Frogblender

I'm going to keep this short and sweet. Suffice to say it ran like this within the period of time I received the car, but I was able to clear it up in some magical way (revving it to 7000rpm a couple times). Now it's back to it's old ways.

-Takes about 6 solid seconds to crank over with choke fully pulled out.
-When cold idling, tach sits at second solid line (relative to 300-400rpm I assume.)
-Engine shakes violently, sounds a bit like a lawnmower.
-After running for a while and warming up, it will rev up properly (when engine is cold, it'll stall if revved above 1000rpm without careful coaxing.) As soon as engine surpasses about 1500rpm, engine smooths out and sounds fine, and vibrations cease.
-At this point it idles at around 800-1000rpm.
-Vibrations can be felt through steering wheel and shifter, although the vibrations in the shifter **** cease when the car has been running for a while.

I will likely post video later on once the car comes back from the shop (its getting a replacement tie rod end to make it driveable). It can't be a blown rotor, as the car revs up fine, but I'm stumped. Any help is appreciated from the more experienced rotorheads

Siraniko

iTrader: (13)

clogged idle circuit.

two79rx7's

my favorite......vacuum leak in the shutter valve/coasting valve section.

see link https://www.rx7club.com/1st-generation-specific-1979-1985-18/car-wont-hold-idle-without-choke-676232/

check all basics, and check for dirty fuel filter, rust in tank?

Kentetsu

Run a can of Seafoam through the gas tank, with about 1/8 full of gas. You might try using less choke when starting. When I had a choke, I think I usually pulled it out about halfway...

t_g_farrell

iTrader: (1)

At 300 to 400 rpm mine shakes violently as well because it's about to die :-)

What year 7 ?

Carb or FI ?

Frogblender

It's an 84 GSL w/ carb, completely stock in every way.

Frogblender

Bump, the more ideas I get the better. I'll be checking into all of this once the car comes back from the shop. Thanks to all who have responded with suggestions, it's really appreciated

t_g_farrell

iTrader: (1)

Ok, I would check the timing, maybe its shifted or been "adjusted" somehow.

The idle and shaking you describe is what my SA 12a does when its cold until it warms up if I don't use the choke on the Dellorto carby I have. In your case are you using the choke? Maybe you just need to pull it out a bit at first even though it seems warm out. Otherwise, its some sort of carb issue like wacky suggested in the beginning. Oh yeah check for vacuum leaks all over the place. If you still have the rast nest it could easily be whats causing your grief.

Frogblender

I do use the choke no matter what the ambient temp outside, recently though I found I could pull it out much farther than I usually do (no **** so yanking on the metal peg is a bitch.) I had a friend yank it while I looked into the carburetor and the shutter operates fine. I might do an idle adjustment and see if it kills the vibration, but I'd like to ask this;

Do I need to use an external tachometer as pictured in the 85 service manual to get it to the perfect idle of 750rpm, or can I just have a friend judge by eye inside the car? I've also heard you can increase the idle at the expense of fuel economy but if it killed the shaking I'd gladly give up a couple litres of gas every fillup.

t_g_farrell

iTrader: (1)

I'm not sure about the FB tach, but my SA tach is pretty accurate and its marked so I can pretty much see where 750 is. I don't use an external tach normally but I have checked it against my cars tach and they agree.

Frogblender

I'm thinking I might just set the idle up a bit higher but I don't want to do a temp fix; it only helps me ignore the problem, not fix it. I gathered together an ordered list of what I'm going to be doing over the next few days, if anyone has anything to add let me know;

1. Drain ALL old fluids to be sure (I know the rad was full of coolant when I got the car so that'll have to go.)
2. About 3/4 bottle of Seafoam into the gas tank with a tiny bit of gas to get by, the rest will slowly be added to the inside of the carburetor.
3. Full vacuum leak check using the 12A Fuel & Emissions section of the service manual (unhooking hoses and checking for suction, etc)
4. Carb tuneup.
5. Timing adjustment (of which I have no idea how to do )

Then I'll have to maybe call someone in. For now though that's what my pea-brain can handle!

EDIT: Oh, and of course, swap all filters, do a spark test, clean the plug cables and do a rotor swoosh test. God I have a lot of work to do

t_g_farrell

iTrader: (1)

One other possiblility is that its a bad or leaky power brake booster. Mine finally went bad (see earlier thread I started) and I noticed that when I used the brakes the idle stumbled, but for years now I've always had a small stumble at idle, not very noticable but just occasionally. Now I'm wondering if this booster may be the culprit. Anyway it is one more thing to check vacuum-wise.

74RX4

iTrader: (10)

Another thought.
Check the hose that runs from the #2 anti-afterburn valve to the intake manifold.
http://intertron.com/ron/images/carb/c6.jpg
http://intertron.com/ron/images/carb/c5.jpg
It is shown in place in the second picture. It is the hose to the left of the open hose in the center bottom of the picture. It connects to the small silver cylinder (#2 anti-afterburn valve) and runs down to the rear of the intake manifold.
The bottom of this hose can develop a hole which will create a major vacuum leak. It is directly above the exhaust. The heat often melts the hose. Sometimes the hose will harden and seal the hole when cold and soften and open the hole when warm. I would remove the hose and inspect the bottom of it carefully.

Frogblender

I didn't have to inspect the bottom of it carefully, it was pretty much obvious. Two huge seams directly on the bottom as you said. I'm going to do a quick temp fix to see if that helps the idle, and in the meantime I'll get a replacement. I almost burned my hand reaching underneath so I'm going to wait until the bugger cools down and I'll post my results. Thanks so much!

Since I've found this though, anyone else know of any common vacuum leak points I can check? Photos help me greatly

Frogblender

I filled up the master cylinder with brake fluid. I know the brakes are shot, so it takes about two or three pumps to get any pressure. When I do pump the brakes like that however, my RPMs go up about 50-100. I'm guessing it's something to do with the brake booster? The strange thing is the idle doesn't stumble but improves.