Help with smoking 12a
 

Hello all,

I'm super new to rotary motors. I just picked up a 1985 rx7. (picture attached) it's got the 12a carbed motor.

It's pretty clean overall, but it's got a little bit of a smoking problem - Not sure if it's possible - but to me it appears that it is coming out of the metal hose that connects under the air cleaner. It's definitely oil based gray smoke. When I take the lid off cleaner after killing the warm motor, it seems like a bit of smoke is seeping out of that spot.

I've done about an hour of searching various service manuals and forum posts and can't figure out what the larger metal hose connects to, or anyone with a similar problem.

Is it the hose going to the EGR valve? Is it possible that it's stuck open?

Thanks All,
Ben

Post a pic of the hose if you can.

I will post one later when I get home. It's on the passenger side of the engine bay. Looks like a mini dryer hose, about an inch in diameter - connecting to the bottom of the air cleaner.

Sounds like the intake heater hose that fits on the snorkel of the air cleaner. It feeds into a flapped
vent that lets warm air in to ease cold start and cold idle. If you see smoke from this it means that
something is probably leaking onto your exhaust manifold and burning off. Likely the intake manifold
orings are leaking coolant onto the exhaust. A fairly common issue to have. Coolant burning will be a
light colored smoke, oil will be dark to black. You can usually also smell the difference. Also does
hows your coolant level? Do you always have to add a little sometimes?

You can see the smoke coming out in the first picture. The hose connects to the large port right behind the inlet snorkel of the air cleaner.


https://cimg3.ibsrv.net/gimg/www.rx7...91ab51aa1b.jpg


https://cimg4.ibsrv.net/gimg/www.rx7...2897def8c0.jpg

That tube is actually open to fresh air. It connects to the exhaust heat shield. The smoke is probably just OMP and other leaking oil burning from the outside of the exhaust. Nothing to worry about.

Similar not long ago.
I "fixed" one of the OMP lines above the thermostat area. But the fix was with a a rubber vac line, which expanded causing the oil from the OMP to blown back and down onto the plate under the carb and then eventually to run down to the top of the exhaust manifold.

Smoked like crazy. Stopped at lights and smoke coming from the hood and wheelwell. Stunk too.

Refixed the line, and cleaned off what I could, then just let the rest burn off.

I did rebuild the OMP earlier. it no longer leaks.

I would verify the OMP lines are still connected properly and not leaking. Mine would come off with the slightest pressure. Replaced the OEM wire clamps with gas-line style clamps. Maybe overkill.

if the car has been sitting for a while before you got it then the manifold is most likely burning off a bit of oil seepage and most likely will clear up in time.

Tim - you have my respect for the cleanest front housing I've ever seen. Way to keep that area clean, as my -SE looks like a Texas oilfield complete with dirt, weeds, rocks, twigs, and prairie dogs. I rebuilt the pump and wiped off as much as I could and it still didn't seem to matter.

To the OP: as the 2nd post correctly identifies - this is the hot air intake from the metal heatshield around your exhaust manifold to the intake manifold. That white trap-door has a bi-metal strip attached which either raises the door or lowers it to allow the right mix of warm air into the carb on cold days. There's either oil or coolant leaking onto your exhaust manifold INSIDE the shroud, and hot air rises - drawing the smoke upward where you're seeing it.

There are 2 coolant passages on your lower intake manifold which are notorious for the O-rings leaking coolant, which drips down. Remove the intake manifolds and replace the O-rings (Mazdatrix):
https://www.mazdatrix.com/pictures/c-intake/c2-j.jpg
Quick link: https://www.mazdatrix.com/c-2.htm

Or, you could block them off when you have it apart (use coins and seal them with RTV or Gasketseal) and never have to deal with this problem again. The only downside is that the intake manifold won't be heated by hot coolant anymore - which is actually an upside unless you live in Siberia. Good luck,

Apologies to the OP.
Explanation to LongDuck.
Parts are easier to clean when they are not attached to anything.
The before was a tar pit.

LongDuck, you should recommend 20mm freeze plugs instead of coins. They work pretty well and Mazdatrix sells them. Your local auto part store also sells them.