Alright guys, I'll get right down to business. Got an '84 GS a few months back and am trying to get it going FAST. Bought all of the necessary equipment and cracked the 12A open for a bridgeport. Everything went without a hitch, I bridged the intakes and streeted the exhaust while I was at it. It actually looked pretty smooth when I was done. Anyways, I sealed it up with all new seals front to back, and slapped in a solid base unsprung cutch just because I could. So I got it back together and COULD NOT get it running. Turned out that my timing was about 90 degrees leading, so I pulled the distributor and got it lined up perfectly, even the lagging was doing perfect. Then I got it cranked, and couldn't get an idle. I played with the two Nikki screws, and ended up with the idler screw all the way tight and the A/F screw almost totally tight. My dilemma: The '7 runs like a piece now. It can barely make it up hills and has incredibly pathetic power. Throttle response is good, and it idles at about 2K, but besides that its a junker now.

TL;DR- Bridged the engine, running the following setup:
-Leading timing spot on
-Lagging timing spot on
-Idler screw totally tightened
-F/A screw almost totally tightened

But it still runs like crap. Please help, I've invested months and alot of $$ into this thing and really want to get it running right. Any help would be greatly appreciated.

 

That Nikki will need mods, a new air bleed arrangement, and probably even a ported intake to run correctly

 

Could you be more specific? What kinds of mods are we talking about here? all the posts I've seen are for general Nikki performance, not coping with a bridgeport. and ported intake? Isn't that what a bridgeport does? I'm fairly new to this so I may be mistaken. Thanks

 

wankel=awesome touched on some of these issues already, but...

1) your nomenclature is odd making it hard to understand you
2) your Nikki needs mods to allow extra air through the venturis and less air through the air bleeds
3) your intake manifold needs some attention
4) your ignition needs to be converted to direct fire

All of this can be searched on the forum.

 

Take Nikki off, throw in trash can, put Webber 48 IDA on, done

 

Jeff I think you're right about the direct fire, and also the manifold, but converting to direct sounds like alot of work and minimal gain. Wouldn't it be better just to adjust the dizzy to lead a little? What do you mean about the Nikki venturis? Is this the same as "boost-prepping"? Thanks for the help!

 

Also Ultimate, I've been considering the swap and heard that Holley's aren't worth my time, but I'm in love with the Mazda air cleaner (I know, I know) and would like to keep it if possible. Are there any other carbs that would let me do this? Thanks!

 

I wonder if I should do a bridgeport with a Nikki.

 

you have the perfect intake manifold for one already, in my opinion. I know its been said that bridgeys dont like plenums, but I think your ported out intake with the open spacer would be perfect for the bridgeport top end.

And theres no way it wont run well down low, its still a 4 bbl, with relatively small venturis. I want to try it really bad, but im having a pretty hard time sourcing parts, lol

 

Direct fire actually is sort of a big deal. I just made a thread in the technical section about how different it made a particular carb run..

 

The nikki IS small for a bridgeport, but thats only because of the intake manifold design. To meet the airflow demands, the non-crossflowing design of the intake manifold has to be changed.

And thats only because the nikki isnt a big carb. But even small carbs can support as much airflow as a large carb, in this case.

The 48 IDA is a 392 cfm throat per rotor, and the nikki is around 190-200 cfm per rotor when modified. Open the area under the carb up, and join the channels, and suddenly both rotors can access the entire 390-450 cfm carb.

Fuel signal and power curve characteristics should remain comparable between both setups, contrary to popular belief,

 

Nikki ran fine on my j-port (extended bridge). 13b, standard Rx5 nikki. Even had it idling at under 1000 rpm.. Sounds like you might have a blockage in the carb.

Ran out of legs early but was fine under 8k

Does it pop or backfire.. Out of the carb or exhaust, or is it just dead..

 

I always remember setting timing by ear and road test rather than by light..

 

48 ida for the kill. No need to re-invent a wheel

 

Aight boys, I just got out of class and am reading the comments. SO:
I guess I should add, I J-bridged my 12 (I mean this baby is OPEN), so she is getting all she can on the engine side. I think you guys are right, its definitely something up with the Nikki. Wankel, you said that I should take the manifold off and do some porting to it as well? I'm not familiar with this concept but it makes sense so I might end up trying that. If it is indeed the air flow problem (Or lack thereof), Then the only options I'm seeing are:
1. Port the crap out of the intake
2. Rebuild Nikki???
3. Remove Nikki and replace with ______ far-superior carb.

What the heck is boost-prepping good for? That sticky on the front page makes no sense, it just sounds like removing as many things as possible while still trying to keep the Nikki functioning. As of right now porting the intake is sounding like the best idea to me, because I would like to avoid re-building the Nikki until I have to. Also, I don't actually know if I've adjusted the two idle screws appropriately, because I was just messing around then. Any advice from a bridgeport owner on the best setup for those two screws? Thanks y'all.

