[CBaby]

Calling all you HEAVY hitters!!!

i can not for the life of me diagnose what the problem is with this CB360 (cafe, pods,re-jetted keihin carbs, 2-1 MAC exhaust), . I have gone over everything that i can think of, two or three times to no avail. i have done so much to this bike that i am not going to list it all here, but hope that one of you more seasoned vets will be able to point me toward a simple mistake i have made or something i may have overlooked.

The symptom is this:

Bike starts great and idles perfectly. It rides great, pulls hard and has power to spare. After 10-15 minutes of hard riding it develops the slightest hesitation (correct term?) so slight in fact, i can not tell if it even exists or if it may just be bumps in the pavement, but it feels like there is the tiniest little buck, or jerk...but then again i cant be sure. The BIG problem happens at the next stop. I get a hanging idle that wont come down, it hovers around 2500-3000 RPMs and stays there for a minute or so before finally settling down to about 1100 RPMs before it wants to dip even more and finally die. It also begins to backfire thru the exhaust and develops this "ploppy" miss-firing (correct term?) "pup-pup-pup-POP-plop-SPLAT-pup-pup-pup" etc... type of idle...you can just tell something is ever so slightly amiss...AND I CANT FIGURE IT OUT!!!!! I'm going to ride it home after work like a rented mule and sync the carbs AGAIN (while hot and having these symptoms) and go thru the points timing AGAIN (while hot and having these symptoms)...i'm counting on you guys!

PLEASE HELP!!!

justin

 

[CBaby]

...one thing i forgot to mention:

If i pull the right plug wire it runs as if nothing happened (almost, of course) but if i pull the left one AT IDLE, it will die. However if i give it a little gas before i pull the plug wire it will stay running, but not as cleanly as the right side.

justin

 

[Gixxer-18]

Sounds like it's leaning off as it gets hot to cause the high idle speed, then dies as it used up the fuel. Does it start again after a few minutes or straight away as the fuel flows back into the float chambers? This leaning off would also give you the sputtering symptoms. How have you routed the fuel pipes? Have you checked the fuel tank cap breather to make sure it's not blocked and not allowing fuel to flow?
Also next time you're out do a plug chop: ride hard as normal until you get the symptoms then pull in the clutch and switch off the engine with the kill switch. Coast to a stop and spin out both plugs and look at the plug nose for diagnosis black/ sooty= rich mixture, Light Tan; correct mixture, and white = Lean mixture. Do this on a safe road not the Freeway!
If you haven't wrapped your pipes their colour could indicate what's going on too. If they are blued you have a lean mixture.
HTH
Nigel

 

[CBaby]

Sounds like it's leaning off as it gets hot to cause the high idle speed, then dies as it used up the fuel. Does it start again after a few minutes or straight away as the fuel flows back into the float chambers? This leaning off would also give you the sputtering symptoms. How have you routed the fuel pipes? Have you checked the fuel tank cap breather to make sure it's not blocked and not allowing fuel to flow?
Also next time you're out do a plug chop: ride hard as normal until you get the symptoms then pull in the clutch and switch off the engine with the kill switch. Coast to a stop and spin out both plugs and look at the plug nose for diagnosis black/ sooty= rich mixture, Light Tan; correct mixture, and white = Lean mixture. Do this on a safe road not the Freeway!
If you haven't wrapped your pipes their colour could indicate what's going on too. If they are blued you have a lean mixture.
HTH
Nigel

let me address these one at a time...

it idles high for a minute and then comes down, it will then idle around 1000-1100 rpms for a good while...i can bump it back up with the throttle to prevent it from dying, or sometimes it will die or even climb back up to about 2000...it is very erratic. it will start right back up without issue. i dont think im starved for fuel?

fuel lines are routed well and are clear so i can monitor fuel flow

fuel cap breather is working fine

i will do a fresh plug chop this afternoon after carb sync and timing adjustment

exhaust pipes are a golden color

thanks,

justin

 

[jacksvintage]

Are the carb diaphragms all good?

 

[doode]

Maybe it's a combination of things?
Lazy floats and intake leak?
What octane gas you use and how old is it?

