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 Post Posted: Sun Mar 10, 2019 9:33 pm 
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Hornet Warrior
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Hi guys. I am here with my “problems” again. I hope you can help me here. I will try to describe the case and at the end I will include a video link. Please read first and then watch a video - this way you will understand what is happening. Here it goes.
I should note that the carbs were cleaned and synced just minutes ago. Mixture screws set to 2.⅜ as per shop manual. Stock jets and needles.
When gently opening the throttle at a constant opening speed, the revs go up together with the throttle. When it reaches 2500 RPM though, it suddenly jumps to 3500 RPM. Please be reminded, that the throttle was being opened at a gentle and constant slow speed. This “jump” is always at the same RPM. It’s a constant “bug”. In other ways engine revs perfectly - can not complain.
Something I’ve tried:
Disconnect TPS - no change;
Introduce DB killer into the muffler to restrict flow - no change;
Partially restrict air box snorkel - no change.

Something to add - after cleaning the carbs and putting them back on the no. 3 cylinder wasn’t getting any fuel. I’ve had to give it a few gentle taps with a rubber hammer - started to be fed with fuel afterwards. Float was probably stuck after putting back the carbs. Not sure if this part is important, but I thought - maybe something to consider.

What are your theories?
Leaky boots?
Other vacuum leak?
One of the pilot jet got clogged with some leftovers in the tank?
Mixture screws need to be adjusted to richen the infeed?

Or should I just wait until the weather clears up and give it an Italian tune-up (ride the sh!t out of it) to settle things in?
Give a tank of seafoam?
Strip the carbs again to look for what?
Else?

Here’s the video: https://youtu.be/GYAAu6yZ-r8

Shoot!

Thanks in advance.

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Honda Hornet CB600F 1999
Honda Hornet CB600F 2005


Last edited by Xmixerx on Fri Mar 15, 2019 7:17 pm, edited 1 time in total.

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 Post Posted: Mon Mar 11, 2019 8:58 pm 
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Hornet Warrior
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A theory popped to my mind. Could this be the RPM range where the needle slide start to open and this jump is the outcome of additional air/fuel mixture that is introduced? This can be easily checked by you guys! :)

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 Post Posted: Mon Mar 11, 2019 11:34 pm 
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True Horneteer
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Hi Xmixerx,

Are the throttle cables adjusted properly at both the throttle and carb side of the cables? They only have to be slightly out of adjustment at the carb end to produce these kind of symptoms.

I'm not an expert (and don't ever expect to be on something as complex as fuelling) so I can't offer any golden nugget of advice here - as you already indicated - there could be various culprits to blame for the problem - the only constructive suggestion I can offer (and it's something I'm sure you have already worked out for yourself) is to go back to your list of potential problems and work through them one by one - starting with the easy to check stuff first.

Personally I would start by going back to the pilot jets - zero them all in and then re-set them with a pilot screw adjustment tool and see if that makes a difference - then check all the other stuff on your list.

If all this fails then take a look at the number three cylinder carb you mentioned - take the cap off and check that the diaphragm is installed properly.


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 Post Posted: Mon Mar 11, 2019 11:37 pm 
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One other thing - check fuel tank breather hose is not kinked/obstructed.


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 Post Posted: Tue Mar 12, 2019 9:15 am 
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Hi, Hoon. Thanks for the input again. Although the cables were adjusted properly and the handle as a proper free play and the cables show no signs of wear, I will definitely check this again. The mixture screws were set precisely – I have big doubts that resetting them will make any difference – the other thing is to try and set them in accordance to engine operation (idle drop procedure as per shop manual). The breather hose is OK – i can blow through it no problem. My biggest concern is now how it will behave on the road – under engine load – maybe this problem is not really a problem after all. This is the reason I want someone of you to check his/hers bike’s behavior on the same conditions.

My checklist to follow:

Check if all exhaust pipe heat up equally at the same time.
Check every vacuum hose and vacuum ports for a leak.
Remove the air box and check the slides again to make sure they are not sticking and move freely.
Check for the slides operation while engine is operating and while the air box is still off.
Drain float bowls to see if all of the have the same level of fuel.

If none of these will reveal any interesting findings, I will just pop the carbs off again and revise all the jets and membranes.

P.S. After watching my own video for so many times over and over again I also have a feeling that the revs drop a bit slow after letting go the throttle. It seems that the drop slows down a bit at the exactly edge of the same 3500-2500 gap if this could be telling something.

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 Post Posted: Tue Mar 12, 2019 10:33 am 
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Sounds like you have every every angle covered mate - good luck with the testing and hope you fix the issue. Keep us posted. :D


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 Post Posted: Tue Mar 12, 2019 1:01 pm 
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Can anyone of you please do the same test-check on your hornet and post the results / video? One guy from my country has the same thing on a considered to be healthy Hornet. Curiosity took over... Maybe I am just looking at the thing that is normal and making it a problem...

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 Post Posted: Fri Mar 15, 2019 7:20 pm 
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Hi guys. So the issue was "solved". After several guys trying the same thing on their carburated hornets, they've found the same "issue". So my theory about slides starting to open is kind of confirmed. :)

Thanks for the attention!

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 Post Posted: Fri Mar 15, 2019 10:02 pm 
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So it's normal and not a fault?


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 Post Posted: Sat Mar 16, 2019 12:40 pm 
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HOON98 wrote:
So it's normal and not a fault?

That's the conclusion actually. Unless three in a row Hornets that this was tested on are also faulty in a same odd way. :)

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