My Nikki carburetors die and stay dead
06-22-02, 03:34 AM
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My Nikki carburetors die and stay dead
Maybe someone can shed some light on my problem. I have an 85 GSL 12a Nikki carbureted. About 2 years ago, my carb started running like crap. I noticed the jets were splashing fuel out unevenly, fowling out my plugs and over heating my exhaust. I had little power and no idle. The floats stayed perfectly level though, like they're supposed to, so the unit wasn't flooding from loose seats.
I rebuilt (complete kit) the carb and same problem. I put my other carb on off my wrecked 84 and it ran perfect for 2 years. Now, about 4 weeks ago, that Nikki has developed the same problem. I tried rebuilding it and same problem. I took it down, had it rebushed and professionally rebuilt but same problem. My jets are putting out way too much fuel, but the carb is not actually flooding.
So, I have 2 Nikkis that have identical problem and have just ordered another used carb because I have no other choice. I have posted on other forums and am finding other people with same problem but no solution. They have rebuilt their carbs also and it hasn't helped.
Could the Nikkis develop and internal crack that leaks inside? If so, it has to be rather common. I would appreciate any feedback.
I rebuilt (complete kit) the carb and same problem. I put my other carb on off my wrecked 84 and it ran perfect for 2 years. Now, about 4 weeks ago, that Nikki has developed the same problem. I tried rebuilding it and same problem. I took it down, had it rebushed and professionally rebuilt but same problem. My jets are putting out way too much fuel, but the carb is not actually flooding.
So, I have 2 Nikkis that have identical problem and have just ordered another used carb because I have no other choice. I have posted on other forums and am finding other people with same problem but no solution. They have rebuilt their carbs also and it hasn't helped.
Could the Nikkis develop and internal crack that leaks inside? If so, it has to be rather common. I would appreciate any feedback.
06-22-02, 06:07 PM
#5
Could the Nikkis develop and internal crack that leaks inside? If so, it has to be rather common. I would appreciate any feedback.
06-22-02, 08:37 PM
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Nikki-Modder Rex-Rodder
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You've checked fuel filter, ect? Have any flakes of rust in the filter?
I don't know what to tell ya.
Are you certain you don't have a vacuum leak? Are you certain that your manifold-to-engine gasket is in good shape?
I don't know what to tell ya.
Are you certain you don't have a vacuum leak? Are you certain that your manifold-to-engine gasket is in good shape?
06-23-02, 02:43 AM
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Ya, checked and replaced all that. Fuel filter, checked return valve, gas and line are perfect. It's the oddest thing. I should have my replacement carb to put on Monday to see. I remember last time I had this problem I spent a week replacing everything I could and it never helped. I replaced my carb just to see and it worked. I put my original carb on my wrecked car and it ran like crap. So definitely a carb problem.
The carb I have on there now originally was leaking out of my first rotor's 2ndary during idle and splashing uneven fuel out of my primaries during cruise. I have capped off all the vac line to the carb no change. I tried a different manifold gasket/vaccum spacer amd same problem. After I rebuilt the carb, the 2ndaries stopped splashing but both primaries still jetted out excessive fuel.
It's a crazy problem. The fuel is supplied via a down draft system. The fuel pump pressure only serves to keep the fuel in the float bowls and does not push fuel itself into the engine. Logic tells me that the carb is sucking too much fuel because there is a leak somewhere, but damned if I can find it. I tried using carb cleaner around the carb while the car was running, but no idle changes to indicate vaccum. I have no fuel leaking anywhere around the body.
Like I said, I am encountering more and more people on the net that have encountered this problem and have no solution. All of them happen to be driving 84 and 85's so far, if that's any help.
I would just use aan aftermarket or get Holley projection kit but it's not smog legal in CA, sigh.
The carb I have on there now originally was leaking out of my first rotor's 2ndary during idle and splashing uneven fuel out of my primaries during cruise. I have capped off all the vac line to the carb no change. I tried a different manifold gasket/vaccum spacer amd same problem. After I rebuilt the carb, the 2ndaries stopped splashing but both primaries still jetted out excessive fuel.
It's a crazy problem. The fuel is supplied via a down draft system. The fuel pump pressure only serves to keep the fuel in the float bowls and does not push fuel itself into the engine. Logic tells me that the carb is sucking too much fuel because there is a leak somewhere, but damned if I can find it. I tried using carb cleaner around the carb while the car was running, but no idle changes to indicate vaccum. I have no fuel leaking anywhere around the body.
