curtissh

So, in this thread I talk about using HEET to pass emissions.

I noted that when I drove the crap out of my car for a while, the idle stuck at 3000 and came down as the car cooled. I thought this had something to do with the alcohol in the tank. As some of you suggested, I'm of the impression that the alcohol had nothing to do with it (though, I'm certain it helped with emissions -- I'll scan the results pages for you guys if you like).

Now I've run a tank of gas through it, and today I drove it hard again. Same thing happened. Screamed down the street at 7000 rpm, slowed as I came to the stop sign and the idle stuck at 3000 rpm. Pumped the accelerator, pulled the choke, nothing (choke caused idle to increase a bit). I turned the car off for a couple minutes, then restarted and the idle came down to like 1800. I pulled the lid off the air filter and the choke plate is vertical. Everything looks fine. The hose that often melts over the exhaust looks fine. Can't really "see" any other vacuum leaks, but who knows.

As the engine has cooled, the idle has come down to about 1050, but it's not settling down to the ~650 it usually idles at. I suspect when I start it tomorrow it will be idling fine again.

You guys have any thoughts? 1981, 12A, NA, all stock. Otherwise, the car runs fantastic. I'd like to get the engine dialed in before I start spending money on steering/suspension upgrades.

As an aside, is there a mechanic in Portland, OR that knows a damned thing about rotaries (other than Pineapple Racing -- they just do rebuilds)? I'm willing to work on it if I have to, but I'd rather just pay someone to dial it in for me.

curtissh

Well, suck. The idle's not coming down like it did yesterday. Even after the choke pops in, it's still idling at around 1200 rpm, rather than the 650 it was idling at before.
I suspect it's a vacuum leak, but damned if I know how to find it. The hoses all look fine to me. Tips? Could I have something stuck in the carb that would get stickier after wringing out the engine? Shouold I try some carb cleaner or something?

I found a couple plugs and one nipple that weren't hooked up to anything. Any of you guys know what these are?

Rotor_king

iTrader: (2)

You might have already checked, but check the nuts on your accelerator cable at the carb. My locking nut came loose once and the throttle was stuck open at about 2000 RPM, so its at least worth a look to eliminate.

curtissh

Thanks man, I'll check that again. I'm on the road for the next couple days, but I'll look into it when I get back.

Here's another idea. My fuel return line was leaking at the fuel check valve (old rotten hose). I replaced the hose, and I may have put the valve in backwards (Haynes referenced an arrow (should point toward the carb), but my valve is old and I couldn't find an arrow on it). I think I installed it so that you could blow toward the carb (which, if it's a return hose, that strikes me as wrong). Would that make the motor idle high? It seems to be running ok, it just won't idle down.

Also, where the hell do you buy a new fuel check valve? None of the auto parts stores around me seem to carry one.

DivinDriver

iTrader: (15)

First pic is the bleed screw for your clutch slave. doesn't hook to anything; it's used to bleed air out when servicing.

Second pic is the connector for your orange solenoid valve, which on an 81 is the "Vacuum Control Solenoid Valve," which cuts vac to the dizzy under deceleration. Its was deleted on Cali cars with manual trans, which looks to be the build you have. The rubber cap, missing orange solenoid, and short looped hose on the rats nest all match the 81 Cali MT emissions build.

Third pic is probably the connection for either the richer solenoid or the vac power valve solenoid, which likely wasn't used on your carburetor build.

curtissh

Dude, you are the ****! You're right that it's a manual that came out of California. F'ing incredible. Thank you so much for sharing your expertise.

Unfortunately, however, that sends me back to the drawing board with this idle issue!

wankelnewbie

iTrader: (2)

Just a thought, if you think its due to a vacuum leak, take a can of starter fluid (and NO SMOKING) while the engine is running and squirt a tiny bit on connections and vaccum lines that you are suspicious of. If the engine speed picks up just a little when you squirt, you found your leak.

curtissh

Well, I can't figure it out. No vacuum leaks that I can find (thanks for the tip wankelnewbie). Even when I screw the idle screw all the way in, the engine just slows a little, then a little valve opens (I see something slide to the left just to the right of the idle screw), and the rpms come right back up. Nothing happens when I screw it out.

