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Need some help with my Nikki carb rebuild. I have an 84 GSL (bought used in 88 with 5K miles...now with 185K and still close to pristine). I've followed the hogging discussions avidly, even printing out most of Jeff's and others' comments, re-reading them again and again to understand. I have 2 other Nikki's from earlier years, perhaps 81 and 83. I'm using them to try the hogging and jet changes, but I'm trying to limit what I do to the 84 body. The jets are all stock. I've gotten rid of the bird's nest of relays, the air pump, the shutter/flapper valve, the air control valve (using the Racing Beat blocking plate). I've sealed all of the vacuum ports, removed the air vent solenoid ceramic piece, pin, and spring. I retained the richer solenoid on the other side of the carb. I did run a vacuum line from the 2nd port on base plate to the vacuum advances. I've implemented the Sterling accel pump mod. I've eliminated the vacuum secondary and made them strictly manual. I've removed the small filters in the fuel lines. I've retained the manual choke and high idle, but eliminated the heat spring pull-off and the rest of the vacuum stuff for it. I've installed a new fuel pump and filter. I kept the altitude compensator only because it was easier to leave than creating a plate to cover and then sealing the vacuum port. All of the anti-afterburn equipment is gone, as well as the throttle opener and dashpot. During the rebuild, I kept the factory float seats as recommended. I have number of tiny twist bits that I used to make sure that the jets and air bleeds were clear. Primaries: main air 70, slow bleed 40, short slow 170. Secondaries: main 140, slow step ??, short slow 60. As I said, bone stock.
The car starts easily with the choke on, and runs at 3K or better with the choke slightly open. When I open the throttle it revs higher on just the primaries (2ndaries do not open, but then again, it's not under a load). It sounds great. I can see the accel pump squirting. However, there's raw gas (or what appears to be gas) on top of the outlet valve screw (the thingy with 2 tiny nozzles). When I open the choke more it idles down to about 2800, but if I open fully, i.e., when it's warm enough for the magnetic pulloff to release, the engine sounds like it's starving for fuel and dies almost immediately. The float bowls show fuel at the half-way point on the glass viewing ports. The idle mixture is set to 1.5-2 full turns from bottom. The idle speed screw is just engaged. I've had it off multiple times (much easier with all the crap gone) to make sure that the ports were clear. What am I doing wrong that it won't run below 3k or so? What am I missing? Thanks in advance for any help.
BTW, in another thread about a dead short and replacing the ignition switch, I've determined that the short is in the wiring harness in the wire from the starter solenoid to the ignition switch. I'm starting the car with a jumper line on the solenoid directly to the positive battery terminal and it works fine. I'll replace the wire as soon as I solve the carb/idle issue.
Indeed, definitely richen your idle a bit to where GSLSEforme mentioned. I call 3.5 my starting point but really anywhere in that vicinity will work.
Aside from starting issues, while reading through I noticed a mention on your secondaries. You first said you made your secondaries fully manual (mechanical) but then later said they probably weren't opening up because it wasn't under load. Here's the thing though, the 'under load' part only applies to vacuum secondaries, not mechanical. If you have your mechanical secondaries hooked up properly they will open whenever you want them to. Heck, your car could be off and they'd act just the same way. A couple things I'd check/wonder would be:
- 1, did you actually floor it when testing? The secondaries only open up on the latter part of the throttle travel, usually somewhere a little past 60% on stock linkages. With mechanical secondaries you can also (usually) feel a change in the pedal when they start to open.
- 2, perhaps you didn't connect them correctly? While I don't know how you went about the mod, it is essential to somehow connect the secondary shaft and its linkage to the linkage that actually manipulates the secondaries (this second linkage is what previously kept the secondaries from opening if the primaries where not open enough). Some people use a wire-tie, some use a weld - though you probably came across that in your reading. If you don't connect them they'll just do whatever they please, which most of the time isn't what you'd like them to do. Just something to check. Helps to narrow down the possibilities.
I wouldn't worry about fuel on the AP screw. While fuel doesn't often find itself there on a regular basis, I don't think it's something to be concerned about right now. Could have just been a spill or some extra fuel up top from using the choke to idle.
