Help with Bike (Won't idle without even tiny bit of choke)

sdhoagies

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Durham NC
As I say in the title, my bike (1974 CB450k7) has been acting up and just will not idle without choke. Here's a list of the problems and some descriptions of what I've done so far. Thanks in advance for any suggestions/help anyone has.

Basics:
- The bike has air pod filters
- Primary jet is 38 and main is 130 on both
- No vacuum leaks can be detected (spraying carb cleaner all around normal problem areas does nothing to RPMs)
- Has good spark, good battery charge, I replace the plugs and clean the old ones off every time I try and change something.
- Floats set to 20mm on the dot
- Have cleaned the carbs at least three times each now, with guitar string through each individual hole...I swear carburetors will make me develop OCD.
Problems:
- The bike does not idle without choke on. It almost does, but the choke needs to be the slightest bit open (or more) in order for it to run. When I open the choke too much, though, the RPMs run away.
- The plugs indicate that the bike is running rich (black and sooty) but the fact that it won't run without choke seems strange.
- When I hit the throttle it can have erratic results. Most often, it raises the RPMs up high, where they hang for a second, before they drop well below wherever it was idling before (this sometimes causes the engine to cut)
- I have gotten it to idle without choke a few times for over 15 seconds, but the RPMs are very low, and adjusting the idle speed screws doesn't change anything, as far as I can tell. Usually it cuts off on its own, though.
- Smoke comes out of the exhaust pipes, usually nothing serious, but just seems to be running rich, but when I cut the choke it seems like it's running too lean to run. Could it be as simple as adjusting fuel mix screws?
What I've done so far:
- I cleaned and rebuilt both carbs (cleaned them 3 or 4 times at this point), as well as reset float heights and replaced a compromised float.
- I reset the valve clearances, reset the cam chain tensioner, and reset ignition timing (it has an electronic ignition timing unit which I triple checked was right)
- I replaced the O-Ring (which was missing) on the right carb air/fuel mix screw and now the bike gets so close to running without choke
-I keep it on a trickle charger and keep replacing or cleaning the spark plugs, so I don't think fouled spark plugs is a problem
- I have good spark, compression, and fuel flow, and I triple checked all of these.
- I have tried toying with the air/fuel screws on either side while slowly lessening choke. I think this was the one time I got it to run without choke on for a little while, but the idle was still barely at 800 RPMs or so. Really too low to sustain itself.

Thanks in advance for any help or ideas. I'm new to working on motorcycles, and carbs, so I keep convincing myself I've found the problem only to do that thing and then convince myself of another one. I wanna get off this hamster wheel!
 
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Knowing which model you’re referring to will really help.
 
sdhoagies said:
- The bike does not idle without choke on. It almost does, but the choke needs to be the slightest bit open (or more) in order for it to run. When I open the choke too much, though, the RPMs run away.
Click to expand...
Your problem is not that the bike won't idle without the choke, you're using the choke to "correct" a completely different problem. Your runaway idle might be caused by improper throttle cable adjustments or loose advancer springs not retarding the timing enough to let the engine settle in at idle.
sdhoagies said:
- The plugs indicate that the bike is running rich (black and sooty) but the fact that it won't run without choke seems strange.
Click to expand...
Obviously the plugs are black because of excess choke usage.

Depends on which EI you're using if the advancer is still involved, but I'd guess it's either Charlie's Place or a Shockwave from those guys in Houston
 
You are running too rich with the choke not fully open. You are running away because of a vacuum leak somewhere. Without examining the bike myself, hard to pinpoint, but I would start on the rubber intake manifold boots. My CB360 had a similar issue. A very fine crack that was very hard to see until you took the rubber manifold off and bend the rubber a little. New rubber intake manifolds fixed the issue. Even not being cracked, the gasket and seals need to be checked. If the manifold boots are good, then it is a possible carb issue. If those are the original boots, they are over 50 years old, and probably very hard. For reliability, I'd consider the boots first, and if they are original, replace them for good measure.
 
So you should have the 723A carbs then.

Like AD pointed out, you’ll want to eliminate a couple of things first.

Check the cables and splitter to make sure nothing is hanging or binding or that one cable isn’t popped out of the splitter.

“Bench” sync them to ensure both throttle arms move in perfect unison, snap back all the way to seat.

Make sure you have the carbs fully seated and take the pods off.

If the EI is firing, it’s firing.

Start the bike.

There’s a decent chance the universal pods on there are partially obstructing the idle air passage.
 
ancientdad said:
Your problem is not that the bike won't idle without the choke, you're using the choke to "correct" a completely different problem. Your runaway idle might be caused by improper throttle cable adjustments or loose advancer springs not retarding the timing enough to let the engine settle in at idle.

Obviously the plugs are black because of excess choke usage.

Depends on which EI you're using if the advancer is still involved, but I'd guess it's either Charlie's Place or a Shockwave from those guys in Houston
Click to expand...
Hey. Yeah, it's a Shockwave. Guy that owned it before me installed it and I went through and made sure the timing was alright. The right sensor looked to be a bit janky (the metal plate holding it down was separating from the sensor, but I got it back together) but I think it's working right, now, firing when it's supposed to on both marks.

I checked the cables and they seem to be alright, not catching anywhere as far as I can tell. The runaway idle is pretty random, though, and it comes from when I open the choke too much. I'll take a video later and see if I can replicate it. It'll be easier to understand what I mean, I reckon.

Thanks for the response thus far, though, and bein' willing to help. I'll send that video out in a few hours.
 
EzPete said:
So you should have the 723A carbs then.

Like AD pointed out, you’ll want to eliminate a couple of things first.

Check the cables and splitter to make sure nothing is hanging or binding or that one cable isn’t popped out of the splitter.

