I've got a 79 Rx-7 stockport with a 45 Weber that has been a ton of trouble. Been trying to get it running the entire time I've owned it. In the most recent bout with trying to get it running, a buddy of mine and I ran a compression test and pressure tested the coolant system. The first time I tested the coolant system, I had a couple hose clamps not tight enough and a small leak at the thermostat gasket that I fixed (which don't leak now.) Once I fixed all of those, I got busy and didn't have a chance to pressure test it again. Unfortunately, after this most recent test, it seems to leak about 3/4 of a PSI over about 2 minutes. I can't see any external leaks anywhere, though the radiator had been repaired, so it might be leaking inside the radiator somewhere we can't see. We got it to run for a little while (until we tried to adjust the idle down from the 3k it was sitting at) it smoked quite a bit, but it didn't seem sweet, more like too much oil and fuel, which it definitely has been subjected too. The compression test ran 80's all around, not the absolute best, but the engine has maybe 100-150 sparse miles on the rebuild my buddy did when he owned it.

I'm thinking I've got a bad carb. It's definitely well-used. Don't buy used, boys. Don't buy used. I don't want to sink a significant amount of money into a fresh carb just to find out I have a blown coolant seal and need at least a soft seal rebuild.

Since it still doesn't run reliably, are there some potential tests I can run and confirm whether or not I have a blown seal?

 

Where/How did you inject the air to pressure test the cooling system?

 

At the radiator fill with Autozone's hand pump tester

 

I'm not sure that will work very well unless the T-Stat is removed. What PSI did you use?

 

We tried 15 psi. How would the thermostat affect readings?

 

The radiator system is not a perfectly closed system. The overflow is open. Try one of these at the water pump housing.

Cooling System Pressure Tester (CSPT)

 

Are you loosing coolant and is the coolant system getting pressurized? If an internal water seal is bad, it can be on the exhaust or intake side. if a seal is compromised, it can cause steam in the exhaust and/or pressurize the cooling system and a lose of coolant. Does your issue exhibit any of these systems?

 

I don't think I'm losing coolant and how can I tell if it's being pressurized if I can't run it?

 

Many times when it's pressurized, you will see small bubbles when observing the water in the radiator. It can, but not allows, pressurize it so much that it pushes water/air into the overflows tank. If it's being burned in the exhaust, it will smell sweet like antifreeze and be white smoke.

I had an engine so bad that it would push so much air through the overflow tank that water would shot out 10 feet via the tiny hole in the overflow cap.

At this point I'm no sure this is your issue. How much coolant is it using? And can you start the car. If the issue is that the plugs are getting fouled with coolant, you should be able to pull the plugs and see/small coolant. If you can't start the car, ensure you have spark, gas, and really good battery. We know you have some compression. if you have spark and gas, try pull starting it and popping the clutch in second gear . This will raise the RPM from 250 of the cranking battery to 2000 RPM.

 

I'm certain the level in the overflow tank has stayed almost exactly the same, if not the exact same, in the year that I've owned it if that helps any. I am also pretty sure it isn't using coolant, or at least not enough for me to notice a difference when I look into the radiator. When I pull the plugs they don't smell like coolant, they smell like fuel.

If I just crank the engine with the starter, would I be able to see bubbles potentially?

I've got a fresh starter on the way to replace my dying one. I wish I had taken a look down the radiator when it was kind of running the other day.

Could I pinch the overflow hose and test it the same way again?

 

I wouldn't worry about the possibility of using coolant at this point. The first thing is to get it started. A fresh battery, fuel and spark are the most important right now. Report back the progress of spark and fuel being present.

To be able to see any bubbles, the engine would need to be running. There is a coolest level sensor in the top of the radiator. You'll know when the coolant is low because this buzzer will go off.

 

It went off when we got it running yesterday, but I can't remember if I had topped off the coolant after I had drained it to replace the thermostat gasket.

It's a tough spot, because the carb I've got isn't at it's best, so getting it running might be difficult. I'll install the new starter when it gets here, and see if I can avoid getting another carb for a little while longer.

 

Good news! After a new starter, new battery cables, and a new carb with decent jets, it ran! The jets are totally off, and I couldn't get it to start again once it was warm, but I did remember to check the radiator for bubbles.

No bubbles coming out of the radiator, nor was there any plumes of sweet-smelling white smoke.

Now just to get this carb running properly. So excited

 

Nice work

 

Thank you very much for your help. Love this forum.