Like I said, I am encountering more and more people on the net that have encountered this problem and have no solution. All of them happen to be driving 84 and 85's so far, if that's any help.
I would just use aan aftermarket or get Holley projection kit but it's not smog legal in CA, sigh.
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06-23-02, 07:16 AM
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Nikki-Modder Rex-Rodder
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A vacuum leak is gonna lean your mixture. Not richen it.
How do you know you're getting too much fuel? If you just stood in the driveway observing the carb, it's gonna look like the fuel is spitting out unevenly when you operate the throttle. You can't tell how much is being metered just by looking at it.
Also, You mentioned excessive exhaust heat. This is due to a lean mixture. You're fuel deprived, I believe.
It's much easier for the carb to be starving. Usually if it's flooding, it's doing so because of a "pre-main circuit" glitch...IE somethings hanging up the float or needle, ect. And it's flooding so bad that sometimes the secondaries fill with fuel!
I think you're not getting enough fuel. Yank off the fuel supply to the carb, and coffee can it (see what comes out). It should be more than a dribble!
Jets don't suddenly "open up"! If something has happened recently to your otherwise O.K. carb, then my guess is that whatever it is is an impedance to your fuel flow.
Bad pump
Bad filter
Bad line
Clogged carb bowl inlet screens
Clogged carb bowl needle seat screens (unlikely)
Don't know about the emissions valve.
If the fuel pressure is fine, then my next guess is that your manifold gasket has rotted.
How do you know you're getting too much fuel? If you just stood in the driveway observing the carb, it's gonna look like the fuel is spitting out unevenly when you operate the throttle. You can't tell how much is being metered just by looking at it.
Also, You mentioned excessive exhaust heat. This is due to a lean mixture. You're fuel deprived, I believe.
It's much easier for the carb to be starving. Usually if it's flooding, it's doing so because of a "pre-main circuit" glitch...IE somethings hanging up the float or needle, ect. And it's flooding so bad that sometimes the secondaries fill with fuel!
I think you're not getting enough fuel. Yank off the fuel supply to the carb, and coffee can it (see what comes out). It should be more than a dribble!
Jets don't suddenly "open up"! If something has happened recently to your otherwise O.K. carb, then my guess is that whatever it is is an impedance to your fuel flow.
Bad pump
Bad filter
Bad line
Clogged carb bowl inlet screens
Clogged carb bowl needle seat screens (unlikely)
Don't know about the emissions valve.
If the fuel pressure is fine, then my next guess is that your manifold gasket has rotted.
06-23-02, 12:03 PM
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No, it's definitely too rich. The exhaust on the RX-7 is a hollow 2 chamber 2ndary combustion area because the rotaries actually do not complete all combustion in their chambers. What is happening, is that excessive fuel is being dumped in the engine and not being burned.
The extra fuel is being pushed into my exhaust manifold and first converter and is burning there via the air supplied by the smog pump. If I disconnect the smog pump so that no air is fed into the converter, I can run longer before I get the heat up but I get trememdous smoke out the back. My cats are both brand new and like I said, the problem just happened abruptly.
I have spent many an hour looking at my carb and cleaning them over the 10 years that I owned my 3 RX-7's. I can definetely say that too much fuel is comming out the jets. They are also very uneven. In fact, it is so much fuel, it looks like someone has put a mini Rainbird sprinkler in there.
The reason I think it may be a vaccum leak is analogous to a baby bottle. The fuel pump just keeps the float bowls fuel, which mine does. The level stays on mark. If you hold a baby bottle upside down nothing comes out because of atmospheric pressure, except for a drip or two. If you poke a few holes in the back, you get more drips. Now if you poke a great big hole, you get a very big drip. Kinda like jugging a bear. The bigger the hole, the more you can suck.
The only thing I can think of is that maybe my jets or emuslion tubes aren't sealing. Also, what about the seats themselves. One thing I notice, is that my float levels don't really drop if I punch it as much as I think they should. Is it possible that the kit I got and maybe the kit that other people use are cheap? Could the springs on the needles be too weak. It's possible that if the floats don't drop properly the mixture won't lean out and will run rich. I don't know. My other carb will be here soon so I'll find out. If CA didn't suck I'd have EFI right now.
The extra fuel is being pushed into my exhaust manifold and first converter and is burning there via the air supplied by the smog pump. If I disconnect the smog pump so that no air is fed into the converter, I can run longer before I get the heat up but I get trememdous smoke out the back. My cats are both brand new and like I said, the problem just happened abruptly.
