Interstate Carburetor Springs

[pancho]

Does anyone have any hard data on the advantages and disadvantages of putting Interstate carburetor slide springs in a Standard or Tourer bike?

[Bagger John - #3785]

Slightly quicker throttle response.

All of my Standards and Tourers got them, along with an I/S ICM. Wakes the mid-range up a bit, especially when used in conjunction with Cobra or Dynojet jet needles.

ETA:

I doubt you're going to get anyone posting A/B dyno run comparisons, though. Seat-of-the-pants dyno showed it to be worth the $12/bike it cost.

[98valk]

u will get better mpg.  it is a tuning device.

weaker slide spring will go up easier reducing the velocity across the needle well thereby reducing the signal to draw up fuel until engine RPMs go up to create a greater velocity.

so if the engine is running too rich for the ambient conditions it can make more power by putting the engine into the right air fuel ratio.

[pancho]

weaker slide spring will go up easier reducing the velocity across the needle well thereby reducing the signal to draw up fuel until engine RPMs go up to create a greater velocity.


So is there any proven way to exploit this to get from point A to point B faster? like a larger jet or raising adjustable needles?

[98valk]

weaker slide spring will go up easier reducing the velocity across the needle well thereby reducing the signal to draw up fuel until engine RPMs go up to create a greater velocity.


So is there any proven way to exploit this to get from point A to point B faster? like a larger jet or raising adjustable needles?

what are u trying to accomplish?
as Marc from FactoryPro told me, "it always is what the engine wants".
so correct air/fuel ratio will make more power.
mikuni states perfect jetting at a prescribe temperature is good for plus or minus 25F.

have u see my thread.  http://www.valkyrieforum.com/bbs/index.php/topic,105991.0.html

also see
 http://www.factorypro.com/tech/tech_tuning_procedures/tuning_carbtune,CV,lower_rpm_engines.html

[f-Stop]

I've had the Interstate vacuum piston springs installed in my '98 Standard since '09.  (It may have been 2010...but still, it is the only engine mod I've ever done to the bike.)  There was a post on the Tech Board back then -- now the Old Tech Archive -- that explained the simple mod.  Without any other carb/engine mods, the vacuum piston spring mod on Standards and Tourers produces a slightly quicker throttle response in the mid RPM range.  It feels like more horsepower, but it is not.  Comes in handy when passing slower vehicles on the twisty, two lane Hill Country roads here in Central Texas.

 

I never did notice any better fuel mileage after the mod.  If there is better mileage, it would be nominal.

For some reason, I still have the original springs stashed away in my spare parts bin out in the garage...

[98valk]

I've had the Interstate vacuum piston springs installed in my '98 Standard since '09.  (It may have been 2010...but still, it is the only engine mod I've ever done to the bike.)  There was a post on the Tech Board back then -- now the Old Tech Archive -- that explained the simple mod.  Without any other carb/engine mods, the vacuum piston spring mod on Standards and Tourers produces a slightly quicker throttle response in the mid RPM range.  It feels like more horsepower, but it is not.  Comes in handy when passing slower vehicles on the twisty, two lane Hill Country roads here in Central Texas.

 

I never did notice any better fuel mileage after the mod.  If there is better mileage, it would be nominal.

For some reason, I still have the original springs stashed away in my spare parts bin out in the garage...

actually less response, since the slide is higher sooner reducing the velocity. higher velocity pulls more fuel out of the needle well.
now if the engine is running slightly rich there are a few reasons then the reduced velocity leaned out that spot and gave the engine more power due to better  a/f ratio.

[Bagger John - #3785]

I've had the Interstate vacuum piston springs installed in my '98 Standard since '09.  (It may have been 2010...but still, it is the only engine mod I've ever done to the bike.)  There was a post on the Tech Board back then -- now the Old Tech Archive -- that explained the simple mod.  Without any other carb/engine mods, the vacuum piston spring mod on Standards and Tourers produces a slightly quicker throttle response in the mid RPM range.  It feels like more horsepower, but it is not.

An area friend who used to participate on this board when the old format was used - around 2000ish - did an I/S ICM/carb spring and needle shim mod to his '99 Standard then posted the before/after dyno runs. Note that peak horsepower wasn't raised by the mods, but the power/torque curves from roughly 1700-4000RPM were definitely enhanced from that of "stock tune". In some RPM regions, doubled. More usable power down low and through the mid-range is definitely a benefit when you're hauling 650+ lbs of people down the road. My friend ain't small and neither is his wife. Think two huge farmer types.

