Nikki Mechanical secondaries

Hope this pic helps explain it to you. I just link these two up with a paperclip, making very sure its fixed properly as it could cause some dramas if not done correctly.

you shouldn't need to disconnect anything else. However you can disconnect the vacuum diaphragm that used to actuate the secondaries, from memory I always did.

As far as wiring it up goes, just hard wire the right linkage to the left linkage... hard up against it and you'll be good to go.
If you want a more permanent solution, weld the joint together

this does create a lean stumble lean stumble when the mech secondaries are jammed open on a nikki, this mod will fix it.

Pretty much anyone can do this, all you need is a little strip of metal with some holes drilled in it and a nut and bolt. What it involves is extending the accelerator pump arm that links up with the throttle, to provide a richer mixture when the secondaries open up.

- background -

The accelerator pump (AP) squirts fuel down the primary barrels whenever you press the throttle. This aids acceleration by providing a richer mixture. Problem with the stock setup when combined with mech secondaries is that the AP will generally finish its shot BEFORE the secondaries are pulled open, so it's not squirting when the secondary barrels let more air in, causing a lean spot which you feel as a stutter or whatever. What you can do is extend the stroke of the pump to provide a shot that lasts longer but is a little weaker - with the same pump VOLUME, making the shot longer means the same amount of fuel over a longer time period which equals a slower rate. Acceleration will suffer slightly because the mixture wont be as rich, but it will be smoother and there won't be that stutter.

- how to do it -

Here's the AP (the rod with spring normally sits through that hole in the AP arm)


Opening the throttle by hand will show that the pump is pushed in early but finishes its shot before the throttle is fully open. That rod with a spring on it will just keep extending out but the pump isn't going anywhere. The idea is to extend the AP arm so that the pump doesn't finish its stroke until the secondaries are open.

First you need to remove that rod with a spring on it. Remove the adjustment nut from one end...
Image
...and the split pin and washers from the other end.

Now for the plate:

Note that the middle hole should be long like that for tuning purposes, and the single hole at the side is shaped out to assist that rod sliding through it more smoothly.

Then just bolt the plate onto the AP arm loosely, putting the bolt through the long hole and the rod with spring through the small hole. Install the split pin and washers as before. Put the adjustment nut back on the end of the rod and screw it all the way in as far as it goes.



- tuning -

There are two things to tune here. One is the position of the plate (that's what that longer hole is for), and the other is the position of the adjustment nut.

First the plate. Put the bolt through about half way, secure it slightly, then pull the throttle open by hand while looking down into the carb. There will be a point where fuel stops coming out of the AP nozzles, you want this to be when the secondaries are about 1/3 of the way open. Move the plate up or down until you find this spot.


Then the nut. If you cant see fuel coming out the AP nozzles basically as soon as the throttle is opened, loosen the nut out until it does. You may have to readjust the plate after this part but probably not. And that's it basically.


When driving it you'll probably notice that low down acceleration is a little weaker, but that stuttering when the secondaries are jammed open is pretty much gone - it WILL still be there if you flat foot it down low, but a slower throttle press should smooth it out anywhere other than idle takeoffs.


Credit goes to Sterling from RX7club.com for this mod, I just copied it and messed around with it a bit.