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Author Topic: Running on one cylinder intermittently (CB450)  (Read 838 times)

Offline redrover

  • Posts: 193
Running on one cylinder intermittently (CB450)
« on: Jun 04, 2018, 15:26:55 »
Brought this CB450 back from the dead.

Valves adjusted
Fresh oil
Rebuilt the carbs
Reg/rec installed
LED H4 headlight (to draw less power from the system)
Pamco Ignition (had it running on points first)

The left cylinder header wasnít getting hot at all... After tinkering with the carbs for days and days, finally fired on both cylinders, but when I ride it... The cylinder will start/stop even under throttle load, the cylinder will die and then kick back in intermittently.

Do I take the carb apart AGAIN (possibly tenth time)? What else can I try?




Offline redrover

  • Posts: 193
Re: Running on one cylinder intermittently (CB450)
« Reply #1 on: Jun 04, 2018, 15:28:17 »
Btw... compression test results:

Right cylinder 179psi
Left cylinder 174psi

Anyone any thoughts?

Offline TheCoffeeGuy

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Re: Running on one cylinder intermittently (CB450)
« Reply #2 on: Jun 05, 2018, 09:21:59 »
Sounds more like a loose wire.  Start with the high tension wires making new connections on both ends.   The wires themselves could be leaking or the caps could be old and they will convey electricity and ground out on the head.  Check the resistance and continuity on the plugs as well.  Then  check the low side wires all the way back for shorts and loose conexions all the way back to the spark generator.
www.thecoffeeguy.ca Not your ordinary Blog site.

1968 Harley Aermacchi ML 125 Rapido, restored
1972 Honda Cl 450 engine rebuild, a day rider soon, now sold
1980 Suzuki GS850GL Street Brat  My other day bike
2000 Harley 1200 Sport S My day bike
1982 Honda CB650 Chopper light

Offline redrover

  • Posts: 193
Re: Running on one cylinder intermittently (CB450)
« Reply #3 on: Jun 05, 2018, 22:54:50 »
High tension wires?

Offline themotoworks

  • Posts: 97
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Re: Running on one cylinder intermittently (CB450)
« Reply #4 on: Jun 06, 2018, 07:58:54 »
how old is your battery? 

Offline sebwiers

  • Posts: 35
Re: Running on one cylinder intermittently (CB450)
« Reply #5 on: Jun 06, 2018, 12:11:54 »
High tension wires?

I'm assuming he means the ones that run from the coil to the spark - IE, high VOLTAGE.  If you bike has just one coil it is running wasted spark and the problem is almost certainly a bad connection from coil to spark plug.  If it has 2 coils then it may be that one of the coils is sometimes not charging / discharging as it should.  That's probably a bad connection to the coil, or maybe the coil itself is bad.

And yeah, in my experience, intermittent issues are usually electric.  This does not sound like a fuel / valve / timing issue, especially as you say you just worked on those things.

Offline redrover

  • Posts: 193
Re: Running on one cylinder intermittently (CB450)
« Reply #6 on: Jun 06, 2018, 16:21:10 »
how old is your battery?

Battery is new, oem. Cranks right up over and over.

Offline redrover

  • Posts: 193
Re: Running on one cylinder intermittently (CB450)
« Reply #7 on: Jun 06, 2018, 16:30:26 »
I'm assuming he means the ones that run from the coil to the spark - IE, high VOLTAGE.  If you bike has just one coil it is running wasted spark and the problem is almost certainly a bad connection from coil to spark plug.  If it has 2 coils then it may be that one of the coils is sometimes not charging / discharging as it should.  That's probably a bad connection to the coil, or maybe the coil itself is bad.

And yeah, in my experience, intermittent issues are usually electric.  This does not sound like a fuel / valve / timing issue, especially as you say you just worked on those things.

Both coils are brand new too, they came pre-wired direcrly into coils, so I just had to twist on the spark plug caps.

All of that makes sense though.. sounds like I have to lift the tank and re-check the wiring. What other wiring should I closely inspect?

Is there a way to test the coils? (Aside from swapping sides)

Offline TheCoffeeGuy

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Re: Running on one cylinder intermittently (CB450)
« Reply #8 on: Jun 07, 2018, 10:13:15 »
Both high and low side coils have Ohms readings and ranges found in the Factorty Service Manual
www.thecoffeeguy.ca Not your ordinary Blog site.

1968 Harley Aermacchi ML 125 Rapido, restored
1972 Honda Cl 450 engine rebuild, a day rider soon, now sold
1980 Suzuki GS850GL Street Brat  My other day bike
2000 Harley 1200 Sport S My day bike
1982 Honda CB650 Chopper light

Offline frogman

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Re: Running on one cylinder intermittently (CB450)
« Reply #9 on: Jun 07, 2018, 13:48:47 »
Left side running like that can be a fuel issue since that has the longer hose. Make sure it flows correctly, no kinks or tough bends. If you are using in line filters take them out and see if that helps.

Also, pamcos are known for intermittent issues, take it out and put points back in to verify.

Sent from my SAMSUNG-SM-G891A using Tapatalk
« Last Edit: Jun 07, 2018, 13:50:47 by frogman »

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Re: Running on one cylinder intermittently (CB450)
« Reply #10 on: Jun 07, 2018, 13:52:36 »
This sounds like it could be a carb sync issue to me. I didn't see you mention that you synced the carbs. My 360 will run like absolute crap if its even the tiniest bit out of sync.
"He broke the mirrors off his Cadillac, 'cause he doesn't like it looking like he looks back."

