thoughts on linkert M74B

[Omarttentmaker]

Doing some R&R on my wife's '65 FLH, and ran into something I'd never seen before. I disassembled the carb, cleaned it, and reset the float. Reassembled and reinstalled. Turned the low speed needle out 5 turns, and the high speed out 2. Fired it up, let it warm up, and began dialing in the carb. Found that I could only turn the low speed in about 1/2 turn before the idle started to drop off. Left that where it was and "clicked" in the high speed while snapping the throttle until it stopped backfiring through the exhaust. Went back to the low speed and took it in another 3 "clicks" and things seemed fine. Was just wondering why the low speed needle is out so far. On every one of these carbs that I've worked on in the past, the low speed needle always screwed in deeper ( like to, at most, 31/2 turns out from closed). For the short time I ran it, the plugs looked fairly decent (not sooty but black). I know its gonna take a road ride to determine the final actual setting. Something else I noticed is that during reassembly was that the knurled head on the low speed needle seemed to "bottom out" on the top of the low speed needle lever, which might imply that the needle end is not seating where it should. Anybody, any thoughts on this? BTW, the low speed needle hasn't been tampered with, it is the correct length.

[T. Cotten]

Omar!

Why did the float need to be re-set?
(Rubber floatvalve needle?)

Modern fuels burn so clean that plugs stay white.

The M74B HS needle is notoriously insensitive, and can only be adjusted cruising.
It should have no effect at idle speed, so snapping the throttle is futile; Please idle faster than "potato-potato".

The lowspeed needle knob has a spring within it to protect the needle point when screwed down too far, but you may want to inspect both.

I routinely sent fresh carbs out with the LS set at 3 1/2" turns (M74 HS at ~3/4"); The fat factory suggestion accommodates vacuum leaks.

....Cotten

[Omarttentmaker]

So, I did reply to this, but I don't know where it went. Anyway, float needle is steel, and I lap and seat it before reassembly. I reset the float because I noticed at disassembly that it was not parallel to the top of the bowl. And you're right about having to road set the HS needle. I did check the spring in the head of the LS needle and it is intact and working. In the process of reinstalling the tanks. I also cured a vacuum leak. Took the aluminum manifold off and measured the round ends. They were out-of-round, so I installed a cast iron manifold with new O-rings and clamps that are a little more robust than the stock ones

[T. Cotten]

..clamps that are a little more robust than the stock ones

As long as they only have a #10 clamping screw, they should do fine, Omar!

"Robust" clamps are what make spigots out-round.

...Cotten
PS: I haven't lapped a needle in many years; Rapped them religiously with a screwdriver handle.

[Omarttentmaker]

I seat them myself after lap. Don't know if lap helps or not, but I lapped and seated the one in the unit i'm working on now, and it doesn't leak.

[T. Cotten]

The reason I stopped lapping, Omar...

Besides 'time is money' and lapping only widens the seat, abrasives, even flowers of sulphur, embed into brass.
Ever wonder why metal needles wear more than the softer seat?

I'm so picky I wave the needles at a compass, and if it moves, I de-magnetize the needle.

Even brand new valves won't pass the suck test without a rap on the benchtop.

....Cotten

[Omarttentmaker]

Believe it or not, I use a paste consistency of olive oil and cigarette ashes. I don't know if this does any good, and the smokes are killin' me, but between that and the rap on the bench, I get pretty good results. Never thought about demag. I figured the magnetism would disappear when you hit it!

[T. Cotten]

I never heard the olive oil part, Omar!

Always got some, although no tobacco ashes. Dumpster across the street does...

The de-mag thing is because I can. So I must. And now I gotta charge for it.

....Cotten
PS: The de-mag hit-it thing needs to be aligned to the Earth's magnetic pole, or so the legend goes?
My compass is so sensitive, it shows that "growler"-style" de-mag'd connecting rods just threw the poles to the middle.

PPS: Even this attachment is one I had previously uploaded, Folks!
Saved me wifi data.
This forum's format is a learning curve, but far, far better than external photohosting, and I am so greatful.