In the pic I posted earlier, reversing the spring connection interferes with the main throttle cable, as does trying to lower the connection so you can use the main throttle cable bracket as the upper connection for the spring. If you go to Sterling's site, and look in the gallery, there are pretty good pictures of this mod, and others, and a "lot" of info. I couldn't figure how to do it, and keep my cruise, and AC throttle opener,(if the car runs) so I went with the photo below.

Someone on here said they had mech secondaries, and could go to red line without opening them if they didn't want to. I would like to see how they did that.

 

There is a writeup in the FAQ section. Great mod!

 

i don't think that's very hard to do. I have mech. secondaries and i can redline 1st gear w/out opening the secondaries up, and i can do a good ways on second gear, but it's really pointless to do it like that all you're doing its leaning your mixture a lot and have no speed/power gains from it.

 

Yeah you could do it with the normal bread tie mod, just hold the throttle at the (roughly) 2/3 open point before the secondaries open up. Pretty empty above 3-4krpm though.

Much better ways to mod the secondaries to come on earlier. All the primaries are good for is economic cruising. Best setup is to have all four barrels open at once but this will drink it, so I just allow about 1/3 throttle for putting around on the primaries. Also has no lean spot when you do this because the AP is still shooting when they open.

 

Well, that's the "point" of having them open, or not, when ever you want them to.
Power when you want, and economy when you want.
I understand how mech secondaries work. It was my impression that someone had devised a way to make them open , or not, in any gear/speed (not like 110mph in 5th). I'm thinking you would run out of power on the primaries, and only reach a certain speed, before it got too lean. Enlighten me.
I tried searching the FAQ, can't seem to find anything.
With vac 2nd's, are they open at cruise 65mph ?
At what speed do they normally open in 4th, or 5th, "not" under WOT?

 

lol, i apologize for miss-guiding you man. what i meant was that its pointless to try to redline any gear w/out opening up the secondaries, but that it could be done .

now to your questions, yes mechanical secondaries give you the control to open them when YOU want, not when the engine feels its necessary lol. it makes your pedal feel like a switch. you step on it lightly and about halfway you come to a bump, this is the threshold between fun, and real fun.

vacuum secondaries work under load. your engine decides when its beginning to starve for fuel, and creates a vacuum which opens up some sort of diaphragm and that opens up your secondaries. so no, i don't think that if you're cruising in 5th gear at 65 mph your secondaries are not gonna open. if you however decide you want to do that in 4th gear, then yes they're gonna open because the engine needs more fuel to accomplish the same speed at a lower gear.

as to exactly what speed they open under vacuum, i'm not sure, i'm gonna say in 4th/5th gear at about 3.5-4k rpm. i'm not sure on low gears, its whenever your mixture gets too lean with just primaries. 4-5K maybe...? idk these are ball park estimates from what i've felt driving my car with/out opening the secondaries.

with mechanical secondaries they can be opened as soon as 2.5K rpm in just about any gear with only a very light hesitation, and at a bit over 2k if you do the Accelerator Pump Mod that's on the archives which makes a huge difference.

 

With vac secondaries it all depends on the amount of vacuum at the venturis, which will vary with rpm, load, throttle position..

I was looking into a way of having electronically controlled secondaries a while back. It can be done but I found mech secondaries easy and effective so didn't end up finishing the mod.

 

I was not misguided, I know how vacuum, and mechanical secondaries work
With mechanical, you can't have the primaries fully open without opening the 2nd's, this is where the vacuum operated system gets better mpg.
It was my impression that someone had figured a method to operate the secondaries at will, not the simple bread tied link.

 

heres one i rebuilt and stripped




[img][/img]

 

Nice and shiny!

 

I would imagine that having the secondaries open with the primaries, as at the same time (all barrels opening at once) would result in a boggy bitch of a car to drive. That would kill the air velocity through the primaries, which is needed for smooth cruising and throttle response.

 

Only way to find out is try it and see. In my experience the opposite has occurred - the earlier the secondaries open, the more bottom end response you get.

 

Actually the best way to find out is to listen to people that have had sucess either with doing it to their carbs or buying one (ahem... Sterling) that has had a ton or R&D put into it. There are reasons that the stock carb comes with vac secondaries, instead of having them all open at once. One is fuel economy, the other is low rpm power. At low rpm the engine only needs and can use a small amount of air. Putting more air into it without a proper signal to pull the fuel in will leave you with a big flat spot, as in a bog. Trust me, I've done it numerous times with my Sterling. You open the secondaries too soon and you go nowhere really fast.

 

I generally figure if a car manufacturer who has to pay the costs to build 500,000 of something takes a more complex and more expensive route on some feature, there's normally a fairly good reason. Saving $1 on each of a half-million copies of something adds up.

That reason is not always 'performance,' but it's always good to understand the reasoning before changing it.

Mechsec's go back a lot further than vacsec's, design wise, and they're a lot simpler and cheaper to build. Had to be a reason vacsec's were used.

 

I'm not saying anything about vac secs, just saying that even at low rpm having the secs open up early has worked well for me. I wouldn't just flat foot it at 2krpm, probably should have clarified this - what seems to work best is having 4 partially open throttle plates as opposed to 2 half open ones for strong low end acceleration. It's not just about signal strength at the venturis - with partially open throttle plates the transfer circuits should still be in operation. As for fuel economy, yes it will be worse..

