Tuning the SV1

/Tuning the SV1
Tuning the SV12017-12-03T21:09:27+00:00

We get lots of questions on our SV1, its features and how to tune on one.

Here is a summary of the SV1 and its features and a photo depicting the ports and their functions.

How to tune your SV1:

The SV1 is infinitely tuneable at idle, light and heavy throttle as well as wide open.  This allows you to tune it to be crisp and clean in any rpm range.

Location of various ports on SV1 (these are on both the left and right sides on the FRONT ONLY). The single blade acts like a giant dispersion tool to atomize the idle and cruise fuel.

The SV1 has a multitude of adjustments.  But in the last year we have found this complexity to be a bit much for some customers. So starting in June of 2012, we have simplified and changed the design.   Now Port # 2 and Port # 5 are your main tuning friends for your SV1 and Ports 1, 3 and 4 have been virtually eliminated from the equation on most models.

INTERMEDIATES:  Port #1 and the new Port #5 are the Intermediate tubes (if equipped). These jets are located about ONE INCH inside the body.  The smaller the jets are in these ports, the LESS fuel will be supplied around 2500-4000 rpm. Most SV1 carbs will either have the lower #1 intermediate tube location (designed to supply extra fuel from 1500-3500 rpms) OR the higher # 5 intermediate tube location (designed to supply extra fuel from 2500-4500 rpm).

But unlike a four barrel three circuit carb, with the SV1, increasing or decreasing this port jet diameter or any of these port jet diameters will not effectively change the overall air to fuel ratio at wide open throttle.  The jetting range is fully open to fully closed.

# 2 is the Lower Transfer port. The smaller these are the LESS fuel will come out in around the 1000 to 2500 rpm range.  The jetting range is as low as .060 to fully open.

# 3 is the Idle port (rarely used) The smaller these are the leaner it will be at idle, but the richer it can be made at light throttle.  The jetting range is as low as .052 to fully open.

# 4 is the Upper Transfer port. (rarely used) Since the introduction of Port # 1 and Port # 5, this Port # 4 is rarely used and is plugged on most models as it was too complex for most to understand so by simplfiying the design with Ports #1 and optionally Port #5 we have eliminated its use on almost every model we build as of June 2012.  Basically, this port #4 creates a fuel curve in part throttle operation as the blade sweeps open.  The larger theholes in this port are, the LEANER it will be at idle to around 2000 rpm.  BUT the richer the curve will become from 2000 to 4000 rpm.   The jetting range is fully open to fully closed.This was very confusing so it was eliminated, but was a very effective tuning tool.

Vice versa applies to the above information.

You don’t need to adjust any of these ports if you wish. They are just in there for the more discriminating tuner.

We can baseline them quite close and often times are dead on for many combinations. You can then simply do normal changes to air bleeds up on the top of the carburetor to effect operation. For example: The larger the idle airs, the leaner it will be at idle and cruise etc….

These 1,2,3, 4 and 5 circuits are simply additional circuits that allow you (if you wish) to fine tune the design to a very fine level of tune that will rival and even surpass fuel injection in idle, throttle response and driveability operation.   The reason is the SV1 design can better atomize fuel than an injector can due to the air speed impacting these supply ports at high and sometimes sonic velocities at idle and cruise.


Also note the boosters simply draw out forward from the front (we have pulled one forward to demonstrate…you can do this by hand with no tools required..simply spray it with some WD-40 or similar for lubricant and pull it through). This is in case you wish to change boosters and vary the cfm of the carb or change the atomization properties.


Note the check ball that orients the booster, this ball is trapped in the body when the booster is installed. Early models used a locating pin.

The boosters float on o-rings mounted in the body. This is to dampen harmonics/vibrations and ensure consistent fuel flow under load.

I hope this helps you better understand the design and its features.