Linkert m74 idle control/throttle plate light leak

[T. Cotten]

I use a pool cue, Bob!

Drop the venturi over it 'til it stops, mark the spigot hole, and then put a caliper on it to be exact.

You would be surprised how much a nominal ID can vary,.. but its only the OD that matters.

....Cotten

[T. Cotten]

The problem with a fat, heavy hose to the testplate, Bob,..

Is that it can move your manifold while your are messing with it, after you have lined it up to the carb with its support.

I suggest light, flexible vinyl tubing; At one atmosphere, you won't even need clamps.

....Cotten
PS: it is always prudent to completely disassemble, and remove the venturi for inspection.
I lost count of how many have come to me full of blasting media.
When clean and re-installed, there should be no daylight around its outside diameter.

Your extreme daylight around the throttledisc reminds me of a Tedd rebuild, where it was bored oversized, but a standard disc installed.

[CAP'N BOB]

I will change and use thin wall hose, Tom. Thank you.

I will remove and inspect the venturi, no matter how much that scares me, never having done that. As I said, this is my first Linkert.

It is clear to me that the throttle plate/disc is not right, and somehow, that must be resolved, even if there are any issues with the nipples and intake manifold when I bubble test them.

These are the clamps I remembered having in a tin where I keep all kinds of old clamps. The split ones are probably what you told me, and maybe the other set in the first photo is chrome.

Second photo is three more sets. One is SS, I think, says 5 Star MFG, Crest Hill, Il, with a 27 and 65M, on it along with 404, leading me to believe that means 404 Stainless. One other set appears to be stainless and says Drag Specialties on the inside. The one with the small screws and covers over the screws says UF4, and 768-36 on the outside, with UF4 C-650-36 on the inside. Not even sure where I got these, to tell you the truth.

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[T. Cotten]

I'd try the bottom set in your first pic, Bob...

(The top set is for later "band seals", the two sets in the second pic with quarter-inch bolts are great for exhausts only. I have no idea what the bottom set are for..)

Please note that the manifold flange and carb flange interface, where they are gasketed to a phenolic spacer, cannot be bubble-tested, so both flanges should be arbitrarily ground to flat.

On to the carb, complete disassembly is mandatory.
Beyond clearances of the throttleshaft to bushings, please pay special attention to the idle bleed holes under the large plug on the 'idle' side of the carb. It is not uncommon for particles, usually glass beads, to become lodged in the slot, and hard to see without magnification.

And of course, make sure you have a float that floats.

Reassembly is by the book, but be certain that the lowspeed lift spring collar has the "top hat" upward, and slides easily upon the body

....Cotten

[CAP'N BOB]

Ok. Will get to work on it. Thank you. Will let you know how this goes, Tom. I appreciate your help.

[CAP'N BOB]

Stoppers arrived today. Set one up and tested both rear (still on the bike) and front intake nipples. No air bubbles anywhere. You were right, Tom, one atmosphere (14+PSI) wants to push the stopper out! :-)

I will test the manifold once I have the front head back on.

As a side note about over-oiling, I reseated the check ball and put in a longer spring (what the restoration manual said belongs), put about 2.5 quarts of oil in, and it does not leak from the open front cylinder as before. When I play with the kick starter to find TDC and 32 degrees, because I wanted to take photos of the Timer, Piston, and Timing Mark in the window, for my own reference, oil does come out of the feed hole in the open front cylinder, so I basically know that is all working. Hope that was the only problem, and I plan to put it all back together, and find out.

This is the stopper and the plate, I made, based on your design, Tom. Thank you, again.
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[CAP'N BOB]

Hey, Tom. I must confess, I gave up and had someone rebuild the Linkert who does that for a living. I did get the clamps you told me to get, and did use the leak tester I made. No air leaks. Hooked up with the new clamps. Set the timing with the mark as you see in the one photo, per my old Harley service manuals for 47 and back knucks and the one for 48 up pans. Fired it up, last night and can control the idle with the throttle and minor adjustments with the needle. Tested the cold starting cycle again this morning, ran it until it was warm, shut it off and started it with the warm starting cycle. Started on one kick with the warm cycle, had to kick it 3 times with the cold. I know it will take some adjusting.
Still over-oiling, even though I put the cast D-rings on. Need to chase that, of course. Oil goes back into the tank with no issues, but somehow it is leaking at the pans.
Thank you for your help. It felt good starting that, last night and having it idle down and let me adjust it without it dying, and again, this morning. You taught me a lot about this carburetor. I think, I can rebuild one myself now and feel confident.
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[BigLakeBob]

Glad you got your carb issue under control. In your first picture is that a screw going into the rocker cover to hold the throttle cable? Never seen that before. Leak waiting to happen and future tightening failure, something has to be better. Reverse the clamp and move it to the top motor mount or get the correct oem parts?

