Author Topic: Bogging down.  (Read 382 times)

Offline brodsord

  • SOHC Associate
  • Posts: 67
    • View Profile
Bogging down.
« on: May 12, 2020, 06:15:04 PM »
Hi everyone,
Can anyone help me with this  issue on my build I’ve been doing.
K5 engine
Starts perfect, idles perfect, when I take her on the road she bogs down completely when i crack the accelerator.
Timing is good, points are correct and the plugs are showing tan colour.
Today I took her for a run to shops and I put the clutch lever to half way and she flew through all gears with minimal bogging.
Thanks in advance for any help.
Gray


Sent from my iPhone using Tapatalk

Offline brodsord

  • SOHC Associate
  • Posts: 67
    • View Profile
Re: Bogging down.
« Reply #1 on: May 12, 2020, 06:16:25 PM »
Choke lever*
F@cking iPhone


Sent from my iPhone using Tapatalk

Offline Nurse Julie

  • 1973 CB750 UK K2.1977 CB550/4 Mongrel Brat. 1978 CB400/4.
  • SOHC Jedi
  • Posts: 5398
    • View Profile
Re: Bogging down.
« Reply #2 on: May 12, 2020, 06:23:06 PM »
Choke lever*
F@cking iPhone


Sent from my iPhone using Tapatalk
🤣🤣🤣🤣🤣.
Im a Nurse, trust me, this won't hurt.....much !!!

LINK TO MY CB400/4 ENGINE STRIP / ASSESSMENT AND REBUILD...NOW COMPLETE
http://www.sohc.co.uk/index.php/topic,14049.msg112691/topicseen.html#new

Offline Trigger

  • SOHC Jedi
  • Posts: 6949
  • Engines built on reputation, not advertising.
    • View Profile
Re: Bogging down.
« Reply #3 on: May 12, 2020, 06:56:32 PM »
If you have pods ? It will bog down  ;)

Offline brodsord

  • SOHC Associate
  • Posts: 67
    • View Profile
Re: Bogging down.
« Reply #4 on: May 12, 2020, 07:09:57 PM »
Thanks Trigger,
Yes I have pods which I want to keep.
Is there an adjustment I can’t make to stop this ?
Thanks


Sent from my iPhone using Tapatalk

Offline Bryanj

  • SOHC Jedi
  • Posts: 6572
    • View Profile
Re: Bogging down.
« Reply #5 on: May 12, 2020, 07:11:53 PM »
Probably not or at least not without multiple jet and needle changes

Offline brodsord

  • SOHC Associate
  • Posts: 67
    • View Profile
Re: Bogging down.
« Reply #6 on: May 12, 2020, 07:17:56 PM »
Probably not or at least not without multiple jet and needle changes
Thanks Bryan,
Is it a case of taking my jets out and seeing what they are then going up a size?
Sorry I have no experience with this


Sent from my iPhone using Tapatalk

Offline Bryanj

  • SOHC Jedi
  • Posts: 6572
    • View Profile
Re: Bogging down.
« Reply #7 on: May 12, 2020, 07:26:22 PM »
Nope, you will probably need pilot jets, experiment at least twice guess at £30 per set, then main jets probably 4 sets at about same per set then multiple changes of needle clip position, maybe float heights and in the end it still wont be right 100% of the time.
Not forgeting every time you make a change all other settings will go out of whack, oh and non oem brass parts dont work right in the first place

Offline brodsord

  • SOHC Associate
  • Posts: 67
    • View Profile
Re: Bogging down.
« Reply #8 on: May 12, 2020, 07:28:07 PM »
Ok thanks for this Bryan.


Sent from my iPhone using Tapatalk

Offline Trigger

  • SOHC Jedi
  • Posts: 6949
  • Engines built on reputation, not advertising.
    • View Profile
Re: Bogging down.
« Reply #9 on: May 12, 2020, 07:35:19 PM »
With pods on it will always bog down somewhere in the range. I have known people feck about for years and spend a fortune and they are still not happy. I have had so many engines in for engine problems that is caused by running with pods.
The only person that I know that has got close to getting his carbs to run right with pods on is a member called MarkCR750 and he is a aero engineer that worked out a mod on the air flow  ;)

Offline brodsord

  • SOHC Associate
  • Posts: 67
    • View Profile
Re: Bogging down.
« Reply #10 on: May 12, 2020, 07:39:21 PM »
Ok thanks for this Trigger, I’ll see if I can try and find out some info on this.


