lordcupkake

So I have an rx7 that I bought running and driving okay with a racing boat manifold mated to a Holley 4150(?) 650cfm carburetor and it was okay for a bit but that carb is obviously too big for the car. I tried reverting to stock with some parts I bought with the car (stock manifolds and carb parts) but could never get it running right with the Nikki and eventually scrapped that realizing I was missing a few crucial parts.
Some time passed with it not running in the garage and I ended up with a Holley 450cfm carb from a buddy of mine. So I figured why not mate that to the RB manifold and get the car running again. Well that carb doesn't have to same bolt pattern as the 650cfm but no worries I made an adapter plate from half inch aluminum and bolted the thing on.
Now, as I'm writing this, the car is in the garage just sitting as I wait for some Permatex MotoSeal Gasket Maker to cure as obviously no one makes gaskets that will fit my custom adapter.
Before I try to fire the 7 up I figured I'd put this message out there to see what you all, the Rx7 gurus, think of this plan. I can't see any real reason it shouldn't at least start and run assuming I connected the carb up right and everything. Am I missing any unforeseen issues?

I know RB uses a 465cfm Holley for their applications (which I know is "specially tuned" and has specific getting replacements etc.) but idk why a 450cfm 4bbl Holley from the same era shouldn't make an acceptable replacement.

lordcupkake

Maxwedge

iTrader: (1)

The first issue would be trying to match a spread bore carb to a perfectly square bore manifold, but... the previous owner carved up the manifold, and you made a spread-to-square adapter, so.... let us know if it works?

t_g_farrell

iTrader: (1)

You should really try to get that nikki running. Trying to reverse engineer that plain jane Holley with all the RB modifications will be next to impossible and will probably not work right anyway. Even folks that get the RB modified Holley have issues with them.

Describe the nikki parts you think you are missing. Maybe we can help you sort that out.

diabolical1

iTrader: (3)

at this point in the game you've already committed and executed about 90% of what you need to do to try it out, so in my eyes at least, it makes no sense to bail and NOT give it a shot. at the end of the day, with all the issues aforementioned (hacked up manifold, using this style Holley, etc.) i think you're probably in for a long, frustrating process, but these are the things we sign up for when modifying cars. i know the frustration of having the car sitting there and not being able to drive it, so i think you should do what you can with what you have WHILE taking steps to do exactly what T G Farrell suggested. work on trying to get a Nikki setup as soon as you can.

lordcupkake

Everyone on here always raves about the Nikki and always tells me to try to get one working. What's so special about the Nikki versus a Holley or other carb? I'd never heard of one til I got the 7 and it seems like virtually every other application people talk about Holleys or Webers. Why not a Holley?

Maxwedge

iTrader: (1)

The Nikki is made for the application. It is the factory carb and is designed/tuned specifically for your 12a rotary engine. No other carb is. You are going to spend a lot of time, trial and error trying to get any aftermarket carb tuned and tweaked just right for your tiny fast reving engine. The nikki was designed for it. That's what they're saying.

t_g_farrell

iTrader: (1)

Holley is mounted the wrong way on a rotary causing issues on turns. Holley is not designed to deal with impulses caused by the rotors as they pass by the intake ports. Many other issues. Just read up on them on here. We are not forcing you to do anything, you asked what we thought and this is what we think. Webers or Dellortos can work well with minimal tuning if you want an easy replacement for the nikki.

rxtasy3

iTrader: (2)

in regards to the holley, yes everybody hates them. i don't autocross or out to drive some twisty roads everyday/weekends. i cruise town and wind it up now and again. my holleys r from the 80s so really any of the issues the holley has hasn't really been too much an issue for me. maybe something has changed since then? i guess maybe it's just how particular u r and what u can live with.

lordcupkake

I didnt get around to it before. But I tried to start it today after everything had a chance to cure and whatnot and there is gas literally pouring from the exhaust when I try to start it and once i pull the key it continues for a bit then eventually stops.

