Carb Problems
 

Can someone please help me with a carb problem? I have a 1985 RX-7 GS (12A) and I believe the stock carb. is not preforming to its MAX. It feels like there is a small bit of power there, but not what I think I should feel. It is almost like it is only using 2 barrells rather then 4 barrells. How can I test and make sure my secondaries are working correctly? Also, I believe my catillitic converter is clogged. How can I test to see if it is? Thank you for your time.

Secondaries open up at 3500 rpm... if that helps any?

Ummm...As far as tesing your secondaries...I would say to take off your air cleaner (REMEMBER WHERE ALL THE VACUUM LINES GO!!) and then have someone step on the gas and look down into the carb and see if the secondaries are opening (the larger holes, right guys?). They should open after the smaller ones. If you dont wanna go that far, I think you could just watch the linkage on the outside of the carb to make sure it moves and opens the secondaries. Im just stabbing in the dark here...Someone else help this guy out :).

~T.J.

I was just playing with my secondiaries today on the racing beat Holley 600 I got. ( BTW, I finally got things straightened out for those who helped me out). The main way to fool with it is just follow the linkage to where the secondaries are triggered. Use your finger and press the accelerator... make sure that as you get close to WOT that you see the secondary linkage move. Adjust if necessary... Thats pretty much about it. If you are looking for a new and more powerful carb then I recommend the Holley :D

So you're suggesting he drive down the street with someone sitting ontop of the engine looking down to see if those secondaries are opening? LOL.....it wouldn't be hard at all with the great visibility on open hood has to offer, oh yeah and finding a sucker to sit on it and watch.....actually that's starting to sound like fun. Sorry revving the gas in neutral won't let you see if your secondaries are working (no load) unless you have mechanical ones :1party:

I'm pretty sure that the secondaries will open in neutral. My vacuum secondries will. I think that for any given rpm of the motor, the vacuum signal to the secondaries is the same, regarless of load on the motor. Correct me if I'm wrong.

I'm gonna have to disagree. The secondaries won't open up in neutral.

The more load there is on the engine the more air it's digesting for any given rpm. This means more vacuum signal to the secondary diaphragm.

I would also like a firm answer on weather or not the secondaries on a stock carb will open in netural. I can't make any powe over around 4K and the engine sounds like is its starving out. (84 gs) and also if some one knows for sure if they are actuated by vacume how does one adjust them to make them work properly. Mine dont open at all in netural at over 5K so I think this is my problem. thanks all.

Like I just said... there is not enough vacuum/load for them to open in neutral.

Damn it, lol. I was thinking about the secondaries on my new RB intake with the Holley carb, they're mechanical :D. Dont I feel like a dumbass :dunce:...Since I just got them I keep forgetting that its not what the car came with, and theyre all I cant think about, if that makes sense...lol

~T.J.

hehe clogged cat eh? i know all about that mess........the mustang actually could help you in the clogged cat catagory! ok the mustangs cat is clogged all to hell and im to lazy to change it.....all i know is the gas mileage is worse,the car quit being peppy, and i think my mom has been poisened by carbon monoxide. a clogged cat will smell like rotten eggs or if you like sulfur.. it will usually take over the car with this smell at a "not now" moment and trust me you'll know

No dude, the larger holes are the primaries. It wouldn't make sense for them to be secondaries, since they aren't used frequently. The smaller holes are the secondaries. :)

Yeah I thought that, it makes sense, but I swear on a stack of bibles that I read somewhere here that the secondaries were the bigger ones...Oh well. Im good now. I just got all messed up in this thread. Shows how much to trust me with what I say :D.

~T.J.

Actually it does kinda makes sense for the smaller ones to be primaries if you think about it...The smaller ones would be good for gas mileage because you dont really use them unless your accelerating or driving hard, and when you get on the gas your gonna need more to get her going more, hence the larger holes for the secondaries...So in a way it would make sense, I think...

~T.J.

Yer joking, right? (I hope.)