Thank you both for your comments. I'm assuming that a full turn is 360 degrees. As such, I tried 4 full turns with no effect on the idle dying issue. With respect to the 2ndaries, I tried welding, but it broke and I resorted to wiring. On the bench the 2ndaries opened faithfully when I got to a certain point with the throttle shaft, so I'm not concerned about the failure to open (since I didn't floor it). During the rebuild, I did pull the 2ndary throttle plates and had a hard time getting them in place so that the opened and closed smoothly. I did NOT pull the primary plates during the rebuild. I'm thinking that I need to pull the carb again and check the idle bypass port again, and perhaps check the float levels. 16mm on the close, but I'm not sure on the open...thought it was 24mm maybe. The fuel levels are at the midpoint in the glasses, but perhaps it needs to be higher. It starts to die at about 2500-2700 rpm, which sure feels like starvation for some reason.
Factory setting for float levels is 1/2 way up sight glass. Raising float levels won't help idle problems. You either have a blockage or a vacuum leak.
Edit:
I believe I misinterpreted your scenario - I thought it wouldn't go above 2700rpm, whoops. I'm also getting this thread mixed up with Carl's so that isn't helping. Anyway... Look for vacuum leaks like GSLSEforme said; with all the things you removed there's a good chance of having missed a hose or nipple somewhere. Blockages are also likely, but I'd say rule out vacuum leaks first if you can. I hope you didn't try replacing the gasket on the phenolic spacer. Those are bonded to it and really shouldn't be messed with. If you did that could be a big vacuum leak.
The S3 carbs also have a couple extra lines running to the altitude compensator. Did you keep those or cap them (it seems you kept the alt comp itself)? A few pictures might be helpful too - I keep getting lost in the paragraph of mods, not sure about others.
Pre-Edit:
I once had an issue where there was this 'brick wall' in the rpm band where I couldn't pass, while also causing issues when returning to idle. Turned out to be a faulty FBVS that caused vacuum in the float bowls as rpm increases. I know you mentioned having removed it, although is there a chance there's still something in there causing an issue? A blockage or vacuum leak are more likely, although it doesn't hurt to check something so simple.
Last edited by Benjamin4456; 04-11-20 at 04:29 PM.
Haven't responded as quickly as I'd have liked. Pulled the carb and broke it into sections. The gasket between the base and the midsection was that thin paper one that Jeff has remarked on before. The ears around the hold-down screws showed some damage.
You can also sort of see how I've wired the secondaries to make them manual. Here's another shot of that.
So, I looked that paper gasket in the rebuild kit and decided to make one out from file folder material, but that turned out to be as thin as the other one. I also had some .08cm thick fiber gasket material and decided to use that.
Here's a couple of the intake manifold with RB blocking plate
The phenolic base plate has its molded gaskets. I have a new baseplate gasket on it as well. I've pulled vacuum from the 2nd port on it, the one that's supposedly timed to rpm increases.
I'm a little concerned about the 2ndary throttle plates not being completely closed. Here's a shot of them with a light source underneath.
They're not really as open as this looks. The light is reflected up the venturi walls a bit so this isn't a true representation, but they are open a crack. I fail to see how this would cause the starvation below 2800 rpm, but what do I know.
Also, I haven't blocked off the holes in air horn as you did, Benjamin (BTW, your posts on your carb work in your signature file are awesome). Should I? The ones that potentially lead to the altitude compensator...I have the top ports on it blocked, but the side port continues to have the plastic line to the port in the throttle plate. I could block them off too if desireable.
I'm going to reinstall it today and see if blowing out the ports and the new gaskets make any difference.
Your thoughts are most welcome. Thanks, in advance.
Eric
Seeing as how you're leaving the choke, richer solenoid, and altitude compensator I don't think I would plug any internal circuits. I also never really looked into how the altitude compensator works with other circuits so I'd either go all in and pull it, or just leave it as you have it now (I'd probably do the latter).
Beware of cheap vacuum caps. The OEM ones found on the rats nest and elsewhere are actually very resilient and hold up well. I and others have experienced cheap caps (essentially the kind you find at a local parts store) cracking and failing, thus causing hard to trace issues. If in doubt and without access to good caps the bolt in a hose method always seems to work.
That's also an interesting way to tie the secondary linkage. Visually that looks like it would not hold it tight, but if it works it works... Also those secondary plates need to be closed at idle. Even very small amounts will lead to difficulties when it comes time to set idle. I spent a few days (mostly because I made new, custom linkages) getting the secondary plates to seal properly in order to get my idle where I wanted.
I think you should examine your secondary wire tie method. It might be what is holding your secondaries open. They need to sit closed like they do on a factory carb.
