Linkert M74 on my 50FL

[50Panhead]

Well I guess the old girl has not forgave me completely. After several test runs of 20 to 50 miles and she still don't like me.

I have repeated the soap bubble test on the intake. I fixed a one little spot that foamed up after a few minuets.
I have readjusted the push rods.
I went back through the carburetor looking for all the suggested suspects.
Bike starts easy. Adjusted low speed till it leans out and opened in counting notches up till it started running rich and back it down until it rain smooth counting the notches.
I let the bike warm up and readjusted. Low Speed jet is running good at 7 notches open from leaning out.

I take it out on the road and when the throttle is just cracked open off idle it spits and coughs like its running out of gas. Open the throttle a little more and it takes off like a rocket and runs great. Back the throttle to where it should be a fast idle maybe somewhere around 1000 rpm or a little more and it goes back to spitting and coughing. Ride the bike at 50 to 60 mph and it never misses a beat.
Now I open the throttle all the way and it dies, well, almost,. High speed trimmer is 3/4 turn open. Adjusted from fully closed to 2 turns open and its still the same, dosn't not change anything. High speed jet is #17.

I'm beside myself. I have checked and triple checked for intake leaks. Carburetor float adjustment. I do not see any "Eye Brow" where the throttle plate closes, Venturi is tight. New Points, condenser, New Plugs. timing in dead on. There is something I'm not seeing but what?

[Rubone]

Open the low speed a couple more clicks. Check your fuel flow for restriction, both within and outside the carb. (piece of crap in a the jet, main nozzle, fuel line, etc.)

[T. Cotten]

50Panhead!

While you are cleaning the carb, the two most common problem spots are the idle bleed slot, which somehow often catches nearly invisible glass beads of unknown origin (first attachment), and the venturi's 'air correction void' that has quite a large opening for dirt to enter upon the side. Complete disassembly is essential.

Your #17 jet is associated with the stepped M74 needle as shown in the third attachment. If you have a common needle with a simple taper, it may be a clue, but don't ask me why; If everything is in order, any needle should have some "sensitivity" of adjustment, but the whole M74/B series is notorious for an insensitive HS needle, perhaps only of use to close for high altitudes or whatever. No sensitivity should mean the fixed jet is barely adequate; If the needle does have an effect, then we know the jet is more than enough.
(Please remember that ethanol fuels will always require more volume than fuels of 1950.)

The "eyebrow" issue creates daylight around the throttledisc, but a poorly-fit disc can have daylight around it even with no borewear.
Please note if the disc has an indication of wear upon either side of the shaft, and visually inspect the disc's fit within the bore with the venturi removed.
Zero daylight is a difficult "ideal" to achieve, but significant daylight is certainly to be avoided. OEM discs vary, and you want one of 1.561" at least, as measured from top to bottom at the throttleshaft's axis.

Back to bubbles, no leak is an acceptable leak, no matter how small it may seem.
And please remember the interface between carb and manifold cannot be bubble-tested, so both carb and manifold flanges should be arbitrarily ground "flat", and often the phenolic spacer as well.

....Cotten
PS: While bubble-testing, did you also inspect the pan cover screws over each intake port, next to the motormount studs?

[50Panhead]

Cotten Most excellent picures.
I just pulled the carburator back off and took these.100_8072.jpg100_8070.jpg100_8069.jpg100_8066.jpg100_8065.jpg
You talked about "eyebrow" I thought you were talking about the brass body having a grove cut into it from the throttle disk wearing into it, Rather than seeing light around the disk. Note: I adjusted the idle screw so the disk would be fully closed and not where I had it set for normal Idle when I took the pictures.
I had installed new throttle shaft bushings as my old ones were loose. It stands to reason the the old throttle disk would be worn and with new bushing and shaft it will not fit correctly. Idle port is clean. Float is set 1/4 inch from the top of the float to the top of the bowl and slightly offset.
Now to knock the Venturi out. How is the best way to go about that? Wood Dowel? Plastic pipe?

[T. Cotten]

Well, yes,..

The "eyebrow" I speak of is indeed a groove into the bore, which adds to 'daylight' of its own. Usually it is most pronounced at the top, and can be felt easier than it can be seen.
Both wear on the bore and upon the disc are a result of slop at the bushings. Usually if the bushings are worn, the shaft is too.
(If the attachment is familiar, it is the one Tedd Cycle stole and published in their catalog as their own service.)

On to the venturi, after removing the nozzle, I put stuck ones under a heat lamp with ample Kroil, before I coax them out.

....Cotten
PS: I think your float is upside down.

[50Panhead]

Cotton to answer an earlier question (did you also inspect the pan cover screws over each intake port) No I did not. I did not know they went into the intake cavity. I will. I sanded the carburetor face flat using wet/dry sandpaper on a sheet of glass as you suggested before.

