New Mixture Screws

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Before I started messing with the mixture screws the bike ran fine. No hanging idle.

Ended up needing new mixture screws after I stripped heads off of two of them. Noticed that the new ones had smaller diameter tips. Installed with the new screw, spring, washer, and o-ring (that order). Then I started greasing the manifold boots and noticed I had torn two of them during carb removal. Ordered new manifold boots.

Installed and started the vacuum sync. The idle is set very low. Hanging idle big time during sync. I would adjust then give a couple revs. 3 and 4 would increase and hang so much they almost sucked the tranny fluid into carbs. Mixture screws started at 1.5 turns out. Put them at 2 turns out. Didn't notice much of a difference. Then 3 turns out. She hung more than ever (3k). Now I'm thinking they should be leaner rather than richer to compensate for the smaller mixture screw tips. Put them at 1 turn out and it didn't hang much. Just a little. Time ran out needed to sleep.

I think I need to go even less turns out since the screws are different than the originals. Does this make sense? Or should I be looking elsewhere? The bike was running fine before messing with the mix screws. I'm thinking this has to be related to the new screws. I did try the propane test (no conclusive results).

No Mods

Oh, the idle would hang after pulling in the clutch. Then the idle would get so low it died a few times. After putting mix screws to 1 turn it didn't die, had a strong idle, and hardly hung.

[CatatonicBug]

What do you mean by "hanging" idle? Set your idle at 1100 to start with, while the engine is at full operating temperature. Once it's hot, turn it off and set up the sync tool. Turn it back on, let it run a minute or so, then start adjusting. Once each screw is adjusted, you'll likely have to turn your idle down. It will rise when the adjustments are all lined up. My screws are over 4 turns out, after a sync/colortune.

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The idle would hang around 2-3k rpm after coming to a stop. It would also hang there if I reved it a couple quick snaps.

Plugs were pretty much black at 1.5 turns. She seems stable and good plug color at 3/4 turns out.

[cywelchjr]

The idle would hang around 2-3k rpm after coming to a stop. It would also hang there if I reved it a couple quick snaps.

Plugs were pretty much black at 1.5 turns. She seems stable and good plug color at 3/4 turns out.

Idle hanging high is a sign of being too lean. One of the sings of being too rich is that the idle drops below normal for a short time when coming to a stop. When the mixture is right, the idle will drop right down to where it belongs and stay there nice and solid, no hanging high or anything like that. If their black at 1.5 turns is may not be the idle mix thats rich, but that it needs to be overly lean to clean them from the mains.

Proper adjustment of idle mixture can ONLY be done with the engine running, and you slowly turn them out till the idle speed peaks, and then back them off slightly, then and ONLY then, is the mixture correct. You will probably find that your idle speed is actually set WAY too high, and the idle circuit is only partially working because of it. I have run into this same thing on more than one bike, and it works out the same every time.

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I was adjusting the mix screws while the motor was running. Was idling at under 1000 which I know is 100 lower than it should. I was doing the ear test while setting. The further I screwed these new mix screws in the faster the rpm got. There was a point that was to far idle slowed so I backed it back out to happy spot. Then idled down again with main adjust, then tweaked next mixture screw...

I am really thinking these mixture screws much different than stock ones. Im going to go spend the 100 on a timing light that was digital induction RPM gauge on it. Then set the mix screws.

BTW Just took the carbs out and cleaned to make sure the problem isnt something else. Carbs look great and clean. No holes in diaphagms. Clean holes everywhere else. Im getting fast with the carb process

[cywelchjr]

I'm wondering if you have wrong mixture screws and that is causing problems. If the tips are significantly different than the originals it may not be possible to get it right with them. Make sure you have the RIGHT mixture screws for the carbs and you should be able to get them dialed in right.

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New Mixture Screws from carb capitol. The threads are the same size. The tips are much smaller.

Put the digital rpm meter on it and adjusted the mixture screws. This was a fast cure. It was a tedious process due to the fact that the rpm meter jumped around, but fast. The screws ended at just past a 1/4 turn. The rmp meter was nice... I could see and hear what the rpm was doing.

If I'm cruising at 4k and pull in the clutch, the rpm drops like a brick and hovers at 1,100!!! 1,130 to be exact.

I have only heard that lean mixtures produce hanging idles here. My experience with carb capitols mixture screws are just the opposite.

Will do my last sync over the weekend. Easy now that I've done it 6-8 times in the past week.

[Ken Talbot]

There's a photo in this thread that shows a broken-off early-model screw and a late-model blunt screw. The early screws have a knurled end that sticks up out of the carb. The late-model screws sit down inside a recess. "Early" means 1978-79. "Late" means 1980-81.

HTH...