I just recently picked up a 79 era Sterling Nikki used, but appears to be very clean and all intact. My old stock Nikki went kaput so I needed a new carb. The old one was developing a clog and became hard to start cold or warm without backfiring and sputtering. Now I installed a new carb and I can't get the thing to hold idle below 2000 RPM. It idles like a pereferal port. brap brap brap. I just need a few pointers to help me diagnose this thing. I just want it back on the road! Here's a couple questions I have...

Can I use this 79 cab on an 84 maifold? Should I be using the 79 or the 84 spacer? I have a spare 79 manifold.

Could my return line be clogged? Whatever the problem is, it's causing the float bowls to over fill and spray too much fuel into the barrels. Evern when I install my FPR the float windows are still a 1/4 inch above the half line. Whats gong on here?

Can I just remove the gas cap to vent pressure and blow an air hose through the return line to clean it out without damaging some sort of regulator or something in the tank?

Should I cap or uncap the brass colored medium sized vauum barb next to the mixture screws? Cap or uncap the small vac line on the top of he carb?

Thanks for all the help!

 

I think the medium size vac port is your fuel vent. that can't be capped. I think you may need to give some more info. Such as are you removing or is you rats nest removed? does it miss. if the brap brap sounds like a miss it may be your shutter valve. I don't have one anymore. but there is a proper way to cap that. I think the big vac line stays uncapped, and the small one gets a cap but correct me if I'm wrong. I know if both are capped it wont idle for crap. other than that look for vac leaks. what fuel pressure are you running? Is it an older carb, or still in good condition?

 

Get your butt over to Sterling's site and he'll help you figure it out. Best customer support for non-customers that you will find other than over at Respeed.

www.sterlingmetalworks.com/bymc

Good luck...


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couple ideas

1. the peripheral port idles really smooth, you're thinking of a bridge

2. if i was using a 79 carb, and a 79 motor, id use the 79 intake and 79 spacer

checking the return line is pretty simple, blow into it. use the compressor and be gentle, you're just seeing if it works

 

I don't think a Sterling modified carb has Brass barb by the mixture screw.

If you can't get the motor to slow below 2k - something is holding the throttle (Primary or Secondary) open.

If the car wont run when you lower the idle speed you have a vacuum leak.

 

It's not a vacuum leak. It's just getting too much fuel.

I unhooked the return line and let it dribble into a bucket while running the engine and it didn't help. I ran my old 79 carb that came on the car stock with an 83 manifold and it ran just fine until I found the 83 carb which was newer and un modified.

 

Do you have a regulator? if not then the pump will just be forcing as much fuel as it wants into the carb.

 

Well I figured out the problem...

I put the stock floats and all the air bleeds and jets into the Sterling and it runs great. The sight window sits right at 1/2 full. It doesn't bog. Idles at 8-900 or so. I can really tell a difference in power and sound. It starts great warm, lets just see how it starts up cold tomorrow...

BTW Nikkis don't need regulators.

So yeah I'm pretty happy... I got my baby running better than ever after sitting for 2 weeks! I just picked up a Miata project, AND I have a week of vacation from work all next week.

 

Your right. A stock Nikki running a stock pump that can barely flow the fuel a stock Nikki needs doesn't need a regulator. However your STERLING Nikki is going to need a new pump to flow enough fuel for the top end and a regulator to properly tune it. Otherwise it will not perform at it's full potential. Good luck with it.

 

What kind of pressure am I looking for? 4-5 PSI? It seems to run great though. I may break down for a Hlley red or something. What's the deal with Carters? Do they flow just a tad more than factory?

 

When I got my Sterling, I was still running the stock pump. It ran great, and was a quite a bit more powerful than my old carb.

After I installed the Carter pump and Holley reg, the performance was even better. I played around with all different pressure settings, and ended up running between 3.75 - 4.25 psi.

This spring I finally got around to doing a little tuning on it, thanks to Orion's help, and using larger primary jets found a shitload more power all across the midrange and the top end.

Tuning the Sterling to fit your car is all part of the fun. Sure it will run on the stock pump, but like Orion just said (and I've been saying for years) the stock pump is barely even adequate to run the stock Nikki carb. And don't get me started on the filters either (I run two filters in parallel so each only has to do half the work).

I would still recommend that you spend some time over at Sterling's site. Otherwise it's like buying a new TV and never learning how to change the channels on it.

 

Wouldn't two restrictive filters just double the restriction? I thought that the Nikki was internally regulated at like 3.75 anyway. I know the bigger pump would just flow more with less work than the stock pump, but you can't physically get any more fuel inside the Nikki. Or am I missing something?

 

The idea behind two filters in parallel is that once they are "half" clogged, they are still flowing as much as one brand new filter. Since the stock filters are so prone to clogging it just makes sense and extends the intervals between filter changes. I don't know whether or not there is an internal regulator.

 

Just because a Nikki is internally restricted at 3.75 psi (not sure if it is) doesn't mean that a Sterling is as well. But it also has to do with fuel pressure needs, which the stock pump won't be able to meet. You should really go to Sterling's forum and ask these questions there, so you can get the answers straight from the horses mouth, so to speak.

