Likely cause of idle loss when stopping hard after a high speed run?

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My bet would be fuel starvation at idle, check fuel tank vent and
jimbo said:
Is the mixture screw is backed out more to richen?
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Left = Lean
Right = Richen

I'm with others who suggest your problem is fuel starvation when closing throttle, check fuel tank vent, fuel flow through banjos, and fuel tank level.
 
Danno said:
Empty was probably the wrong way to express it, but float levels drop during full-throttle runs and the main jet can still pull fuel, but the sudden stop and reduced fuel level could keep the idle circuit from picking up fuel at that fuel level. JMO, no empirical evidence.
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The idle circuit picks up fuel at about the same level as the main jet. So, nope.
Likely cause of idle loss when stopping hard after a high speed run?
 
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One possible check on fuel starvation is to open the reserve tap - it worked for me when I had the high speed power drop and misfire mentioned by Fast Eddie.
 
concours said:
The idle circuit picks up fuel at about the same level as the main jet. So, nope.
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Then why are fuel level and idle so closely related? If the floats aren't set high enough, idle is problematic. Mine seem to like fuel level about as high as you can set it without constant flooding from the float needle not seating.
 
Heres another question; If float bowl gaskets or warped bowls allow air into the idle circuit fuel passageways could that be causing problems ?

Likely cause of idle loss when stopping hard after a high speed run?
 
Float level at idle affects the mixture because the higher the level of fuel in the bowl, the more fuel is pulled into the carb idle circuit simply due to the "head" of the fuel level. The higher the level, the greater the 'fuel pressure." You should be able to adjust the air screw to suit pretty much any (reasonable) float level at idle.

Any issue re venting as far as fuel feed would be much more apparent at speed than at idle.
 
At the end of the day what you are after is being able to live with bike and the adjustment will have to be whatever it ends up being to be able to satisfy. Often I find my plugs sooty because the idle mix is too rich but being rich there is no problem with transition.
Agree that compromise is what you will have to do.
 
My knacker amals used to hang on to the slides when I had been giving it stick. Pulling up sharpish at lights it used to stall never idled fluffed unless I caught it
 
concours said:
The idle circuit picks up fuel at about the same level as the main jet. So, nope.
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Nominally, yes, but in application the slope of the carb exposes the idle pickup to starvation

To my mind (and happy to admit I'm wrong), the OP is describing cut out after snapping the throttle down from WOT. The transfer from main down to idle circuits would be very quick, and I would guess that any deficiency in fuel flow or level would result in the very conditions the OP is describing

I would just throw a colourtune on the bike when warmed up, rev to WOT then snap close and observe mixture
 
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acadian said:
Nominally, yes, but in application the slope of the carb exposes the idle pickup to starvation

To my mind (and happy to admit I'm wrong), the OP is describing cut out after snapping the throttle down from WOT.
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I think he's complaining about stalling after hard braking. Not throttle related.
 
I have the same issue. I have always thought it was carb sloshing. The commando carbs are at a slight incline. Bike runs perfect otherwise. I would check your float bowl heights.
 
maylar said:
I think he's complaining about stalling after hard braking. Not throttle related.
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yes I am complaining about running 70+ then pealing off an off ramp and stopping quickly, that's when the bike wants to die.
 
jimbo said:
yes I am complaining about running 70+ then pealing off an off ramp and stopping quickly, that's when the bike wants to die.
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same thing, you're still snapping the throttle shut from a circuit that's gobbling lots of fuel
 
acadian said:
Nominally, yes, but in application the slope of the carb exposes the idle pickup to starvation

To my mind (and happy to admit I'm wrong), the OP is describing cut out after snapping the throttle down from WOT. The transfer from main down to idle circuits would be very quick, and I would guess that any deficiency in fuel flow or level would result in the very conditions the OP is describing

I would just throw a colourtune on the bike when warmed up, rev to WOT then snap close and observe mixture
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That's what I thought as well. The WOT changes the vacuum applied to the idle circuit due to the greater vacuum of the main jet, so there's a lag in the idle jet circuit kicking back in. Blipping the throttle keeps the engine going which allows the circuit more time to refill. Certainly the greater heat produced by the WOT would be an added factor to consider, but I don't have a well conceived explanation for that. Maybe someone more knowledgeable will account for that possible effect.
 
Oh sure, who wants less hassles, better mileage, better running? Come on now !
 
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