ChunkyMonkey

iTrader: (1)

keep us posted....I have the same prob....After the choke goes in, the car with idle with a pulse and then smooth out or some times dies. But, when I start it back up, it's good.

PT Ray

Are we all dealing with a stock Nikki carb in its original 20 year old condition? Would this be an indication of needing a rebuild? I like the idle air theory but I also wanted to see if we were all dealing with original Nikkis. I will add that the other day, I started my 84 GSL and let it idle in front of the house. After the initial warmup and the choke goes back in, it was not but a minute later it started to choke like it was going to die. This would have been where it would have normally died if I was driving. After that it was business as usual.

brandon davis

iTrader: (3)

here is a way to find if it is vac leak. you can do this when its cold or warm and it worked for me. start the car if cold with choke of course pull choke and keeping revs around 2-3k open hood and use a full can of carburater cleaner over the whole thing mainly on vaccum lines and around intake manny i used the whole can with the red straw on it so i have more accuracy to find out which rubber vac line is cracked. if the car starts to die while spraying then you have leak somewhere now to find it is the fun part. btw i start my car in the morning and let it warm up while im in the house getting ready a couple of weeks ago i cam eout to the car and it wasnt running but had reached operating temps and choke had gone in i did the mentioned above and found a few silly leaks and no more of anything you have complained about above just my 2 cents.

brandon davis

iTrader: (3)

oh yeah i have a stock nikki with k n filter and chopped up canister for more air flow and whenever i drive the car without letting it warm up all sorts of **** happens. rotaries dont like cold weather and neither do i.

ChunkyMonkey

iTrader: (1)

did the vac leak cause a constant low idle? I'll have to try this in the morning....You can use wd40 also right??

Aviator 902S

Vacuum leaks usually cause the engine to idle faster and rougher, not lower. As for having the choke retract on warmup and then having the revs drop lower and lower, that sounds more like a too rich mixure than anything else. On cold days the choke takes longer to retract (ie:longer period of time running with a relatively rich mixture), so more carbon-fouling takes place. If idle mixture screw is too rich on top of that the engine would "load up" until it dies.

I took mine out today for its first highway test run (outside air temps down around zero F) since I turned the idle mixture screw out 1/2-turn last night. While the car now idles at 900 rpm and therefore is less prone to falter in city driving, the problem still persists coming down from highway speeds. The revs just drop down below 600 before recovering in city driving, but shoot right on through to zero when letting off the gas with clutch depressed at highway speed.

I also noticed that the heat duct from the exhaust manifold shroud to the air inlet horn has a small (ie: 1-1/2" long) crack in it near the base. The purpose of this duct is to heat up incoming air prior to having it enter the intakes so it does not upset the air-fuel ratio (ie: making it too lean due to the denser cold air). These older cars don't have a mass airflow sensor to do this job. I'm wondering if this cracked duct may be a factor. Problem is, the car still has this problem even when outside temps are just above 32F.

The other thing I noticed today was that while the temp guage was reading its usual 1/3rd in town at low speeds, it dropped to about 1/4 on the highway at 70 mph, which is where it read when the engine quit. Sounds more and more like a mixture problem since air entering at that speed would be colder and denser than in stop and go traffic, making the mixture leaner than optimum for those conditions--- especially with operating temp lower than normal.

I could richen the mix even more, but I don't want to be idling at 1200 rpm. Leaving the choke out on the highway isn't a viable option either, unless I want to get a measly 8 mpg all day long.

And yes, this is a bone-stock, un-molested Nikki carb. The Haynes manual (useless, I know) shows a 1980 carb with both an idle speed adjustment screw and an idle mix adjust screw directly under it. Mine is an '85 (originally from California) with only the one screw. It's in exactly the same location as the idle mix screw in the manual, but I'm now wondering if it is in fact an idle speed adjustment screw, since the only thing that seems to have been affected by the adjustment I made was idle rpm. Anybody have input on this?

