super-mega-choke?

[Rema1000]

When chilly (say, 40F morning), I find that my GS starts best if I turn the throttle 1/4 turn, let it snap back, wait a couple of seconds, then hit the starter.   But even then, sometimes the bike will start, RPMs will climb for 2-3 seconds, then drop, cough, and die!  Another twist of the throttle, another press of the starter button, and this all repeats.  Each time I do start it, the bike runs for a little bit longer before it dies.   The 3rd or 4th time, it may keep going.

However,  if I give it a _tiny_ bit of throttle right after it starts, then I can get the RPMs to stabilize at 2Krpm, and not stumble and die.  After 10 seconds at 2k rpm, the bike seems to wake-up, and the idle takes-off up to 5k RPM.

Also, if I pipe some propane into the airbox, then it will start and not die.

The fact that it will start if I goose the throttle before starting, but then it will die again, makes me think that it just wants more/richer fuel at cold starts.  There's no reason I can think of why it should stumble and die once both pistons are firing, unless there's an enrichment or fuel delivery problem when cold.

Is there a way to adjust the range of the enrichment circuit, to make it even richer when the choke lever is fully engaged?

Caveat: this is only a problem when cold.  I burn 85% ethanol, which is also probably not what the enrichment circuit was designed for.  I bored-out my jets by 30+%; I wonder if the enrichment circuit also needs manipulation?

[scratch]

Technically, snapping the throttle doesn't do anything on a carbureted bike; you're moving the butterfly, but not really affecting anything. Although, I'm not familiar with ethanol, it should still be in a liquid state, very much like conventional gasoline, in a carburetor.

What I'm seeing here is simptoms of being too rich (assuming conventional gasoline properties). My first suggestion is to back off the choke just a hair (or more) from full choke.
In the first paragraph, as rpm's rise it draws more fuel, get's rich, and dies. It runs a bit longer each time because the piston is warming up and the rings are sealing a little better each time.

When you say

...if I give it a _tiny_ bit of throttle right after it starts, then I can get the RPMs to stabilize...

Tells me that it needs more air. When you give it a tiny bit of throttle your admitting additional air into the mix.

Now, I admit, the addition of propane has me confused...but, if it's true, and what you need is more fuel out of the enrichener, the only thing I can think of is to purposely flood the engine.

Now, in humor, I suggest finding a set of Amal carburetors off an old Triumph, or, due to the diameter of the Amals probably being too small, a set of Bing carbs off any BMW made before '77, and tickling the death out of them (just to let people know, this act of "tickling" comes from plungers on the floatbowls that you push down to force your floatbowl to flood, thereby "enrichening"). Otherwise, find a thumper owner and ask him how to flood an engine. :lol:

[Blueknyt]

while the GS does not, some bikes have Pumper carbs, like my Honda XL 250R.

just try bumping your choke lever  1/3 the way. should work

[scratch]

Also, Rema, what's your idle supposed to be set at when running ethanol? Wouldn't it be a little higher?

[davipu]

I think that this thread just went from redneck engineering to some backwoods,"git da big pounder Pa"

[Rema1000]

Funny you should mention it, but the idle is currently set high, at about 1500 rpm. It seems like in winter, if I try to idle it at 1200 rpm, it kills now and then.  In summer, I can get a smooth idle down to 1200 or even 1000.  

But I have been blaming this weirdness on the fuel: E-85 ethanol is actually only 70% ethanol in winter (November through March).  But I rejetted during the summer, so I think the mixture is a tad rich at warm idle in winter.  Sometimes at a stoplight, I smell booze .  I'm looking forward to summer gas.

Now that you mention it, that 30% gasoline could make the bike overly rich at starting.  I'll give it a try with less than full choke tomorrow.  There's a low of 38F tonight.

[John Bates]

.......................

But I have been blaming this weirdness on the fuel: E-85 ethanol is actually only 70% ethanol in winter (November through March). ..............

70% ethanol? :dunno:

My owners manual says: ".....ethanol may be used in your vehicle if the ethanol content is not greater than 10%."

Is 70% ethanol correct?

[sprint_9]

How does your bike run with ethonal, any negative effects after 12 years of regular and then going to ethonal, 10 cents over the coarse of the summer will add up quick.

[Rema1000]

The main difference is that I can only fill-up at E-85 gas stations.  This means that I have to bring a gas-can if I'm going for a ride in Wisconsin.  The next difference is that ethanol has is lower gas mileage (I get about 75% the mpg of what I did on gasoline... which means 25% less distance on a tank of gas).   I could probably improve the gas mileage if I tuned it on an O2-sensor-equipped dyno.

The third difference is that the bike is more reluctant to start in cold weather: it has a long warmup time at 40 degrees, and and 30F and below, it takes some extra care to start it in the morning.  If you don't ride below 50F, you won't notice any of that.

The fourth difference is that the jetting had to be enlarged quite a bit.  The different jetting has changed the feel of the friction zone.  Either:
-the bike has more power at low RPMs, making the friction zone smaller
or
-the bike has no power at low RPMs, so I have compensated by over-revving at take-off, making the friction zone smaller
Whichever it is, I think that I use the clutch longer, coming off the line, than I did with gasoline.  So it seems a little touchier off the line.