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2000's CB600 dying with choke

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hornet_guy
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PostPosted: 15:41 - 24 Jan 2021    Post subject: 2000's CB600 dying with choke Reply with quote

Hello guys,

I have a 2000's Honda CB600 Hornet. Since the moment I bought it does the same thing:
- If I try to start it with a little bit of choke it won't start.
- If I give it a bit of choke when running, it dies.

In this bike the 'choke' is of the type that injects more fuel instead of choking the air.

In order to start the bike, I must give it a bit of throttle.

I watched some videos of other users and I'm astonished of the seamless start ups of their bikes, no way close to mine:

https://youtu.be/DqgZ9wg0-CQ?t=14
https://youtu.be/xOG1IuuqzXI?t=87

What can be the cause?
Thanks in advance.
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Hong Kong Phooey
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PostPosted: 15:49 - 24 Jan 2021    Post subject: Reply with quote

Carbs or injection?
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Nobby the Bastard
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PostPosted: 15:52 - 24 Jan 2021    Post subject: Reply with quote

If it starts fine without the choke why are you trying to fix something that isn't broken?
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hornet_guy
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PostPosted: 15:52 - 24 Jan 2021    Post subject: Reply with quote

Hong Kong Phooey wrote:
Carbs or injection?


It's a carb bike.
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hornet_guy
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PostPosted: 15:56 - 24 Jan 2021    Post subject: Reply with quote

Nobby the Bastard wrote:
If it starts fine without the choke why are you trying to fix something that isn't broken?


Because that's not the way it's supposed to work. And I wouldn't say it starts fine really. When it's cold it's difficult to start and I can't use the choke for the reason above.
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trevor saxe-coburg-gotha
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PostPosted: 16:44 - 24 Jan 2021    Post subject: Reply with quote

how often is it used and where is it stored? Also, how many miles has it done since it's had a decent service - carbs balanced, valve check, new plugs?

My 1999 zx9r starts easily every time - if it's being used a few times per week. If not, it will quite quickly turn into a lethargic starter - especially in cold weather (even if it's been on an optimate). It will still start, and relatively easily at that - but it will definitely require a bit of nursing. Full choke, no revs. But I may have to keep the starter button pressed for a few seconds once it (seems to have) caught.
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Hong Kong Phooey
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PostPosted: 16:45 - 24 Jan 2021    Post subject: Reply with quote

Does it run OK otherwise?

How does the throttle respond, laggy, revs hang, or instant?
Starts OK when warm?
Any fuel smell out the back?
Service history?
Valves done recently?
Runs fine at large throttle opening?

It sounds fuel related so far, rich mixture. Other than being air filter clogged, it looks like carbs are going to be coming off for a clean, rebuild and adjustment. Incorrect float height, and poorly set pilot screws are areas that could cause it.
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Last edited by Hong Kong Phooey on 17:18 - 24 Jan 2021; edited 1 time in total
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trevor saxe-coburg-gotha
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PostPosted: 16:51 - 24 Jan 2021    Post subject: Re: 2000's CB600 dying with choke Reply with quote

hornet_guy wrote:


okay, the second one wasn't even on choke - dated October. Not even been any decent frosts, probably. Looks molly coddled to fuck. It's just been run up to temperature, i'd bet. So - my question: are you comparing like with like? if your bike was in that condition, and was up to temperature, are you saying it would not start on first or second press, and would need choke? Because if so, yes, you're right. There's something bizarrely awry with it.

As for the first clip, the engine starts racing so promptly that it'd probably have started quite easily just off the throttle. So basically, same points apply.
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hornet_guy
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PostPosted: 17:05 - 24 Jan 2021    Post subject: Reply with quote

trevor saxe-coburg-gotha wrote:
how often is it used and where is it stored? Also, how many miles has it done since it's had a decent service - carbs balanced, valve check, new plugs?

My 1999 zx9r starts easily every time - if it's being used a few times per week. If not, it will quite quickly turn into a lethargic starter - especially in cold weather (even if it's been on an optimate). It will still start, and relatively easily at that - but it will definitely require a bit of nursing. Full choke, no revs. But I may have to keep the starter button pressed for a few seconds once it (seems to have) caught.


