Linkert MR-4 A

[41craig]

I got this carb. from Doc's H-D in St. Louis about 20 years ago. I've seen MR-4's, but none like this with the inner body being the venturi. It looks like the air cleaner side of it was machined and the air cleaner mount was made and welded ( soldered ?) to it to give that end a larger bore. Doc raced 45's in the '40's and his son Ralph race K Models and CH's in the 1950's and '60's. Any info would be great.
Thanks Craig

[T. Cotten]

Many thanks for the pics for my collection, Craig!

...Cotten
PS: Beyond that I have no clue.

[Rubone]

Craig, many of those MR4-As had full length custom venturis. I have one as well. Here is a copy of a factory blueprint for them..

[41craig]

Robbie; Thanks for the blue print !!

Cotten; Here is a couple more.CIMG1160.JPGCIMG1161.JPGCIMG1162.JPGCIMG1163.JPG

Craig

[T. Cotten]

Thanks to both of you!

But Craig's smells wildcat to me.. and it ain't even in my hand.

The one Factory mod that was anyway similar, that I did hold in my hand, was Michael Breeding's offering of a Reiman carb at D-port years ago, and I barely knew what I was looking at. (Although I met the Reimans of course; They were local,.. but I'm ignorant.)

It was a machined body for a large venturi sleeve, not a sweat-soldered assembly like Craig's.

Such a bowl extention is also displayed at http://www.beautyofspeed.com/gallery...rt/linkert.htm

You can never have too much reserve!

....Cotten
PS: It came with two bowls, Craig?

Fabulous.

[41craig]

Cotten; Yes. It was in a bin box upstairs in the shop. There may have been DC carbs and Tillotsons with it. Possibly race carbs, but I know nothing about them. Except that I have a few boxes of them.
Craig

[duffeycycles]

Erwin "Smitty"Smith,Rck Island Indian dealer,had a box full of carbs.Many were NOS M74B from police dept.
He also had many race carbs with mods in the box.
Several had modified larger reserve bowls.He said none of them helped much.

[kitabel]

The blueprint's venturi ID dimension is 1-5/16", the same as the original 4-bolt large venturi since 1940. I would guess it flows more air than the plain tube due to internal streamlining.
The MR-4A venturi shown looks really small by comparison, have you measured it?
I had a 1-3/8" spun aluminum full length venturi, unknown use but obviously required internal machining.
The bowl extension doesn't add any power, the purpose is to prevent the fuel level from dropping (and leaning out mixture) on a long straight, otherwise the engine uses more than the needle & seat can deliver continuously. Branch recco in June '65 KR article.

[T. Cotten]

Reserve isn't so critical at a constant speed, Folks!

Its when you accelerate hard and often, as some racing requires.
The volume of the cutaway of the main nozzle is discharged, and must re-fill quickly.

Although the float is slightly lower to keep the valve open, the reserve volume is between 5/8" from the top, and the HS needle seat, or slightly lower if fed by a fixed jet. Fuel below that is not available.

As you can see, the float occupies some of that. If you have to sink a fat float deeper because its heavy, it robs reserve significantly.

...Cotten
PS: Your 'full length' venturi sounds a lot like the Reiman carb, Kitabel!
PPS: Anybody notice how restrictive Colony's floatvalves are?

[41craig]

I took off the bowl and tried to remove the main nozzle, which is stuck, to see which nozzle was in it. I don't remember if I put one of the bowl on it or it came like that. Untightened NOS bowl nut and gasket lead me to think that I put the bowl on to keep them together. No main nozzle spring and where the spring would go, there are female threads. ( see pics ) I tried a DC carb. bowl nut and it threads in perfectly. I put a few drops of Kroil on the main nozzle to see if it would loosen after a day or so. No corrosion in the carb. to interfere with the nozzle removal.
Cotten; Any thoughts on nozzle removal ?? I'm thinking about a long machine screw with a washer under the head, from the bottom and a nut on top to draw it out.
CraigCIMG1168.JPGCIMG1167.JPGCIMG1169.JPGCIMG1165.JPGCIMG1164.JPG

[T. Cotten]

Now that's different, Craig!

Although Type A DLX Scheblers were tapped like that to retain the nozzle, which may explain the missing spring.
(Please measure the threads.)

The nozzle shouldn't be as hard to remove as some..., (Like GX Scheblers).
If a cable doesn't work, then I resort to various pullers I have made.

The closest thing I can relate any of this to is the M-53 series, and I not only have very little experience with those, the 'drool pit' to the bowl headspace baffles me entirely.

The experimental blueprint spec's a -54 fixed jet; Is that a #9?
(I have no K literature.)
Whacking the nozzle spigot is another mystery.

The lack of lift lever and metering air jet to the LS needle bore on Craig's confirms that sort of lineage.
How ironic that they went from a restrictive bombsight to wide open with an integral "airhorn" .
They had to be intended for two very different duties.

...Cotten

[41craig]

The threads are 3/8x24.

[Rubone]

There is a plug that goes in there Craig, and it acts as a nozzle retainer/seal. I'll try to get a pic of one for you.

[T. Cotten]

The threads are 3/8x24.

The Schebs were larger, Craig,..

But their design may be a clue.
Note how the 'tit' that presses up against the nozzle is slotted to allow fuel and air to enter.

Viewing down the bore, is the nozzle spigot about an eighth inch below the centerline, or more like a quarter?

When the nozzle does come out, please observe for a gasket at the top shoulder.
And whether the nozzle bore is continuous to the body bore, or the nozzle is retained by the casting instead of the venturi.

Looking forward to it,

....Cottem

[duffeycycles]

A hot air gun,heat the carb up a bit usually helps.Doesn't take much heat...no torch!Same with the little plugs.