Advise

[allankelly1]

Hi

Need some advice pointers please

Got the old girl back on the road



Before she would not idle only run on two to three cylinders  from cold and generally run like a bag of nails unless you nailed the throttle to the stop
But after several carb rebuilds due to leaks etc and still more uneven running  (keeping the original brass wear)  she is running well to take to work every day

On cold starts and idle she sits there and tick over very smoothly but on pick up from idle it’s a little hesitant till about 2500 and then all seem ok

It’s got a Boyer ignition system coils and the other electronic bits and bobs and this is all timed correctly and done all the other checks and plugs look a little black  but not real sooty so I presume she is running a little rich




So would playing around with the air screws help or is there any other tips or tricks I could try?

Obviously the carbs are in theory 40 + years old and have 35k on them but wondered if I am missing anything obvious I need to check or adjust to improve this flat spot

Thanks in advance to all

Best wishes Al


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[McCabe-Thiele (Ted)]

I can't help with your issue as I am still a Tenderfoot on 400 fours but I do like the look of your bike - twin discs - bar end mirrors - I'm having a bit of a moment - bike pawn.

[allankelly1]

Yes really cafe style with the rear set and ace bars

Waiting for the single seat to arrive next

More porn




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[Nurse Julie]

To my eyes, that plug looks quite sooty, so running rich. Clean the plugs, turn idle screws out, ride and recheck plugs. What are the air screws set at at the moment? Not all 4 air screws will be set at the same turns out by the time you have finished fettling.

[allankelly1]

They are the 2 1/4 turns out at the moment as din not want to lean here out too early without a plug chop first


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[allankelly1]

I presume adjusting mixture screws can muck up your carb sync slightly?


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[K2-K6]

I presume adjusting mixture screws can muck up your carb sync slightly?


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No it won't affect carb sync at all. There's so many myths about on t'internet that are mostly wrong and lead people to do things which are incorrect.

Carb sync is parity of the throttle slides to give equal air volume to each cylinder,  although it affects idle smoothness when maladjusted it's not the final setting of idle smoothness. Once the balance of synchronisation is set that's ok for all engine speeds and remains in parity if the adjustment is properly secured.

The idle air circuits then trim the fuel demand at very small level to bring parity of combustion for each of the cylinders, in effect the "icing on the cake" of tickover refinement.  Moving these screws has no impact on throttle slide sync.

In addition,  the idle jet size sets it's ultimate flow which is tempered by the air screw adjustment.  Going in or out with the screw doesn't change the final full flow of the idle circuit but alters the angle of the slope leading to that final full flow. So you can play with the airscrew with no other detrimental effect,  just remember where you've set them , try it out and go again with another adjustment to see the affect as Julie indicates above.

Airscrew out further = weaker to lighten the plug, with of course the opposite if you needed rich.

What plug gap are you running?

[Nurse Julie]

I presume adjusting mixture screws can muck up your carb sync slightly?


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No, it doesn't affect the sync. 2¼ turns is a long way out to be showing soot like that 🤔 What position are the needles in and do you have standard size jets fitted? You're not running pods I take it? Edit... No, I can see the plenum chamber now I've put me specs on 🙄🙄🙄

[allankelly1]

I presume adjusting mixture screws can muck up your carb sync slightly?


Sent from my iPhone using Tapatalk

No it won't affect carb sync at all. There's so many myths about on t'internet that are mostly wrong and lead people to do things which are incorrect.

Carb sync is parity of the throttle slides to give equal air volume to each cylinder,  although it affects idle smoothness when maladjusted it's not the final setting of idle smoothness. Once the balance of synchronisation is set that's ok for all engine speeds and remains in parity if the adjustment is properly secured.

The idle air circuits then trim the fuel demand at very small level to bring parity of combustion for each of the cylinders, in effect the "icing on the cake" of tickover refinement.  Moving these screws has no impact on throttle slide sync.

