Scribbles

iTrader: (1)

I've read a quite a few posts, done many searches, and have some good ideas on the issues re: my carb. But I would like to ask a question to see if there is a simple answer that I may have overlooked.

I am only able to start after pumping the gas pedala few times, and the rpm will raise to about 2000 rpm, and slowly drop down to about 1200 until it warms up where it either stalls, or sits around 800 ish. I have found that I am able to rev without any problem, as long as the rpm is above 1000. If it falls below that, and I attempt to press the pedal it will immediatly stall, otherwise if left on its own it will drop down to 0 and stall slightly slower.

I have read that this may be a vaccum leak, that the filters that fill the bowl my be dirty, or that there may be something wrong with the accelerator pump.

It just seems odd that everything appears to be fine as long as the rpm stays above 1000, or if at somewhat normal idle (750 - 800) it will die as soon as the gas is pressed.

Any insight to the problem would be greatly appreciated.
Thanks for the help in advance.

kgray

How cold is it up there? Use your choke to start it and let it warm up. Replace the fuel filter by the fuel pump and run a can of seafoam through the tank. Sounds like it may have a vacuum leak or be running a bit rich. After you complete all of that, you can adjust mixture and speed screws.

Scribbles

iTrader: (1)

It was a pleasent 23'C up here in Toronto today, and yes I start it with the choke till it warms up. But if I push the choke in too early as well it will stall. Not sure if that has anything to do with the situation, but I thought I should add it.

I will replace the filter, and possibly some new fuel, as I beleive it has been sitting for quite a while before I got my hands on it, the previous owner could not get it to start at all..

trochoid

iTrader: (6)

Check and see if the accelerator pump is squirting fuel out of the jets. almost sounds like the ap jets/ways are plugged or the ap diaphragm may be shot. If you're not getting a shot of fuel, it's time to go through the carb.

Online FSMs and carb manual are in the link in my sig line.
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meenuh

This sounds kind of like what my car does, only my car will start without pumping the gas pedal first. Are you pulling the choke out before you start it? When it's idling at around 800 and you step on the pedal, are you stepping fast or slow? In my car, I can let it idle around 750, without the choke being pulled, but if I step on the gas pedal too quickly while the engine is still cold, the engine falls on it's face and stalls out. But if I slowly step on the pedal, I can get the revs up as high as I want, and THEN I pull out the choke, first all the way, and then after a second, push it back in so it's idling right between 1500 and 2000 RPM. At that point I can drive it, and once the engine warms up, there are no problems at lower RPM.

It sounds like you definitely might have to adjust your accelerator pump, as a 1/4 turn on mine made the car drive 300% better. . .(I was having problems after a carb rebuild), or possibly even your idle mixture.

It's not really odd that the problem occurs once the gas is pressed, as that's when you're manually changing the fuel and air that is feeding the engine, and if the mixtures are wrong, the car will stall.

Sorry for the tome.

vipernicus42

iTrader: (4)

650-900ish is where the idle circuit on the carb is working, anything above that and you're out of the idle circuit and into the off-idle and main primary circuits. (when I say circuit I'm talking about the path gas flows through the carb)

From what you're telling me, when your carb is idling properly (like 800ish) the idle circuit functions normally, but when you open the throttle plates to transition into the main system, it chokes out and dies.

If your car is already in the main system (1000+) then opening the butterflies doens't require a transition, it just continues on th emain circuit, so your car won't stall out.

What makes the transition smooth from what I can understand is the accelerator pump. I have the same thing going on with a carb I'm using right now. Accelerator pump diaphragm is cracked and so if my car goes under 1000, pressing the gas just stalls it out since it gets too much air (from the throttle plates opening) and not enough gas (no accel pump squirt).

Does that make some sense?

You can check your accelerator pump rather easily. Take off your air cleaner assembly, and look down the primary (smaller) barrels of the carb. Reach your hand down and work the linkage with your hand (or have a friend press the gas pedal) and watch closely. You should see gas squirt from little nozzles in the middle. If no gas comes out (and if you have a hard time doing cold-starts), then your accel pump has a problem. If you can cold start it without physically pouring gas from a gas can (like I have to right now) then chances are your accel pump either just needs an adjustment, or isn't as badly cracked as mine is.

The diaphragm (if you need one) can be found in a carburetor rebuild kit, the best brand to use being "Standard" or "Hygrade" (same parent company). CarQuest I believe can order them, I get them through a local supplier called "Côté Pièces D'autos". Canadian Tire *does not* have good quality rebuild kits, don't get yours from there. And when they ask you for the serial number of the carb, it doesn't have one, and they'll give you crap saying they can't find it, but just insist that you need "A rebuild kit for a 4 barrel Nikki carb for an Rx7, they don't have a serial number, and there was only ONE carb on the first gen Rx7, so you should be able to find it!"

