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Discussion Starter #1
So I just did the $0.22 mod, and have put everything back together. I am reasonably sure my issue is an unseated diaphragm, but I would like to describe the bike's (lack of) performance and run it through the gauntlet of counsel before going back in and trying again.

I can start it with the choke on if I give it plenty of gas (around 4-6000rpms), and then it sounds so rough (and at such a high volume!), that I imagined my valves were out of sync. If I let go, it will die immediately. Black exhaust when I have it "started" and running at high RPMs. Does this sound consistent with a "no seal" situation in the carb?

The reason I'm almost sure it's a diaphragm issue is that I fumbled for about 10 minutes with getting the diaphragm edge into the groove on the carb slide. Whenever I got the edge into the groove on one side, it would not stay while I got to the other side, or if it did, I'd be left with a bulge that in no way would fit into the groove. At this point, I assumed that I was approaching it wrong from the beginning and just lay the diaphragm edge around the carb slide edge and put the cover on, thinking may the pressure from the cap was supposed to keep it down. Anyway, that's my theory for what's happened, but would love your advice! Thanks!
 

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Doesn't matter what your symptoms are, you will have some sort of issues if the diaphragm isn't right.

If your diaphragm is not fitting well it may have swelled oversize from some contact with a solvent. If that is the case it will likely recover if left to dry for a bit. I haven't ever tried accelerating the drying, but the gentle application of a hair dryer might help.

It may be helpful to put a bit of Vaseline in the groove to help hold the diaphragm in place. When the cap goes on you should be able to wiggle it just so and it will 'feel right'. I know that is vague, but it will feel like the diaphragm is properly seated, there will be no feeling that the diaphragm is bunched on one side or out of the groove. You'll be able to set it down and move it very slightly in any direction with no change in how the cap feels in any direction of movement. It's a Zen thing. It helps to gaze into your navel and say 'OOOOMMM".

Installing the cover over an unseated diaphragm may have damaged it. It may be cut and thus leaking vacuum badly. If that is the case then you'll want to replace the diaphragm with a new one. The $20 diaphragm in the 5th video (you watched the videos, right?) is really quite easy to install and definitely easier on the pocketbook than buying a complete slide assembly.
 

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Discussion Starter #3
Hmm... I guess that's partly why I'm confused, is that it did "feel right" when I put the cap on at the end. Furthermore, watching your videos of the 22 c. mod, my diaphragm looked exactly like yours did when you take the cap off. The diaphragm edge appears to kind of just lay over the groove — is that just because you hadn't re-seated it since you were just making a video?
 

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Discussion Starter #4
Ok; took it apart again and re-checked the diaphragm and mixture screw. If the diaphragm isn't in right, there's absolutely no way it will ever be "right." It seems like it's pretty much in the groove all around, and when I put the cap on, it feels exactly what I would expect it too feel like if it were in right. But I guess it's hard to explain without actually seeing it. No rips, tears, or anything in the diaphragm. Also, I reset the pilot screw to 1.75 turns out after being seated. Still AWFUL performance, running incredibly rough with significant throttle, won't idle at all. I took some videos, but I'm not sure if the forum supports them?
 

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Discussion Starter #5
My gosh, I'm a freaking dumb-a$$. I was putting the white cage in before the needle/washer. So that sucker was a good 3/4in higher than it was supposed to be. I guess I just wasn't paying attention to the order when I took it out. Ok, so the washer I have is a #4, but it's quite a bit wider in outside diameter than the one you use in your video, such that the it will not fit "inside" the cage — instead, the feet of the cage will sit on top of the washer. Is this a problem, as long as the feet are still down far enough to catch the positioners as the bottom of the slide cage? The spring would keep it in place right?

Man, I'm an idiot. 😂
 

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If making a mistake or two makes you an idiot then I'm no better than a shovel full of pond scum. I always figgered that the only person that makes no mistakes is the one that does nothing. You're not the first to position the needle like that.

Now, that washer just can't be right. For it to be large enough to be the same diameter as the white cage it also has to be way too thick. It's hard to imagine it could be that large in diameter yet have an inside diameter of 1/8" unless it is some kind of fender washer. If the washer is too thick it will lift the needle higher than you're wanting to.

You need a real #4 washer; the kind of washer that fits a 4-40 screw. It ought to be not much bigger in outside diameter than the head of the needle with a 1/8" hole and it ought to be about .020-030" thick. That's the same thickness as 10-15 sheets of paper, your thumbnail, or a couple of business cards.
 

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Discussion Starter #7
Of course, I meant it all in love (to myself) 🤔 Thanks for the encouragement, all the same.

I went back to the hardware store to check. The washer was indeed labeled #4 and was in line with the #2 and #6 washers. But I found a brass #4 which was the right size. Everything is running great now. Not sure if it was worth all the trouble of my mistakes, but I'm happy with it!

Thanks again for the help, Tom.
 

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I figure if I did something, learned something, accomplished something, and am happy with something, then it was well worth it.

It's better than piloting a bar stool drinking something.
 

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That black smoke was a pointer to the problem. Too much gas for the air passing through the carburetor.
 
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