[CAP'N BOB]

20210818_173738.jpg20210818_173749.jpg20210818_185435.jpg20210818_185439.jpg20210818_185443.jpg I made the part and powder coated it. I was having trouble making any stock-like parts work. The throttle is a push throttle mechanism and my customer wanted a pull throttle, which I could accommodate by coming in from the left side the way you see it.

[T. Cotten]

.... I was having trouble making any stock-like parts work. The throttle is a push throttle mechanism and my customer wanted a pull throttle, which I could accommodate by coming in from the left side the way you see it.

I'm a little confused, Cap'n,..

Whether the control spiral is the early one that pushes the wire (proper for a Pan Linkert),

..or the late one that pulls the wire, the twist of the wrist is the same for the rider.

Sounds like a difficult customer.

....Cotten

[CAP'N BOB]

That makes sense now, since even though the hand grip is pulled, the throttle plate is pushed open, so my running the cable in left side of the bike versus in on the right side would not have mattered, it would just have taken a different linkage, probably. I could not find a way to make sense of the cable coming in on the right side, but could make sense of it coming in on the left side with this bracket. As I have said, I normally do not do "restorations or rustorations" and have learned a lot and gained a much greater respect for people who keep these old bikes stock and running. It has been interesting.
Thank you.
The customer is not difficult, I am, due to lack of knowledge and spending a lot of time learning!

[T. Cotten]

Its really hard to tell from your pics, Cap'n,...

But it looks like you have the swivel "cable block" butted up against the control wire sheath. You will want good clearance, as both sheath and wire will flex.

The stop limit for both open throttle and idle must be the carburetor throttle lever "tower":

image_31592.jpg

I cannot discern if you have the correct throttle hardware, which makes it all easier;
Note that this one has the swivel in the wrong hole (as well as missing a washer, and farmer wire instead of a cotter pin.)

....Cotten

[CAP'N BOB]

Not sure I can send a video, but if I can, I just shot a video of using the throttle, opening and closing. Works smoothly and when the bike is running it works smoothly. Nope, says I cannot upload an MP4 video. Are there any I can? The 9 second video shows how smoothly this works, but hopefully the still photos will also show it. The stills make it look like the cable hits the top motor mount, but it does not hit. Clears all the way through the process and I left about 1/2" clearance where the wire comes out of the sheath to the linkage.

I remembered part of why I did not like the cable coming in on the right side, the bend coming out of the handlebar seemed too sharp and I think the way I ran the cable there is less stress on the cable. Not being a Factory engineer (or any other kind of engineer), I could be wrong, but then, I also did not like the brake lever on the left, so moved it to the right. Seemed pretty unsafe to me to have to clutch, brake and hand shift, almost at the same time. I have NEVER ridden a tank shift bike, so I may be wrong on that. Time will tell, since I will need to at least test ride this bike before giving it back to the owner. He wants me to ride the first 50 miles of the engine rebuild, but, again, time will tell if I am willing to do that..

Hope these help.

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[T. Cotten]

That's a common Knuck throttle lever, Cap'n...

And you might notice all of the exposed threads on the top motormount bolt; Early Pan cable brackets take that up, and they clamp the sheath.

But pleasing the customer comes first, and all of the "correct" hardware would nickle-dime him sorely.

So you might as well leave it alone if it works!

....Cotten

[CAP'N BOB]

Now, there's a thought, I could make a bracket that fits under that motor mount bolt that would put a different angle on the cable and it would be a spacer and flat washer, taking up space, though that may not be a straight shot in. Hmm. Gotta think about that, but, this way does work. And, since he was foolish enough to ask me to build this for him, he deserves my unique way of restoring! :-)

If the cable is still to come in from the left side, because that makes sense to me, the throttle linkage would need to be different and stick out farther to the front, right? Making a new bracket would be easy, the geometry of the bracket coming into the linkage would need to be maintained to make the cable work smoothly. I had to spend some time designing and shaping the bracket I made to get the cable angle to allow smooth operation of the linkage; no binding.

I wish I could send you the MP4 video I shot (9 seconds), but the platform does not allow MP4 apparently, at least I got a message saying so. I saved it in another format and still could not send it. Anyway, if you could see the video, you would see how smoothly this operates. And, when running the engine, the throttle seems very smooth. You are probably right, if it works leave it alone, though if I could make it a '48 style I would like that. This is an icon, being a first year Pan, and I would actually like to maintain as much of that as I can for him. He did not want me to paint any of it, just make it rideable and as correct as I could. Been a long process, finding parts that he did not bring me, making others, rebuilding the engine from the bottom up, etc. I am getting close, now and would like it finished and safe to ride, that's for sure.

Thank you, again for all of your help.

Bob