off the head of one of the two throttle plate screws. No big problem, though, as the old screw can be drilled out and re-tapped once the throttle shaft is removed.

Similarly, and more importantly, caution should be taken when removing the high-speed adjusting needle(11-192S), and nozzle (12-329). The nozzle, especially, is notoriously easy to ruin by careless removal attempts. The one on this carburetor showed evidence of an earlier, possibly aborted, attempt at removal:



With an item like this, you don't want to just grab the first screwdriver you can find that fits down in the hole. The cards are stacked against you as it is. Because the nozzle is recessed down into its threaded hole, you cannot utilize the full length of the slot. So you need to use a driver which just fits into the threaded hole. Plus, the hole in the center of the nozzle means that you have even less slot to engage the screwdriver blade. This makes it very difficult to obtain a solid "purchase" on the nozzle for applying torque.

An approach I've used before involves taking an inexpensive screwdriver bit (5/16" hex drive) and grinding down the O.D. to just fit in the threaded hole. The thickness of the blade can be carefully thinned, by grinding, if needed, to fit snugly in the slot:



(to be continued)


 

Quenton Guenther

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Hi Paula,


Might want to reconsider the float condition and or float setting. If possible you should consider finding a new float, as they are available. If not you will need to set the float level slightly different to make up for the reduction of buoyancy caused by the collapsed float. I had several floats identical to the one you are using and had to alter the float level to avoid problems at higher speeds. None of them leaked or overflowed, but had issues with the amount of fuel in the bowl at higher mid-range and W.O.T.

As always, I enjoy your fantastic posts, keep it up.

Have fun,
 
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Thanks for the reply, Quenton!

Such a small of a loss of internal volume makes a noticeable difference in bouyancy? I'm surprised to hear that. I guess it does make sense though, given that it's a very small float to begin with.

I think I can fix it fairly easily. Just need to open up the sealing hole, put enough pressure on the float to pop the dent back out, and solder it closed again. I'll give that a try.

Paula
 
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Repairing the slightly collapsed float went well. Brass floats like this have an "equalization hole" that is soldered shut after all other soldering procedures are done, and the assembly has fully cooled. Then the hole is soldered shut.

To repair this one, I opened the equalization hole using a de-soldering tool. This is a soldering iron with a hollow tip which is connected to a small spring-operated vacuum chamber. The tip of the iron is placed in contact with the small blob of solder closing off the hole in the float. Once the solder melts, a small release button on the de-soldering tool is pushed, drawing the molten solder into the vacuum chamber.

With the hole opened, a rubber tipped blow gun was placed over the hole to inject low pressure air into the float. Fortunately, this caused the collapsed top to pop back out to its normal position. Then it was just a matter of re-soldering the equalization hole shut. Here's a picture of the result:



Continuing the disassembly process...

Because the slot in the nozzle had already been damaged by someone's previous attempt at removal, I took some preliminary steps before trying out the custom-ground screwdriver bit. First step was a liberal application of PB Blaster, and allowing a day or so for it to soak in and begin working. Next, I gave it another shot of Blaster, and began a tapping routine. This consists of carefully supporting the body, engaging the screwdriver bit in the slot, and tapping the bit lightly with a small brass hammer for several minutes. Not hard blows -- just light, quick taps. This sets up a vibration which greatly helps loosen things up. Following this, the nozzle came out with no further damage to the slot.

The high speed needle was also stuck, and was removed in a similar fashion, except that a short piece of wooden dowel rod was used to protect the knurled knob from the hammer taps. In cases like this, damage can often be prevented by following the solvent-soak-and-tap procedure before applying any significant torque.

With everything disassembled, I commenced cleaning up the carburetor body. This began with a day-long soak in some lacquer thinner. The soaking loosened up some of the crud, but further effort was needed using various wire brushes, Scotch-Brite, WD-40, steel wool, and a skinny, pointed wooden stick to clean down in the various cracks and crevices.