My filters are plumbed in parallel, not in series. Parallel means you've got a gas line from the tank, it splits into two lines (each line having a filter), then rejoins into one line before the pump. That way, as long as each filter is flowing at least at 50% capacity, I've still got 100% flow in the system. Each filter only has to work half as hard that way. There are some pictures and a whole lot of information on filters in this thread: https://www.rx7club.com/1st-generation-specific-1979-1985-18/dual-fuel-filter-mod-528445/

If I had plumbed them in series (fuel line, filter, filter, pump) then you would be correct. You'd get double the filtering but twice the restriction.

 

I guess I should mention this. Just so your clear, the Sterling Nikki is not a Nikki. They are very different once Sterling finishes with them and do not behave the same or have the same demands. You need to forget that this was once a stocker. It is a serious performance carb and needs to be treated as such.

 

Ok this makes more sense to me. What sort of fittings are you using to split the lines?

 

Check the link I posted, I believe I had pictures in there showing part numbers etc. All parts either came from Autozone or Napa.

 

There is no interior pressure regulating mechanism in the Nikki carb, modified or no. Line pressure appears directly at the needle orifices.

 

I played around with more settings and jetting. BIG improvement. It turns out the Sterling jets were just clogged up. One of which was so badly clogged I could not blow air through it with my mouth (gasoline tastes awesome!!) I just hooked a can of carb cleaner up to them and they cleaned right out. Has a little bit more pull and feels smoother and more steady when the mech secondaries are tapped open.

 

Incorrect.

 

Please elaborate: what pressure regulation occurs in the Nikki carb prior to the needle bores?

I don't have your level of experience with them, (who does?!?) but every one I've been in, the fuel inlet spider drops straight thru to the needle bores, in line with the return line.

Whatever presure is measurable at the fuel line is the same pressure that exerts on the needles. Line pressure = needle inlet pressure.

If not, I no unnastan.

 

The fuel pressure is regulated by as primative means as you might imagine; A simple orifice of specific size drilled into the inlet line internally defines the rate of fuel going through the return line, thus regulating the pressure. This works in conjunction with the 5-5.5 psi, small volume stock pump, as the orifice is calibrated to give between 3.75 & 4.25 psi of regulation depending upon the year of the carb.
Though (I believe) the pumps all pushed the same (certainly could be wrong), I have found four sizes of orifice in Nikkis from years 76-85.

Slap a big volume/pressure pump in, and that orifice will change characteristics. It can only flow out so much into the return line. That's why a regulator is necessary after the Nikki is modded. -It needs higher volume than the oem pump, but not higher pressure. It seems to like 1.75 - 2.25 psi the best, as this supplies the necessary fuel without overwhelming the emulsion system.

 

Ahhh... back-pressure limitation based on expected flow rate. Like using a resistor to develop voltage drop in an electrical circuit; a voltage divider.

It only works as "regulation" though, if the input pressure is constant & fixed to a specific value...

I could argue that it's not *really* pressure regulation since it's output is directly proportional to input, but that would just be splitting hairs. It quacks like a duck in the right circumstance, so it's a duck, all right.

I learned something new; thanks!

 

If were just talking street driving though... It's not a big issue to run the stock pump correct?

Also I'm curious...

How is redline determined? Is it the maximum amount of stress the engine can take? Or is it the point when the engine stops making power or cannot turn any faster? I'm wondering if my redline is the same as stock with my setup or if I can take it a little further? I notice that tuners run their engines higher on a dyno after installing a bigger carb and better ignition. I usually take mine to 7k on a spirited run.

This is my setup

79 stock port motor/transmission/chasis (117,xxx original miles)
79 Sterling/stock pump
RB Nikki intake with foam filter
2gdfis with BUR7EQP leading and BR8?? stock 12a plugs
1000 mile old NGK wires
emissions removed
heat wrapped header, RB mini silencer, RB PP muffler
Excedy clutch
OMP no mix
All fluids changed regularly

I realize the larger volume pump would help at top end, but this setup really seems to kick *** already. What are your opinions on Carter pumps?

 

Both Kentetsu and I are running Carter 7LB pumps. You can find his very well done installation write-up here - https://www.rx7club.com/showthread.p...p+installation

They are noisy, but get the job done. Even for street driving your stock pump is going to hurt top end performance. You may not think so yet, but one day your going to get the itch to see what your car can really do, be it on a drag strip, road course or cone lined parking lot. That is where it's really going to show up, and you'll be kicking yourself for not putting a better pump on sooner.

Redline is the manufacturers bean counters trying to stave off warranty claims. Most engines can be spun a little higher than that. I regularly take mine to 8K rpm, although the worn out oil control rings don't like that much. I generally will burn about a litre of oil in a single autocross due to high sustained revs. Your actual redline, or shift point will be right before you feel power drop off. It is noticeable, the car just seems to stop pulling as hard. For me thats near 7.5K rpm, but if your engine is stronger or more worn out than mine your number will be different. After a few hard pulls you should be able to figure out where you should be shifting.

By heat wrapped header are you talking about a Racing Beat header or just the stock manifold? And you mean your running the stock OMP, not premixing, correct? I believe the 79 intake manifolds are said to flow better, hopefully someone will chime in to either support or deny that claim. If so you should definitely put that one on, since the next restriction after the exhaust and carb is the intake manifold. They flow less than even what the engine needs, which is quite certainly hurting performance on stockport cars, and more so on ported engines.