NewWorldDan

Towards the end of the Haynes manual they have a chapter or two of info pertaining to later model RX 7. most of it is about the GSL-Se but they do have info and a pic or two of the idle speed and idle mix screws. If your carb is as bone stock as mine then the cap might still be on the idle mix screw so the only exposed screw you'll see is the idle speed screw. I've learned all this recently as my '83 is doing something very similar to yours.

brandon davis

iTrader: (3)

i have an 84 with a bone stock nikki and i have two screws air fuel and all the way to the right looking at it from drivers fender youll fine the curb idle screw way down in there youll need a fairly long phillips to reach it is connected to the throttle linkages it is there just look real hard. i too had to play around with idle and air fuel to dial in the a good idle all the time.

Aviator 902S

Found it. At the bottom RH corner of page 263 it sez "idle speed is adjusted by turning the throttle adjust screw...", and on the following page it sez that only the dealer service dept should adjust mixture--- and nothing else. Typical Haynes lack of useful info.

The photo was more helpful. It confirmed that unlike the 1980 carb shown in earlier chapters, mine has only one screw in the usual location, ie: on the LH side of the carb, in the throttle body, and at about the center of the carb looking fore and aft. The throttle adjust screw is about two inches further aft and directly horizontal to the mixture screw.

I guess my car isn't quite as bone stock as yours is--- the cap is missing from the mixture screw, as I suspect is the case with most of these cars. It was a stupid idea on Mazda's part. There is absolutely no other screw in this location (capped or otherwise) on my car.

Aviator 902S

Thanks, I just found it. (See my previous post to this one). So it was definitely the mixture I adjusted yesterday, not idle speed. Although the net result of turning that screw 1/2 turn counter-clockwise was a 100-rpm increase at idle. Problem still exists though.

NewWorldDan

I'm glad you found it, that confused the hell out of me too. I actually never got around to messing with the idle mix screw because i gave up on trying to pop the damn cap off after fighting with it for about 15 mins with a pair of pliers. it didn't help that I was too lazey to pull off the air cleaner to actually get some decent leverage on it.

masonrx7

Well, when you guys find the perfect solution that solves this problem completely... or atleast almost completely, let us know. My 85 GSL has the same problem and its also got the stock Nikki carb.

minocqa

personally i think its time you should ask RX7 Carl or Sterling about this.
they are the best bet for solving this problem .....these guys know there ****....it seems that a lot of us are having the same problem,including myself once my car is warmed up..the choke goes back in.... then you can either be driving it or i'm just sitting in the drive way reving it as soon as I let off the gas the tach drops to zero and the car stalls. and then its a bitch to restart. i plan on getting a sterling carb in febuary, and changing the fuel pump and installing a regulator i sure hope that solves some the probelms. but i dont know this sounds like a question for them.

Rx7carl

Sounds to me like you all may have different problems, resulting in similar symptoms. Aviator, it could be a partiallly blocked passage in the idle circut. Crank the idle speed up to 1500 or so and test it. You might want to test your dashpot as well. And as usual, check for vacuum leaks in general. I would also replace all the vacuum hoses is there is any doubt of their condition if nothing else works. The stock carb mixture adjustment is 3 1/2 turns out from bottom. Thats bottomed out in the carb BY HAND! Or VERY GENTLY with a screwdriver. If you over torque it you will ruin the needle on the end of the screw and oversize the hole.

Aviator 902S

Thank Carl. The 1/2-turn adjustment I made on the idle mixture did not solve the problem so I turned it back to where it was. That's the only time I've ever touched it on this particular 7, and the car was running fine before, when outside temps were above freezing.

I'm not following you on the adjustment of idle to 1500 rpm to test, or the dash pot test. How and what exactly am I looking for? According to Haynes, the idle is adjusted via turning a throttle adjust screw. Wouldn't this simply circumvent the problem rather than fix it?

Also, if I gradually lift my foot off the gas to allow the revs to settle at idle everything is fine, ie: the revs do not drop below idle but remain smooth and stable at idle. It's only when I abruptly let off the gas that the revs drop below idle and then settle at idle in city traffic, but stall out completely dropping from highway speeds. Would it EVER idle normally if the idle was partially blocked?

minocqa

Did you figure out what was causing you the problem?

Aviator 902S

Update: weather here in Calgary warmed up from overnight lows/ daytime highs of zero F/ 25F to about +40F day and night. Driving home from my gig at 2am at highway speeds produced no stalling problems or dips below idle at all.