During the body cleaning process, I happened to notice that the mounting flange was slightly warped. Not too severe, but worth fixing to assure getting a good seal between the carburetor and the engine. Here's what it looked like with a straight edge placed on the flange:



The amount of warp was on the order of .025-.030" -- a small enough amount that it could be machined off without difficulty. The body casting was clamped to the mill, and then several passes with a fly-cutter, lubed with WD-40, brought the flange back to level:



(to be continued)
 
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Two items on the carburetor, the Fuel Strainer Nut (15-48S) and the Bowl Nut (15-49), were in good shape, functionally. But they were both kind of dinged up, and showed signs of careless wrenching, so I decided to make new ones. They are simple brass parts, and not difficult to make on the lathe. Here is how they turned out:



Another thing I wanted to do was re-cut the knurling on the high-speed and idle mixture screws. Often the knurling on this type of part is not very deep, and it can be difficult to make adjustments by hand, as is intended. It can lead to folks resorting to using pliers to turn the screws, which can then cause damage to the needle. On this carburetor, it looks like someone used a pliers on the high-speed needle, but fortunately only the knurling suffered any damage.

Knurling is not normally a cutting process, but a "displacement" process. Hardened wheels with ridges on their periphery are forced against the workpiece as it rotates in some kind of lathe. As the hardened ridges are forced into the metal, grooves are formed in the workpiece. At the same time, metal from the workpiece is forced outward between the grooves, enhancing the depth of the knurl. Some metal is also forced out axially, creating a burr which is usually removed by chamfering.

Re-knurling a fragile part like a carburetor needle can be a very dicey process. Relatively high tool pressure is involved. This operation is typically performed early in the manufacturing process, before the part has become weakened by subsequent cutting and threading operations. An added problem with re-knurling is finding a knurl which has the same pitch (groove spacing) as the original.

There is a better way, and it involves re-cutting the grooves with a rotating cutter in a mill. the workpiece is mounted in some kind of indexing head, and rotated in discreet increments corresponding to the pitch of the original knurling. The process is similar to cutting spur gear teeth on the mill. What I did was mount a rotary table to the mill using a right angle plate. A 3-jaw chuck mounted to the rotary table held the part. A tapped arbor was made for holding the part in the chuck:



Here is a close-up picture, showing the 60-degree angle cutter that was used to deepen the knurled grooves:



Admittedly, this is kind of a tedious process, but it does give a nice result. On the high-speed needle, I believe that the original knurling had 32 grooves. It was necessary, therefore, to index the rotary table at 11.25 degree increments between successive cuts. The depth of the cuts was about thirty thousandths of an inch. The deeper grooves did not interfere with the existing engraving on the top of the screw.

Well, at this point, all of the parts have been either cleaned, replaced, remade, and/or refurbished as required. I managed to get them all together (except for the bowl) for a group photo (click on the photo for a larger image):



Next: Putting it all together!
 
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Hi,
I loved to see the pics and written detail and energy expended in this restoration. It reminds me of "anything is possible" with a little, skill, tenacity, and a machine shop in your basement LOL!
 
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Moving on to assembly of the 703S…

A good place to start is the throttle shaft assembly. Start by inserting the shaft into the top of the carburetor body, with the center flat area facing toward the mounting flange (toward engine.) The throttle plate is a close fit, so it can be a bit of a headache getting it aligned on the shaft. Since the edges of the plate are beveled to fit the throttle bore, it's important that the plate be properly positioned end-for-end. The stamped trademark "C" on the plate should be towards the idle port side of the throttle bore (arrow points to idle port):



Another ticklish operation is getting the throttle plate screws started. Some kind of screw-starting tool is almost a must. I used one of those screwdrivers with a split blade. The two halves of the blade are expanded apart by moving a collar on the screwdriver shaft, thus lightly gripping against the inside of the screw slot:



The screw-starting tool is only used for getting the screws started -- a regular screwdriver should be used for final tightening. There is a process for tightening the screws: first, just run the screws down to where the heads are barely contacting the throttle plate. Then, gradually advance the screws while simultaneously rocking the throttle shaft lever back in forth. This allows the plate to align itself within the throttle bore. With the screws tightened, check for free movement of the throttle shaft, and complete closing of the plate. Also, it's a good idea to use Loc-Tite on these screws, and be careful not to to over-torque them.

