Linkert throttle disk questions

[marksg]

IMG_8972.jpeg I had a good elementary understanding of Linkert Carbs until my newest issue.
new restoration with a m36 on a 1949 FL.
hard time getting a good idle and a huge flat spot when throttling up for speed. Great full throttle power.
i have had the carb apart a few times and now for another deeper look.
i have swedged the Venturi to get a better fit and now have a good snug fit at the manifold end.
next issue is i think the throttle disk fit.
appears to be no wear groove from the disk but plenty of daylight mostly top and bottom.
i believe it should have a #12 disk but it currently has a x9
Am I correct the the disk fit is an issue?
measuring the disk it seems the wear is mostly top to bottom with little wear side to side.
from what I can see online it appears the disk is much smaller than new.
looks like I should not need an oversized disk?
it looks like ther is about .0010 clearance disk to body.

[T. Cotten]

You might notice, Mark,

The discs are oval, not round, as they must close upon a round bore at an angle (or else they could just spin. (The angles provided different duty characteristics, naturally.)

Thus they must be measured at the shaft axis center, in line with the screw holes, as that should closely approach the carb's bore diameter. (A disc cut to the bore diameter, at proper angle, produces the rest of the oval.)

And yes, that's excessive daylight; Its a real trick to get the screws in from the front of the carb like that, unless its just in backwards and that's causing most of the daylight. Please remove it and inspect the bore a for a wear groove anyway Then reinstall the disc with the throttle lever opened fully to its stop.
The screws and locks can then be easily installed where they will seat upon the flats machined upon the shaft.

It takes great patience to center a worn disc to a worn bore to where it best fills the gap, if possible, before tightening.

...Cotten

[marksg]

Thanks Tom,
The pictures were taken with the screws out. However the gap is the same with them in.
The picture I attached with the screws in alignment show a disk diameter of 1.558". I was wondering if that is standard size. The bore size appears to be about 1.568".
I am not sure if the bore is worn and I need an oversized disk or if the disk is worn and I just need the correct #12 disk.
Here is a picture if the bore and there is no wear groove. I can run a fingernail over the wear area and feel no groove.
Also is part of the problem that it has a 9X rather than the correct #12 disk?

[T. Cotten]

The original bore was 1.5625", Mark,

So I would arbitrarily grind the flange, torqueplate and pass a hone through it for certainty, cut an oversized 12º disk, and then swage and fit the venturi accordingly.

....Cotten

[dukekleman]

Mark,

I agree with Cotten. You have many issues causing your problems. Correcting all of them properly will remedy the calibration issues your experiencing.
Be sure to look over your main nozzle for correctness. It may have been changed over the years or altered in the many ways I've seen in the past.
Lastly verify engine integrity, this includes cylinder compression, cylinder leak and valve clearance adjustment. If these items listed are not correct, the calibration will not work as intended.

Hope this helps,

Duke Kleman

[marksg]

Thanks again Tom,
So when I go that route I will need to have about .002" - .003" disk to bore clearance top to bottom?
The only oversize #12 disk I see are .025" over. That seems like a lot to hone?

[marksg]

Thanks Duke,
I have been through the bike a half dozen times trying to get it perfect.
It is ridable but not what I want at idle and I hate the hesitation when I roll the throttle.
The main nozzle looks unaltered and it runs great in the mid-upper range. Nozzle also appears just like the one i found online. 1258-40
27331-40.jpg

[T. Cotten]

Thanks again Tom,
So when I go that route I will need to have about .002" - .003" disk to bore clearance top to bottom?
The only oversize #12 disk I see are .025" over. That seems like a lot to hone?

Honing .025" oversize could blow through the idle bleeds, Mark...

And rob the carb of more lifetimes even if it didn't; Most obviously worn carbs clean up under seven over. You only want to remove wear and distortions...

1½Distort.jpg

Once you know your finished bore size, perhaps the commercial oversize disc could then be cut down to just under it, on a 12º mandrel:

DSCMNDRL.jpg

I aimed for a half-thou less than the bore, as when cut exact, the carb had to be re-torqued for the disc to be assembled!


.....Cotten

[marksg]

Ah that makes sense. Thanks.
Pretty trick mandrels.