Linkert idle speed

[108]

I was going through the Knowledge Base gathering info recently while working on my M35TP and saw Cotton's post that the acceleration fuel surge from the main nozzle chamber wont function properly when the throttle is opened fast if the idle speed is too low. I have my hot idle speed about the same rpm as the new Harleys--is that too slow ? I hope not , I really wouldnt want it any faster, but some times I can make it pop at will--other times I cant. Maybe I'm just jerking it open faster than the carb can handle ? It's fine during all normal rideing .

[Cotten]

108!

I do not remember the original post, but yes,.. too low of an idle speed is not beneficial to a smooth transition to that ever-so-elusive perfect midrange.
And it doesn't splash the crankcase oil the way it should, either.

And I must confess that I have no clue what the idle speed of modern models might be...
Has it changed?

If all other variables are covered: valve adjustment, ignition, linkage slop, and the most evil vacuum leak gremlin,..
Then the carb concerns are those familiar ones like the float, or a shrunken venturi, or the evil borewear-from-the-throttledisc gremlin.
All can affect the midrange on a carb with only idle and highspeed circuits.

The nozzle is supposed to eject a volume of emulsion upon a sudden demand. This has the effect of an 'accellerator pump'.
Carburetors which have been run for long periods with a loose venturi will often wear the nozzle spigot to an hourglass shape, and/or elongate or widen the venturi's spigot hole as well. Certainly these gaps would inhibit a smooth draw upon the nozzle, and should be remedied.

And finally, I must remind everyone that rapping an idling motor to see if it chokes might be harmless for a time or two....

But please remember that a motor really needs a load to keep from tearing itself apart.

...Cotten

[partshunt]

Cotton:
The newer Harleys are idling around a thousand RPM. I havent tached my 54FL idle speed, probably like 550RPM,
"potato, potato, potato" if that explains it....I set the idle a coupla clicks on the rich side on M74, gives it extra fuel ready to accelerate, no stumble. seems ok that way.......Joe

[FlatHeadSix]

108,

You have to remember that idle SPEED and idle MIXTURE are two completely different settings and have to be adjusted in sequence. Adjust the mixture first using the low speed needle, once you are satisfied with how it starts, idles and accelerates when comming off idle then you can set your idle speed using the screw on the throttle linkage lever.

The 2 most important "don'ts" are: Don't set the mixture too lean and don't set the idle too slow.

mike

[socalrider]

so, what is the right idle speed?

[FlatHeadSix]

SoCal,

Good question.....

Its pretty hard to measure scientifically, I don't know of any way to set one to an exact rpm because I've never found a tach that will work on the old 6 volt systems.

I have all of mine set so that they idle fast enough to keep the generator light off and the oil light flickering after they get hot, if that tells you anything. I think the important thing is to keep oil circulating, you don't want to let a hot engine idle too long at a really slow idle.

mike

[Cotten]

It has been decades since I have tuned an American motorcycle with a tach, so I can only guess that the proper idle speed has not changed.

They do not sound different, when they idle at the bar across the street.

Those that go lupp-ity-lup are always customs
Curiously, they are also the ones that lunge when navigating the parking lot, and then fart when leaving.

Ladies with stockers that go putputputput seem to do fine.

....Cotten