Revs at stops

I've been riding my bike to work the past few days. It starts great (enriched out all the way at first then clicked in after a few moments. And it runs fine. Then about the third stop light I get to (3 miles?) it starts hanging at about 3k at stops. If I turn out the idle speed screw it drops back to 12-13.... Then about three more lights same issue... What would cause this?

I have pod filters (no plastic h-pipe) and a 2-1 exhaust, so my '78 is a bit modified.

I find that I have to adjust the rpms once the bike warms up fully. When the bike is cold the rpms are lower; as it warms up they rise a bit. I have to adjust the idle once the bike reaches full temperature to bring it back down to around 1000-1200. I suspect this has to do with my modifications. Once I adjust the idle back down at full temperature it does not fluctuate at all and seems to run perfect (this takes around 20 minutes of riding on a warm day).

I will do an experiment soon and see if adding the plastic h-pipe back on makes any difference. Some people say that pods directly on the carbs cause turbulence.

Anyway, describe your intake and exhaust modifications if you have any.

Thanks bcware, it's reassuring just to know others have to adjust after warm up. Stock intake and exhaust. I did notice on my ride home tonight that if I start to let the clutch out while the bike is in first from a stop the revs drop back down just before the bike starts to go (I hope that's clear enough). Also it wasn't as bad on my ride home tonight as my ride in.

The idle mixture is lean. Clean and adjust the carbs correctly. There are plenty of threads regarding these topics.

Once correctly adjusted, a cold engine should idle decently around 900 - 1000 RPM after a minute or 2 of running with the enricher/choke, and reach 1200 RPM once at operating temperature. Daily adjustments should not be required.

I richened the mixture a bit and it does seem to be doing better. I also checked for leaks with an unlit propane torch. It's no longer hanging and there are no leaks.

If the bike idles for a while the idle speed eventually drops and the bike dies. What would cause this? I thought it would be caused by the same issue but it is still doing it even though the other issue has been resolved.

You might be a little too rich, the timing might be a little off, the valves might need adjustment, the carbs might need to be synced, etc.

A lot of these things can contribute to an idle that won't stay steady and low.

Additionally, when you adjust the mixture screws it id common that they will be slightly different on each carb; if you're just setting them to a particular number of turns out without listening you may have issues.

There is a procedure to set them in the manual I believe. The bike should be fully warmed up, but if any other issues are contributing it might all be in vain until they are addressed.

I had checked everything on that list except valves. Turned out the intake on the right was quite a bit off (much too loose) got it back into spec (not too tight of course). Engine sounds way better and it stopped dying at idle. Thanks for mentioning it.

That's an easy fix for sure!