JSmith0101

iTrader: (6)

So here's the deal. I just got the carb back on my 84 GS and it's still not running quite right. At this time, it's not idling without the choke being pulled out just a hair.

What could be some causes and solutions for this?

Rx-7Doctor

iTrader: (13)

I'd say there is a really good chance that you have a big vacuum leak.
Did you do any other work such as recently putting on a header system and removing the emissions rats nest?

And what was the symptons that you decided to rebuild the carb?

JSmith0101

iTrader: (6)

I didn't rebuild the carb, but I had planned on it. The car wasn't running right, and it was my opinion that the carb was gunked, as it had been sitting for at least two years without really running well. I ended up taking the carb off, removing the hard lines on it and spraying in carb cleaner, then finding that the secondary throttle blades (the big ones?) were seized and I gently massaged them into working.

I also was a moron and didn't tighten one of the bolts on the hard lines and it spewed fuel everywhere... but that's another story. :LOL:

Anyway... I reconnected everything and then sprayed it all with starting fluid and it didn't do a thing.

Rx-7Doctor

iTrader: (13)

You need to verify that the fuel bowls are filling up by viewing into the sight glasses.

Also by removing the carb you could have a misrouted or leaking vacuum hose.

There could be clogged jets also.
I would get a can of carb cleaner and get the engine running and then spray along the intake,carb, and vacuum hose area to see if the RPM picks up.

BigPimpin'

iTrader: (5)

Adjust the idle screw.

JSmith0101

iTrader: (6)

The what?

Rx-7Doctor

iTrader: (13)

Meant to say. Bumping up the idle screw is just a temp solution of a bigger problem.
At the front and rear of the carb are clear sight glasses. They allow you to see into the fuel float area to see if the fuel is getting into both fuel areas of the carb.

JSmith0101

iTrader: (6)

No kidding?

Wow... do I feel like a horse's patoot.

Rx-7Doctor

iTrader: (13)

There are some really good write ups on these carbs in the archives. I recommend that you take alook at them. It will probably shed some light for you.

Rx-7Doctor

iTrader: (13)

I also have to include some other things here that I always take for granted.

The shutter valve that is attached to the intake manifold could be leaking. If there is a weird honking noise coming from the air cleaner area then it is leaking.

The more common things that are taken for granted that do cause driveabiltiy issues are.
The condition of the following ignition parts.
Dist cap,rotor, ignition wires and plugs.
Fuel filter.
Timing, has it been checked?
Compression, has it been tested?
Fuel pressure and volume.
Those things should be checked and considered.
I'm still leaning towards a vacuum leak and or clogged jets.

JSmith0101

iTrader: (6)

There are only 49,xxx miles on it, if that helps at all.

blwfly

iTrader: (4)

nice check list doc.
ild say follow his list mate

two79rx7's

I vote shutter valve soleniod.

I think I have a problem here too.
this controls the assoc. coasting valve which works with the shutter valve
See FSM fotr 85 section 4A -6 .17 and 4A -8 .33

coasting valve supplies fresh air into rear primary port when decelerating to prevent excessive vacuum
shutter valve shuts off rear primary port during deceleration

IE: engine is to pull in air through rear primary port by way of the coasting valve during deceleration to prevent vacuum when shutter valve closes off intake manifold feed from carb. If this system sticks open also during idle and acceleration you have a big vaccum leak ( see rx7doctors post ). But this is not the same as a broken hose causing a vac leak

empericaly this is the personality of an engine with this problem

there is a small hole on the inside of the rear drivers side in the air cleaner case with the engine running you will probably hear alot of air getting sucked into that hole. It might sound like a horn blowing. Put your finger over this hole or plug it up with something that wont get sucked in. the engine should now idle without any help.