Float: So the flat side of the float goes Down. I'll turn it over.

I replaced the throttle shaft along with bushings. I had to buy a reamer to ream the bushings for fit.
Awhile back I replaced the float needle and seat. And as for as replacement parts that has been it. Along with your Float.
I'll order a new Throttle disk. Is there any other parts that should be replaced at this time. High/low speed needles, seats, main nozzle.
I did feel some eyebrow after I took the throttle shaft out along the top, but none on the sides.

I'll work this evening on removing the venture. I hope I find it like the photo you posted. I'm guessing but the machined area on the OD of the venture is it designed to create a Low Pressure area to improve draw on the high speed nozzle? Is this the accelerator pump effect you talk about? Do you sell parts or do I stick to J&P.

Herman

[T. Cotten]

Herman!

The pan cover screws only perforate into the ports long after they leave the factory, but too frequently nonetheless. Often the hole has been drilled and tapped for a longer screw when the original threads have given up to abuse.
I have only discovered a handfull myself, but without bubbles, the machines were doomed to be lemons passed from owner to owner.
(Attached is one that was even weld-repaired, yet still leaked up past the screw.)

The problem with ordering a new throttle disk is that there is zero control over what will arrive. There is no such thing as one-size-fitz-all.
(And yes, I only offer services, as catalog crap is.... .. .
And please remember as I announced at Davenport, Liberty must shut down for the winter months.)

...Cotten

[50Panhead]

After a couple days soaking in penetrating oil the Venturi came out. It was caked with carbon around the main nozzle hole. I ran a brake hone through the carburetor to lightly clean up the carbon and it revealed the eyebrow. It made it look kind of bad but its hard to feel with the fingers. I have found a NOS throttle disk and a new main jet which are on the way. I feel a lot better about things right now. Sorry it took so much to beat this into this thick headed German from Missouri.
100_8078.jpg100_8076.jpg100_8075.jpg100_8074.jpg

[BigLakeBob]

In pic #4 the needle in the carb is stepped, is that correct?

[duffeycycles]

50 Pan,This is all good,and thanx again to Cotton for teaching the class...I use a heat gun on all linkerts before removing parts.The little 10-32 plugs come right out.

[T. Cotten]

Yes, it is stepped, Bob.

But that wouldn't stop me from trying a #19 jet.
(Or get a catalog crap repop to drill and lapp as you please. The ones I got from Tedd were tiny.)

Duffey!

You have never resorted to a torch with a stubborn plug? Beware of Scheblers.

Herman!

Please inspect (after cleaning of course) the fit of the main nozzle into the venturi. Slop defeats the 'accelerator sump', but easily remedied.

We look forward to your observations of the fit of an NOS disc. (Sometimes I think all the 'seconds' went on the shelf. No, I'm certain that NOS means New Old Sh... nevermind.)
If it mic's close to 1.562 at all, the bore becomes the issue.

With luck, a slightly oversized disc can close substantial daylight upon a moderately worn bore, but its a short-cut rarely taken.

....Cotten

[50Panhead]

I found some rebuilding videos on you tube.
This guy has several. They helped.
https://www.youtube.com/watch?v=dU3n5nkXjms

One he had solder the eyebrow and reamed it out

So I gave it a try.
100_8081.jpg

I checked the fit of the main nozzle, I can feel a little bit of movement when I hold the spring in with one hand and stick my finger down the throat on the nozzle and try to wiggle it. Hard to guess how much. Not much. It drops in and falls out. I don't have to push it in or pull it out.
If I remove the venturi and insert the main nozzle in it there is a fair amount of play... Maybe .020 to .030

[T. Cotten]

Golly Herman,

I shut off the video when he picked up the hammer and molested the nozzle.
A pro would use a proper tool!

Meanwhile, since you have your soldering iron hot, why not solder up the nozzle spigot and turn it down to a sweet fit in the venturi.
Any leakage at that interface defeats the "accelerator sump" effect of the nozzle.

Myself, I use PEEK seals.

....Cotten

[50Panhead]

Cotton
I thought about building up the nozzle some. I did not know if it was the right thing to do.
no guts no glory, I'm going for it.

And Yes that guy beat the hell out of that carburetor.

[T. Cotten]

Just shave the soft solder to a taper with a blade, Herman,

And then tap upon the bottom of the nozzle (gentler than your video star), with something less destructive than an EZOut, to conform the solder into the venturi. (Assuming the venturi is in order...)

Nine ways to skin a cat, but mine's the easiest.

How long did it take you to dress out your bore solder?
I only know it doesn't agree with a Sunnen stone much.

...Cotten