As for warm-up, don't push your choke in early if your automatic choke system is working. There are only two real parts to it, the temp sensor and the magnet inside the choke **** assembly. If your choke automatically retracts on its own when the car reaches operating temp, let it. Otherwise, wait until you car is well into operating temp range before pushing your choke in.

Jon

vipernicus42

iTrader: (4)

I forgot to add: the link in trochoid's sig to the page with the manuals on it has a really good "Carburetor Training Manual" that gives awesome insight into how the carb works at different stages. Between that manual and the other carb manual on that page you can find all the info you ever wanted about your carburetor, including step-by-step instructions on how to rebuild it.

Jon

Scribbles

iTrader: (1)

I took apart the accel pump, and the diaphram is in very good condition, and functions well. I've tripple checked for leaks with my stethoscope and found nothing.
For the following please forgive my lack of correct terminology, as I'm an EFI type of person and this is my first carb.

On close inspection of the primaries, I've noticed that the formost, (closest to the nose of the car) brass tube that eminates from the driver side of the carb towards the center aluminum ring, is touching, or has impacted the aluminum center ring, and that the ring does not seem to be as well ceneterd as the rear one.
again please forgive my complete lack of correct terminlogy.

Might this be a cause of the problem ?

As well while running it today, I could not go below 1000 rpm at all without stalling.

This is rather troubling. I do have a rebuild kit, as well as a spare scrap nikki to learn on before attempting the operation on the semi-working one. I'd prefer not to have to take it to the point of a complete rebuild though.

thanks again

trochoid

iTrader: (6)

Not quite following your description of parts. Download the carb manual from the link in my sig line so you can desribe the parts with their correct terms. It might help if you post a pic too of the item in question.

If you've never rebuilt a Nikki, having a complete spare carb is often much better than all the diagrams in the manuals. As old as these carbs are, most of them are in need of a rebuild, a good cleaning at the least.

vipernicus42

iTrader: (4)

Too bad you weren't closer to Ottawa, I'd give you a hand with that rebuild. Are you going to the meet at RPM Performance on the 14th of July? (See the Canadian Section, there's a thread there that Joe made about a meet at his shop). I might be able to give you a bit of a hand there since I'll be in the area.

Definitely grab a good quality pic of your primaries and post it, I'd like to see what you're talking about.

Jon

XLR8

iTrader: (52)

I would recommend a rebuild. My first time went smoothly. Follow the manual, get a big table to lay everything out, and clean everything thoroughly. Blast every jet and little passage with carb cleaner.

Good luck

Scribbles

iTrader: (1)

Ok, so I've run about half a can of carb cleaner through it, and there has been some improvments.

Howerver if left on its own, it will not idle, and will stall out, but it it drop below 1000rpm I am able to pump the pedal and revive it so to speak back above 1000. I'm thinking the idle fuel mix is off ?
How might I go about adjusting it correctly ?
There doesn't seem to be anything else wrong with it.

vipernicus42

iTrader: (4)

To me it doesn't sound like idle fuel mix, more like a vacuum leak...

But idle fuel mix is pretty easy. There's a screw in the middle of the base of the carb on the driver's side. With the car off screw that in until it's *LIGHTLY* seated. It's a needle inside, so you don't want to crank it in there, you'll seriously mess up the needle and that's never good. From "lightly" seated, back out 3.5 turns.

That should get the mix in the right range to idle, IF that's your problem. There's also an "idle speed" screw which is much harder to see/get at unless you have your rat's nest removed. It's to the right and upwards of the other screw. It basically changes where the throttle comes back to rest. If you turn it clockwise, it will raise the "base" of where your throttle comes back to rest, thus raising the idle.

If having the mix screw 3.5 turns out and turning the speed screw in a notch or two doesn't idle for you, then that's not your problem.

If you do get idling (around 850rpm) you'll want to then turn that idle mix screw out until it starts to stutter, then go back in half a turn. That's the proper setting from what I remember.

Do you still have your rat's nest? Can you take a pic of that area?

Jon

Scribbles

iTrader: (1)

It is 100% oem factory nest of rattitude.

I am picking up a holley 4 barrel later in the week. I think that with the tunability and simplicity of it, I should be in a better situation.

I looked at the RB manifold, but I don't think I can justify the price at the moment, I have also looked into a simple adapter plate, and am unable to find one as my searches have sent me on "ebay" so I may have to build one myself, I've seen many people through my seaches on this board that have completed one, and I am wondering if I should join both primeries/secondaries together respectivly, or just leave it as 4 holes.. I have heard mixed results from both.

thanks