If your so inclined strip the carb down to remove alot of "stuff" not really needed see

contact vipernicus42 for his excellent pdf tutorial carb strippin
and
see his post " Need a few good *carb* guys for review"

I beleive this covers the coasting valve and shutter valve and S.V soloniod

an additional step after this part is sorted out is to:
remove an aging rats nest which will plug up all potential vacuum leak sources; or you can plumb all new hoses and do a complete diagnosic of this system to make sure it is completely 100%

One post I read said shudder valves go up all the time but I think they are only on later FB's maybe only 85's

One thing I notice with my very similar problem to yours is if I run the 12A car hard at 80 to 85 on the highway which is where these cars shine. for a half an hour or so...really run the car out in 3rd 4th and 5th, then afterward at least for a while your car will at least hold a really rough idle instead of conking out. And if you bump the gas while at a light you can prevent the same.....What you are doing is giving extra gas into the big vacuum leak by way of the accelerator pump enriching the mix enough to keep an idle. This is what RX7doctor was refering too about the vaccum leak.

if this did not help my next best guess is:
the anti afterburn valves 1 + 2 which sends air into ports during decl. just like coasting valve. so if defective same problem. see 4-A .5 for decription
check idle compensator in air cleaner ***. 4A-.51
check altittude compensator see 4A .51

Hope all of this info helps to get a handle on your situation.

regards
two79rx7's

Rx-7Doctor

iTrader: (13)

Good post two79rx7's.

All 81-85 models have a shutter valve. It is a very common problem.

darkblaze

when you put the carb back on the car did you recconnect the BIG vac line on the firewall side of the carb that goes to the intake manifold? i had the same problem on my 83 gsl. cause i didnt hook that line back up. Rob was nice enough to let me know about it when i bought a carb from him.

JSmith0101

iTrader: (6)

I installed it all. My memory is almost photographic, and I documented everything on the digicam.

two79rx7's, thank you for such a well-put post, I will most certainly give plugging that hole a shot. If this is the problem, what would be the solution? Keep it plugged? *shrugs*

I appreciate all the help thus far and tomorrow I will get cracking on it again.

JSmith0101

iTrader: (6)

I looked through the glass on the front of the carb and there was fuel in it, how much should there be?

kgray

About 1/2 way full on both sides.

JSmith0101

iTrader: (6)

The front looked window looked good, I couldn't see the back.

Also, I went and took the carb off again, took the windows out and sprayed carb cleaner in them,... better safe than sorry, I figure. The front looked good, I couldn't see the back.

But while I was doing that, something went "spring" and something is now off, posted below is a picture of the carb in its current state, three forum bux and an expired oil change coupon for the first answer.

Rx-7Doctor

iTrader: (13)

The secondary spring popped forward, it happens. Just pull up on the top section of the tetter totter looking piece with pliers and hook it back over the arm. You can keep the hole plugged if the shutter valve is leaking. When members do the stripping of the Nikki Carb down to the bare minimum they no longer have the function of the shutter valve.

JSmith0101

iTrader: (6)

The valve... I should have taken a picture, but it's on the rear left barrel thingy of the carb manifold (I think it's called that)?

I feel like such a horse's ***, I know nothing about FBs, I had an FC...

darkblaze

i hate that F%^*^ spring it came off on me all the time when i pushed it to full throttle and it ran like **** until i put it back on

two79rx7's

Stopped by again to check up on things.

In regards to your question to me Wotnartd, here goes,

Refer to my prior post a few days ago….If you find the condition that I described there, then you’ve got a problem in this pneumatic circuit which means one or more parts are bad and a remedy is needed.

SECTION 1.

There are 3 parts that must work together.

1. Shutter valve solenoid---- an electrically controlled pneumatic solenoid w/ yellow dot on top in rats nest.

2. Shutter valve ( S.V. )---- a butterfly in the rear throttle plate port under the carb ( i.e. top part of intake manifold).

3. Coasting valve ( C. V. )---- .
Is the control valve that regulates the on or off state of air flow from air cleaner into the vacuum of the intake manifold at a location downstream to the position of the shutter valve. The C.V. simultaneously also has an arm that actuates the shutter valve to be in either a closed or open position. The C. V. state is determined by the vacuum signal it gets from the S.V. solenoid

SECTION 2.

Start with diagnostics of the S.V. solenoid with engine off.

On the solenoid:

Step 1.
The port ( 1 ) pointing up and closest to the carb goes to the coasting valve, disconnect the rubber tube on the side of the C. V.
The port ( 2 ) parallel to the body of the solenoid and adjacent to the electrical connector goes to vacuum source at the base of the carb., disconnect rubber tube at solenoid.
Blow through C. V. tube ( 1 ) and air should come out the vacuum port of solenoid ( 2 ).

What does this mean.... vacuum gets supplied to coasting valve when NO power is applied to the solenoid ( hint, engine is off )... See the next step which further confirms why this is true.

