DC Linkert Idle Tube

[silver65]

Just finished my DC rebuild a few months ago carb works great, the throttle shaft end seats up against throttle body the washer and spring will stop air from entering the Venturi I used a little dab of grease at each end 0.005 is not bad and my even be a factory ream alinement I don't know but if the butterfly dose not stick open and moves freely you should be fine good luck with idle tube.

[chuckthebeatertruck]

Let's clear a few things up.

there was no sacrificial metal, nor that intention. The material chosen has a reasonable service life for a then new bike. Seems odd to us, but the bikes weren't built thinking about the tenth owner some sixty years later.

Second, ever wonder why the throttle body is separate from the carb body on a D.C.? After some fifty years of carb manufacture, linkert might have noticed trends and came up with a "new" design that allowed for super fast repair to worn bodies. Drilling and bushing is archaic compared to bolting on a new body in five minutes. Seems someone was thinking about service as well as changes to the carb. This becomes a key point in a moment.

As to all this reaming business, try a sunnen hone. More precise. No need for fixtures or extreme expenditure. Just a correct mandrel.

Finally, the shaft position is way, way more important than you may imagine. The D.C. Throttle disc is orienteted to uncover a series of bleed holes in the carb roof. When the shaft wears that positioning is lost. Dudes blame air bleed around the shaft, but in reality, it's throttle disc orientation. Shoving in new bushes may or may not reestablish the orientation and may or may not address wear to the throttle disc. Thankfully, the D.C. Is forgiving and you can tune around the screwed up position with float height, but now your bike is a bit rich at idle and speeds up to 30 or so.

Again, many bushes have been done at home in a drill press, and you often hear about hard starting and a fluffy low end response. There's a correlation.

With the tube, I sold a mess of D.C. Spares recently or I'd just send you one. If no one can come up with one, I'll pull one from a running bike in the coming weeks and measure one.

[chuckthebeatertruck]

Please see the attached sketch - I hope it's inserted (not the most user-friendly system).
The measurements shown are as close as I could get using a mechanical Caliper.

Bill see my post about making intermediate jets for l series carbs. The tube design is a copy of the D.C. Except it screws in vs being held in. It's two piece and so I solder them into the screw end. you can easily cut the swagged end separately, solder it to main tube, and be done. .040 id tubing is readily available. The drilled hole is a standard size. A pin drill kit from 60-80 covers most bleed hole sizes, but it's too early for me to remember if .042 is the final size in that range.

[T. Cotten]

The reason to rough-ream first, Chuck,..

Is because honing from .250" to .3155" is a lot.
Not only would it be trickier to keep alignment and axis, it would eat up stones. And Sunnen stones ain't cheap!

The orientation of the disc to the bleeds is determined by its bevel angle. If the bore is honed at all, whether to arc the bushings or remove a wear groove, you must cut a fresh disc anyway.

Does anyone know the differences between common 9º, 9/, 9/X, and the DC's 9/A discs? Whatever they are, they are very subtle.

....Cotten

[billpedalino]

Let's clear a few things up.

there was no sacrificial metal, nor that intention. The material chosen has a reasonable service life for a then new bike. Seems odd to us, but the bikes weren't built thinking about the tenth owner some sixty years later.

Second, ever wonder why the throttle body is separate from the carb body on a D.C.? After some fifty years of carb manufacture, linkert might have noticed trends and came up with a "new" design that allowed for super fast repair to worn bodies. Drilling and bushing is archaic compared to bolting on a new body in five minutes. Seems someone was thinking about service as well as changes to the carb. This becomes a key point in a moment.

As to all this reaming business, try a sunnen hone. More precise. No need for fixtures or extreme expenditure. Just a correct mandrel.

Finally, the shaft position is way, way more important than you may imagine. The D.C. Throttle disc is orienteted to uncover a series of bleed holes in the carb roof. When the shaft wears that positioning is lost. Dudes blame air bleed around the shaft, but in reality, it's throttle disc orientation. Shoving in new bushes may or may not reestablish the orientation and may or may not address wear to the throttle disc. Thankfully, the D.C. Is forgiving and you can tune around the screwed up position with float height, but now your bike is a bit rich at idle and speeds up to 30 or so.

Again, many bushes have been done at home in a drill press, and you often hear about hard starting and a fluffy low end response. There's a correlation.

With the tube, I sold a mess of D.C. Spares recently or I'd just send you one. If no one can come up with one, I'll pull one from a running bike in the coming weeks and measure one.

Chuck,
Again, we agree. By 'Sacrificial' my meaning is that from a physical wear standpoint, both the brass shaft and the cast iron body have sacrificed material, although at different rates in proportion to each material's hardness. My suspicion is that this particular carburetor has seen at least one throttle shaft replacement with the body being original. My position is that replaceable bushings, like in the M-Series is a better design, although not as profitable for Linkert. From their prospective, purchasing a new casting would have made better business sense for a number of reasons while probably not favorable to the customer's wallet. But I also agree that its easier to bolt-on a new casting than re-bush old one.

[chuckthebeatertruck]

I'd like to hope that even a rank amateur mechanic would understand the difference between boring, reaming, and honing.

knowing that both reaming and honing are finishing techniques for the last wee bit of material: Who would consider REAMING let alone honing from .250 to .3115?

