Tuning a stripped Nikki?
 

So I figured since so many folks recommend removing the rat's nest and cleaning up the carb, I decided to find out for myself. I took out the rat's nest according to this nicely done tutorial:

http://maz_tutorials.ten15.net/Tutorial_1.pdf

I'm pretty sure I got everything hooked up right but I have pictures if there are any questions on that.

Then I rebuilt a stock Nikki and stripped it down according to:

https://www.rx7club.com/1st-gen-archive-71/intake-carb-rebuild-how-strip-nikki-down-648376/

Again I was pretty meticulous and I think I got everything right, but I have photos if that would help.

The problem is, while the car has more spunk and is kind of fun to drive, especially when you've got the rpms up above 3000, I am also having some problems:

1. I can't get a smooth idle below around 2000 rpms. Whenever I adjust it down to about 1500, it dies right away. Even if I tune it a little higher (around 2000) it will only idle for 10 or 20 seconds, then it dies out. It's kind of like having a serious vacuum leak, but I've checked and rechecked and can't fine a leak.

2. I'm getting quite a bit of back firing when I let off the gas pedel at speed. I know some folks like this "pop-pop" sound, but I'd just as soon have some peace and quiet and not draw attention.

3. The gas mileage has slipped quite a bit from what I was getting with the stock Nikki, down from 23-24 mpg to about 16 mpg.

So I'm wondering if I've got something wrong or if these "problems" are just normal when you remove all the emissions and carb "accessories".

Any help would be much appreciated, if I can't get it to run better it looks like I'll be reinstalling a stock Nikki and rat's nest this weekend.

Thanks
Ray

I don't know much about carbs yet Ray, but here is my idiot's version for you. :D Between the poor idle, and crappy fuel economy I'd say you are running very rich. Plus the backfiring makes me think this as well. I'm guessing that when you idle down there is so much fuel, the lack of air to mix with it kills the car. Your mixture sounds like it's so rich that its just fuel and practically no air. As far as finding out what is causing this, hopefully one of the carb brothers will show up and help out.

Rx7Carl?! Sterling!!!??? :D Where are you guys?

ray, my advise to you coming from another who DDs a nikki. go undo what you did about stripping down the carb. this seems ratehr odd for you to be doing anyways. we all know your reputation;) id install all the stuff you took of the carb. i dont really see why anyone who DDs their car would want to do that anyways. esspecially the mechanical secondarys.

keep the rats nest off. if im not mistaken you removed your AC recently, correct? i dont really remember what all you still have to have hooked up to the nipples below the carb. i suggest keeping the vacuum advance. i also suggest plugging it into the nipple fartheest to the left(closest to front of the car). i had mine on a different nipple and when i switched it here noticed good results.

mine backfires if i full throttle for a little bit then let off, but mine is due to exhaust leaks.

try this and see what you think. dont throw the rats nest back on just yet.

The high idle and backfiring are being caused by a large vacuum leak.

also whenb you let off the gas you can get the backfiring from A: running rich or B: a removed or malfunctioning shutter valve. are you still using your coasting valve or did you remove it?

He removed the rats nest, that means the shutter valve would be inoperative because it is controlled thru the emission system.

That's correct Doc, the shutter valve is blocked off and I'm sure this is contributing to the backfiring. Also I wonder if removing the anti afterburner valves might have something to do with it.

Also I removed the AC, PS, cruise control, hot start assist and vacuum secondaries (they are wired for mechanical), but I don't think these would be a factor.

I wish I could blame it on a vacuum leak, but I've been over the whole system several times and I'm sure I have every hole blocked, so I'm guessing that this is just what life is like with a stripped Nikki and the rat's removed.

The engine bay looks terrific right now, but all those emission controls and clutter are looking pretty good too, in retrospect. Looks like I might be putting them back it.

I would like to get a second opinion from Rx7Carl or Sterling, since they seem to have had better luck, or anyone else that's had good success with this approach.

But if I can't get it worked out by tomorrow morning, in goes the stock Nikki and rat's nest.

Anybody interested in a freshly rebuilt stripped down Nikki?

And thanks for the suggestions folks, keep them coming!