Unless by some miracle I figure out the problem, I'll be taking it into the only shop in town that works on NA rotaries, the Mazda dealership. I suspect I'll trade my left nut to fix the problem. Fudge.

curtissh

Well guys, I took it to the mechanic. I picked the car up and it was running great. Idled back down to ~750. However, as soon as I took it out and got on it, the idle stuck back up around 1500. The mechanic said he didn't find any vacuum leaks. Sounded like he might have played with the linkage some and it just fixed itself.

I don't think he fixed it. I think I have some kind of faulty valve. You guys have any thoughts? Is there some kind of idle control valve I should be checking? The ACV? What do you think?

DivinDriver

iTrader: (15)

Could be getting stuck up on the fast idle cam. Or a kink in your throttle cable. There's a number of ways the throttle plates can get hung up slightly off closed.

curtissh

With he air cleaner off, would I be able to tell the throttle plates are slightly off closed? If it's just a throttle problem (as opposed to some mystery valve), I feel like I should be able to handle it.

How hard is it to rebuild one of these carbs?

diabolical1

iTrader: (3)

i second this ....

if you're comfortable that there are no vacuum leaks, then this would be where i'd focus attention to solve your issue, the cables (throttle, choke, cruise control) and the springs that open and close the throttles.

DivinDriver

iTrader: (15)

Depends on the exact carb config, but for me on my 80, I'd locate and look at the idle stop. If the linkage tab isn't touching it, then the throttle isn't closed.

This would be a good time to go to the link in the FAQ that would let you download the factory carb manual - - there are differences across the 1st-gen years, one of which is the method by which idle is set on the carb.

Nikkis aren't hard to rebuild, so long as you can follow directions and are careful about organizing all the little parts. It's detailed work, but not difficult, and no special tools are required.

curtissh

So, I looked and looked for problems with the linkage. Didn't really find anything. Took it out and ran it up to 7000 rpms a couple times and, as usual, the engine was pretty warm (but the temp guage is only about 1/3 of the way up), and the idle wouldn't come down below 3000 rpm (running pretty hard). Note that it's now idling at around 1500 rpm when the engine is still pretty cool (just after the choke pops in), but when I string it out a little it sticks at 3000 rpm.

I opened up the hood and the exhaust manifold was glowing. Here's a picture and a video.



[youtube]LUVhGT5jMEY[/youtube]

Think I have a plugged cat? Could that cause some kind of feedback and high idle?

trochoid

iTrader: (6)

If you haven't turned that one valve in the return line around, do so. It flows away from the carb to the fuel tank.

curtissh

Thanks man. I figured that one out a couple weeks ago (and made the change). This forum is a wealth of knowledge.

curtissh

So, I think I melted my catalytic converter. After the idle racing last night (see glowing manifold in video above), the car wouldn't idle without stalling tonight. I drove it to my mechanic (not the dealership I took it to before). Hopefully Scott will be able to figure it out. I told him to start with the cat. Then check the linkage. Then drive the crap out of it. Then fix it. I gave him a budget of ~$1,000.

Here's hoping . . .

curtissh

Mechanic called me and told me I need a new carb. Vacuum leak at the base, and, apparently, between the two halves of the carb. Going to cost me $600 for the new carb and time. For that price he'll adjust the timing too.

He said that a vacuum leak was causing it to dump fuel (running rich to compensate) and that that's why the manifold was glowing.

Sound right to you guys? The mechanic's a good guy, but he's relatively young. I don't know that he's worked on NA engines much. He is ASE Certified and seems to know what he's doing.

jdi_knght

I'd be surprised if a vacuum leak required a new carb. The carb comes apart into 3 main sections (not 2), and if there were a leak in between those, you should just need a new gasket unless somebody tried to pry it apart with a screwdriver once upon a time damaging the actual metal.

At the base just above the intake manifold there's a big fat black permanent gasket/spacer thing, and I *guess* something could go bad there, but then I'd think you'd just need a new one of those - again, not an entire carb. Heck I'd probably go the cheap route and just re-seat it with a thin layer of silicone on either side.

Now I could be wrong, but unless something's physically damaged the carb, or something cracked, I really can't see the entire thing needing to be replaced.

If you're dishing out money for a new carb though, I'd probably look at getting a Sterling.


Maybe in a fuel injected engine since there's an O2 sensor that'll get all sad and stuff and report a lean condition if there's a vacuum leak. If there's a vacuum leak in carb'ed engine it should just run lean though as far as I know.


Best of luck!