“Bench” sync them to ensure both throttle arms move in perfect unison, snap back all the way to seat.

Make sure you have the carbs fully seated and take the pods off.

If the EI is firing, it’s firing.

Start the bike.

There’s a decent chance the universal pods on there are partially obstructing the idle air passage.
Click to expand...
I checked the cables and it all looks alright, as far as I can tell. The carbs are bench synced and then synced in terms of throttle. Carbs are fully seated, and I've ran the bike for a little bit in the garage with no pods on, but nothing really changed. I'll try again later and take a video. Hopefully that'll help. But seeing as nothing changed last time, and that design of the pods doesn't seem to obstruct the idle air passage, I don't think that's the problem! Any other ideas? I know there's a famous saying like 90% of carb problems are electrical/ignition and vice versa. But is there anything else I can eliminate before having to possibly really dig into the ignition system?

Thanks for reaching out and for the help so far
 
sdhoagies said:
I checked the cables and it all looks alright, as far as I can tell. The carbs are bench synced and then synced in terms of throttle. Carbs are fully seated, and I've ran the bike for a little bit in the garage with no pods on, but nothing really changed. I'll try again later and take a video. Hopefully that'll help. But seeing as nothing changed last time, and that design of the pods doesn't seem to obstruct the idle air passage, I don't think that's the problem! Any other ideas? I know there's a famous saying like 90% of carb problems are electrical/ignition and vice versa. But is there anything else I can eliminate before having to possibly really dig into the ignition system?

Thanks for reaching out and for the help so far
Click to expand...
Pictures are going to help here. Particularly with the Shockwave in play - mixed bag on that thing. The intermittent runaway idle thing is really commonly caused by aftermarket throttle cables hanging up at the splitter, leaving one carb open.
 
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Here's the latest test. The right carb actually ended up falling off somehow on one of the times trying to get this video, and the left one was firing pretty perfectly on its own - seemed to run without the choke on, even. Not even sure what that is supposed to tell me - does this suggest an ignition timing problem (dreading the idea of having to take out this EI and put in the points again, but I thankfully have it at least)? I've triple checked the splitter cables and I've pretty much ruled it out, if not for the very least that the throttle doesn't get touched at all when I'm doing this. I've been actively checking on each side when it happens, and neither of them seem to be stuck open. Here are some videos below to show what I mean - for the record I had warmed the bike up, too. It wasn't like these were starting from cold.

Here's the first video:
As you can hear/see pretty immediately after I cut the choke it peters on for a second or two and then the RPMs just drop out. Plus, in the very beginning you hear it revving up and up, even after checking the throttle cables were good and unopen, before starting this recording.

In the second video here it goes a little while longer, but just ain't quite right and doesn't last long:


You can hear me fiddling around with the choke raising/loweriing the RPMs (and not touching the throttle at all).

Here are some random pics of the carbs, as well:

Carb1.jpg
CArb2.jpg
wires1.jpg3.jpg


Thanks again for any help.
 
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I know its random, but one of the PO's of my bike replaced the gas lines and I think cut them to short. Because of that, my left side carburetor will sometimes get stuck slightly open, and mess everything up. That has been the cause of my hanging idle most recently.
 
cellomaster said:
I know its random, but one of the PO's of my bike replaced the gas lines and I think cut them to short. Because of that, my left side carburetor will sometimes get stuck slightly open, and mess everything up. That has been the cause of my hanging idle most recently.
Click to expand...
Hmmm I'll take a look again when I get home and report back. I know that my left carb's gas line often actually feels a bit too long. There was a worry at one point that it was having to go above the petcock and that that might have caused fuel not to get there at all, but I haven't thought to check and see how/if that line plays with the choke bar at all. Will take a look and report back. Thx for the idea
 
sdhoagies said:
Hmmm I'll take a look again when I get home and report back. I know that my left carb's gas line often actually feels a bit too long. There was a worry at one point that it was having to go above the petcock and that that might have caused fuel not to get there at all, but I haven't thought to check and see how/if that line plays with the choke bar at all. Will take a look and report back. Thx for the idea
Click to expand...
Proper 5.5mm Honda fuel line fits correctly and does not even need clamps, though Honda used thin wire clamps on it anyway. The routing looks okay but you should really get quality fuel line instead of auto parts store 1/4" line that is too big and needs clamps.
 
ancientdad said:
Proper 5.5mm Honda fuel line fits correctly and does not even need clamps, though Honda used thin wire clamps on it anyway.
Click to expand...
This is my problem...I had to put little clamps everywhere, and really, I just need to buy some proper gas line. Would fix my hanging idle due to the obstruction too.
 
OK - Fuel line conversation aside. Few things have jumped to mind here:

1. Your cable adjustment points look off. I know I keep coming back to the splitter but once side is adjusted way more than the other - that's usually what happens when one of the cables has less free play due to not being completely seated in the splitter.

2. That's a lot of idle adjustment - if you back the screws out all the way until they're not touching the "landing" tab do both arms drop the same amount? What happens if you start from there?

3. If a carb fell off, it's not seated properly. They should hold in just fine without even the ring clamp (sitting still in the shop). Make sure the little groove on the carb is completely seated with the ridge on the insulator.

4. Any chance when doing one of the carb rebuilds that there's an extra o-ring on the right side fuel/air mix screw? Seems to be standing a bit proud.

5. Vacuum caps are cracked - have you done the blow test to make sure the vacuum pistons rise evenly?

6. This involves pulling the carbs all the way, but check the butterfly valves to make sure they're oriented correctly (they have a barely perceptible bevel that affects how they seat at idle) - also make sure they're centered. If they got completely disassembled at some point, it's incredibly easy to flip them the wrong way or get them a hair off center and they bind.
 
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