klabatzie

Done one of the new tubes

Seems to fill quite nice exept for the last hole and the one at the bottom

Jeff20B

iTrader: (13)

Those holes are not connected. Leave the bottom set of holes alone. Only fill the upper dual holes including all the way up to the top of the tube if you need to. That is how i do it.

Jeff20B

iTrader: (13)

That ought to work for you.

I make sure mine are both filled but remember I do mine for boost so I leave nothing to chance.

These tubes are pretty easy to fill so please play around with them some more if you need to. Otherwise, what you have pictured is probably good enough.

t_g_farrell

iTrader: (1)

Jeff, I never solder filled anything but then I never measured my venturis to see how much I
expanded them. Whats the purpose for solder filling it? Its for boost or a general mod depending
on the venturi size?

Sorry for the thread jack but I was curious.

Jeff20B

iTrader: (13)

Ok, I'll see if I can explain it. The way the stock Nikkis are, they have really big air bleeds from the factory. The whole carb is calibrated to work on a stock ported 12A with a stock intake manifold of whatever year spread it is; 79-80 or 81-85, and the stock exhaust system which we know to be pretty restrictive. We also know the carb is factory calibrated to use a stock choke flap, stock vacuum secondaries, stock altitude compensator and anything else I normally delete for boost and NA performance.

All Sterling Nikkis with mechanical secondaries experienced a bog until he figured out how to increase the length of the accel pump shot, but you still had to wait until about 4000 before you could floor it.

I was also experiencing a nagging secondary delay with boost that lasted from 1.5 to 2 seconds.

Something wankel=awesome said about reducing the air bleeds to "speed them up" rang a bell so I started experimenting. The end result is a sec delay reduced to just 1/4 second initially and then finally eliminated entirely. All from making the air bleeds smaller. But then I ran into a different problem of flooding and just running too rich until I a) reinstated the anti-siphon bleeds which are the nickel plated 60s, as I had swapped in a set of solder filled brass primary ones, which would empty the float bowls faster than they could refill at 2.5psi. Interesting phenomena as you might imagine. Oh and then I machined the stock 140 secondary main air bleeds to accept pilot jets drilled to only 80. I tried other sizes but ended up at 80 as the perfect size for boost and NA.

This allowed me to floor it at 3000 and get instant power and boost with no delay, and never a bog. Heck I can floor it at 2000 if I want to, but there is no power down there. However it never bogs. It just feels like only the primaries are open but more throaty sounding.

One other thing I noticed is by reducing the secondary air bleeds, I must also reduce the secondary fuel jets now. The stock 160 is too big. I found 140 to 145 is the ideal size now. In order to use the factory 160 jets, I'd need secondary venturis at 32.7mm like I tried experimentally, intended for my half BP. We shall see how it goes. At least it handled boost with no sec delay or other problems, thankfully. And before you ask, no I will never do another set of these. Ever.

So to answer your question, filling the sec long slows is the mod responsible for getting my sec delay down from its original unacceptable 1.5 - 2 seconds to just 1/4 second. That was a huge step in the right direction. Further sec delay reduction and final elimination was accomplished by going from factory mains at 140 down to 80 and correcting/refining the primary circuit a little more. The nickel plated 60s are fine as they are.

To put it another way, the factory Nikki is so tiny and asthmatic that any way to get additional air in was employed by the factory. Hence the giant air bleeds. But when you start increasing air flow through these things the way we all want them to be, you need to reduce the air bleeds quite a bit. Otherwise the Nikki will never perform at its best.

Yaw, Sterling, Dave *******, and the new guy who just posted pics of his hogged out 79 racing Nikki yesterday (that might be a Dave ******* build), all suffer from this giant air bleed syndrome. It makes the carbs only capable of running within a narrow window of ambient temps and RPM range. Hence the constant need to retune them for EVERY track altitude and EVERY weather condition. Which is VERY idiotic and wastes time! My carbs are the exact opposite approach where they run well across a very wide range, from vacuum and up into boost as far as I've taken them at 7 to 9 psi so far. There is a reason no Sterling, Yaw or ******* carb ever handled boost. It was all in the air bleeds the whole time. Ironically, a stock Nikki handles boost better than any of the big name carbs ever did, and Robert at Rotaryshack knew this, as did bad_83 and anyone else who has done a Nikki the way they did them for boost (with stock teeny 20mm venturis and stock giant air bleeds with only a minor sec jet increase?) which leads to only a minor sec opening hiccup, is all that was ever observed, problem-wise from their carbs when boosting, other than gutlessness at low RPM while in vacuum, of course. It was a carb that was like a light switch that went from too gutless to too powerful depending on throttle position and RPM and was not all that fun to drive, apparently. My carbs aren't like that. Big hogged out primaries are the key. And reduced air bleeds. Anyone can do this stuff. I hope others take the "plunge".

I hope I cleared up the "clear as mud" explanation a little bit.

t_g_farrell

iTrader: (1)

Thats interesting, I should measure my venturis. I have no bog on the secondaries of any kind.
I can mash it at any rpm basically and it rips. Like yours, doing it down low (

klabatzie

Thanks for the explanation.

There isn't much progress at the moment I'm figuring out what the best(cheapest) way is to getting my parts but it seems that I need multiple resellers so will cost a pretty penny on shipping.

I've made a rough piece of metal for the AP and wil make it fit on a mock up carb pictures ot that will come later

klabatzie

I'm going to bring the venturis to the machine shop Monday. I'm thinking of one set of 24 mm and a smaller set just in case wat how large can you make them without the 1700rpm dip?