Regarding the alt compensator air stuff: there is a small air bleed with the number 40 stamped on it under the lip on the secondary side of the air horn. I block these with solder because they let in some unwanted air at idle. It won't solve your lean problem you are experiencing at 2800 as that sounds more like a transition circuit and idle circuit problem. Maybe your primary fuel jets are too small and maybe your idle circuit is still letting in too much unwanted air from some other source.
And just in case you were wondering, yes all of the primary circuits are intimately linked and communicate with each other. You change one set of air bleeds and it effects the entire primary side of the carb from idle to full primary operation.
I'll see to the 2ndary throttle plates immediately. I haven't swapped any jets at all. All of them are the stock ones. I have another earlier FB (I believe) that I've hogged the primaries to 24mm almost exactly (I have internal mic spring-loaded gauges and a metric micrometer). I'll play with those jets as you and others have recommended, but I'm leaving the 84 with stock jets. The AP mods seems to work well when I goose the throttle. We'll see when I can get it to idle.
I have a mix of the cheap caps just installed and the old tried and true hose with screw. As to the 2ndary tie, it snaps open and shut. I just haven't gotten the plates seated correctly. I did try welding it with my MIG, but it popped loose, so I went to the wired approach. I'll get the plates set correctly and then see if there is an immediate need to go back to the welded approach. I kept the choke because my car always needed it to start. That may have changed with the elimination of all of the extraneous stuff, and if so, I'll remove it too.
Getting rid of all of the extra crap makes it so much easier to get the carb on and off.
So, I worked really hard to get the 2ndary throttle plates completely closed. They're hard to adjust, but I was successful. Jeff's comment about the air bleed in the air horn set me to looking for a 30 bleed. When I popped the air horn, this is what I found:
Yes, an empty hole. I looked all over for the air bleed and could not find it. The other 2 carbs I have are older and don't have it. I found a brass plug from amongst the carb parts.
I also found one of the floats was not properly adjusted and fixed it. Dropped it back into the car, primed with a little gas in the primary throats, and it started right up (with choke on) and ran at about 2500 rpm. As I let off the choke, it idled after warming down to about 1200 rpm and stayed that way. Clearly the missing air bleed was the culprit and the subsequent plugging of it (Thank you, Jeff, for mentioning it and then saying that you normally plug it) fixed the basic problem.
After running it for a while at idle, I found that when I gave it gas from the pedal, there was severe hesitation, but then it picked up and revved. Somewhere around 4000 or 4500 the 2ndaries kicked with a roar (wire-tied) and up to about 6000 (didn't push beyond). I'm going to have to look at the AP and make sure it's pushing enough fuel. I may also adjust when the 2ndaries kick in. There was some previous discussion that I read from y'all about doing that. It used to idle at around 700 with the birds nest, other vacuum components, air pump, and solenoids. When I use the mixture screw I can get down to maybe 1000 and then it dies. The throttle stop is completely free so it's not that. I'm wondering if the vacuum advance has anything to do the idle. I may try pulling that and see if only the mechanical advance allows it to drop down. I have the Mazda carb manual and I'm going to review it again to see if there's anything I missed. I can live with the idle being a little high, but the stumble has to go. Again, the jets and air bleeds are what the car originally came with and are unmodified in any way. Thanks again for the suggestions and help. Most appreciated.
Just a heads up on the vacuum advance; it isn't in operation during idle. If you've got it hooked up wrong (perhaps it sees vacuum at idle unintentionally) or if there's a leak (which would only affect light throttle to almost WOT, not idle) then it might be doing something wacky. Otherwise you probably just have a vacuum leak somewhere else.
An addendum. Life intervened, but got back to the RX7 the other day. It's a little hard starting, but when it catches it runs great. The idle issue was that I had the accelerator cable too tight and when I loosened it, I was able to adjust the idle with the mixture screw and the idle speed screw to 700 or so. Still have a little hesitation when giving initial gas, but if I feather the pedal it comes on strong. Due for some road testing to see if the improvements have given it some testosterone. May have to play with the AP some more, but so far so good. Still not clear on why starting is a bit harder. Could be the AP or I'm just not pumping the pedal enough before trying it. I did move the vacuum advance to another port and that seems okay.
Now on to the other carb that I hogged out (24mm on the primaries) and the jet changes. Y'all stay safe!
04-10-20, 01:10 PM
