Linkert DC discharge port

Classic short-frame models

Linkert DC discharge port

Postby xlh59 » Tue Sep 28, 2021 6:47 am

Hello Forum,

unfortunately I have to adress a major problem with my Linkert DC-11 -- I was just about to finalize my XLCH build by overhauling the carburetor. For that reason I disassembled the carb and cleaned everything in the ultrasound bath. When I took out the carb and cleaned it with air, this happened to the discharge ports of the idle speed mechanism:
IMG_20210928_123505_895_small.jpg
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IMG_20210928_123631_794_small.jpg
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That was the view before ...
P1110169.JPG
P1110169.JPG (480.81 KiB) Viewed 2602 times


After checking I realized, that the body material above the bore is paper-thin (which is abviously a result of the larger bore). I lost every port besides the first one. My solution is to braze a thin metall plate on top (inside) of the ports and rebuild the bore underneath and re-drill the ports. So my question is: Can eventually somone give me the distance and size of the ports? I assume, that originally all ports have the identical diameter and that they are equidistant between each other?

I could take measurements from my DC-6, but as this one is used on my XLH, I dont want to take it off and disassemble it. Eventually someone has a throttle body flying around to take measurements.

Greetings, Ralf
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Re: Linkert DC discharge port

Postby Rubone » Wed Sep 29, 2021 6:54 pm

Those casting appear on a fairly regular basis on eBay. Often with an ear broken off. :( Typical from the use of wrong bolts.
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Re: Linkert DC discharge port

Postby dr dick » Thu Sep 30, 2021 7:51 pm

the dc 11 is an r model carb.

id venture a guess you could get buy with a replacement -57 throttle body.
got a strong feeling the dc-11 used the -57 body.

if so:
these throttle bodies have never been changed from the original dc-1 to the last dc-6.
sportster dc series chronologically were:
dc-1
dc-1L
dc-10
dc-12
dc-6
also the 1966 big twin dc-7 used the -57 body.
i cant say if the trike dc-2 used the -57 throttle body, you would have to check that.
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Re: Linkert DC discharge port

Postby Ferrous_Head » Thu Sep 30, 2021 9:09 pm

Sorry, but the smallest number drill I have at the moment is too big to get a measure.

They are tiny, tiny.

They do appear to be the same size on the 1L, 6 and 12's that I looked at.

So most probably the same size on all. I doubt they would have modded them for racing.

So, might be best to just buy another body off ePray. Bore it to suit (carefully) and go again.

I'm thinking the boring job would be easier than trying to plug it with bog and re-drill such tiny holes. A watchmaker could probably help you.
"I know only too well the evil that I propose, but my inclinations get the better of me."
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Re: Linkert DC discharge port

Postby epinut » Fri Oct 01, 2021 1:11 pm

img175.jpg
img175.jpg (377.26 KiB) Viewed 2425 times
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Re: Linkert DC discharge port

Postby xlh59 » Sun Oct 03, 2021 12:43 pm

Hi All,
thanks for your replies. -- @epinut: thats exactly the information I was looking for ...

The DC-11 carburetor was mounted on my 59XLH, wenn I bought it back in the 90s -- I have tried to use it on the XLH, but without success. Especially idling and the acceleration from idle speed on was causing problems. After mounting a DC-6 I aquired, I was pretty happy with the DC on my XLH. Although I still think the CV carb was the best option so far.

Anyway: The DC-11 was a lucky coincidence, as it would fit (more or less) perfect to my XLCH build. The Dr. might remember this, although ist been a loooong time since I started. It is a full ball bearing engine with a 59XLCH engine number in a XLRTT frame. Inside are KHR flywheels and big rods (the 55R type) with aluminum cylinders with (now) 3,3" bore. The Dr. helped me a lot in designing the pistons, which I had custom made by "Wahl" -- The engine has 77cui, so a bored out DC might work or might be to small -- I will find out.

I would have gone for a new-used throttle body, but as I live in Germany, its hard to get them in a decent shape or it takes a few weeks -- yeah, that doesn´t matter, if it took 6 yeards already, but I am close to the finish line.

First I fabricated a small plate that fits into the body and has the 4 wholes already pre-drilled.
IMG_20211002_235522_792_small.jpg
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After that I positioned the plate and fixed it with an aluminium plug from the top side. To make sure, that no brazing material closes the holes again, I plugged them with toothpick tips ...
IMG_20211003_002612_259_small.jpg
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Last but not least, I brazed the plate in place and cleaned the bore out again -- with good results, although the holes have a slight angle (which should´t harm functionality)
IMG_20211003_125117_821_small.jpg
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All holes are now pre-drilled with 0.6mm or 0.0236" -- now a last question:
From reading different sources, I understood, that these ports are a type of idle speed or "throttle-just-opening" valves and that S&S used two or three ports. What would you recommend for the size of the ports (also considering, that this is for a 77cui engine) -- my idea was, that I could use two small und two bigger ports (the bigger ports to the ends and the small ones in the middle)? Any comments?

Cheers, Ralf
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Re: Linkert DC discharge port

Postby xlh59 » Sun Oct 03, 2021 12:45 pm

My 59 team:
IMG_20210825_231410_296_small.jpg
IMG_20210825_231410_296_small.jpg (318.4 KiB) Viewed 2351 times


The XLH will get new clothes this winter ... :D
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Re: Linkert DC discharge port

Postby wz507 » Sun Oct 03, 2021 2:04 pm

Nice job on your repair. Just curious, in the image you provided it appears your idle hole insert is set below the carb bore radius. Is my impression correct or is it an illusion of the photo? Also, when the throttle disk is closed tight, where does the disk contact the idle hole plate, i.e., how many holes are upstream of the disk and how many holes are downstream of the disk, or does the disk sit directly over/atop a particular hole? Thank you.

DC idle hole repair.jpg
DC idle hole repair.jpg (41.95 KiB) Viewed 2342 times
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Re: Linkert DC discharge port

Postby xlh59 » Mon Oct 04, 2021 3:22 am

You are correct -- The idle hole insert is "below" the carb bore (on the picture), but if you turn the carburetor in the correct position, its "above". What I did is, that I dropped the disc from above into the idle speed channel (that gets closed by the big brass plug), positioned it and fixed it there. As I had one hole left, I used that for positioning of the new plate. The only problem was the slight angular shift.

There is one hole pointing towards the manifold when the disc is closed -- three towards the air cleaner. Once the disc opens, two, three and four holes face towards the manifold. So in my logic, these ports mainly serve idling and the very first throttle action.
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Re: Linkert DC discharge port

Postby xlh59 » Tue Nov 23, 2021 4:19 pm

Hi to all,

finally, (after a 7year assembly period) I am at the point to start my 59 XLCH stroker the first time. Apart from one "coff" at the second kick, the engine stays silent -- nothing!

First of all, I do not have any hints on the initial settings of the carburetor with this engine -- remember: this is a 77cui engine with KHR flywheels and 3,3" bore. Adding the fact, that its a DC11 carburetor with (hopefully correctly) repaired idle discharge ports and temperatures below 40° Fahrenheit. So where to start? I used the standard Linkert DC settings and opened the choke plate 1 klick (as I would on my XLH at this temperatures).

What I realized is, that the spark plugs stay comparebly dry. The carburetor throat is covered with fuel after kicking, but even after 20kicks, the spark plugs are not wet as they definately would be with my XLH. Any hints where to search for? Is it a manifold leak or should I rise the float level?

Thanks in advance, Ralf
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