Well, today was the first cold(ish) morning this season and the first time the S40 has been reluctant to start. It would turn over and fire but would stumble a few times and die. Only had the bike since early August, I have never needed to use the choke in warm weather and figured this was the appropriate time.

Much to my surprise the choke made the situation worse - bike wouldn't fire if I hit the ignition with it out and bike would instantly die if I pulled it out when it was in stumble mode.

I ended up just starting it, no choke, and running with the throttle slightly cranked for 10-15 seconds. That seemed to do the trick and I was off to work like any other day. Question is - if the choke is killing the bike does that mean my jetting is slightly off??? Maybe my idle mix is too rich or too lean?

As a general rule, "full choke" is used for cold starts.  Once running, you would set it to "half choke" for a warm up period to help maintain an idle until warm.

It sounds like your bike was looking for a bit of extra fuel but probably not a full choke.

I've been commuting a decent amount on my bike lately and on colder mornings.  I've really only need to use the 1/2 choke to keep the idle up after starting it up.  And my bike is rich (previous owner put a 55 pilot in it).  

I run 1/2 choke for a few stops in my neighborhood and turn it off as soon as I hit my first +mile run.  By time I get to my next stop it's warmed up and holding it's idle. If you don't have any longer runs early in your ride, you might need to keep the choke on for a few extra stops before the bike reaches operating temps.

Thanks - it's very possible that I might have pulled the choke out more than halfway. Will try again on the next cold morning that isn't a rainy downpour.

I  DO  NOT, use the ‘Choke’, unless it is really, Really,  REALLY, cold.

I Took a little piece of alum, about 1/16” thick.  ( or -)
Crack open the throttle, (Engine Off)
Put it between the throttle stop and carb.
And start.

What it does, is Start the engine, with OUT, putting gobs of gas, on the cylinder, it Starts, let it idle (UP RIGHT),  while I am sitting on it, put on my jacket, and helmut. then, with out moving they throttle, go down the 900’ drive, in 1st, about 12 mph,  stop at the Co Rd. Look and go. (Using the throttle).  

Can count on one hand, (and have 3 fingers left over), the times I need the Choke.

The little shim, then attached a little very durable cord, to a place, so it just drops out when I open the Throttle,
Then it is their next time.

Other thing that possibly works, Is that when coming home, I shut off the Pedcock, (Raptor), (Learned where to do this on the road), so the gas in the Carb, is 1/2 or 3/4  Less. Then going, first thing, is turn on the Pedcock, while rolling it out of the shed,  So it is,
‘fresh’ gas in the Carb.

Try it.  

Not sure why....my stock carb never wanted any choke in the 50 degree and up weather that I ride in.  The carb was jetted conservatively with a #150 main, #50 Pilot, and it wanted only 2 washers on the needle to cure the mid range lean surge, and I checked the float level.  I used an oxygen sensor and meter to confirm the jetting was correct, and not too rich or lean.  It just fired right up without using and choke (and the throttle in the closed position).

Once running, it did idle a bit slower then when it would after it was warmed up - but that is normal for an engine with a carb and my right hand is on the throttle when I am riding.....so I would just crank in a bit of throttle to keep the idle where I wanted it until the bike warmed up.  When riding from home there are only 2 STOP signs in the first 2 miles - so it really was never a problem that required any fancy trickery to get a faster idle speed for a cold engine.

Now that I am running a Mikuni Round slide....it likes to have the choke (enrichment lever) whenever the engine has cooled off - but only to get it started.  The choke comes off immediately after the engine fires.

HAPPYDAN wrote on 09/29/16 at 08:25:21:


Yep:

1)   Dyna Muffler
2)   Wiseco
3)   Webcam
4)   Mikuni Round Slide
5)   Head port work
6)   Kawasaki Pulleys
7)   Shawn's Big Brake kit
8)   Big Fuel Tank
9)   Comfy Seat
10) Saddlebags
11)  Windshield
12)  Speedo/Tach with trip odometer and clock!

MnSpring wrote on 09/29/16 at 18:42:31:

Kris01 wrote on 09/28/16 at 18:53:44:

Your "throttle shim" is essentially doing the same thing as the choke.

The Choke and Throttle are two different things on a  ICE

True, but if you have an OEM carb on your S40, then the "choke" is actually an enrichment circuit. Not quite the same as giving it a bit of throttle, but pretty darn close.

Mine like half choke below about 55 deg and full choke at around 35 or below. It will pop and sputter without the choke but never start and run in those temps without it.

I don't use it if I don't need it.  The bike warms up quickly.  Well, it's a little slower warming up when the temps are around freezing.

The little ninja wants choke any time the temps are below about 70. And, it insists on warming up a bit before I take off or it'll just die. The heater blowing back out of the fairings is nice.  Now, if I could just figure a way to direct the warm air a little better for those cold days.