Step 2.
Now apply battery power to the solenoid directly with test clips by removing the electrical connector ( I am not sure if you have to worry about polarity, my strong guess is you don’t but check this out carefully by looking at the connector )
Blow through tube ( 1 ) and air should come out of the vent of the solenoid and NOT the vacuum source ( 2 ).

What does this mean.... vacuum gets disconnected to the coasting valve when power is applied to solenoid...right.

Make sure both of these events happen.

*****************

SECTION 3.

Now on to the coasting valve:

Hook all hoses back up….. get engine to idle.
As I referenced in my prior post, plug the hole in the bottom of the air cleaner with something that wont get sucked into it or put a finger over it. Apply or remove this seal as needed while doing the test below. ( Don’t let anything fumble into the carborater!!!). Again this hole is easy to find as it is sucking air in madly and making a horn like sound at you. Remember, it should not be doing this at idle…This is the flag waving at you to tell you there is a problem with this pneumatic circuit.

What is supposed to happen.
At idle, no air should be sucked into this hole. Then bring engine speed up to 2000 or 3000 rpm and then drop the throttle immediately down to idle. Deceleration---this is when air should be sucked in and routed to the intake manifold while simultaneously the shutter valve is closed. Once the engine speed has dropped down to near idle the reverse becomes the correct condition of operation again.

So far , there is still a disconnect in the logic as to how this system works . For instance and directly related to our problem of no idle…Does the S. V. solenoid need to supply a vacuum or no vacuum signal to the coasting valve for it ( the C.V. ) to open the shutter valve and shut off the air source from the hole in the air cleaner on route to the intake manifold.
To further illustrate:
When power IS NOT supplied to the S.V. solenoid, which means vacuum is supplied to the coasting valve, as we found in SECTION 1., does this cause the coasting valve to open the shutter valve and shut off the air source being supplied to the manifold.
Or is it the opposite, the shutter valve closes and air is supplied to the intake manifold.
Without taking known good parts off a car and testing them in your hand, the key is to trace what the power state of the S.V. solenoid is versus the engine operating state. So what is the source of power to the S.V. solenoid?

Ok, I looked through the FSM ‘85 and found
1. The emissions control electrical system for 12A engines section 50 B-1 shows terminal Q on ECU connects to this solenoid for a power source but it does not say what the power state of the solenoid is for any particular operating state of the engine or commented about anything in regards to the problem at hand.
2. ECU state condition, section 4A -44 shows Q at < 1.5 volts when ignition is ON but engine is not running... this is also the initial state when the engine begins to run.

********SO there is the answer.*********

Voltage is not 12 volts, which then must be reserved for the state of the solenoid during the deceleration condition.

An aside:
{ it is possible that it does not follow this pattern but instead }
{ ign. ON - ECU/Q = < 1.5 V: }
{ engine now running but not decelerating - ECU/Q = 12 V: }
{ engine decelerating ECU/Q = <1.5 V: }
{ my vote is this is highly unlikely, just needs to be verified at the car }

To continue:
So voltage is NOT supplied to the solenoid accept for the deceleration condition.
Putting all of the pieces together:
During all conditions other than deceleration a voltage is NOT supplied to the shutter valve solenoid as a signal, vacuum IS supplied to the coasting valve as a signal and the diaphragm in the coasting valve OPENS the shutter valve and DOES NOT allow air to get sucked into the intake manifold through the opening in the air cleaner.

Before, we could have found an offending part by the tests in SECTION 1. and SECTION 2 but the operation of the system state was unknown and determining a suitable remedy was vague at best. Now its all very simple.

For instance:

1. Is the shutter valve solenoid stuck as though it has voltage supplied to it and has disconnected the vacuum signal to the coasting valve? This would shut the shutter valve ( now the word shutter valve starts to make sense ) and cause air to be routed to the intake manifold when not wanted and would kill the idle. Also is the ecu electrical signal bad or is there a problem with the wiring shorted to hot ( always giving a 12 Volt signal to the S.V. solenoid ), this would give the same result.

2. Is there a hole in a vacuum tube to the coasting valve? Same result

3. If none of these conditions exist, then the coasting valve diagram, or the coasting valve actuating arm or the shutter valve is defective in some way. This will require installing a working coasting valve and/or repair of the shutter valve

4. It is possible all of these conditions can exist at the same time or each exist intermittently and independently, so be though.