Ray

Here're some pictures of the situation:

http://memimage.cardomain.net/member...7_225_full.jpg

http://memimage.cardomain.net/member...7_226_full.jpg

http://memimage.cardomain.net/member...7_227_full.jpg

http://memimage.cardomain.net/member...7_228_full.jpg

.

I'll give it a try aws after I give that stripped Nikki one last go around today, if it doesn't improve out goes the stripped Nikki, in goes a stock one.

One nice thing about ripping out the rat's nest is I've learned more about what all that stuff does, so I can eliminate things I don't really need, if any. If I put the nest back in I'm going to paint all those manifold tubes black, that should look pretty cool.

hi ray i have done what u have several time's now and you should be able to idel at 800rpm no sweat and get at least 20mpg

when i stripped my nikki i alway's jb welded the alt compensator holes and the vaccum secondary holes also i have found if you use the gaskets provided by the rebuild kit for between the carb and spacer plate and between the spacer plate and manifold it allways seemed to cause leaks

are your float levels correct maybe this could affect it's running ability
are you positive you cleaned out the idel circuit with compressed air cause bits of shit will affect it to:)

just my 10cents mate
have a good one

"hi ray i have done what u have several time's now and you should be able to idel at 800rpm no sweat and get at least 20mpg"

This is what I was hoping to hear, now I know it is possible, thanks blwfly!

I JB welded the altitude compensator holes, you can see the job in this photo:

http://memimage.cardomain.net/member...7_227_full.jpg

I put rubber caps on the secondary holes, they are in this picture, right? I'm not sure exactly which ones they are without looking at the diagrams:

http://memimage.cardomain.net/member...7_226_full.jpg

Here's a close up that might be a little more clear:

http://memimage.cardomain.net/member...7_230_full.jpg

The float levels are correct, the fuel level in both view ports is halfway up the glass.

I used solvent and compressed air to clean out and blow out ALL circuits at least twice and checked each one individually for good air flow with the compressor, so I don't think there are any problems there.

Thanks, an idle at 800 rpm and 20+ mpg would do me just fine!

You've gotta love those diagrams. So are these the secondary holes that blwfly says needed to be sealed with JB weld?

http://memimage.cardomain.net/member...7_231_full.jpg

I was looking at these when I did the rebuild and thought they were just screws mounts for the secondary diaphragm assembly. Also I checked the holes when the car was running but detect any vacuum leaks.

But with a closer look I see the second hole down is a port. Does this need to be sealed and could that be causing some of the symptoms?

Thanks
Ray

Yep.

Thanks Jeff, I'm mixing the JB now.

Here's the secondary ports sealed:

http://memimage.cardomain.net/member...7_234_full.jpg

And I touched up the altitude compensator ports while I was at it:

http://memimage.cardomain.net/member...7_233_full.jpg

So I'll wait for this stuff to dry, hook it up tomorrow and see what happens.

In case it doesn't work, I also fixed up the rat's nest:

http://memimage.cardomain.net/member...7_235_full.jpg

Ray, you stil have the shutter/coasting valve in place. I remove them entirely, then tap the hole left by the shaft and JB Weld an allen plug or bolt in the hole. If you've removed the butterfly from the valve, you can get away with leaving it in.

I know you can get more than 20 mpg. I just got 20.5 coming back from the Iowa meet with the 1/2 bp and the DCDs. My mileage is down a bit, it it's very close to the correct tune.

hehe there usally is allways somthing ya missed:)

yeah and do what scott said cause that will have a major affect if the butterfly is still there itl be blocking the second rotors primary maybe why you cant get a low idel and your having to use you secondarys to keep the car goin

Thanks for maintaining this thread Ray. I'm sure that I'm going to be looking back at all of this in a couple of weeks when I start my Nikki rebuild. :D Please let us know how things turn out once you JB Welded those ports.

BTW: Did you follow those diagrams in the archive that I put together? The ones where everything is all red and green? I'm interested to know if this set of plans will actually work when building the carb. Please let me know if you followed the plans, with Rx7Carl's recommendations of course. :)

Well I've still got the problem, won't idle under 1500 rpm. Sealing the secondary ports and tying that shutter valve butterfly open didn't make much difference, unfortunately. I might have some timing issues, I'm looking into this.