 

OK, Jeff, just peel that scab right off. We've been down this road before, but if you want, I'll keep chasing you around the forum cleaning up your bullshit story until you get it right.
We had a blow-out here about this in the past, folks, so don't let Jeff fool you into thinking he was never given any explanation. I'll let you all know what he already knows well...
After weeks of helping Jeff here out with modding & jetting his project Nikki, he asked me how to do "the linkage mod", as if it were some simple, easy five step answer. When I explained that there were already plenty of pictures of my carbs floating around the net and my website for him to look at, he got pretty bitter about it. I guess he thought that I really had nothing better to do than to waste my time holding his hand & walk him through the entire linkage redesign so that he could complete his Sterling Nikki knock-off because he was too cheap to buy one, I dunno.
Harsh? No, I don't think so at all. I have been more help on the subject of Nikkis, both stock and modified, than anyone else who's ever sold them before. I have gone far out of my way to help people who have never bought a carb from me. Luke here from Brisbane can even tell you, as I just got done this week feeding him all kinds of free info so he can start modding Nikkis for sale in Australia. He doesn't know everything yet, so he should be more careful giving advice in this thread, like saying the primaries are only good for better MPG, but he'll learn eventually. But he can tell you that I have given freely & openly.
Others here will say the same. But Jeff, this really irks the snot outta me because it's the one thing I pride myself on that separates me from anyone else who has modded Nikkis, and you're a pillar of this rotary community. So when you brush on this "incident" where I didn't feel like sending you a two hour video of how I do the linkage reconfiguration and you call it a "flat out refusal" to help, I'm more that a little friggin miffed.

I may not be on time with my orders, but I make up for it with quality craftsmanship and I stand behind my product. Above all else, the number one thing I want to be remembered for when I finally stop modding Nikkis is that I never left anyone behind. That includes you, Jeff, but I can't make everyone understand everything. If you can't figure out my simplified linkage reconfiguration from the dozens of photos just on my website, then you should probably hang up your wrenches, man!



I always encourage rotorheads to mod their own Nikkis, but I also stress that the R&D Carl & I did is really good stuff. Just read my website, and you'll see all kinds of things that can be done. Most are not big performance improvements by themselves, but they work together to deliver great throttle response and increased high end.

SOME RULES / TIPS:

The Nikki carb is metric, but the fuel jets can be replaced with Holley Air Jets, even though they are SAE. The threads are so close in size, and there are so few of them, that the jets don't bind.

For STOCK bores...

Don't exceed .063 in the secondary main. (The stock is .063)

Stock primary jets are .036. Pop these up to .046 on a vac-sec setup, and as high as .052 on a mec-sec setup.

When yanking all of the extraneous linkage for simplification, SAVE IT! Save it ALL!!!
Then you find you can modify these bits you would normally toss.

As for vacuum secondaries vs mechanical, why not do both?




Keep in mind that some of these linkage mods can only be done on certain models. This mod is tricky to get right the first few times, but then it's easy. It requires the tab that isn't used for anything to be bent out wards, and then honed down with a file so it will fit in the little slot on the secondary throttle shaft bung.
It allows you to flip that modded link around to go from stock vacuum secondary operation to locked mechanical secondary operation in about three minutes. Simply keep the vacuum box in place & hooked up. It doesn't impede mechanical operation when it's hooked up.

Always make sure all 4 valves are fully opened at WOT.

Essential for smooth transistion with mechanized secondaries is an increased accelerator pump volume & travel. A couple extra gaskets between the housing & AP cover gives the added fuel volume, and a modded piece of linkage can be added to the AP lever to give the necessary extra travel to spread out the pump shot. (Just an inch is all that's needed.) I use the throttle position sensor link, and just cut off the tab. You can see from the photos on my site.

I generally keep to my own forum these days, so feel free to swing by and ask Nikki questions.

 

(off topic) Hey Sterling, congratulations on your new baby girl.

 

Thanks for the input Sterling!

 

+ Thanks for the photo, with the 2nd(emergency) throttle return spring. I think have found a way to do this and keep the cruise cable. So much cleaner looking, and easier to pop the top off the carb(like I would know what to change out).

I think Sterling has every right to keep all his mods confidential, if he has, fine, if he has not, thanks again.

 

Yes without help from Sterling and his website there's no way I could sell modified nikkis, and would only understand half as much of how they work.

After further testing it seems you guys are right, hitting the secondaries below 2k bogs out and almost dies. My ideal setup before was getting them open at around 1/3 throttle which worked very well and was smooth as, the first third on the primaries gets you up to a point where opening the secondaries can be done without bog and makes a very smooth transition. I kind of generalised from these particular results and wasn't very clear about it.

 

1/3 throttle on the primaries gets you completely past the idle and transition circuits, and working well off the main jets, so that makes good sense.

 

Yup, that's the part that the engineers made easy for us modders; They already had the primary / secondary timing optimised, so all we have to do is be sure that all the valves are opened fully at WOT.

 

I love mechanical secondaries. One of my favourite mods I've done to my car yet. I have yet to modify the accelerator pump at all, I've never really had much of a bog when turning them on. Can anyone here with experience (Sterling) fill me in on how much of an improvement modding the accelerator pump would provide? Is there any extra power because of the extra fuel or is it used simply to get rid of the flat spot when turning them on? Cuz unless I click them open under 4k the little bit of bog doesn't bother me any.

 

As far as I can tell, having done the mod on a stock Nikki, then replacing it with a Sterling that had the modified accelerator pump, it means you can floor it a bit lower in the rpm range without getting the bog.

 

@ blwfly how did you get that airhorn looking so crispy!?