At the moment the bike is used once every week or once every 2 weeks for 1 or 2 hours, which I know is unfortunately very few usage... In the past I used it every day and it started easier but always with a little bit of throttle. The choke (or enrichment) never worked right.

The last time the carbs were serviced was about 4000 miles ago. The spark plugs were checked around 1000 miles ago.
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Kawasaki Jimbo
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PostPosted: 17:07 - 24 Jan 2021    Post subject: Reply with quote

I’d begin by making sure the air filter was ok, ie. clean.
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Hong Kong Phooey
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PostPosted: 17:19 - 24 Jan 2021    Post subject: Reply with quote

When it does start, after warm up what RPM does it idle at?
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hornet_guy
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PostPosted: 17:31 - 24 Jan 2021    Post subject: Reply with quote

Hong Kong Phooey wrote:
Does it run OK otherwise?

How does the throttle respond, laggy, revs hang, or instant?
Starts OK when warm?
Any fuel smell out the back?
Service history?
Valves done recently?
Runs fine at large throttle opening?

It sounds fuel related so far, rich mixture. Other than being air filter clogged, it looks like carbs are going to be coming off for a clean, rebuild and adjustment. Incorrect float height, and poorly set mixture screws are areas that could cause it.


- The throttle responds OK once it's running.
- When warm it starts OK, but always with a little bit of shake of the throttle. Choke (or better said, enrichment) never works, always dies if used, no matter cold or warm.
- If you mean, smell of fuel from the exhaust, yes, a lot. My motorcycle jacket or backpack always stinks. I thought this was normal due to the fact that it's a bike without catalytic converter from factory.
- The bike has less than 15k miles. Carburetors where tuned by previous owner in a workshop around 4000 miles ago. Air filter is OK.
- No valves serviced to my knowledge.
- I think so. No problem in my opinion running at large throttle opening.

In the following link there are several pictures of the spark plugs last time they were checked:

https://imgur.com/a/ithDGFt

To my eye, they doesn't look out of the normal, what do you think?
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hornet_guy
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PostPosted: 17:40 - 24 Jan 2021    Post subject: Re: 2000's CB600 dying with choke Reply with quote

trevor saxe-coburg-gotha wrote:
hornet_guy wrote:


okay, the second one wasn't even on choke - dated October. Not even been any decent frosts, probably. Looks molly coddled to fuck. It's just been run up to temperature, i'd bet. So - my question: are you comparing like with like? if your bike was in that condition, and was up to temperature, are you saying it would not start on first or second press, and would need choke? Because if so, yes, you're right. There's something bizarrely awry with it.

As for the first clip, the engine starts racing so promptly that it'd probably have started quite easily just off the throttle. So basically, same points apply.


I'm comparing with my bike in the same situation which I believe is:
- After starting for a while
- but still cold, since the temp gauges are in both videos indicating that.

Setting my bike to the same conditions you'd find:
- Starts OK but with a little shake of the throttle. Otherwise, I doesn't.
- Applying choke kills it, even warm.

In the videos, they don't even touch the throttle! It starts seamless like a modern fuel injected bike!
I do think, something is not right in mine from day one.
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hornet_guy
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PostPosted: 17:42 - 24 Jan 2021    Post subject: Reply with quote

Hong Kong Phooey wrote:
When it does start, after warm up what RPM does it idle at?


After warming up, 1300-1500 rpm, spot on as the manual says.
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stinkwheel
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PostPosted: 18:47 - 24 Jan 2021    Post subject: Reply with quote

Sounds like it's running rich. You have a standard air filter, airbox and exhaust system? Any modifications to the carbs?
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hornet_guy
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PostPosted: 19:06 - 24 Jan 2021    Post subject: Reply with quote

stinkwheel wrote:
Sounds like it's running rich. You have a standard air filter, airbox and exhaust system? Any modifications to the carbs?