Sent from my iPhone using Tapatalk

Online K2-K6

  • SOHC Jedi
  • Posts: 2735
    • View Profile
Re: Bogging down.
« Reply #11 on: May 12, 2020, 08:27:09 PM »
As the others have already posted,  you can really chase your tail on this sort of stuff.

Basic problem is not that the engine will burn more fuel,  but that the original airbox / intake etc cause more vacuum that pulls the correct amount of fuel from the float bowls.  Going to pods gives you less vacuum in the carb venturi for the same engine speed,  and consequently pulls less fuel up from the float bowls,  hence the weak mixture. 

As a test / see,  you could lift the needle in main jets by dropping the circlip two notches, setting the float height a couple of millimetres higher,  turning the idle jets in by 1/4 from standard setting and using resisted spark plugs with resisted HT caps as well.

It would push it toward where you need to be and at least see if it improves without significant cost.

Edit;- also make sure the plugs are at their minimum specified gap too.
« Last Edit: May 12, 2020, 08:28:56 PM by K2-K6 »

Online K2-K6

  • SOHC Jedi
  • Posts: 2735
    • View Profile
Re: Bogging down.
« Reply #12 on: May 12, 2020, 08:38:37 PM »
A question Brodsord,  which number and type of spark plug are you currently running?

Offline Trigger

  • SOHC Jedi
  • Posts: 6949
  • Engines built on reputation, not advertising.
    • View Profile
Re: Bogging down.
« Reply #13 on: May 12, 2020, 08:54:15 PM »
As the others have already posted,  you can really chase your tail on this sort of stuff.

Basic problem is not that the engine will burn more fuel,  but that the original airbox / intake etc cause more vacuum that pulls the correct amount of fuel from the float bowls.  Going to pods gives you less vacuum in the carb venturi for the same engine speed,  and consequently pulls less fuel up from the float bowls,  hence the weak mixture. 

As a test / see,  you could lift the needle in main jets by dropping the circlip two notches, setting the float height a couple of millimetres higher,  turning the idle jets in by 1/4 from standard setting and using resisted spark plugs with resisted HT caps as well.

It would push it toward where you need to be and at least see if it improves without significant cost.

Edit;- also make sure the plugs are at their minimum specified gap too.

If you use resisted plugs and resister caps that with give a weak spark  ;)

Online K2-K6

  • SOHC Jedi
  • Posts: 2735
    • View Profile
Re: Bogging down.
« Reply #14 on: May 12, 2020, 09:05:26 PM »
As the others have already posted,  you can really chase your tail on this sort of stuff.

Basic problem is not that the engine will burn more fuel,  but that the original airbox / intake etc cause more vacuum that pulls the correct amount of fuel from the float bowls.  Going to pods gives you less vacuum in the carb venturi for the same engine speed,  and consequently pulls less fuel up from the float bowls,  hence the weak mixture. 

As a test / see,  you could lift the needle in main jets by dropping the circlip two notches, setting the float height a couple of millimetres higher,  turning the idle jets in by 1/4 from standard setting and using resisted spark plugs with resisted HT caps as well.

It would push it toward where you need to be and at least see if it improves without significant cost.

Edit;- also make sure the plugs are at their minimum specified gap too.

If you use resisted plugs and resister caps that with give a weak spark  ;)

It's commonly given that way but it doesn't look true to me.

Raising the resistance builds more voltage in the coil before the spark will start with breakover ionisation across the plug gap. It actually raises the energy deployed at the plug but elongates the spark duration,  which more effectively ignites leaner mixtures.

 

SimplePortal 2.3.5 © 2008-2012, SimplePortal