1983 RX-7
mods: 2.5in exhaust, front mount oil cooler, (mechanical secondaries?)

Looking for some opinions on the running condition of my car
-The car has little power and won't idle under 1.5k rpm until it has warmed up completely (around 30mins)
-Once warm the car runs idles great and has fantastic mid-high end power however the low-end feels lacking. like if i shift 1-2 at 2500 rpm or lower the car bogs a little into the next gear until the revs get up.
- If I am idling in neutral and get on the gas quickly it bogs down quickly then revs up (nastily) and returns slowly to idle

I have already found a few upgrades done to the car i hadn't known about when I had purchased it (upgraded oil cooler) and thought maybe it had mechanical secondaries installed? The is my first rotary so maybe this is all normal?

 

Engine should be normally be up to operating temp within 5 mins or so.

Rotaries have little low-end torque compared to piston engines, but you shouldn't see a bog coming off idle in neutral, and the car should pretty easily pull out of a shift at 2000rpm.

 

thanks for the response!
so i guess this isn't normal then. after 5 mins of warming it up it has little low end you have to rev the crap out of it to get it going but the more you drive it the better it gets. although the low end power never really gets up to where it should be

 

How do you warm it up? Is that 5 minutes sitting or driving? Does the coolant temperature look like it's in the right ballpark fairly quickly? How long until you can see movement in the oil pressure gauge that would suggest the oil is warming up and thinning?

Oh, and does it still bog when you give it a little choke, or does that make it worse?

 

The choke is weird so i pull it out to about 2200 rpm and slowly let it down to about 1000 rpm over the course of like 5-6 mins but in order to do this I have to physically hold it there it won't stay by itself.
The coolant temp. starts to register after about 3 mins of running the car idk if you'd classify that as quickly
As for the oil pressure that gets up pretty much right after the car is started.

Not sure about giving it a little choke, I'll check asap, but why do you ask?

 

Does the choke 'snap' back in or does it 'creep' in? The original choke on these slowly creeps in as the engine warms up.

Regarding the oil pressure gauge, I was wondering how long it takes for the pressure to noticeably fluctuate - as the oil gets warmer, it gets a little thinner, the pressure at idle is a little lower than the pressure at higher rpm and when the engine is hot, you see a very noticeable movement between idle speeds and higher engine speeds.

In other words I'm wondering if your oil is actually warming up properly at all.

 

the choke snaps back in. been like that since i got the car

but yea the oil pressure definetly appears to be acting normal. once warm its sits around 15-20 at idle and increases with the rpm

 

If the choke snaps back in and the car is still on the original Mikuni, that would suggest the choke mechanism is broken and that it runs rather lean when cold. That's certainly not good and if it's only bogging down when cold, that's the likely culprit.

I'm not sure if that's also the cause for the slow warmup; I'd look at the thermostat and also check if your oil cooler has a thermostat or not, otherwise you're probably overcooling the oil.

 

thanks!

 

wait so even if i held out the choke manually it would still be running lean?

 

If your choke won't stay out, you have a malf in the choke magnet (assembly just behind the dash panel that the choke cable passes through) or in the #2 Temp sensor, located on the rear of the water pump. Or in power or wiring for same.

 

No, if you hold the choke out manually it shouldn't run lean. Rotaries need an awful lot of fuel while they're warming up due to the combustion chamber shape, hence the stumble if it's luke warm or cold and you don't hold the choke out all the way.

I'd look at the choke mechanism first as described by DivinDriver and get that working again, see if that improves warm-up times, then look at the coolant thermostat and finally at the presence of an oil thermostat.

 

what exactly is a malf?

 

Malfunction, I would assume...

 

Yes, sorry; shorthand for malfunction.

 

What exactly are you talking about?? There is no such thing as an oil thermostat in a pre-86 engine. The 86 and later engines had thermo wax pellets, but not in a FB.

For th OP, sounds like there could be several things going on here. Most of them will probably be related to fuel delivery. It could be anything from a clogged fuel filter to a carb in need of a rebuild. You could keep checking this thread for random things to try, like a monkey humping a doorknob, or you could go to the FAQ/Archives and download a copy of your Field Service Manual and start troubleshooting your vehicle. Start with a basic tune-up and go from there. Be warned that the NIKKI carb (not Mikuni) is not the simplest design in the world, especially for those that are not very carb literate. Your car needs to be in good mechanical order before anything else can accurately be troubleshooted.

