How does the engine perform between rich vs lean?

If it's broken or just needs tweaked

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juntjoo
Posts: 320
Joined: Fri Nov 10, 2017 6:19 pm

How does the engine perform between rich vs lean?

Postby juntjoo » Wed Mar 06, 2019 6:06 pm

I have two situations where it struggles a bit,

1, before engine warms up, and

2, in particularly warmer, 70+ farenheit tempuratures, as I've noticed when it's colder I barely notice any performance issues...

which come down to hesitations with higher rpms or rapid throttle action. If I turn the throttle slow enough no issues but one day I might need to outrun the cops.

In general I'm trying to understand what of the fuel/air mix can be determined by the engine's performance if anything at all.

I'm planning to take a closer look at the plugs immediately after(shutting off engine) symptoms occur, but I also want to understand better what different behaviors indicate If anything in particular.

Thanks!
82" cb650 Nighthawk

juntjoo
Posts: 320
Joined: Fri Nov 10, 2017 6:19 pm

Re: How does the engine perform between rich vs lean?

Postby juntjoo » Thu Mar 07, 2019 2:17 pm

What I notice most besides high rpms struggles, if it's not the same problem is this cooler(SWFL temps) starting stumbling /stalling upon rapid throttle action. Check out my plugs though
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I thought they'd be darker but apparently I'm running lean. I checked these right after a cold start condition a couple times(10+/- seconds) to try to ensure the plugs would show the immediate signs.

Tell me, a carbureted engine that's struggles/stalls upon rapid throttle action can be due to either a rich or lean condition or would it be more likely one or the other? And I should note I've nodded from stock here a bit
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(k&n 1/2 carbs behind a foot of hose, check pic) that complicate the situation but I just wanna understand the mechanics /physics here better whatever anyone can offer. Thanks!
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82" cb650 Nighthawk

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Volker_P
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Re: How does the engine perform between rich vs lean?

Postby Volker_P » Tue Mar 12, 2019 4:56 am

K&N's usually shift mixture towards lean but your plugs look really all right.

With air filters like that placed on positions shown in your pictures pressure conditions at your carbs might become strange, especially when you operate the throttle. Things may even depend on the positions of your legs.
I am not going to say that a setup like yours cannot work fine but if you have problems in such case most probably there is nothing wrong with your carbs.
Two ideas to see if things change by that to better or worse:
1. One may try to connect the here open T-vent tubes together with a T and another longer, common hose (still with open end).
2. Or even lead them into the pod filter housings.
Cosky's great (free) online manual: http://cosky0.tripod.com

forum links to common technical issues

If you really like this site and you would not like to see it vanish soon, have a look there: Urgent: Future of HondaCB650.com Forum

juntjoo
Posts: 320
Joined: Fri Nov 10, 2017 6:19 pm

Re: How does the engine perform between rich vs lean?

Postby juntjoo » Tue Mar 12, 2019 1:46 pm

Volker_P wrote:K&N's usually shift mixture towards lean but your plugs look really all right.

With air filters like that placed on positions shown in your pictures pressure conditions at your carbs might become strange, especially when you operate the throttle. Things may even depend on the positions of your legs.
I am not going to say that a setup like yours cannot work fine but if you have problems in such case most probably there is nothing wrong with your carbs.
Two ideas to see if things change by that to better or worse:
1. One may try to connect the here open T-vent tubes together with a T and another longer, common hose (still with open end).
2. Or even lead them into the pod filter housings.


Thanks volker. I was wondering about the t-vents. Cuz normally they're closed reconnected to the carbs. So you suggested reconnecting. Being open, what does that do to the carbs? Something to the vacuum pressure? Something to decrease fuel pressure upon significant acceleration? Thanks. I think I'll try that next. I did sushi read a thread on another site about someone having them open and it affecting performance
82" cb650 Nighthawk

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Volker_P
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Location: southern Germany

Re: How does the engine perform between rich vs lean?

Postby Volker_P » Wed Mar 13, 2019 2:29 am

The T-vents are usually connected by a T into a single line that further goes to the airbox.
The pressure conditions in the carb bowls (and therefore at the jets) depend on the T-vents and what comes behind. From experience of several people here it makes a difference whether they are just open or connected by a T and go to the airbox or just through a bit more of hose to the free air. Others reported no difference however.
So no real explanation, I could imagine that in the very moment when you turn the throttle these things play a role for the movement of the slider piston and the pressure in the floater bowls. And these are decisive if it just accelerates fine or hesitates a bit.
Maybe the (possible) sensitivity to the T-vents stuff depends on the tightness status of the actual set of carbs.

From your plugs your carbs at least do not seem to have an obvious lean or rich basic setting issue. CV carbs are reported to be less sensitive to the air side than the PD/piston carbs and many people here seem to run pods on them without a need for rejetting. But no idea on their sentimental requirements on throttle response. E.g. I prefer very direct throttle response so I would not like even perfect CV carbs at a CB650.

So it is try and error until you either are happy or go back to stock. :wink:
Cosky's great (free) online manual: http://cosky0.tripod.com

forum links to common technical issues

If you really like this site and you would not like to see it vanish soon, have a look there: Urgent: Future of HondaCB650.com Forum


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