 

[Mydlyfkryzis]

I had a similar issue with mine. There were small cracks in the intake boots. Cold, no vacuum leaks, bike ran well. 15-20 minutes into the ride and the same situation occurs. The intake manifolds (boots) got softer when they heated up. They only leaked when they were hot. Cold they ran perfectly. See here: http://www.hondatwins.net/forums/1-...ing-now-e-advance-ignition-17.html#post173120

Might be a similar problem. If your manifolds are at all, old, replace them anyway. The new boots allowed easy install and removal of the carbs.

 

[Gixxer-18]

^^^^What He Said^^^^

 

[HerrDeacon]

I had a similar issue with mine. There were small cracks in the intake boots. Cold, no vacuum leaks, bike ran well. 15-20 minutes into the ride and the same situation occurs. The intake manifolds (boots) got softer when they heated up. They only leaked when they were hot. Cold they ran perfectly. See here: http://www.hondatwins.net/forums/1-...ing-now-e-advance-ignition-17.html#post173120

Might be a similar problem. If your manifolds are at all, old, replace them anyway. The new boots allowed easy install and removal of the carbs.

I agree with Richard, especially since you mentioned you are using pods so I'm assuming there is no longer anything supporting the carbs (i.e. the air boxes in the stock setup) so then as the manifolds heat up they get softer and the carbs could be pulling them down exposing the small cracks.

 

[CBaby]

Are the carb diaphragms all good?

carb diaphragms were good when i did my last re-jet...going up another main jet size so ill check them again.

Maybe it's a combination of things?
Lazy floats and intake leak?
What octane gas you use and how old is it?

Floats checked out and properly adjusted during last re-jet, i will check them when i re-jet my mains again this next week...no discernible intake leak, using fresh regular unleaded from chevron, have also used 92 octane with zero effect...

I had a similar issue with mine. There were small cracks in the intake boots. Cold, no vacuum leaks, bike ran well. 15-20 minutes into the ride and the same situation occurs. The intake manifolds (boots) got softer when they heated up. They only leaked when they were hot. Cold they ran perfectly. See here: http://www.hondatwins.net/forums/1-...ing-now-e-advance-ignition-17.html#post173120

Might be a similar problem. If your manifolds are at all, old, replace them anyway. The new boots allowed easy install and removal of the carbs.

Intake manifolds are brand new OEM with new OEM gaskets

^^^^What He Said^^^^

Intake manifolds are brand new OEM with new OEM gaskets

I agree with Richard, especially since you mentioned you are using pods so I'm assuming there is no longer anything supporting the carbs (i.e. the air boxes in the stock setup) so then as the manifolds heat up they get softer and the carbs could be pulling them down exposing the small cracks.

Intake manifolds are brand new OEM with new OEM gaskets, i also fabricated a steel bracket to support the carbs and take the load off of the intake boots.

i appreciate the input guys, keep it coming!

justin

 

[doode]

Re sync your carbs. Even if you think they're correct. Start at the beginning. Post your procedure.

 

[CBaby]

Re sync your carbs. Even if you think they're correct. Start at the beginning. Post your procedure.

i did this last night...engine at running temp, synced with vacuum gauges... however when i tried to tune the idle/air screw to highest RPM as instructed in the shop manual it will NOT idle back down regardless how far out you turn the idle adjustment screw so i had to turn them back down to 1-1/2 - 2 turns. afterwards i still suffered an idle hanging around 3000 rpms and would eventually drop to 1000-1200 rpms and i still had to play the throttle a little to keep it running.

justin

 

[doode]

If it were me, I would

1- check the pistons move freely
2- check the floats don't have holes, and set the height at an angle, not 90 degrees
3- sync them so the butterflies open the same amount at the same time.
4- how did you vacuum sync your carbs? Pls post pic.
5- set idle around 1200rpm, even adjustment both sides.
6- go for a ride

 

[CBaby]

If it were me, I would

1- check the pistons move freely
2- check the floats don't have holes, and set the height at an angle, not 90 degrees
3- sync them so the butterflies open the same amount at the same time.
4- how did you vacuum sync your carbs? Pls post pic.
5- set idle around 1200rpm, even adjustment both sides.
6- go for a ride

i appreciate the input doode!