5. If 1. and/or 2. exist then an immediate simple solution would be to hookup a good piece of vacuum tubing from an always on vacuum source DIRECTLY to the coasting valve as a signal to cut off the air source to the intake manifold and OPEN the shutter valve. Just plugging the air source to the intake manifold as described earlier will allow the engine to idle but it wont open the shutter valve. This will for all intents and purposes block supply from the rear primary port of the carb. intake port until the shutter valve can open.


Vipernicus42 reports he finds shutter valves become seized in one position over the years. Check this out some time when you can because if this has happened and is fully or partly closed you will never get balanced flow between front and rear primary ports for all but granny driving.
He also reports to this effect ( just from memory, ‘the reason for the design of the shutter valve was to eliminate backfiring during deceleration . However if everything is tuned right there should be no backfiring to warrant a shutter valve.’

I have a 79 rx7 which backfired to the extreme! There is no shutter valve on these manifolds. It was being serviced by a Mazda tech at a dealership at the time….they never got it right…. only worse. I will vote that the dealership did not know what they were doing.

My recommendations contact Vipernicus42 to get his excellent tutorial
Stripping a Stock Nikki, The essential guide to removing the extra crap
from a stock rx7 carburetor.

Get a second Nikki and for a baseline install it to see how it functions then clean and rebuild it ( as an aside, never touch the floats unless absolutely,,absolutely did I say absolutely!!! necessary ) but include selectively the changes or modifications you want as shown in the how to step by step tutorial above.
You will always have your original nikki to fall back on or refer to.

For instance depending on my final goals I may want to keep the shutter valve operating if I need to set other aspects of the operation of the engine which could promote backfiring. In my ‘85 12A car.

On an aging car, remove the rats nest or rebuild it to 100% spec. if you are going to keep it. The above is an excellent example why you need to do one or the other.

I should be able to let you know what my findings are for what the voltage signal state is to the S.V. solenoid by checking my car in the next few days to confirm that point.

Note how the FSM leaves you in the dark about all of this, it only spells out the go or no go tests to trace if a part is faulty and it did not cover all of the components involved.
A small chapter with a summary explanation of each system would have made the FSM much more complete.
As an example I will repeat from above:

*******************
“Putting all of the pieces together:
During all conditions other than deceleration a voltage is NOT supplied to the shutter valve solenoid, vacuum IS supplied to the coasting valve and the diaphram in the coasting valve OPENS the shutter valve and DOES NOT allow air to get sucked into the intake manifold through the opening in the air cleaner.”
********************
I probably need to edit this more but for now just wanted to get this posted.

I hope this meager attempt above will:
Help anybody to understand the operation this particular system and to allow them to modify it in any way they choose and,
Give anybody a path to follow so they can compartmentalize and understand the operation of any other system. To lay out the areas you do understand and to present it so you can ask questions for the parts you don’t understand.

Two79rx7’s

P.S. any comments are always welcome.

JSmith0101

iTrader: (6)

After chasing problems all day and night and the day before x2, my dad finally got ahold of a mechanic budy that is familiar with OUR CARS!!! He's going to rebuild the carb Monday night. I pray this works.

Thank you for all the help, let's hope this works.

Could I remove that valve? Just undo the screws and worry no more?

two79rx7's

wotnartd,

see my last post to you,, details everything for you including the whys and hows
take the time to read it and refer to the FSM and the tutorial from Vipernicus42 and you should be OK.

Directly to answer your last question, in my last post refer to:

Do you have a hole in the air cleaner base that is sucking at in loudly and sounds like a horn blowing at you?
Did the test of putting your finger over this hole in the air cleaner as in my discription cure the problem while the hole was sealed?
If so that is where you need to focus on first not rebuilding the carb.!!!!

Then see:
My recommendations near the bottom of my last post at #5. about using a vacumm tube as an immediate but temporary remedy...this should take 5 minutes.
and should fix the problem.

If it doesnt look into the coasting valve/shutter valve and make sure that is working right. About removing this part and fixing this refer to my last post, the FSM and

Contact Vipernicus42 to get his excellent tutorial
Stripping a Stock Nikki, The essential guide to removing the extra crap
from a stock rx7 carburetor.

I would check these things out before getting someone to rebuild a carb.

regards
two79rx7's