 

Um, don't rebuild the Nikki. That is to say it will be ruined with a rebuild kit if you swap out some of the OEM parts with the poor quality aftermarket parts. You will need to research and study the info on this forum to learn more about the dos and don'ts.

I won't say the weber is a superior carb. It is a different carb, meant for different purposes. But for a rotary, the Nikki could be considered superior if you go by a certain definition. However sometimes a weber can work for those individuals who have experience with them and can't get a Nikki to do what they want.

I happen to know the Nikki really well and I can get it to do what I want. So if I do a BP, I'll use a Nikki on it.

It sounds like you don't own a wideband. Get one. It will tell you what the screws do.

I don't even know what year your carb is. You say two idle screws? Some carbs had three screws while later ones had two.

 

I run a Holley 650 on a supercharged Bridgeport. Happy as a clam.

 

It was a stock '84 RX-7 GS so its running whatever Nikki came on a stock '84 GS, pretty sure there are only two different Nikki models right? And wideband, noted. I would like to keep the Nikki on it if possible. When I say "rebuild", I'm using the term loosely. All I mean is getting the appropriate gaskets/seals to put it back together properly. I wouldn't swap any components for aftermarket unless they were broken/non-functional. Still sounding like poor airflow through the Nikki is the major problem, so I'm going to investigate exactly what porting the intake means.

 

I have experience with both, Rx2/3 carbs and weber 48/51 IDA, and have built and tune street port and bridge port; currently buiding a bridge-semi pport. For the amount of work that the nikki require and, no guarantee that it will work right on a bridge, do yourself a favor a get a IDA period.

There will be a long debate on what will work best but...

 

Here is one way to hog out your intake manifold.


This, according to wankel=awesome, along with a properly hogged out Nikki, should be enough to allow your bridge to breath properly.

I intend to find out at some point. I still have the manifold, the spacer and the hogged out Nikki that came on it. I will redo the air bleeds so they are up to my standards and try this setup on a bridge at some point. I'm thinking full bridge as I have not done one of those yet. I've only done a half bridge so far. Gonna need carbon apex seals I'd think. I still have some research to do.

 

Thanks for the pic Jeff, it cleared up alot of questions. So I'm going to get set up to rip the intake open and bridge that baby out. A quick question, I'm looking for both gaskets on amazon (So that I can get them here by this weekend) I've found the engine side here:

But I can't find the carb side by itself.I'm thinking of buying this kit:

Just to use the carb gasket. Will this do it? Its a total of like $30 so its no big deal. Thanks guys.

 

You may need a set of o-rings for your rotor housings on the coolant ports. Maybe. You should have tapped in a set of 20mm freeze plugs and confirmed they don't leak by now. You also need to get some kind of plastic putty for the ACV port and fill it in. I have used quicksteel for 10 years now but recently went to go buy some and couldn't find it. But I suppose any two part putty stuff like that could work.

The intake manifold gasket looks ok.

As for the carb kit, the only parts you can use from it are the accel pump (to be used in the accel pump mod I mention on the forum in my Nikki threads) and the... um. Well that top gasket is for an old school carb so won't work right on your later carb. The baseplate gasket, where it fits between the main body and baseplate, is not usable due to its thinness other than as a template to trace out onto thicker paper, and then you only need some of the holes but not all of them (and please choose the correct one as I see two pictured here). Requires study and understanding of the carb's circuits you intend to use etc.

The site glass window o-rings ought to work but are not necessary if yours are not leaking and you don't disturb them. The site glass gaskets are too big and need to be trimmed.

None of those orange fiber washers can be used so don't even think about it.

The two big square gaskets need to be thrown in the trash. They are thick, permeable and not a good idea to use. Do not try to take off the permanently bonded gaskets from your stock phenolic spacer!!

DO NOT EVEN TRY TO SWAP OUT YOUR STOCK NEEDLES AND SEATS, OR ADJUST YOUR FACTORY FLOATS. EVER!!!!! That's my one and only warning about that.

As you can see, almost nothing from that kit is usable.

 

Jeff I think there may be some confusion here. I'm not doing any work to the Nikki yet, just the intake manifold, so I don't need any of these gaskets, I'm just looking for the gasket to reconnect the intake when I'm done, and I haven't found just that one yet. Also I already have the rings for the coolant passages, so I'm not really worried about that.
So to clarify: Manifold is being worked on, no Nikki work. As far as I know this should only require two gaskets. I'm not going to mess with the actual Nikki mechanics until I have to. This kit is just an example of what I'm trying to find.

 

One gasket. For the intake manifold where it connects to the engine, and two o-rings.

 

So I don't need a gasket to reconnect the intake to the carb? Well that makes things alot easier. Thanks for the heads-up, it probably saved me some time.