The choke valve can also be a bit of a pain to install, but mainly because of the spring-and-ball detent mechanism. Start by coating the spring and ball with multi-purpose grease (I used "Superlube" synthetic grease.) This is not only for lubrication, but also to help "glue" these parts in place during the first phase of assembly. With the carburetor resting on the bench with inlet end facing up, insert the spring into the correct hole (opposite the lever side), and carefully place the 1/8" diameter detent ball on top of the spring. Looking through the choke shaft hole, you should see something like this:



Next, temporarily thread some kind of 8-32 screw into the hole just above the detent ball. It only needs to go in a few threads -- not so far that it enters the cross hole for the choke shaft. (It's only purpose is to prevent the ball from hurtling skyward, should the installation process go horribly wrong.) Next, insert the choke shaft into the carburetor body, from the end opposite the spring and ball, just to the point where the end of the shaft contacts the spring and ball. With the choke shaft held in this position, use a small flat-blade screwdriver to compress the top of the ball against the spring, whilst simultaneously applying light pressure to the lever-end of the choke shaft. The idea here is to compress the ball and spring to the point where the choke shaft can pass over the top of the ball. Here's what the process looks like:



With the choke shaft in place, the choke plate can be installed in a manner similar to the throttle plate. The choke plate is easier, since it is closer to the open end of the carb. Note the semi-circular notch in the plate which goes toward the bottom. I installed mine with the trademark "C" toward the outside, but it really doesn't matter in this case.

The fuel strainer, strainer nut, and gasket can be installed next. The brass fuel strainer should be a close fit in the strainer nut. It is held in place by three ribs in the bottom of the inlet well, once the fuel strainer nut is tightened.



With the new inlet valve needle, seat, and gasket installed, the float level can be set. With the carburetor inverted, and the float resting lightly against the needle, the "lower" edge of the float should be 13/64" from the machined surface of the bowl flange. This should result in the float being almost exactly parallel with the bowl flange:



If it's not, remove the float and bend the small tab which contacts the needle. Only very slight movement of this tab is required to make a significant difference in float height.

The remainder of the assembly is pretty straightforward. Temporarily remove the float, so it doesn't get wrenched out of alignment, until just before installing the bowl. The nozzle (12-329) can now be installed in the lower end of the body. Avoid excessive tightening. The high speed adjusting needle (11-192S) and spring can now be installed from the top side. Hand-tighten the needle until it just seats against the nozzle, then back it off 2 full turns, for a preliminary adjustment.

Likewise, the idle adjustment screw (30A-46) and spring can be installed. Hand-tighten the screw until it just seats, then back it off from 1 to 3 turns, for a preliminary adjustment. Install the throttle stop screw in the throttle lever. Adjust it so that the throttle valve is held open about 1/32", or so.

Install the new bowl gasket. Since this gasket expands somewhat from fuel contact, it will have a considerably smaller free diameter than the corresponding slot in the bowl flange. It takes a bit of deft finger manipulation to work the gasket down into its slot, but it's not all that difficult. All that remains is to re-install the float, and install the bowl. Be sure to visually center the bowl on the bowl gasket before tightening the bowl nut. Also, don't forget the bowl nut gasket.

Here are a couple of views of the assembled 703S carburetor:





For final adjustment of this model carburetor, the following instructions are copied from the Carter/Whizzer instruction sheet:

"After rebuilding and installation on engine is complete, the high speed and idle screw adjustments must be made.

The high speed needle should be adjusted for the leanest possible mixture which will allow satisfactory acceleration. With the high speed needle turned counter-clockwise (from closed position) 2 full turns, and idle screw turned 1 to 3 turns open, start engine.

Accelerate engine and check response. If the engine misses and backfires, the high speed mixture is too lean and the adjustment screw must be turned counter-clockwise to correct this condition. If the engine loads (heavy exhaust) and is sluggish, the mixture is too rich and the adjustment screw must be turned clockwise to correct.

To make the final check of the high speed adjustment, operate the engine under load and adjust. The idle screw should be adjusted intermittently while making the high speed adjustment. The final idle adjustment should be made at approximately 1000-1200 RPM until smoothest possible idle is obtained. This adjustment must not exceed the limits of 1 to 3 turns from closed position. DO NOT USE EXCESSIVE FORCE ON THE HIGH SPEED NEEDLE OR IDLE SCREW AS DAMAGE MAY RESULT."

Paula
 
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