I never did notice any better fuel mileage after the mod.  If there is better mileage, it would be nominal.

I've done a similar mod to every Tourer or Standard I've owned (3 and counting). ICM, I/S springs and Cobra or Dynojet adjustable needles. Saturday night I ran out to a friend's and back on my '99 CA-model Tourer, which sports a lot of I/S bodywork in addition to the carb/ignition changes. Smog stuff is still attached and working, and it retains the CA-spec cams. By the way, none of these bikes have had airbox or exhaust mods done to them apart from pipe tips. All stock there.

At 65MPH average speed across a 50 mile round trip - 2/3 highway, the rest secondary 2-lane roads - I was able to get ~45MPG. When I bought my first Tourer in 2000, it averaged 32-33MPG in stock form when ridden at those speeds. After the mods, I got similar mileage figures with it along with a stronger mid-range. From 2007 onwards, the Tourer wore the same Memphis Bat Wing that's on my '99 so the frontal area between the two was roughly the same.

I don't ride either of my Valks at sane speeds if traffic and weather conditions permit, so all those mods are for naught when they come fully on the mains... 

[98valk]

I've had the Interstate vacuum piston springs installed in my '98 Standard since '09.  (It may have been 2010...but still, it is the only engine mod I've ever done to the bike.)  There was a post on the Tech Board back then -- now the Old Tech Archive -- that explained the simple mod.  Without any other carb/engine mods, the vacuum piston spring mod on Standards and Tourers produces a slightly quicker throttle response in the mid RPM range.  It feels like more horsepower, but it is not.

An area friend who used to participate on this board when the old format was used - around 2000ish - did an I/S ICM/carb spring and needle shim mod to his '99 Standard then posted the before/after dyno runs. Note that peak horsepower wasn't raised by the mods, but the power/torque curves from roughly 1700-4000RPM were definitely enhanced from that of "stock tune". In some RPM regions, doubled. More usable power down low and through the mid-range is definitely a benefit when you're hauling 650+ lbs of people down the road. My friend ain't small and neither is his wife. Think two huge farmer types.

I never did notice any better fuel mileage after the mod.  If there is better mileage, it would be nominal.

I've done a similar mod to every Tourer or Standard I've owned (3 and counting). ICM, I/S springs and Cobra or Dynojet adjustable needles. Saturday night I ran out to a friend's and back on my '99 CA-model Tourer, which sports a lot of I/S bodywork in addition to the carb/ignition changes. Smog stuff is still attached and working, and it retains the CA-spec cams. By the way, none of these bikes have had airbox or exhaust mods done to them apart from pipe tips. All stock there.

At 65MPH average speed across a 50 mile round trip - 2/3 highway, the rest secondary 2-lane roads - I was able to get ~45MPG. When I bought my first Tourer in 2000, it averaged 32-33MPG in stock form when ridden at those speeds. After the mods, I got similar mileage figures with it along with a stronger mid-range. From 2007 onwards, the Tourer wore the same Memphis Bat Wing that's on my '99 so the frontal area between the two was roughly the same.

I don't ride either of my Valks at sane speeds if traffic and weather conditions permit, so all those mods are for naught when they come fully on the mains... 

agree and that is my point.
EPA requires engines to be tuned to 14.7:1 in the 3k rpm range. that is much too rich for an engine going down the hwy. actually looking at tuning charts over the yrs, an engine never wants the EPA ratio for best mpg and HP.  hence the I/S springs actually lean out that area increasing mpg and power.
when an engine is rich it will shown bigger torque numbers but the HP will be down.  HP is how fast the engine will accelerate.

[pancho]

Note that peak horsepower wasn't raised by the mods, but the power/torque curves from roughly 1700-4000RPM were definitely enhanced from that of "stock tune".

That is basically what I'm looking for, just getting to higher RPMs as fast as possible. I'll look around and see what if anything is available these days for needles.

have u see my thread.

Yes, I have looked at the information you provided, as always good informative stuff.

[98valk]

Note that peak horsepower wasn't raised by the mods, but the power/torque curves from roughly 1700-4000RPM were definitely enhanced from that of "stock tune".

That is basically what I'm looking for, just getting to higher RPMs as fast as possible. I'll look around and see what if anything is available these days for needles.

have u see my thread.

Yes, I have looked at the information you provided, as always good informative stuff.

I use the FactoryPro needles.  dynojet/cobra/viking needles are richer than the FPs.