Lookit;
The vaccuum operated secondarioes are not gonna open in yer driveway. If they do, then something is wrong with the set-up, and probably not to your benifit, either.
About the only thing you can ever do in your driveway is tune the idle mixture.
EVERYTHING else needsto be tuned (jets changed, ect) after observing the power under load. The engine has alot different fuel/air requirements when it's dragging around 2400 lbs of shit.

rix, if you think your cats might be plugged, then either get new cats, or drop the exhaust for headers. But you can't possibly be sure of anything regarding your carb or anything else if the cats are in fact plugged.
It's kinda crazy to point at a component that you know not much about, and say, "That's it! That's what's fucking me all up!" You don't even seem to know if it's the stock carby or not! There are just too many variables, and you need to slim them down, one at a time.

Not much can go wrong with the stock carb. It may need to be tuned, and rebuilt, but that's about it, unless it's been monkeyed with. You need to check your plugs to see what color/build-up is on them, ect. In fact, changing the plugs to brand new can sometimes make you wet yerself with the difference!
Change all filters, oil, everything. Make everything you can into as perfect operating condition as you can.
Then tune your carb to the best it can be tuned.
If it still feels like there's a problem, you'll need to do something a little more invasive; like take off the exhaust or rebuild the carb.

I don't know how to check for clogged cats.
Read the write-up in the archives entitled, "Carb Crap...Nikki Mods". It explains alot about how the linkages of the stock carb work.

ijust told him how to check for a clogged cat.......wanna come smell my car!!!! :)

The larger ones are the secondaries. No carb that I am aware of has a secondary that is smaller than the primary.

The EASIEST, SURE-FIRE way to tell on any carb, is that the primary barrel(s) will have a choke plate over them while the secondaries never will.

And no, the secondaries will not open if you free-rev the engine, unless you floor it from idle and rev it to redline. Maybe.

It's tricky to see if they move, but what I do is, WITH THE ENGINE OFF :) , hold the throttle open to full throttle with my left hand, and reach under with my right and grab the lever coming out of the secondary diaphragm, and see if it moves. It's not uncommon for the secondaries to be stuck shut. If they are stuck, the easiest way to un-stick them is to remove the carb from the engine (not pretty) and use tons of penetrating oil and patience.

Given all that, first things first - replace the fuel filter if it's more than a month or two old. Make sure the air filter isn't a solid brick of clay. (Never ever run without an air filter either) Check the ignition timing and make sure the wires are on the correct plugs.

WOOHOO!! So your saying I was right about the primary secondary thing?? Im so happy!! I was right!! Yay!! Ok...On to the next challenge...:D

~T.J.

wheres the option in the poll for dell'orto?

Ok things I think we have determined for sure.
1. the larger holes on a stock carb are secondary.
2. the stock carb has vacume actuated secondaries.
3. the best way to check if your cats are cloged is to take them off and look down there with a flash light. because you can't be sure if the performance hit is becaused of the cats untill you look.

Now is there a way to look down the carb with the engine off and actuate the secondaries by hand to see if they move freely and seem to be able to move as they should. the primaries will move by hand and inject some fuel with the engine off is the same true for the secondaries on a stock 84-85 12a

See above... I desreibed how :)

The secondaries have no accelerator pump, and as such, will not squirt fuel when you move them by hand.

I have seen the secondaries open in neutral in 3 different stock carbs. All of them runing fine. You just have to have someone stab the trotle all the way down and hold for about a 1sec so it climbs to 5krpm of so and they oppen and you can se both jets squirt fuel.

After reading all the above comments? Vacuum secondaries will start to open once the linkage and vacuum allows.The best way I can tell is that very quick increase in RPM's once they start to come in while driving. Usually they are set up to start to be able to come in at 1/3 - 1/2 throttle once the vacuum is there.

The way to check the cats are to start the engine,and
let it idle,put your hand over the tail pipe tips, and feel
if any presure is coming out, no presure,,cloged cat,

That's also a good way to check for a clogged muffler, or an engine with bad compression. The pressure should blow you across the street...