Hi there

A few weekends ago, I was out crusing my RX7 SA22C, and started noticing idle issues. First, the engine idled to almost conking out, and eventually it did, and then it didn't at start at all. However, it does crank, but does not crank over.

While cranking over, it blows a lot of white smoke, which I think could be a sign of coolant o-ring degradation. I also noticed fuel bubbling up in the four carburettor chambers, and the spark plug electrodes are pretty much black.

Possible Cause

I don't drive it very often, probably let it warm up for too long, and rarely rev engine beyond 6,000 RPM.

My plan...

1. Service the carburettor. I unplugged and unbolted it yesterday. I'm close to purchasing the Atkins Rotary carburettor rebuild kit, unless someone thinks of a better idea. I think there is an issue with the float, since fuel bubbled up and almost over flows out of the barrels.

2. Replace the plugs. Again, Atkins rotary is where I think I'll get those from.

3. Replace the fuel filter. Purchase from Atkins rotary.

4. Pressure test the cooling system. Since it was blowing white smoke, and there is a small puddle (15ml) of coolant sitting on top of engine case, I think the coolant o-rings have degraded. Is pressure testing the cooling system without the carburettor connected okay to do?

I welcome any opinions on my plan, thanks, and happy holidays to all.

James

PS. I have pictures of it all.
PS2. I'm a learning mechanic (first year apprentice, I want to try and solve the problems by myself, with the assistance of the RX7 community)

 

If the engine gives is having running issues and you suspect coolant seal failure, you can pull the spark plugs after the car has sat to see if they have coolant on them. Secondly, you can pressurize the cooling system to cap pressure from the radiator with a cooling system pressure tester. Monitor the gauge and see if the system hold pressure or drops pressure. It should hold pressure.

Fuel bubbling in the carburetor is a new one to me. Can you elaborate more on this? Is fuel coming out of the top of the carburetor's air horn? If thats the case? This would indicate a stuck float or both floats. The floats will rise as gas fills the bowls and they will push the needle into the seat, causing fuel to stop flowing into the carburetor. If the float or both floats are stuck down, fuel will continuously flow into the carburetor and will overflow..

You can get your spark plugs locally. In an SA, they should be the three ground electrode type, NGK BR7ET. The 81-85 RX-7 used NGK BR8EQ-14 spark plugs which had four ground electrodes.

 

I think you have outlined the proper steps to help troubleshoot, but I would be a bit hesitant to take the carb apart until you can pinpoint it as the problem.

It might be a good idea to check the fuel pressure first. Find a way to hook up a 0-5PSI fuel pressure gauge to your system, Tee it in between the firewall hardline and the hose that goes to the carb.

I believe the SA is like the FB, in that it has a feed to the carb, and an outlet from the carb that returns to tank, in the carb is a simple fuel pressure regulator. This means to get the real fuel pressure reading, you will need to plumb the carb in, can just set it back on top of the intake temporarily, maybe leave a rag between it and manifold incase it floods.

You should see quite low pressure, I think like 2psi or so? Lets see what the Nikki carb gurus say.

The consensus on the forums with Nikki carb rebuilds kits, is that they all use sub-par needle/seats which can make your problems worse. If your fuel pressure is good, then open up the carb, but try to re-use your original needle/seat.

 

Thanks for that.

The spark plugs have been taken out. Would it be a case of putting them back in, cranking the engine over, taking them back out shortly after, and inspecting the electrodes for a coolant leak? I can do that, though the carburettor is currently disconnected.

I'm organising a pressure test kit. I'm expecting to see a very slow pressure drop.

Not sure about the location the air horn, but I took a picture of the carburettor pointing to the area which I think might be it.


From memory, before I unmounted the carburettor, fuel surge upwards in the four chambers, so the idea of the float being stuck down seems right to me.

The plugs I pulled out have three ground electrodes. I'd like to stay factory as possible so I'll shop for the NGK BREQ-14 plugs.

 

Thanks for your reply.

I just checked fuel pressure by turning on the fuel pump and seeing if anything comes out of the main fuel hose. It's looking like at least 2 - 3 PSI at that point in the system.

I'll def need a carburettor rebuild kit. I might not replace all gaskets, but the base gasket definitely needs replacing.

 

What do you mean "base gasket"? Be very careful of not disturbing the structure of the black composite separator that fits between the carb. and manifold. It does not use gaskets at this point

 

Yes, I now mean the black composite separator that fits between the carb. and manifold. Okay, if they're not to be replaced, I won't touch them, but I think some gentle cleaning could be in order to ensure a good seal.

 

The picture you posted reference the air horn is in fact the air horn. You can clean the carburetor base and gaskets by wiping them with something like simple green and a cloth but I would avoid harsh chemicals. Nothing abrasive and do not attempt to remove the gasket and replace it.

 

Got it, noted. The rebuild kit and other parts have been ordered from Atkins. Don't know when they will get here as I'm located in Sydney Australia.Thanks for your help so far.

 

If the rats nest hoses are hard, now would be a good time to replace them since you have access to them.

 

I agree with replacing all of the vacuum lines. When I replace them, I buy a roll of vacuum line and remove each line one at a time and measure it next to the new line and cut a piece off the roll to the exact length I need and replace each line individually. This way nothing gets mixed up and there is no confusion as to where a vacuum line routes.

As for the carburetor rebuild, ensure you clean each part to near perfection. Take your time and ensure its done right. No need to do it twice. Many suggest not replacing the needle and seat. I have and have had good results and bad. I've left them original and have never had bad results. Take care to check and measure the float levels per the FSM. If you don't have a factory service manual, let me know the year of your car and I will go in my library and pull the manual you require and post pictures of the adjustments.

 

Great resource for manuals: Factory service Manuals

 

The vaccum lines feel okay - not too hard or brittle, some softness to them. I tried removing one line though, using a fine point bit to ungum it, but the sun started to burn my efforts, I'll try again in the evening.

The link to the manuals is awesome, the one on carburettors looks more detailed than the Haynes' manual. Thanks.

 

There is a float bowl vent solenoid on the air horn below the fuel in let and return on the driver side. If that solenoid is bad or not getting 12v with key on it will flood the carb. Test it with 12v when u have top of the carb off and test to see that your getting 12v to it. I recently had this problem.

 

Thanks for the heads up. That could be my issue too...

The carburettor is unmounted though. Does it need to be mounted and plugged back in to carry out that test?

I've got a 12V battery, a test light, and a multimeter btw.

I'm back in the workshop at 7:30am (AEST), 5 January.

 

No in fact having the air horn off to test it is better. U can see if the actual plunger is sealing. Power to the plug. ground to the body of valve.

 

Update

The carburettor rebuild kit arrived from Atkins, but the problem runs deeper than a carburettor rebuild. Coolant is leaking, it's sitting on top on the rotary housing. I wiped it clean and it has since returned in fresh form. See picture below, look for the green puddle.


Coolant leak

My diagnosis is coolant seals are worn and it's time for a complete engine rebuild.

I'm contacting Raceonly tomorrow to book it in.

Thanks again for the all the pointers.

 

You do not have faulty coolant seals. The issue is failed o-rings between the intake manifold and the rotor housings. The o-rings fail and coolant seeps out and pools on the engine in that exact location. You will pull the intake manifold and replace the o-rings and intake manifold gasket and be back in business!