People describing the same issue on other cars said it's probably a busted pressure regulator but that just doesn't seem right to me... why would a busted regulator cause this much gas to come out of the exhaust?

lordcupkake

Also for those of you championing the Nikki, this is the Nikki I have in front of me, with a manifold to match. I also have an entire box of Nikki parts but despite all this I could never get this nikki to start and run either. Idk why but I just never could.

lordcupkake

For some reason my phone struggles to put multiple images on a post. Also for anyone curious that is the 650 cfm carb that came on the car when I bought it. It ran with that guy on the RB manifold and the same regulator and everything I have out there now.

GSLSEforme

Sure that's a 650 cfm carb? Looks like a #1850 600 cfm carb. # will be stamped in front of airhorn.

Maxwedge

iTrader: (1)

If the motor ran with the 650, but wont run with the 450, I think the problem(s) is in the 450. Aside from it not being calibrated for your motor (which you can tweek), there is no telling how rough a shape it is in until you rebuild it. Rather than your regulator being bad (since it worked with the other Holley) I'd bet your needles & seats are stuck open with dried gas residue. It could also be the floats way out of adjustment, which could act the same. This is letting gas pour through and flood out the motor. You need to rebuild that carb before it burns your car to the ground.

And after you rebuild it so that it is (sorta) functional, you can start swapping out jets until you find what works for your motor. I am not trying to talk you out of using a Holley, but it sounds like you have a bunch of crusted-over junk carbs. Also, they sell adapter plates to put spreadbore carbs on squarebore intakes, and gaskets, so you don't have to mess with gluing it together.

Curious, how did it drive with the working 650?

EDIT - In your picture of the spreadbore holley in your engine bay, that gauge isn't a regulator. It's just a gauge. If you really do have a regulator somewhere it should be set to 6psi for a holley (2.5psi for a nikki).

lordcupkake

Update for everyone who has been helpful and given advice. Maxwedge- I took your advice and rebuilt the spread-bore. It was easy and I live like 20 minutes away from the summit racing retail store so I just picked up a rebuilt kit yesterday. I have never rebuilt a carb before and there were not really any directions but it was pretty easy.

I then plopped the bad boy on my manifold/spread bore adapter and with not really very much coaxing it started up (albeit quite smokily). I only had it running for about a minute due to the fact that the way it was rolled into my garage the exhaust faced into the garage and was smoking the place up. Tomorrow I will roll it out into the driveway and get it running better. But it seems to run okay in the brief period I had it started. The smoke was kinda heavy but I've had the engine tested before by a Mazda dealer and they say the engine is healthy and not leaking coolant so i assume it's just a matter of starting an engine that hasn't been started in awhile and a matter of poor mixture adjustment with some old previously premixed gas. I'll put fresh gas with a proper pre mixture in tomorrow too. I am going to have to rig up a custom throttle cable/choke cable setup here too before I can drive it but this is promising and I'm so glad to have a car that hasn't started in about a year now started.

Thanks to all those who have commented thus far and anyone curious about it I can send a video/pictures of the current setup.

I'll also update this thread in a bit after a test drive to let yall know how it drives compared to the old 650 (or possibly 600 as someone pointed out)

lordcupkake

I haven't test driven it yet because I'm slow and whatnot. Here's a couple videos of it running. It runs but obviously it's running rich. I've only had it running for a few minutes and I obviously need to lean out the idle mixture a bit. I was a little concerned because there is a bit of fuel splatter which is quite dark in color, not the color of gas. My inclination is that it is gas that is getting carbon buildup in it before it gets exhausted as it is running rich and not completely burning all the fuel - thus the fuel is exhausting with some carbon. I am positive that is not the color/consistency of the fuel and pre-mix coming from the tank (I checked that - the gas from the tank is fresh and clean).