74 CB360 - Luna - http://www.dotheton.com/forum/index.php?topic=63294.0 - Sold
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Offline redrover

  • Posts: 193
Re: Running on one cylinder intermittently (CB450)
« Reply #11 on: Jun 08, 2018, 01:40:34 »
Ok Iíll check the Ohm levels of the coils to eliminate that possibility.

Regarding the Pamco, installed it just a week ago in order to try to resolve this issue since it was doing it long before the Pamco came near the bike and thought maybe bad points were acting up intermittently.

And yes, although I thought I did sync the carbs, it is an art that I havenít perfected yet on the cb450... Need to do more research on how to master this. Does anyone have any tips on syncing 450 carbs?

Offline focusinprogress

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Re: Running on one cylinder intermittently (CB450)
« Reply #12 on: Jun 08, 2018, 10:35:21 »
what I've been doing on carb sync's lately is a neat trick I learned from a brit down in georgia. I sync with gauges the old-fashioned way, and then do a double check with an infrared laser thermometer. if the cyl's are within 10* of each other....you aren't getting any better than that....just have to make sure you're shooting temp the same distance away from the head on both pipes up by the clamps/mounts.

another thing to double check is make sure you're floats are set identical and you're getting equal fuel in both carb bowls....if one is slightly low, it could be intermittently running short of enough fuel to fire that side.
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Offline redrover

  • Posts: 193
Re: Running on one cylinder intermittently (CB450)
« Reply #13 on: Jun 10, 2018, 00:39:09 »
Ok so after checking the ohms on the coils... The coil on the side thatís been acting up was bouncing all over the place, and when it did stabilize it was 23ohms (other side was solid 17ohms).

I was going to swap the coils just to see how it would run, and noticed that the black power cable to the suspeft coil was barely hanging on and literally fell off. It didnít look salvageable... I replaced both coils.

Fired up on both cylinders! Idled perfectly. I shut it down to button everything else up and take for a test ride. When I started back up, the opposite cylinder wasnít running!

I shut it down, wheeled it to the street, fired up on both, but when I hit throttle, it would bog down and almost die, otherwise idled fine. I revved more and more and seemingly got better and better.

Finally running on both sides... bike is a screamer, but starts sputtering intermittently when I punch it in third gear. Even under level throttle, in third, sputtering with power coming in and out.

Any ideas?

Offline redrover

  • Posts: 193
Re: Running on one cylinder intermittently (CB450)
« Reply #14 on: Jun 10, 2018, 00:44:59 »
I checked the fuel lines, they seem ok.

I didnít have time to really get in and re-sync the carbs, not check the float bowl levels, but those are my next step.

Regarding the Pamco, does it work immediately upon setting the timing? Or does it take a few moments to learn the timing and stabilize?


Offline redrover

  • Posts: 193
Re: Running on one cylinder intermittently (CB450)
« Reply #15 on: Jun 24, 2018, 22:51:13 »
Adjusted the floats to the correct height and wow does she fly now!

Still sounds a little off... especially when I give it just a little throttle, but I think I just need to keep refining the syncing of the carbs.

Are the 500T carbs a direct bolt-on?

(they came with the vacuum ports, which should make syncing way easier).

Offline TheCoffeeGuy

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Re: Running on one cylinder intermittently (CB450)
« Reply #16 on: Jun 25, 2018, 20:50:53 »
they have been called high tension wires since Christ was a cowboy.    Ssounded electric to me form the start.
www.thecoffeeguy.ca Not your ordinary Blog site.

1968 Harley Aermacchi ML 125 Rapido, restored
1972 Honda Cl 450 engine rebuild, a day rider soon, now sold
1980 Suzuki GS850GL Street Brat  My other day bike
2000 Harley 1200 Sport S My day bike
1982 Honda CB650 Chopper light

Offline focusinprogress

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Re: Running on one cylinder intermittently (CB450)
« Reply #17 on: Jun 26, 2018, 13:42:51 »
Adjusted the floats to the correct height and wow does she fly now!

Still sounds a little off... especially when I give it just a little throttle, but I think I just need to keep refining the syncing of the carbs.

Are the 500T carbs a direct bolt-on?

(they came with the vacuum ports, which should make syncing way easier).

Yes they are...just may have to tweak jetting and such.

the trouble with these carbs is the individual idle set screws, individual throttle cables, and the sync of course.

What I do first is run the idle screws all the way out so they're both bottomed out. Then adjust the throttle cables so that both are pulling the plate open at exactly the same time. Then get the bike fired up (probably holding some throttle) and set the idle screws where the bike idles happiest and where a blip of the throttle below 1/4 turn doesn't cause a stumble. From here, on the 450 grab a $15 infrared laser thermometer and read your temps at the head pipes about an inch from the mount. if they aren't within 10* of each other, play with the sync until they are.

If after all of that you're still having trouble...it's bad float height(s) or not a carb issue.
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Offline davidricci

  • Posts: 78
Re: Running on one cylinder intermittently (CB450)
« Reply #18 on: Jul 21, 2018, 14:03:27 »
Double check timing or triple check it, buggered me once like this!