Post by: brodsord on May 12, 2020, 06:15:04 PM
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
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Post by: brodsord on May 12, 2020, 06:16:25 PM
F@cking iPhone
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Post by: Nurse Julie on May 12, 2020, 06:23:06 PM
Choke lever*🤣🤣🤣🤣🤣.
F@cking iPhone
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Post by: Trigger on May 12, 2020, 06:56:32 PM
Post by: brodsord on May 12, 2020, 07:09:57 PM
Yes I have pods which I want to keep.
Is there an adjustment I can’t make to stop this ?
Thanks
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Post by: Bryanj on May 12, 2020, 07:11:53 PM
Post by: brodsord on May 12, 2020, 07:17:56 PM
Probably not or at least not without multiple jet and needle changesThanks 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
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Post by: Bryanj on May 12, 2020, 07:26:22 PM
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
Post by: brodsord on May 12, 2020, 07:28:07 PM
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Post by: Trigger on May 12, 2020, 07:35:19 PM
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 ;)
Post by: brodsord on May 12, 2020, 07:39:21 PM
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Post by: K2-K6 on May 12, 2020, 08:27:09 PM
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.
Post by: K2-K6 on May 12, 2020, 08:38:37 PM
Post by: Trigger 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 ;)
Post by: K2-K6 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.
Post by: philward on May 12, 2020, 09:17:12 PM
One of the main issues MarkCR750 pointed out was the step from the pod to the carb body that the pods create - ruining the smooth airflow. Mark adopted the standard airbox rubbers to the pods to maintain the airflow I think (there's a post on here somewhere). Marks build uses PD carbs though I think.
My CR runs standard carb with foam pods (no step to carb bodies) and ended up with 135 mains, 45 primary jets (I had to drill 40's out to 45 as no longer available), air screws 1 3/8's out and needle on middle groove. I'm running 4 into 4 race exhausts with K0 baffles in and standard compression 836 kit. This may not help as you will be running a diiferent combination but will give you an idea - took about 10 changes of combination to arrive at the right setting that gives a reasonable tickover, smooth step free mid range and good top end.
Hope that helps
Post by: brodsord on May 12, 2020, 09:30:22 PM
As the others have already posted, you can really chase your tail on this sort of stuff.Thanks so much for this info K2.
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.
I’m running just the standard plugs for a k5 engine from DSS
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Post by: brodsord on May 12, 2020, 09:32:40 PM
I have messed with jetting etc for some time on the CR750 Rep (road use) and now got it pretty much spot on across the range. I can quote what my settings are but there are so many variables on each build. I had no choice when building a CR Rep as you can't have a CR Rep with std airbox and exhausts but on the K6 Cafe racer project I'm building I've re-fitted the airbox and std exhausts (which was a pain as the previous owner cut the airbox and exhaust brackets off and I had to weld them back on!) to make the carb set up easy - ie, standard..Thanks so much Phil, very helpful
One of the main issues MarkCR750 pointed out was the step from the pod to the carb body that the pods create - ruining the smooth airflow. Mark adopted the standard airbox rubbers to the pods to maintain the airflow I think (there's a post on here somewhere). Marks build uses PD carbs though I think.
My CR runs standard carb with foam pods (no step to carb bodies) and ended up with 135 mains, 45 primary jets (I had to drill 40's out to 45 as no longer available), air screws 1 3/8's out and needle on middle groove. I'm running 4 into 4 race exhausts with K0 baffles in and standard compression 836 kit. This may not help as you will be running a diiferent combination but will give you an idea - took about 10 changes of combination to arrive at the right setting that gives a reasonable tickover, smooth step free mid range and good top end.
Hope that helps
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Post by: brodsord on May 13, 2020, 11:06:22 AM
Thanks for this Phil, yes I think I’m going to do exactly what you have said here to see if it improves any, and move on from here if needed.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 ;)
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Post by: brodsord on May 13, 2020, 11:07:48 AM
Choke lever*
F@cking iPhone
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Hate predictive text Julie
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Post by: K2-K6 on May 13, 2020, 02:09:05 PM
It's worth fitting the equivalent in higher heat range while you work on the jetting. So DR9ES as they are more resistant to the plug tip going over temperature during your mixture exploration phase. It reduces the risk of pre-ignition that could cause damage to the engine.
Post by: brodsord on May 13, 2020, 02:25:05 PM
DS have DR8ES listed as NGK plug spec for the K5.Thanks K2 that’s a very good point.
