I realize I'm beating this topic to death, but hopefully I'll learn something from it.

I'm completely unhappy with my seat-of-the-pants (roll-off) test for the main jet. I just don't have enough experience to be an unbiased judged.

Enough complaining, on to my real question.

I understand that a cold engine is not a valid condition under which to test a carburetor. That said, I noticed something today. It was about 70 degrees when I started my S40 this morning with the choke one notch out. It didn't idle well, so I revved* the engine and pushed the choke in. It idled smoothly with no choke, a little slow, but smooth.

*It dies if I push the choke in without a little throttle, is that normal?

I pulled into the street and attempted to cruise down to the corner at about 1/8 throttle. The engine did not like that. It surged horrible. I assume because it was too lean for the cold engine.

I had thought that at 1/8 throttle the pilot system would still have a significant effect on the mixture. I guess I'm wrong.

What I learned was my mixture is much richer at idle than at 1/8 throttle. The questions are: which is wrong and how do I fix it?

I hadn't thought my idle was too rich because the plug looked good last time I pulled it.

We don't have a "throttle cut away" so that's not something I can adjust.

I guess the next option would be to reduce the spacer from 3 washers to 2 washers.

Thoughts? Corrections? Angry letters?

-D. Dwarf

1st start bike and keep it runnin,when it will idle (will be low) w/o choke, then do your safety check,then put on your protective gear,
now ready to mount and ride..
idle speed is 1 >1.2 K set on a fully warmed up engine..
i have a tach and an oil temp gauge sometimes it takes a few miles for er to totally warm up even on the hottest days..

some one here said "dont ask her to scream untill her throat is warm"

Serowbot wrote on 08/19/09 at 16:35:07:

See signature:
Pearl White 2007 S40; Dyna exhaust; Current jets: 55 (1 turn out) / half spacer / 150
See Profile:
Rochester, NY

Elevation: 500 ft

-D. Dwarf

My bad....

For what you've done,.. you should be in the ball park...

Never test anything in a cold engine... also don't test during unusual weather...
You want a good average for your usual riding conditions...

LANCER wrote on 08/19/09 at 17:44:03:

Color me confused.
Let me repeat the steps I took, perhaps there was a miss communication.

• Start motorcycle with "choke" on first notch
• Let idle for 30-60 seconds, notice it's not a smooth idle, rev and push choke in - idles smoothly
• Let idle for 30-60 seconds
• Attempt to leave, as soon as I open the throttle the engine behaves badly. I don't know the technical term. I'd describe it as a surging or hunting. RPM varied wildly.
• Pull choke out one notch.
• Runs better (not perfect) at 1/8 throttle, idle still rough
• Once warm, push choke back in, runs "fine" at all throttle openings

Caveat: cold engine is not a valid test configuration

What this tells me is the engine is getting a richer mixture at 0 throttle than at 1/8 throttle. Perhaps it's too rich at idle, perhaps it's too lean at 1/8 throttle - that'll require a warm engine to identify.

Since that whole range is primarily controlled by the pilot jet and mixture screw, I'm not sure how to fix that. Or if it's something that needs fixing.

-D. Dwarf

LANCER wrote on 08/20/09 at 06:32:48:

I've tried the "Lancer's Straight & Simple Carb Tuning" several times and always end up 1 turn out with the 55 pilot. I assumed that meant it was "in range".

I'll post again after gathering more info with the smaller pilot.

-D. Dwarf

Surging is not rich, surging is lean. Most rich issues relate to lack of power and soppy sound and soppy feel as well as black or white smoke (if you can see that from the exhaust) and smelling of gas when you try to accelerate.
Surging, misfiring etc on cruising and steady throttle is lean.
Trying to accelerate and you get a weak and lousy response that is rich.
Cool.
Srinath.

LANCER wrote on 08/20/09 at 17:16:10:

So the pilot circuit is both lean and rich. Whoohoo!
That's why I haven't already moved down a pilot size.

The weather here hasn't been cooperating either.

-D. Dwarf