Carburetor and starting

[otis71]

My JD has a Schebler and I have 2 other bikes with Linkerts. All 3 bikes start easy when cold but can take a few tries, sometimes more once warm. Is there a common cause for this or things to check? Thanks.

[Rubone]

Most Linkerts are not opposed to a bit of choke when warm. Or just a prime kick with choke, then off to kick. The fuel evaporates in the intake tract when hot, and lines can also try to vapor lock, especially on Flatheads and early models like Js. A prime kick overcomes that. and do not adjust your low speed too lean just to get a certain idle. It needs a bit of fuel for transition from low the midrange.

[T. Cotten]

Otis!

Holes get bigger when warm;

The only way to eliminate vacuum leaks, even the tiniest, is to first find them with bubbles: http://virtualindian.org/11techleaktest.html

Then the carburetors themselves can be addressed,

....Cotten

[otis71]

I bubbled tested the manifolds per your advice when the engine was cool in the past. Can the same procedure be done with the carb in place and the engine at operating temperature?
Thanks Tom

[duffeycycles]

best you can do is drop water over the connections while running..if leaking it will change the running

[T. Cotten]

best you can do is drop water over the connections while running..if leaking it will change the running

Yeah, if its a HUGE leak, Duffey!

Bubble-testing doesn't need the motor to even run to be absolute.

I bubbled tested the manifolds per your advice when the engine was cool in the past. Can the same procedure be done with the carb in place and the engine at operating temperature?
Thanks Tom

Otis!

The carb must be removed as described in the discussion.
With a constant 15 psi applied, and careful scrutiny, even the smallest of leaks should be found at normal temperatures.

The one interface that cannot be bubble-tested is the seam between carb and manifold, so those flanges must be arbitrarily dressed flat.

If we are certain the manifold assembly is sound, then it's on to the carb itself.
Has it fresh throttle bushings and shaft, etc.?
Does it have a float that actually floats, and not a heavy one that would produce a rich condition, good for starting but not beyond?

....Cotten

[otis71]

I haven't checked the carb itself but have installed floats I got from you.

[T. Cotten]

Otis!

Let's talk about dialing it in.

If the low speed needle is leaned to where the motor idles smoothly when warm, and the high speed is turned out to where runs smoothly through the gears on the road, then it should start easily when warm, if all other things are in order.
A choked kick before turning the switch for a cold start is expected. (And more choke with colder weather..)

If the needles must still be turned out beyond ~4 turns for the lowspeed, and 1½ for the high speed, the last variables of a vacuum leak can sometimes be diagnosed with an un-lit propane torch around the throttleshaft, and manifold/carb gasket while idling.

Once the needles have found their sweet spot, they normally start predictably, unless somebody is watching.

....Cotten