Low Speed Cough

[T. Cotten]

.. Is there something else in the bore to be checked? ....

If there was something other than the wear groove, you would notice it, Otis!

If a slow acceleration doesn't cough, but a normal one does, then we must consider the 'accelerator sump' main nozzle assembly: If there are air leaks at the nozzle spigot or around the outside of a shrunken venturi, it defeats the accelerator function.

(My remedy for worn spigot holes was to fit each with a thin PEEK seal, and venturies were re-sized and lathe-cut to a light press.)

As I posted, little things can add up, making it harder to find one culprit.
(My philosophy was to just do absolutely everything imagineable while it was on the bench. It allowed me to successfully send out dozens and dozens of carbs that there would be no practical way to test. Still couldn't compete with ebay.)

.....Cotten

[otis71]

The cough subsides a little as the engine warms. The throttle disc fits nicely in the bore with a visual flashlight test if that’s what you mean. Is there something else in the bore to be checked? Also I never run a bike with a low idle speed.

[T. Cotten]

Wear spots add up, Otis!

The spot of wear that most affects the transition from idle to power is the bore itself.

If the eyebrow of wear reaches the idle bleeds, it can only be tuned for one or the other.

eyebrow.jpg
If there is a lot of daylight around a fully-closed disc, it needs attention.

....Cotten
PS: We assume, of course, your bubble-test was thorough (like even the cover screw over the intakes on Pans), and your idle speed is not "potato-potato"....

[dukekleman]

Otis,
Is this issue heat related according to engine operational temperature?
Is a very consistent in its issue no matter what the engine temperature range?

Duke

[otis71]

I recently put a correct M35 on my FL. Before I did I cleaned everything and replaced the throttle shaft bushings and flattened the gasket surface. Also bubble tested the manifold. Once installed l adjusted the low speed 7 clicks out from lean starvation at idle. Adjusted power needle to where it was most responsive and not running rich. The bike is starting super easy and runs good other than at a stop when idling, upon takeoff it sometimes coughs complicating takeoff. I’ve tried leaning and richening the low speed with only marginal results. Could it be the power circuit is too lean or something entirely different?
BTW: it didn’t cough with the M35TP that was taken off leading me to believe it’s the new carburetor.