The elusive carburetion "Sweet Spot"

[jim snyder]

The quest for the carburetion sweet spot is something Steve from Florida has mentioned here before but I wanted to elaborate on it a bit more after finally finding it this past week. The "Sweet Spot" we speak of is
that perfect combination of fuel, air, exhaust, and the resulting throttle response that it provides. After installing Steve's jet kit I began the search for the perfect amount of air flow into the airbox. As many of you have discovered this can be frustrating at times. And when Steve tells you that little adjustments can be big, LISTEN TO HIM. I have been fooling around with the airbox opening for the past 6 months looking for that perfect amount of air.  Last week I found that perfect amount of airbox opening. Just before this past weekends Wildflower ride I violated my own rule of tearing something apart the day before a ride, but when you are so close to something like this its hard to just let it set. I built a completely new intake snout to accomidate the new found airflow. Long story short, the sweet spot has been found. The ride saturday was awesome. Throttle response was crisp, roll ons were great, and the best part was the 48 mpg mileage figure I discovered after the first fill up, and I am running Steve's "power" jet kit. My point of this post is to say that the sweet spot is out there, and sometimes its hard to find, but keep looking because it "is" out there. And when you find it the rewards are well "sweet".

[Sparkie]

You must elaborate on this new intake snout. Does it have an adjustable opening for different altitudes? Mark

[jim snyder]

You must elaborate on this new intake snout. Does it have an adjustable opening for different altitudes? Mark

No this is a non adjustable one. But my adjustable plate is what you need.

[midnightrider]

Thanks for the post Jim. I have been close for quite a while and just keep riding the way it is. You have inspired me to keep looking.

[Centex]

..... Long story short, the sweet spot has been found. The ride saturday was awesome. Throttle response was crisp, roll ons were great, and the best part was the 48 mpg mileage figure I discovered after the first fill up, and I am running Steve's "power" jet kit. My point of this post is to say that the sweet spot is out there, and sometimes its hard to find, but keep looking because it "is" out there. And when you find it the rewards are well "sweet".

I was so happy with results on intalling SISF's kit that I've really not touched it, but maybe it'd be fun to get into chasing this optimization.  For me, the variable would be limited to the intake air .... I'd not touch the jets as setup with Steve's kit and I'm locked-in on my OEM headers with Staintunes.

Seems that making and adjustable plate would be the place to start.  I'm thinking it should have a leg bent into the snorkel & fitted to act like a 'plug with thickness' like the foam, as opposed to a sharp-edged thin-plate restrictor at the face of the opening.  Air flow and volume at varied RPM will be very different through a plate restrictor vs a plug restrictor of the same width(all else being equal), correct ?

Jim, have mileage calculations and your Butt Dyno been the primary instruments in your research?  In your ventures as you've pursued this, did you ever reach a point of concern about over-lean damage?  Have you noticed that engine temp at the dash gage is any help in tracking this?  How 'bout doing cut-and-read of the sparkplugs?

Sorry I missed meeting lots of the SCA folks at the wildflower run but I had a CMRA race to work this weekend .... looking forward to meeting everyone at the National!


TIA

[jim snyder]

I was so happy with results on intalling SISF's kit that I've really not touched it, but maybe it'd be fun to get into chasing this optimization.  For me, the variable would be limited to the intake air .... I'd not touch the jets as setup with Steve's kit and I'm locked-in on my OEM headers with Staintunes.

Seems that making and adjustable plate would be the place to start.  I'm thinking it should have a leg bent into the snorkel & fitted to act like a 'plug with thickness' like the foam, as opposed to a sharp-edged thin-plate restrictor at the face of the opening.  Air flow and volume at varied RPM will be very different through a plate restrictor vs a plug restrictor of the same width(all else being equal), correct ?

Jim, have mileage calculations and your Butt Dyno been the primary instruments in your research?  In your ventures as you've pursued this, did you ever reach a point of concern about over-lean damage?  Have you noticed that engine temp at the dash gage is any help in tracking this?  How 'bout doing cut-and-read of the sparkplugs?

Sorry I missed meeting lots of the SCA folks at the wildflower run but I had a CMRA race to work this weekend .... looking forward to meeting everyone at the National!

TIA

Yes the butt dyno was used, but the ears were also a key tool as well. And don't get me wrong, some may install Steve's ket kit and hit it right off the bat. Steve has said many times that every bike is different and that is more true than you know.
As far as my temp gauge it runs right on the edge of the cold mark. My plugs are running a very light tan coloration. Steve also stresses that float levels are critical.
I sent my carbs to him for a once over and had him set my float levels so I knew they would be right. Like I said sometimes you may hit it right on the nailhead the first time, and sometimes it takes a little longer. But when its right its really good.
And big KUDOS to Steve Sefsick for all of the help by phone and email, (I sorta bugged the crap out of him during this whole process) but thats why he's the carb guru.     

[Steve in Sunny Fla]

Centex, no worries on getting it to lean, it will haveobvious flat spots and hesitations before you get it bad enough to hurt anything, and even then you'ld be having to dragrace WOT with no foam or restrictions to cause a problem. typical plugs will have a small kernel of yellowy / tan on the end, at least with 10% ethanol fuel - - Steve

[snarf]

typical plugs will have a small kernel of yellowy / tan on the end, at least with 10% ethanol fuel - - Steve

Hey Steve is that a corn joke or was it completely accidental??

[Steve in Sunny Fla]

Oh, that's just my "unitentional wit"

 In other words it was just pure DUMB luck! Steve

[snarf]

Oh, that's just my "unitentional wit"

 In other words it was just pure DUMB luck! Steve

I still chuckled on the inside 

[kzz1king]

So what are some "hints" that one is getting close? Mine runs great. I cut 1/4"tad better so cut another 1/4. Runs so good I hate to mess with it. I think I may be as lean as I want to go. It runs great but it needs to be warmed up well to avoid any flat spots.

Before the kit the fuel level was a tad high, mileage good and it ran ok (not near as crisp). It must have been to rich because it didn't require much choke or warmup.

Maybe I will trim more latter but it runs to nice to mess with it right now.!
Wayne

[roadkoan]

I always thought that the "sweet spot" for carbs was in Florida?