It's worth fitting the equivalent in higher heat range while you work on the jetting. So DR9ES as they are more resistant to the plug tip going over temperature during your mixture exploration phase. It reduces the risk of pre-ignition that could cause damage to the engine.
I’m just taking the carbs of now to see what jets are in there.
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Post by: Nurse Julie on May 13, 2020, 03:14:19 PM
DS have DR8ES listed as NGK plug spec for the K5.David Silver has 'R' plugs suggested for many of our bikes but thats totally the opposite to what the shop manuals / Haynes says. Its a known fact that the original metal shroud HT leads needed resisted plugs but as many of those caps were binned on PDI and rubber (or maybe they are plastic 🤔) resisted caps fitted, non resisted plugs have been fitted as standard since.
It's worth fitting the equivalent in higher heat range while you work on the jetting. So DR9ES as they are more resistant to the plug tip going over temperature during your mixture exploration phase. It reduces the risk of pre-ignition that could cause damage to the engine.
Post by: brodsord on May 14, 2020, 09:56:47 PM
As the others have already posted, you can really chase your tail on this sort of stuff.Hi K2,
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.
So I took my carbs off and stripped them down and gave them an overhaul, they were in a shitty condition.
Carb one had a blocked fuel bowl vent so it was probably struggling filling up with fuel, carb four had a broken float pillar.
Sorted both issues and renewed the various seals orings etc as I had some carb seal packs a bought a while back from DSS
Polished up jets and needles with some 600 wet paper.
Fitted needles with clip retainers on the bottom setting as you suggested.
Just did basic eye up setting with slides as I’ll sync them tomorrow.
Pilot jets are 1.5 turns out and pods are on.
So,
I took her for a test ride and she goes like a rocket, no spluttering or bogging down, just goes like the clappers!!
The pilot jet is 40 and main is 105.
I’ve set the spark plugs at .024 and I’ve raised the floats by a couple of millimetres.
I did about 25 miles earlier and I’ve taken the plugs out to see how they look, seem ok (https://uploads.tapatalk-cdn.com/20200514/5b75ab18b9f9110beb6283b45b73d6ea.jpg)
Thanks for your advice
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Post by: Nurse Julie on May 14, 2020, 10:00:16 PM
Post by: K2-K6 on May 14, 2020, 10:59:30 PM
I'd agree that it's a little lean, but not drastically as the earth bar is "milky coffee" tone.
Definitely fit ngk 9 grade plugs to bring the tip temperature down. They have wider heat transmission path to more easily get the heat out of and away from the electrode. It's this that ultimately causes a holed piston as if it gets too hot then it ignites the mixture prior to timing point. Classic "pre-ignition" that you can't feel until it's too late.
With the needles up at maximum you've no more to add on mains so it would look wise to go up to 110 jet size that would give you more safety with the needles set as they are.
That should give you a decent baseline for longer assessments to be made along with reducing risks.
Post by: K2-K6 on May 14, 2020, 11:18:41 PM
Does the bike have red or black NGK plug caps fitted?
If it does those are the wrong type plugs.
I feel it's beneficial to run both cap and plug as resisted to help burn a leaner mixture and gives more margin against the effects of detonation.
As it's non standard intake tract then setup is not necessarily going to follow std manual specification.
Post by: brodsord on May 14, 2020, 11:35:10 PM
Good news that you've got it running more as you want it.Thanks K2,
I'd agree that it's a little lean, but not drastically as the earth bar is "milky coffee" tone.
Definitely fit ngk 9 grade plugs to bring the tip temperature down. They have wider heat transmission path to more easily get the heat out of and away from the electrode. It's this that ultimately causes a holed piston as if it gets too hot then it ignites the mixture prior to timing point. Classic "pre-ignition" that you can't feel until it's too late.
With the needles up at maximum you've no more to add on mains so it would look wise to go up to 110 jet size that would give you more safety with the needles set as they are.
That should give you a decent baseline for longer assessments to be made along with reducing risks.
Yes I’m going to order the jets tomorrow and the 9 grade plugs you’ve suggested.
I’m happy that it’s on the right track anyway
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Post by: brodsord on May 14, 2020, 11:36:44 PM
Does the bike have red or black NGK plug caps fitted?Yes it has the black plastic ngk caps Oddjob.
If it does those are the wrong type plugs.
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Post by: brodsord on May 14, 2020, 11:38:18 PM
Blimey, that's running lean. You will burn a hole in your pistons and burn the face of the valves if left like that.Thanks Julie,
K2 has mentioned different plugs and bigger jets to help with this will order tomorrow
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