Lotus Elan and Lotus Elan Plus 2 Forums

rgh0 wrote:............... no air/fuel ratio cheers
Rohan

SJ Lambert wrote:

rgh0 wrote:............... no air/fuel ratio cheers
Rohan

Hi Rohan - do you use an air fuel ratio analyser in setting up your race motors?

SJ Lambert wrote::D Any good dyno operators in your neck of the woods?

lotocone wrote:Regarding the hypojets that Keith sold, does anyone know how to lean them out ? There are 4 settings for lining up the holes in the 2 parts of the hypojets. I don't have the instructions from Keith's Yahoo group which has moved somewhere else.

Source: http://autos.groups.yahoo.com/group/sid ... ssage/4630
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This initial run of Hypojets is tailored for folks that DO NOT have a wideband AFM. The step sizes of the adjustments are on the coarser side so it'll be easier to tune by the seat-of-the-pants method. If this is successful I can supply ones later on with finer adjusts to squeeze out the optimal fuel mileage but you'll need an AFM to do it.

First is a warning to not overtighten the Hypojets when installing them into the carburetor, they can be crushed. A torque of one pound per inch is plenty. If you just grab the screwdriver between your thumb and forefinger that will limit the amount of torque to be about the right value.

The easiest approach to tuning the idle/transition circuit is to start on the lean side and move in the fatter direction incrementally until all the misfiring and partial misfiring behavior subsides. When it's really way too lean you'll be able to tell by just elevating the rpms using the idle speed screw(ISS). As the mixture gets closer to the ideal you'll need to drive the car to test the tractability.

Even with a too lean Hypojet there is usually enough fuel being supplied so it can be tuned to idle to perfection. Go ahead and set the idling mixture with each idle mixture screw(IMS). The newer DCOEs use a finer pitch thread on the IMS so about three turns from closed is required. The early carbs with the coarser thread will need about one to one and a half turns.

The Hypojet is comprised of two components which when slipped together are a completed assembly. There is an outer brass jacket that looks like a stock jet but it has four different sizes of air holes spaced 90 degrees apart. The jacket is universal and works in conjunction with every size of the other component which is the insert. The insert carries a piece of hypodermic tubing and there is a variety of tubing sizes to choose from. There is a chart that depicts the size of the tubing via a barcode system of grooves. To add more fuel overall one needs to use a larger inner diameter tubing. The insert has an oversized air hole bleed hole. To make an adjustment to the amount of air passing through the Hypojet the insert is rotated so it's air hole lines up with one of the four air holes in the jacket. The Hypojet is designed so that when the assembly is tightened into the carburetor the insert is loaded and therefore captured so it cannot rotate out of alignment.

Here's how a Hypojet works. Again the inner diameter of the hypodermic tubing is the main means to control the overall amount of fuel flow. The air adjustment allows some leeway to control when that fuel gets delivered. The general rule is the smaller the air hole, the more fuel will be delivered when coming off idle but at the other end of the dynamic range of the transition circuit it will run leaner. A larger air hole will have exactly the opposite effect. It sort of acts like a teeter totter so you have the ability to tilt more or less fuel to where and when you need it.

Be forewarned that if you already have a serious off-idle stumble the Hypojets will likely not cure that problem. That requires the position of the butterfly relative to the first progressive hole be altered.
-Keith Franck