M53A Linkert Carb

Production K Models

M53A Linkert Carb

Postby JerrryR » Wed Nov 26, 2014 1:33 am

Hi, I was hoping someone might be able to shed some light on what model and year K model or other bikes used the M53A Linkert Carb. I am not confusing it with the M53 used on the 52 & 53 K models seen below:

M53 Compressed.jpg
M53 Compressed.jpg (31.36 KiB) Viewed 6284 times


or with the M53A1 used on the 54, 55 & 56 K models seen below:

M53A1 Compressed.jpg
M53A1 Compressed.jpg (30.96 KiB) Viewed 6284 times


The M53A is shown below:

M53A Compressed.jpg
M53A Compressed.jpg (32.71 KiB) Viewed 6284 times


Any insights would be appreciated,
Thanks,
JerryR
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Re: M53A Linkert Carb

Postby EKHKHK56 » Wed Nov 26, 2014 5:09 am

Jerry, Very interesting...does it have a BombSite Venturi Booster like the other 45" Ks? The M-53? Erik
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Re: M53A Linkert Carb

Postby sean » Wed Nov 26, 2014 7:12 am

i picked up a m53 for my 52 k with bombsight,the one that came with my 52 project ended up on my fathers 36 knuckle back in the 80s...the m53 was replaced by the m53a1 and covers 52-56 according to my parts book.there is no mention of the m53a in my parts book...im sure someone here can shed more light on the numbers.
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Re: M53A Linkert Carb

Postby John R » Wed Nov 26, 2014 9:11 am

Pick the bones out of this lot!

According to factory Harley carb notes**, there was an M-53A with Big Twin venturi (27363-41), 53 idle bleed and 7 jet and was listed for K and KH models (then came the M-53A1 with Big Twin venturi, 50 idle bleed and 9 jet also listed for K and KH models). As listed for both 750 and 883 it seems like the difference in jet size could be accommodated for both the 750s and 883s via the needles. Either that or Harley weren’t too fussy! It also may suggest that it was fitted to later Ks and KKs or may just have been an acceptable retrofit.

In short: the M-53A had the later venturi in the early body and the M-53A1 had a slightly different bare body but body functionally the same.

By-the-bye, I have read different explanations for the hole drilled from carb inlet into the float chamber. My explanation is simpler than most – it was a drain-away for liquid fuel that you can get if kicking when over-choked.

Some main nozzles have an extra .035” air bleed hole at the top, but not in line with the other holes (see photos at foot). This suggests to me that this hole was drilled in a separate operation to the other holes (otherwise, why not in-line whilst jigged-up?).

My suggestion is that this was a modification necessary after early experience. The early bomb-sight venturi may have created too much ‘draw’ on the nozzle (especially with the unique ‘gasket’ – fibre washer – sealing the nozzle tip to the body) and the bleed was added to pull less fuel whilst emulsifying it better, correcting the mixture.

My experience on the KK was that the carb wasn’t ‘quite right’. Perfect mixture at tick-over gave ‘hunting’ at 40mph, consequently I have set the float a little lower (see below) and get a better balance.

My next suggestion is that the M-53A1 with standard venturi did not produce quite as strong draw so the top air bleed was no longer necessary. That’s my guess why the nozzles with the extra hole are usually found in M53s. Incidentally, the precise vertical location of the lower 5 holes varies but I don’t think this is operationally significant.

**The same Harley data gave a float height of 3/16” for 9 carbs, including the M53 family. It also mentions a “reformed float lever” for M-45A, M-74 and M-74B – could this be 27381-50? If so, they should have included M-53 as that's the part listed in our parts books for that.

We’re often told that there was only ever one lever for all Linkerts but the old number 1272-33 converts to new number 27381-33 not -50, so 2 lever types. 27381-50 didn’t exist till 1950, so probably the “reformed lever”? What is the difference between 27381-33 and 27381-50? I believe the -50 was cranked to give that 1/16” higher float level.

The float bowl assembly is not like other side-valve models. There’s a different bowl listed for the M53 family – 27370-52. Not sure, but is the only difference that it takes the pivot pin in a hole drilled straight in the casting, doing away with the older screwed-in seat? There’s a different float valve assembly to other models 27382-52, the key difference being the lower-fitting accepting the steel line and nut (not the Big Twin compression rubber bush type).

The same data sheet lists a “loaded float screw” for M-36A, M-61 and M-54. This has me baffled. What are they calling a float screw? The one that secures lever to float or the pivot-pin? Either way, I don’t have a clue what a “loaded one” is! Does it apply to M-53 series?

Well all this shows I ought to get out more!!
Attachments
M53 nozzle 2.JPG
One side
M53 nozzle 2.JPG (43.09 KiB) Viewed 6269 times
M53 nozzle 1.JPG
Other side
M53 nozzle 1.JPG (45.52 KiB) Viewed 6269 times
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