And how far should the venturi be machined? Until the flat edge at the top and bottom or all the way to the maximum diameter?

And do the secondary have to be machined the same as the primary? Exept for the diameter enlargement?

wankel=awesome

24mm is perfect. My turbo nikki will be an 85 with 24/28.

Jeff20B

iTrader: (13)

You can leave the flat edge at the top alone. It allows easier venturi installation back into the carb. Also leave the bottom alone. You will see there is no advantage to making it sharp where is sits above the baseplate.

Yes, 24mm and 28mm.

klabatzie

Oké than that it will be 24 and 28.

Jeff20B

iTrader: (13)

And use the little hole as your landmark! Make it the narrowest point. It can be a little bit sharper than stock, but not pointy and not as rounded and lazy as stock.

klabatzie

I know you only said it a hundred times haha

It will be 24 at the vacuum hole and then be strait to the top and bottom

klabatzie

I'm ordering parts but can't find the secondary main jet. In your writing it says it has to be 145 but the jetsRus doesn't go any larger than 138 should i buy that and make it bigger?

Should I order some more sizes for the primary to fine tune it?

Jeff20B

iTrader: (13)

yes and yes

Get several sets around the sizes I told you to get for fine tuning. 112 to 122 should be your range.

I buy the 138s and drill them out. Drill to 140* first to see where your WOT AFR is.

*Note: You will discover the stamped sizes on the jets are actually very close to actual metric. For example, their 138 is actually 136 or 1.36mm. This goes for all of them in their full range from 108 to 138 (106 to 136).

Oh, and their 114 is not listed. I use a 112 drillbit to drill my own in that size.

klabatzie

can't seem to find the drillset with such small steps as you have.

This is the best I can find

http://www.biesheuvel.nl/spoeier-boren-set.html

Jeff20B

iTrader: (13)

They sell the 112:

Drill Sizes: .038" to .0785" - Drill Bits Unlimited.com

klabatzie

A little update from me because it is about time haha

Got the 120 no2 slow jets in so mounted them that was easy enough.

Looks like the Holley jets arrive on wendsday.

I've emailed two company's in Europe that probably can help me with the Hitachi main jets so that will be nice. One also has bigger sizes for the secondary mains.

Also I have made the bracket for the AP pump and mounted it on a spare Nikki for measuring. It will need some altering for when there are multiple gaskets but I will work that out later.

I can't seem to find the post about drilling out the AP pump nozzles can you tell me what size drill you used and what else I need to drill?

I also got a teaser photo from the metal shop

Jeff20B

iTrader: (13)

The accel pump bracket will need two bends in it, not just one. You'll figure it out.

The nozzles require 1.10mm drilled holes, along with the banjo bolt at the two holes. As for the bottom hole, I like to do 1.18mm.

Teaser looks good.

klabatzie

Got the venturi back today looks good to me. The do have some casting imperfections but that won't hurt I guess.

Also made the gaskets for the AP an i used 1mm gasket paper so maybe two will be enough to clear the housing and spring

Next step is to clean the carburetor and drill the holes from the AP.

Later this week I will get the wiretap to make the Holley jets fit the stock Nikki ones.

Then the outside modification like stripping the not needed stuff and making the simplefied choke

Some other thing that caught my eye was that there are different baseplates one has smaller secondary shafts with smaller screws in it haven't looked if they are exactly the same but since I already stripped them maybe a good idea to uhe the smaller one?

Jeff20B

iTrader: (13)

Whatever you do, please don't use holley dominator air bleeds as fuel jets. Yaw, Sterling and other tried it and they hurt cornering ability. The air bleeds lack a nice funnel inlet shape. Fuel can't flow in very well.

Otherwise, good progress.

Oh it is a good idea to maintain FB with FB. Don't swap in an SA baseplate. Oh and don't worry about the size of screws. Some people believe they hurt flow but that has not been my finding.

klabatzie

Got the two main jets in today but the one for the secondary looks not quite right to me. It doesn't have the nice conical inlet as the Hitachi ones

This one is from an kehin carburetor

Jeff20B

iTrader: (13)

The kehin looks like an air bleed and will not work correctly as a fuel jet.

klabatzie

Some progress today. Made the Holley air jets fit the stock jets, I made it M5 and it fits a bit loose but I can screw them pretty tight so it will work.

Bored out the AP nozzles and Banjo Bolt. You told me to drill the lower hole in the carburetor body but this hole already is a lot bigger so it won't be necessary or you must mean an other hole. Did I also read something about using Teflon tape on the bolt above the AP or is that just for the boost prepped nikki

Mounted the venturi and all the airjets and going to assemble the rest of the carburetor this week.

As I can't find a suitable secondary main jet I'm going to drill out an primary to 1.4mm as a starting point and will fine tune from there.

I'm looking into a wideband lambda sensor and seems that AEM and innovate are the best choice. I like the AEM best for looks but the Innovate has more options

Jeff20B

iTrader: (13)

Good job!

You don't drill anything in the main body. I'm not sure where you got that. Only drill the little jet in the bottom of your banjo bolt if there is a jet installed from the factory. If it is empty like 79, leave it alone.

Teflon tape is for boost prepping. ts usually still leaks but it's the best we can do right now other that resorting to RTV or some other sealant which is messy. The amount it leaks is very small.

Your plan for drilling the primary jets to 140 sounds sensible.

I like AEM.