Get some new plugs, wires, rotor and cap, change the fluids, check the houses/fuel lines, replace the fuel filter, pull the carb off and hose it down with some carb cleaner, replace the air filter, check for any vacuum leaks, and see if that helps. Worst case scenario, pick up a Nikki rebuild kit and tear that thing apart. There are plenty of Archive threads about rebuilding and modding the Nikki as well as an entire chapter devoted to it in the FSM.

 

The OP mentioned that his FB has an upgraded oil cooler and he's in a place where it doesn't really get super hot (not like Vegas on a Summer afternoon...). So there is a chance that if the oil cooler is constantly in the oil flow, it'll noticeably prolong the warm-up of the engine, which might contribute to his general warm-up issues. This is of course under the assumption that the oil cooler fitted to the OP's car is more efficient than the one it replace. In this case you'd hope that the new cooler has been plumbed in via a thermostat.

Good point about the vacuum leaks; I'd also replace the coolant thermostat with a good quality new one.

 

thanks, now that i think about it the car probably needs a new fuel filter anyway so I'll try that

 

Yet again I will state... there is no oil thermostat in a pre 86 engine. The OP's car is an 83, which came with the liquid to air oil cooler (beehive), he is likely saying that the car has a front mount oil cooler instead of the beehive. Either way, whether it is a beehive, a stock mazda front mount, or an aftermarket front mount there is still no oil thermostat. If the engine is running, then oil is flowing through the cooler. Also, most post 86 engine, upon rebuild, replace the thermo wax with a thermo pellet, or at the very list shim the spring so that the "thermostat" stays open constantly as the old thermo wax has a tendency to fail, and when it does it cuts off flow to the front rotor thus causing bearing failure.

Also, if you're going to be replacing the thermostat you need to use an OEM mazda unit as they have the famous "jiggle pin" that aftermarket thermostats lack which can cause the thermostat to fail, overheating the engine.

Like I said before, download your FSM, read through it and then start making the car road worthy, not only will you learn alot, but you'll likely be presently surprised when you find out your problem works itself out along the way. You can't be lax with these cars, improper maintenance and driving the car under those conditions is the number one cause of blown engines on stock to lightly modified cars. Rotary engines will run forever if properly maintained, but if neglected the are not as forgiving as a piston engine, and they are MUCH more expensive to rebuild. A little prevention goes a long way when dealing with rotaries.

 

If he's using an original pre-beehive 1st-gen FMOC, then there IS indeed an oil thermostat - - but not in the engine. It's in the oil cooler, bottom left side. Bypasses the oil cooler until the oil reaches a given temperature. If it failed, he'd be routing oil through the cooler all the time.

 

Ok so I swapped in a new fuel filter today. The car now runs AMAZING! shifts a 1800rpm no problem! Thank you all for the help!
btw when i drained the old filter the gas coming out was literally orange

 

Well since it looked that bad in the filter I can almost guarantee that it looks that bad in the carb as well. Get a rebuild kit and clean it out. Or a better alternative is that you buy one and rebuild it so you have your running one still available just in case.

 

Glad to hear it's running better.... but if the fuel filter was that bad you've likely got many other things that need attention. Don't beat on it, until you get everything sorted.

And for those of you that care.... yet again there is no oil thermostat on a pre 86 engine. I just tore down an 84 12a,today, with a beehive, and I can promise you there was NO oil thermostat in the beehive. I can take pictures if anybody wants, before I throw it in the trash!!

 

damn. do i really have to do a full rebuild on the carb? I mean it runs great
btw random but what brand do you guys use for distributor caps/rotors?

 

If it runs great, your carb may be just fine. If it was badly sludged up, you'd know as it wouldn't run well.

If your tank is badly crapped up, you'l know as your oil filter will get dirty fast. You may want to look into dropping the tank, getting it boiled out at a radiator shop, then re-coating the interior.

There are threads on the process here or in the archives.