With that said, I brought this up so Bill understands he doesn't need to pay a tool maker to reproduce a fixture to do a one off job and that he might just find it more worthwhile to swap the whole throttle body for a better one unless he has a mill handy to re-establish center on both axis.

[T. Cotten]

Who would consider REAMING let alone honing from .250 to .3115?

Its .3155", Chuck!

And it was routine for me,..upon bronze and potmetal.

After all,.. I had to make a living at it.

Cast iron is a different animal of course,

....Cotten

[chuckthebeatertruck]

Given that standard tooling rules have powered CARBIDE reams removing a maximum of 2-3% of finished diameter . . .that means a .3155 hole subjected to those tolerances would start reaming at .306 to .309 . . .so starting at .250 seems a wee bit more involved when getting that .050 out of the was is but a letter drill away. One ream operation vs. several.


Could you do it all by reaming? Sure you can. One can also file a cylinder oversize and finish it with sand if they have enough time on their hands and are a good craftsman.


I counter that the average enthusiast reading this forum and attempting this work themselves at home in their garage will have much more satisfying results drilling/boring to a proper size and then reaming or honing to final size.


The advantage of honing is that you don't have to buy any tooling. Almost any automotive shop which hones valve guides will have the mandrels and stones . . .which again makes what I'm saying more accessible to our fellow enthusiasts in the middle of nowhere. A lot of small engine repair shops also have the older, smaller sunnen k drives for valve guides which also are a treat on these types of holes.

To be clear -- I am not disagreeing with fixturing and reaming.

Quality reams ain't cheap.

[T. Cotten]

Quality reams ain't cheap.

Ain't THAT the truth, Chuck!

I had to inherit mine.

Note the tapered leading flutes for roughing a much smaller bore;
The ground section ahead of the spiral flutes is ~.309", and ~.3115" after the flutes.

To finish the job, an extra-long Sunnen 5/16" mandrel, dressing sleeve, and long stones ain't anything like cheap neither.

....Cotten

[billpedalino]

Bill see my post about making intermediate jets for l series carbs. The tube design is a copy of the D.C. Except it screws in vs being held in. It's two piece and so I solder them into the screw end. you can easily cut the swagged end separately, solder it to main tube, and be done. .040 id tubing is readily available. The drilled hole is a standard size. A pin drill kit from 60-80 covers most bleed hole sizes, but it's too early for me to remember if .042 is the final size in that range.

Yes, the tube seems to be readily available and I'm thinking that because the bottom 'button' only serves as a sealing bulkhead and backstop surface for the spring, I might be able to thread-in a small brass screw and insure its seal using silver solder. The screw head would also help keep the tube centralized within the spring on the its bottom

[chuckthebeatertruck]

Silver solder is overkill here. Believe it or not; on properly cleaned and fluxed brass -- oately gp electrical is fine as is lead-free plumbing solder. You need only a very, very thin tinning of the main tube. Let it cool; flux your parts; heat to liquid; assemble and let cool -- in 30 seconds you are set.

Double check your .042 measurement. That's an awfully big hole compared to the #69 and #70 sizes listed in the FSM on page 3F-20 (5-68 rev.) The size of that hole will directly impact your road manners (along with float height) up to about 45-50mph.

Don't re-engineer it; just copy what is to be there so you don't induce baseline error.

[T. Cotten]

Agreeing with Chuck, Bill,...

Silver-solder isn't necessary, and a lot more difficult on anything that delicate.

Soft-solder works great for me on main nozzle spigot replacements.

If you have access to a lathe, just cut a brass 'button' to sweat on some tubing, when you find it.

....Cotten

[chuckthebeatertruck]

Ain't THAT the truth, Chuck!

....Cotten

I do miss Davenport . . .

And am also pretty convinced people think we must be cooks.

But, really, who doesn't like unusual tools and tooling?

Or doing the "impossible?"

[chuckthebeatertruck]

Agreeing with Chuck, Bill,...

Silver-solder isn't necessary, and a lot more difficult on anything that delicate.

Soft-solder works great for me on main nozzle spigot replacements.

If you have access to a lathe, just cut a brass 'button' to sweat on some tubing, when you find it.

....Cotten

or a plumbing olive . . . I like to dumpster dive too :-)

[billpedalino]

Silver solder is overkill here. Believe it or not; on properly cleaned and fluxed brass -- oately gp electrical is fine as is lead-free plumbing solder. You need only a very, very thin tinning of the main tube. Let it cool; flux your parts; heat to liquid; assemble and let cool -- in 30 seconds you are set.

Double check your .042 measurement. That's an awfully big hole compared to the #69 and #70 sizes listed in the FSM on page 3F-20 (5-68 rev.) The size of that hole will directly impact your road manners (along with float height) up to about 45-50mph.

Don't re-engineer it; just copy what is to be there so you don't induce baseline error.

Interesting,..

I have two tubes from other carburetors. The bleed hole in one is about 0.028" and the other is about 0.042". From my research, all idle tubes for DC Linkerts are the same. If this is the case, then it Looks like one bleed hole was was opened up.at some point in the past.