Hoping for a quick answer, Honda CB question

Morning all,

My wife is taking her motorcycle test today and the DMV is a little far so I took the bike to work which is about halfway. On the way here, like a light switch, something happened and it lost power. It struggled to get past 3-4K rpm unless I'm in first. Idles normal and if I keep the RPM down I can get it up to speed just be moving through the gears. Opening the throttle way up I can hear more Intake noise but power doesn't increase. Seems to be running on both cylinders, plenty of gas in the tank. It's been running well for weeks and this came out of nowhere. 
I would love for this to be a quick fix I can do within the next 2 hours. It's been such a struggle just to get this far but that story is for another day. 
Any ideas?

Ah, Bike is 1975 CB360T. All stock 

Fuel petcock partly closed?

NOT A TA said:

Fuel petcock partly closed?

This or maybe flipped to reserve?

Open the fuel cap and see if things improve? If the cap vent is blocked you may not get enough fuel flow.

Also, unless it's been changed, the bike should have points ignition, so I'll check the points.

Petcock is correct. It happened about 20 minutes into a ride. I pulled away from a light and suddenly it was super lazy. 
Choke makes it worse. 
I haven't tried the cap. I'll see if I can try that in a bit. I should be working lol

it does have points. I have a feeling it's not ignition but it could be. Gut feeling is that a carb diaphragm gave out suddenly. Or the timing slipped but if that were the case it should run poorly everywhere right? It feels normal until 3-4K and then the power just  stops

Ive been learning about carbs and points and all that but I don't know it well enough to diagnose effectively. 

Should be a fuel vent line off the carb that is a combo vent/overflow. Pop that off and see if it improves. Sometimes it clogs and causes a similar issue, but it's more likely that a piece of something floated it's way down to the carb or the points are doing something weird. 

In reply to spandak :

Is it strictly RPM, or does throttle position play into it?

Wondering whether the main circuit on a carb got blocked up. OTOH, I wouldn't expect choke to make that worse.

The quickest sanity check diagnostics for a couple things on your mind are:

A: pull air filters and see if both carb slides are behaving similarity while idling/blipping. If one isn't, that would reinforce your diaphragm idea. It dawns on me that if a needle came unclipped, you'd also get bad fueling even with the diaphragm in fine shape, though I can't recall exactly how the clips are arranged and thus whether this is really possible. At least if the clip above the slide came off, you could see the needle sitting there in the jet, probably.

B: set the points again. If the plate wasn't sufficiently snugged down it could shift. I'm not sure how likely it is, but it can be verified and ruled out pretty quickly. Fewer question marks is always good.

Are the tank and fuel lines completely clear of any debris like rust? 

I go here for CB info - http://forums.sohc4.net/index.php?board=2.0 

It seems to be a power issue. In first if I stay on the throttle long enough I can get it over 5-6-7krpm but it takes time. On the higher gears it doesn't have enough power. More throttle gives me more induction noise but no more power. It does hiccup a little I can feel the power return for a moment and then it's back. 
Apparently a bad condenser could cause this'll problem too?

It looks like I won't be able to do much diagnosis on it right now. I'm looking to just get it to the DMV so she can take the test and then limp it home. It runs normal at parking lot speed and that's all we need today. But I'll try the quick checks and see if anything changes. Oye
damn old things. 

I'm starting to get the impression that even if you don't mind all the maintenance of points, the declining quality of available condensors makes a strong case for electronic ignition conversion.

But I'm inclined that direction anyhow.

Hope the test goes well, and that being able to take your time on the diagnosis helps!

It's something to think about. I found a kit that converts to a common GM condenser but it might not be worth it. 
thank you!

Sounds to me like a fuel issue.  Something stuck in a carb jet or other orifice in the carb.  

Late to the party but check your throttle cable. They stretch.

I'm guessing vacuum leak.

But those things might not have many opportunities for leaks beyond the intake boots....

see if spraying starting fluid around the carbs (but not the throats) makes any difference

Check the air box. A critter was living in mine and built a tidy little house. One day it got dislodged and blocked the screen. Same situation, it was getting very little air.

Just a thought.

Actually I thought the same thing; something is blocking the intake be it the CV slides or a dislodged piece of air filter element.

Sounds carb related. Check jets for clogs and no lines are blocked including the vent lines.

On my CM200T, Honda cheapened out and made the battery part of the wiring circut. When the battery gets old, it starts dropping cells, and it completely fubars the ignition. Not sure if the 360 does the same thing. Check the battery.

Just to wrap this up,

We pulled the carbs and found that the PO sealed the float bowls with (way too much) high temp silicone. It melted, and we found a string of it sucked up into the main jet on one side. The other side was partially clogged and I have a feeling it has been that way for a while. I wouldn't have guessed that problem. I haven't had a chance to ride it further than around the block but I think its going to run much better.

Thanks for the replies everyone!

Dang, I thought I'd seen most motorcyle-related berkeley ups (including carpet underlay as an air filter "substitute"), but high temp silicone to seal the carb float bowls is a new one.

Glad to see you found the issue.