In addition,  the idle jet size sets it's ultimate flow which is tempered by the air screw adjustment.  Going in or out with the screw doesn't change the final full flow of the idle circuit but alters the angle of the slope leading to that final full flow. So you can play with the airscrew with no other detrimental effect,  just remember where you've set them , try it out and go again with another adjustment to see the affect as Julie indicates above.

Airscrew out further = weaker to lighten the plug, with of course the opposite if you needed rich.

What plug gap are you running?

Hi

Plug gap is the Haynes manual 0.7 to 0.8mm

Best wishes Al


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[allankelly1]

I presume adjusting mixture screws can muck up your carb sync slightly?


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No, it doesn't affect the sync. 2¼ turns is a long way out to be showing soot like that What position are the needles in and do you have standard size jets fitted? You're not running pods I take it? Edit... No, I can see the plenum chamber now I've put me specs on

Every thing is standard other than exhaust

When I was rebuilding the carbs jetting was standard but they are the original jets and correct to the Haynes manual 40 pilots and 75 mains so I have no idea if they have been attacked with a piece of wire in the past judging by the rest of the bike when I got it

As for needles not sure what clip position they are’s in

Haynes manual is not very clear on how the slides disassemble so any advise on how to take out and check they are in third groove?  should be most helpful as I guess maybe I need to drop the needles one groove maybe?

Also before the rebuild plugs were very sooty and the current plug is much better


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[allankelly1]

Or question for all as it looks a tad rich at 2 1/4 turns out do I drop the pilots to 38s?

From where it was to now is light and day but want just to crisp up the initial throttle response


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[K2-K6]

Or question for all as it looks a tad rich at 2 1/4 turns out do I drop the pilots to 38s?

From where it was to now is light and day but want just to crisp up the initial throttle response


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Yes to this. If you are running a certain size idle jet and you have to wind the airscrew out near to 3 turns, then that indicates it "wants" a smaller jet.

Essentially the airscrew should be somewhere near to 1 1/2 turns out to give a linear response with using a slightly smaller jet to then bring the circuit into competent range.

Equally,  if you had to use less than 3/4 turn airscrew just to get it rich enough, that would prompt a larger jet size to approach from the opposite direction.

Just to test and asses, try it with plugs at 0.5 gap. It won't change the jetting at all but may improve the flat spot by more consistent combustion propagation.

[allankelly1]

Or question for all as it looks a tad rich at 2 1/4 turns out do I drop the pilots to 38s?

From where it was to now is light and day but want just to crisp up the initial throttle response


Sent from my iPhone using Tapatalk

Yes to this. If you are running a certain size idle jet and you have to wind the airscrew out near to 3 turns, then that indicates it "wants" a smaller jet.

Essentially the airscrew should be somewhere near to 1 1/2 turns out to give a linear response with using a slightly smaller jet to then bring the circuit into competent range.

Equally,  if you had to use less than 3/4 turn airscrew just to get it rich enough, that would prompt a larger jet size to approach from the opposite direction.

Just to test and asses, try it with plugs at 0.5 gap. It won't change the jetting at all but may improve the flat spot by more consistent combustion propagation.

Hi K2-K6

Ok I will order some 38s and while I am waiting for them I will close up plugs to 0.5 as suggested

To be honest from where I was to get where I am is fantastic as it’s gone from a bag of nails to something that pulls right thru the Rev range other than the initial pick up

If I can just crisp up this that would be the icing on the cake

Will update all as I do small changes

Ride safe all Al


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[allankelly1]

Ok last question please

Where is the best place to get the pilots please?

Any recommendations

 I have used Allen performance for my rd but customer service was sketchy at best so any other supplies or does anybody on here supply please

Saw this supplier on eBay??




TIA

Best wishes Al


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[K2-K6]

No recommendation as haven't bought any for a while, perhaps someone more current can suggest.

Sounds like you're quite close in how it's running,  certainly good when you get decent progress in sorting something out like this and with a little fine tuning left to get there.

Just a quick thought though, have you a good condition air filter installed as they can be fairly sensitive to anomalies there.