I recently replaced the intake gasket as the O-rings were leaking on my stockport 12a Rx-7 and I decided to block the coolant passages to the intake manifold and fully flushed and replaced the coolant.

it was idling smooth when I put the carby back on and flushed the cooling system.

I know blocking the coolant passages makes it a bit rough on idle when the motor is dead cold
but it keeps missing even when at operating temperature the idle never starts to smooth out.
it never did this before always idled smooth from when it was first started.

it idles like its missing and got a bit of a port,
I haven't really driven the car over the last year, just been starting it and letting it get up to temp by it self.....could it be fouled plugs or leads??

 

Pulling the plugs takes 5 minutes - have a look to see if they're fouled. Also, simply removing excess heat from your lower intake manifold should not appreciably change the A/F mixture to affect idle, as the A/F mixture is nearly into the engine already by that point.

Are you sure when you put the carb and upper intake manifold back on that you got all the vacuum lines hooked up right? A miss at idle or poor idle is most likely a vacuum leak, and with the age of the hoses, brittleness could have cracked one and you didn't notice it, yet.

 

I took it for a run around the block to open the secondaries and blow the cobwebs out
it helped a bit and idled smoother before i shut it off.
i let it cool a bit then went to move it from out front into the driveway and it was idling like a Bridgeport and wanted more revs to get going seems to have gotten a bit worse.

ill have a look at the plugs when I find my ground down spark plug socket,
any tips on what to look for when checking the plugs??
im pretty sure black is signs of running rich and chalky is running lean, but by the smell of it its running pretty rich.

i know the crankcase vent vacuum line has a tiny little crack in it, but when i first put the carb back on i forgot to hook up a few lines when i started it up and it still didnt idle this rough, that's why i think it could be the plugs.
iv changed a few vacuum lines but may aswell change them all when i find all the different size hoses.

 

I can think of a few problems you may be having. Let's see if I can help.

Is your carb rebuilt? If so, it probably has the awful aftermarket needles and seats. If so, I feel sorry for you. All of the aftermarket seats are machined incorrectly and always lead to flooding. It's an industry wide problem. The solution is to order some brand new ones off of Mazdatrix at 40 dollars a piece. You only need two. Expensive mistake to ever get rid of the original needles and seats. You may also need new floats if they were adjusted to make up for the bad needles and seats and you are unable to bend the tabs back to stock.

Since you blocked the coolant seals, you may be getting too much heat into your intake manifold now that the ACV port is still pulsing exhaust heat up into the intake manifold about a thousand times a minute at idle (1k rpm). Without coolant there to regulate the intake manifold's temps, it causes the manifold to get really hot unless you block the ACV port with quicksteel like I do or some sort of JB weld putty or something. I find I have to explain this about every other week. It must not be common knowledge yet. It becomes pretty obvious when you sit down and actually study the way the intake manifold works.

You probably didn't delete the rat's nest properly. There must be something not quite right like a small vacuum leak somewhere, that you've adjusted the carb to compensate for.

The carb, as it is from the factory, needs to be improved in the air bleed department. This too is not common knowledge yet. The stock short slow primary air bleeds are massive and only work if all the stock choke mechanisms and systems are in place. When you tamper with things, the low RPM area of the carb will not run right until you reduce the air bleeds a bit. There are several ways to do it. I'll just tell you the size of the original bleeds, which is around 170 but can range from 150 to 190, and the size you really should change it to, which is around 118. Here is a possible option for you: Genuine Mikuni CV Size 115 Air Jet B42 55 115 | eBay They thread right into the primary side but do go a little deep so be ready to see the head sit flush or slightly below. Still works though.

 

I noticed where you said you need to find your ground down spark plug socket. Does that mean you have non stock spark plugs? If so, that could be your problem right there. They are probably motorcycle plugs and totally unnecessary on a stock engine. Get yourself some stock spark plugs for your year. That would most likely be BR8EQ-14 for 81-85 and should work for the '80 as well. If you have a 79, well, good luck with points.

 

im not sure if the carb was rebuilt at some stage
I didn't rebuild it when I took it off, thanks for the tip ill remember never to replace the stock needles and seats.
I herd of people blocking the ACV port but I didn't want to devcon/epoxy it while the motor was still together. or is it safe to do??
haha yea I have seen you mention it in a few other posts

some of the rats nest has been deleted but I cant take it all off yet as I still got to go for registration.
but when I brought the car I didn't touch the rats nest, but it idled around 1Krpm and was too loud for a stockport with the 2.5 exhaust that's on it so I adjusted the idle speed so it sat at around 750rpm as the FSM says. I did this before the O-rings in the manifold busted and it had no problems idling at all after that.

it bucks a little bit in the lower rpm but pulled fine all the way to redline when I took it out yesterday.
I might have to look into air beed side of things like you have mentioned.

ill pull the plugs shortly and ill try get some pics up.

thanks for the help Jeff.

 

I just had a look I don't think I need a ground down socket, the car is running NGK's BR8ET spark plugs both front and rear are they any good?. im pretty sure they have 3 electrodes on them and the BR8EQ plug you mentioned have 4.
whats the difference running 3 compared to 4 electrodes??

its a 79 but no points dizzy, could a rotor button on the dizzy be causing a problem??

 

Follow Jeff20b on the carb recommendations, certainly - and for BR8EQ-14's, these are standard issue for our generation engine and have 4 electrodes which help to burn off fouling and prevent issues with spark. They do get carboned up from time to time and a good cleaning could help with idle. Also a distributor cap and rotor is a cheap investment, as sometimes hairline cracks will form which account for a lot of "just-pulled-my-car-out-of-storage-and-now-it-runs-crappy" threads every spring. Usually a new cap and rotor fix it up.

 

ill have a look and see if the plugs are fouled.

whats the difference between resistor and non resistor type plugs??

i might get the BR8EQ's with the extra electrode cant be a bad thing,
unless the fuel delivery is no good and it will probably start to detonate.

iv seen other people recommending B8EGV's with good results, or is that more for fuel injection?

 

TOP PIC IS LEADING AND BOTTOM IS TRAILING.

they look pretty fouled and motor seems to be running a bit rich
im ganna clean them and put them back in and see if it changes a bit, before i got buy new ones

 

it was the plugs!
put them back in after cleaning and it idled smooth. it even started easier with less cranks.
ill have to get a fresh set once I get it on the road.

thanks for the help.