Can anyone confirm my suspicion that it's just a matter of carb tuning at this point? Or is it something else causing the exhausted fuel to look so dark and muddy. That white board in the videos/pics was just put there to more easily see the fuel being exhausted. The smoke in the video I assume is just unburnt fuel and premix that is there due to the rich mixture rn.

This is a link to a google drive folder with a couple vids/pics in it. The forum wouldn't let me attach the mp4s directly and imgur threw a fit too so I figured I'd just directly share the videos. (Apologies for mediocre quality the videos got compressed when I transferred them online)
https://drive.google.com/open?id=1--...f_uiwBDywao-7j

EDIT: I forgot to mention, the original carb I had running was in fact a 600 cfm Model 4160 (list 80457-2) in case anyone was still curious.
Also, someone mentioned that possibly the old carbs are better and that Holley's in general have a tendency to have issues around corners, I suspect this 450 cfm won't see those issues because of the way the fuel bowl is located in the center of the barrels and this carb is from '78 (as confirmed by the date codes stamped on it).

GSLSEforme

Listened to your videos,what’s coming out of muffler is not too concerning but is indicative of a couple things.
1st,pull dipstick and smell oil to see if it has a gas odor presence. Not uncommon for engine to accumulate gas in oil if been running in a flooded condition. Also likely engine oil level will be overfull if sufficient rich running/flooding has occurred.I didn’t reread your whole thread to see if this had occurred

Did you happen to note #s on primary jets while apart?
Engine running at a high idle,have you tried adjusting idle speed down and then adjusting idle mixture?
If you are unable to lower idle speed,see iif idle speed adjust screw is in contact with throttle plate tab. If there’s a gap it could be throttle cable has insufficient free play and preventing primary throttle plate from closing completely.
Look down thru secondary part of carb to be certain secondary throttle plates are closed fully,if they are not,the engine will pull air/fuel from secondaries that results in a higher idle speed that can’t be adjusted lower with base idle adjust screw and a richer than normal mixture.
If adjustments of idle speed and mixture don’t lower idle speed,look for a vacuum leak.
If the oil smells at all like gas,change oil and filter as engine running with gas in oil will be running rich from that as gas thinned oil slips by oil seals much easier than clean gas free oil and can be burned in chambers as well as being pushed out exhaust pipe.

Post back what you find.

lordcupkake

First, your write up was amazing, thank you for the quick and accurate response.

First, the oil definitely smelled like gas and the car had had flooding issues ever since I've had it (with the 600 cfm before and obviously in the videos). I replaced the oil and filter with STP High Mileage 10W-30. I live in Ohio so I went with the 10W-30 as opposed to the 20W-30 as some warmer climate folks recommended. I replaced the filter with the correct STP oil filter (although I'll probably go Mobil 1 next time as I saw that filter is highly recommended).

Then, I proceeded to start the 7 after taking the idle mixture screws all the way in. No smoke/gas coming out of exhaust, but idle speed still about 2500 rpm or so, obviously too high. The idle speed even with the 600 cfm on there was somewhere around 1000-1100 rpm, so even compared to my old high idle I'm still idling way too high.

The idle speed screw isn't making contact with the throttle plate. The secondaries are completely closed, and the throttle cable is currently a non factor as it's not even connected to the carb (I've just get hand revving it so far from the carb). As far as I can tell, the primaries and secondaries are closing as expected.

I can't see any immediate vacuum leaks as I've replaced almost all the vacuum hoses I can see since owning the car (about a year). I will try to get a new intake manifold gasket on there tomorrow just as a precautionary measure since that hasn't been replaced since I've owned the car, although the manifold has been off since ive owned it (I know I shouldn't have tried to reuse an old gasket, but it seems in like-new condition as if the previous owner had just slapped the 600 cfm/RB manifold on right before selling).

Any common spots I should look for the vacuum leaks? Or should I do something different with the idle mixture screws?

Oh and I forgot to note the numbers on the jets.