...but i am WAY beyond this stage. The pistons move freely, the engine has been rebuilt and has +3 pistons...i have rebuilt the carbs 3-4 times already trying to get the jetting correct, i have been running very lean. I have some new slow jets on the way and am going to do another carb rebuild next week. I will be running 38/70/115 jets at that time (35/68/100 were stock and i am currently running 35/68/112). The floats are fine and have been set to 16mm. The carbs have been bench synced each time before being installed on the bike and i have these vacuum gauges:

When at running temp it is impossible to set the idle at a reliable 1200 rpms (it does great when cold: put-put-put-put-put...right at 1200 rpms)...it wants to idle high (around 3000 rpms) when you turn the idle screw down to get to the desired 1200 rpms you have effectively turned it to the point where it is no longer engaging the throttle at all and has been taken out of the equation entirely, and the bike will NOT idle smoothly at 1200 rpms it will want to jump up to the 3000 rpm mark, or stagger around 1100 rpms and eventually die.

justin

 

[tytim]

Hi
I'm no way any kind of expert an these 4 strokes, all my other bikes are 2 stoke.
But in your last post you advise you have set the float height at 16mm.
I have been watching the common motor youtube videos and on their CB360 the set the float height at 23mm.
Might be relevant

 

[CBaby]

Hi
I'm no way any kind of expert an these 4 strokes, all my other bikes are 2 stoke.
But in your last post you advise you have set the float height at 16mm.
I have been watching the common motor youtube videos and on their CB360 the set the float height at 23mm.
Might be relevant

i appreciate the feedback...the factory settings are listed as 18.5mm however i was running EXTREMELY lean at this setting (backfiring thru the carbs and bluing my headers) the smaller measurement here increases fuel depth inside the bowls, and if my understanding is correct any excess fuel should drain out of the carb overflow vent tubes, which i have never seen a drop. This leads me to believe that i am not suffering from too much fuel in the carburetor bowls.

...another symptom i have is an excessive popping and backfiring thru the exhaust during deceleration.

thank you!

justin

 

[doode]

Oh man, I thought this was for a 350. I don't know much on the 360s, but can't hurt to try a higher float at the dude above suggested? If 18.5 is spec then 16 will drown your carbs. Is it possible to put the carb pistons on backwards on this model?
I don't know if it's frowned upon, but maybe try higher float and shim the jet needle to compensate?

 

[Mydlyfkryzis]

Oh man, I thought this was for a 350. I don't know much on the 360s, but can't hurt to try a higher float at the dude above suggested? If 18.5 is spec then 16 will drown your carbs. Is it possible to put the carb pistons on backwards on this model?
I don't know if it's frowned upon, but maybe try higher float and shim the jet needle to compensate?

Float height for a cb360 is 18.5 mm. 23mm is a lower fuel level in the carb, will cause leaner running. 16 mm is likely to be close to overflowing. 0.5 mm either way can help trim mixture, but I wouldn't go more than that.

Also, may be new carb manifolds, but symptoms are similar. You likely have a warm engine vacuum leak. Might be throttle shafts seal, or even a new manifold that leaks hot. New parts can be bad. Are they genuine Honda parts or third party?

Valves can expand when hot...so triple check valve clearance, especially exhaust. Slight loose is better than slightly tight.

Sent from my SM-T800 using Tapatalk

 

[doode]

To clarify, by higher float height I meant go to the stock 18.5mm and shim the jet needle to richen things up

Oh man, I thought this was for a 350. I don't know much on the 360s, but can't hurt to try a higher float at the dude above suggested? If 18.5 is spec then 16 will drown your carbs. Is it possible to put the carb pistons on backwards on this model?
I don't know if it's frowned upon, but maybe try higher float and shim the jet needle to compensate?

 

[CBaby]

Float height for a cb360 is 18.5 mm. 23mm is a lower fuel level in the carb, will cause leaner running. 16 mm is likely to be close to overflowing. 0.5 mm either way can help trim mixture, but I wouldn't go more than that.

Also, may be new carb manifolds, but symptoms are similar. You likely have a warm engine vacuum leak. Might be throttle shafts seal, or even a new manifold that leaks hot. New parts can be bad. Are they genuine Honda parts or third party?

Valves can expand when hot...so triple check valve clearance, especially exhaust. Slight loose is better than slightly tight.

Sent from my SM-T800 using Tapatalk

They are genuine Honda OEM manifolds...i checked the valve clearances several times as well (just a touch on the loose side)

i will double check the manifolds when i reinstall the carbs this week...maybe put a little three bond on the gaskets

thanks Mydlyfkryzis

justin