So it would appear that the problem has been ambient temperature related the whole time. The threshold where problems start appears to be any temp below freezing.

But this problem didn't exist last winter. The only changes made since then are the under-rad air type oil cooler swap (cools way more efficiently than the beehive) and the small crack in the heat duct between the exhaust manifold shroud and the air intake.

I'll replace this duct when I can and swap in a different thermostat and see if that helps.

And Carl -- thanks again for the info. As far as I know Florida never sees the kind of cold temps that those north of about the 42nd parallel do, so it's not likely that outside temps there would ever have the kind of negative effects we see here. But if my remedies don't fix the problem I'll revisit your solutions.

minocqa

i store mine over the winter here in Illionois
the ground clearance is so low and i hate to tear anything up with snow and SALT
plus i'm having pretty much the same problem as you are having.
i havent changed the vacuum hoses yet. but its in the plans.
Don

mar3

iTrader: (8)

My problem was in city driving, occasionally from the highway but, amazingly....my temperature gauge said the exact same thing about the operating temps being in the normal "hot" range when the choke popped loose, but that turned out to be completely irrelevant...the choke is releasing too early and my morning routine completely solves it. In fact, the red '84 that I sold to a friend did the same thing as well when it got cold here in Texas and, since he started doing my routine, he no longer has this problem, either....

minocqa

i'm going to try it with mine
but one question if your choke goes off to early then how do you prevent that from happening?

minocqa

hi
i went out and started mine today i let it run for about 7 minutes lie Mar3 said the choke went off but i kept it running . then shut it off for about 10 minutes when i went out to start it again it didnt want to start.
its about 15 degrees F wind chill here now. i have always had flooding probelms in the cold.
any ideas would be very much appreicated
Don

minocqa

^ my car is a 1985 gs 12a

Aviator 902S

Sounds typical for higher-mileage (ie: lower compression) engines. Best to not pump the gas at all while starting. Just hold down all the way until the engine catches.

If already flooded, pull plugs out and dry them off. Next, pull fuel pump fuse and then crank engine over for 20 seconds or so with plugs removed. (engine will crank very easily and quickly in this condition. Now re-install plugs, put pedal to the floor and hold while cranking. Car should now start.

minocqa

Aviatar
Thanks
my 1985 Gs only has 77k on it i'm the second owner and the compression is good. i'm looking for my chart i got form madza when they checked it last year. but anyway it was fine.
i do know i need to get my carb rebuilt nad replace my vacuum lines do to age.
its just frustating when it does this.
plus i never really thought about pulling the fuse ...thanks
Don

Aviator 902S

Yet another update: This one appears final---

Ok, so the problem went away for the most part during warmer days, but then returned. And it's still warm here, daytime highs around 45F and overnight lows just above freezing.

The fact that the stalling and dropping revs now appeared intermittent caused me to re-visit my earlier speculation that the problem might be ignition related. I pulled the plugs to confirm that they were ok. They were, but the spark appeared weaker than normal. A quick check under the distributor cap confirmed that the contacts were in pretty rough shape, even though the cap and rotor were only a year old.

I swapped in new ones but this didn't solve the problem. I then remembered a few months back when the car started but immediately dropped revs to zero a couple of times before catching and staying lit on the 3rd try. (The engine was warm at the time and had only sat for two minutes). Could it be the ignitors, as previously speculated?

So I pulled two used ignitors off a spare distributor, cleaned the contacts and swapped them in. Viola! Problem solved. When letting off throttle and disengaging clutch at highway speeds the car now drops steadily but slowly to idle where it levels off. It appears that the weak spark (which also kept the engine from warming up completely and caused excessive fuel consumption) wasn't strong enough to stay lit when dropping to idle. This was exacerbated during cold weather, when the air was denser than normal, creating a lean mix condition. It also took several cranks for the engine to catch but not any more.

If you are experiencing similar problems, try removing your ignitors and cleaning the contacts, then reinstall to see if that helps. It's only a ten-minute operation and only requires a flathead screwdriver and a fingernail file or sandpaper. You'll also need a wrench to undo the alternator mounting bolt so it can be swung up and out of the way of the distributor, providing access to the aft ignitor.