Trochoid, I just wired the butterfly open with some stainless steel wire so it was in the vertical position, since I might need to be putting the rat's nest back in. I tried to unscrew and remove the butterfly, but those little phillip screws won't back off easily, probably because the engineers didn't want small screws and butterflies dropping into the intake manifold.

Mr. Ham, yes I used your annotated diagrams throughout the procedure, they were very helpful for identifying parts and issues. Then I crossed that with Carl and Dennis's de-ratting tutorial. Other than JB'ing the secondary ports, I think I had everything right the first time.

So I don't know what to think about the problem with the idle, could be the stripped Nikki or could be the guy that stripped the Nikki.

But it's an interesting problem, I think I'll kick it around another day or two before I put the rat's nest back on.

Again, thanks folks, especially Trochoid, for the info.

Ray

I hated the mech secondaries when I did them. Sure, the power was there, but I couldnt stand the hesitation and loss of gas alll the time. Plus, when I wired them and drove it, I parked later and looked at the car and saw some residue (gas?) on the side that wasnt there before.

jsut my 2 :)

So it turns out the timing is according to the book, pin straight up and the dizzy pointing to L1, the way I had it all along.

This will start the engine, but I can't get it to idle unless I advance the timing by setting the pin 5-10 degrees clockwise relative to the first notch. That's the best idle I can get and it still needs to be 1500 rpms or more to keep running, if I reduce the idle speed below that it dies out. Also, if I set the pin toward the first timing mark, it dies out.

It's this weird timing behavior that made me think the timing must not be right, but I've checked, rechecked and rechecked. Then read some FSM's and tutorials and rechecked again, and it looks like the timing was correct all along.

So it must be the stipped Nikki.

Other than the idle problem that the engine seems to run strong, screaming in fact. It revs like it's never revved before. But all for nothing if I can't sit in traffic and not cause a scene.

What about those cut off valves, the ones wired to large brass fittings that are sticking out on each side of the carb? These operate a pair of cut off pins and they have weird names and functions I don't fully understand.

Using the best info I could get from Carl's tutorial, I just unplugged this one:

http://memimage.cardomain.net/member...7_234_full.jpg

And I took the spring out of this one, then just reinstalled it (hard to see in the photo, but it's the one with the brass fitting in the upper center):

http://memimage.cardomain.net/member...7_226_full.jpg

And here is one more photo showing the plumbing more clearly. The vacuum advance is unhooked and blocked off because I was setting the timing. It's tube is lying right underneath the dizzy connections and it hooks into the second port at the base of the carb which you can see in the photo above:

http://memimage.cardomain.net/member...7_240_full.jpg

Could the cut off valves be cutting off an idle circuit or something and causing the idle problem? If anyone has any ideas or info on whether this could cause the idle problem I'd sure be grateful.

Stu, the jury is still out on the wired secondaries, I want to see what they are like once I get this tuning problem fixed. But it's a slippery slope, once you put the vacuum secondaries back in, then reactivate the choke, shutter valve, etc, you might as well use a stock Nikki and rat's nest.

A rotorhead visited yesterday for parts, had an exceptional 85 GSL with fresh paint that was meticulously maintained and virtually all stock, cats installed, all the power accessories and yes, it was an automatic. Beautiful car and it ran perfectly. The driver said it even had balls.

So anyway, I'll give this experiment a few more days, maybe I'll start randomly messing with those shut off valves and see if that helps.

Carl, where are you??!!

Ray

That is for your idle compensator. You should have 12 volt ignition running to it. If you are shure that you have everything hooked right, try this before you go back to the rast nest. Disconnect every vacuum line running to the carb base plate, including your vacuum lines going to the dizzy. Set the leading timing to 8* degrees advanced. This will move your trailing to 12* retarted, providing you had the trailing at 20 before you advance the leading. Your mechanical advance will still work.

I had a similar problem a while back but never really figured out what exactly went wrong (maybe a throttle/choke shaft seal)... Just for shits and giggles, try spraying a little carb cleaner around the back of the carb, around the float window and throttle/choke shafts and see if your rpms change if you haven't already sprayed there.

I forgat to add, if you want a FB intake with the shutter valve removed, block off plates installed, and cleaned to pristine condition, I can hook you up.