Air box and caburetors are stock. Exhaust tail is aftermarket.
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stinkwheel
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PostPosted: 19:24 - 24 Jan 2021    Post subject: Reply with quote

Nobody would have inexpertly fitted a dynojet kit to it in the past and just bunged in extra large mains?
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hornet_guy
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PostPosted: 19:36 - 24 Jan 2021    Post subject: Reply with quote

stinkwheel wrote:
Nobody would have inexpertly fitted a dynojet kit to it in the past and just bunged in extra large mains?


Very unlikely. When I bought the bike it was completely stock. Wouldn't make sense someone installed that.
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Hong Kong Phooey
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PostPosted: 00:50 - 25 Jan 2021    Post subject: Reply with quote

Rich, plugs look a bit dark but hard to be sure - could be exposure of camera.

Fuel economy probably shit too.

I would hazard a guess the pilot screws are not set in the range, IIRC between 2-3 turns out from fully seated is good. It's the second thing I'd try after the air filter as it's the last thing you can adjust before the carbs have to come back off.
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colink98
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PostPosted: 10:11 - 25 Jan 2021    Post subject: Reply with quote

i have an older CBF600 which apart from lacking the power is the same engine as the CB600.

for reference...

from cold (be it a day or a week or even several months)
full choke and no throttle at all.
Choke has to be physicaly held out as it wont stay out on its own.
anything else and it will not start.
depending on how cold it is the choke has to remain open for 60 seconds or so before throttle can be gentle applied and i can ride off.

from warm
no choke at all.

it is some what specific with little room for variation.
however once you have the knack, it never fails to start.
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hornet_guy
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PostPosted: 11:25 - 25 Jan 2021    Post subject: Reply with quote

Hong Kong Phooey wrote:
Rich, plugs look a bit dark but hard to be sure - could be exposure of camera.

Fuel economy probably shit too.

I would hazard a guess the pilot screws are not set in the range, IIRC between 2-3 turns out from fully seated is good. It's the second thing I'd try after the air filter as it's the last thing you can adjust before the carbs have to come back off.


I did some visual inspection and pilot screws are definitely manipulated since the position is different depending on the carb. I wonder if I could reset the screws to factory spec (I can look for the correct number of turns) or if this can mess even more the tuning. Since this is an old bike, is it possible that factory screw spec is not valid anymore? What do you think?
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hornet_guy
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PostPosted: 11:30 - 25 Jan 2021    Post subject: Reply with quote

ColinK98 wrote:
i have an older CBF600 which apart from lacking the power is the same engine as the CB600.

for reference...

from cold (be it a day or a week or even several months)
full choke and no throttle at all.
Choke has to be physicaly held out as it wont stay out on its own.
anything else and it will not start.
depending on how cold it is the choke has to remain open for 60 seconds or so before throttle can be gentle applied and i can ride off.

from warm
no choke at all.

it is some what specific with little room for variation.
however once you have the knack, it never fails to start.


Thank you for your answer. I think the behaviour of your bike is close to what I'd expect.
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weasley
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PostPosted: 12:26 - 25 Jan 2021    Post subject: Reply with quote

Before fiddling with jets can you verify that the choke mechanism is operating correctly on all carbs? Maybe one (or more) is stuck open? Also verify that the choke lever is correctly actuating the fuel enrichment at the carbs - it is all free and smooth.
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hornet_guy
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PostPosted: 12:32 - 25 Jan 2021    Post subject: Reply with quote

weasley wrote:
Before fiddling with jets can you verify that the choke mechanism is operating correctly on all carbs? Maybe one (or more) is stuck open? Also verify that the choke lever is correctly actuating the fuel enrichment at the carbs - it is all free and smooth.


The operation is smooth and all chokes seem to open and close correctly.
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stinkwheel
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PostPosted: 12:40 - 25 Jan 2021    Post subject: Reply with quote

If I went downstairs to Mrs stinkwheels 2000 CBR600F right now, I would put the choke fully on and push the start button without me even getting hold of the handlebar and it would fire up within a couple of revolutions and settle to a fast idle.

I did have some trouble with the fuel pump recently, points had got stuck. Also the pre-bent, varying diameter fuel line split as I was taking it off which caused a real headache. This wouldn't cause the issue you describe though.

I find myself wondering if the needle positions are correct.
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I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.
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