I have spent many an hour looking at my carb and cleaning them over the 10 years that I owned my 3 RX-7's. I can definetely say that too much fuel is comming out the jets. They are also very uneven. In fact, it is so much fuel, it looks like someone has put a mini Rainbird sprinkler in there.
The reason I think it may be a vaccum leak is analogous to a baby bottle. The fuel pump just keeps the float bowls fuel, which mine does. The level stays on mark. If you hold a baby bottle upside down nothing comes out because of atmospheric pressure, except for a drip or two. If you poke a few holes in the back, you get more drips. Now if you poke a great big hole, you get a very big drip. Kinda like jugging a bear. The bigger the hole, the more you can suck.
The only thing I can think of is that maybe my jets or emuslion tubes aren't sealing. Also, what about the seats themselves. One thing I notice, is that my float levels don't really drop if I punch it as much as I think they should. Is it possible that the kit I got and maybe the kit that other people use are cheap? Could the springs on the needles be too weak. It's possible that if the floats don't drop properly the mixture won't lean out and will run rich. I don't know. My other carb will be here soon so I'll find out. If CA didn't suck I'd have EFI right now.
06-23-02, 01:45 PM
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Nikki-Modder Rex-Rodder
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With all yer emissions control **** still in place, don't you think that it's more likely a failure of that system? Cracked hose / malfunctioning solenoid?
Is your float bowl solenoid hooked up with a good secure connection? That can exhibit both flooding problems as well as starvation.
You say you see the float level during throttling, but in reality, there's not much you can tell from just sitting in yer driveway. You need to have load on the engine in order to really see what's going on.
As far as emulsion tubes not sealing, well that would lead to a lean condition at hi rpms. However, if they were suffed up with **** somehow, then you would be sucking fuel through the circuit with no air mixed in beforehand.
The main venturi airbleeds are only the "fine tuners" of bleeding off the signal. The idle airbleeds, and step airbleeds - as well as the primary airbleeds all share the same circuit. (There's a hole drilled through the top of all of these that joins them together.) That means that if you were to plug up the idle circuit bleeds, it would dramatically effect the mixture that that particular circuit was sucking up.
The whole point is that there could be a clog anywhere in that circuit.
Causing Lean conditions...
Secondary vacuum box trouble,
Secondary linkage trouble,
oversized airbleeds,
crap in the fuel path into carb,
crap blocking fuel jets,
Vacuum leak in the emissions system, carb, or manifold.
Leading to Rich condition...
Crap blocking air bleeds,
Jet has fallen out (never heard of that happening.),
Needles not seating,
Floatbowl solenoid stuck shut (coupler not plugged in).
Emissions system problem.
S'all I Got.
Is your float bowl solenoid hooked up with a good secure connection? That can exhibit both flooding problems as well as starvation.
You say you see the float level during throttling, but in reality, there's not much you can tell from just sitting in yer driveway. You need to have load on the engine in order to really see what's going on.
As far as emulsion tubes not sealing, well that would lead to a lean condition at hi rpms. However, if they were suffed up with **** somehow, then you would be sucking fuel through the circuit with no air mixed in beforehand.
The main venturi airbleeds are only the "fine tuners" of bleeding off the signal. The idle airbleeds, and step airbleeds - as well as the primary airbleeds all share the same circuit. (There's a hole drilled through the top of all of these that joins them together.) That means that if you were to plug up the idle circuit bleeds, it would dramatically effect the mixture that that particular circuit was sucking up.
The whole point is that there could be a clog anywhere in that circuit.
Causing Lean conditions...
Secondary vacuum box trouble,
Secondary linkage trouble,
oversized airbleeds,
crap in the fuel path into carb,
crap blocking fuel jets,
Vacuum leak in the emissions system, carb, or manifold.
Leading to Rich condition...
Crap blocking air bleeds,
Jet has fallen out (never heard of that happening.),
Needles not seating,
Floatbowl solenoid stuck shut (coupler not plugged in).
Emissions system problem.
S'all I Got.
06-24-02, 02:05 AM
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I have been suspecting the 12v solenoid in the front of the carb as a possibility. It would have to be something that can happen to both carbs, so the solenoids were my first guesses. I tried switching the solenoid with my old one, but if it is the problem, then I just switched a bad one with a bad one.
When the problem first developed, it was only a momentary problem, the car would pick up power again and run fine for a few minutes. Eventually the problem just stayed consistantly. It happened over about 30 minutes of driving on the way home.
If the solenoid fails, does it stay stuck open or shut. I think it stays shut but I need to look at my other carb again.
I was hoping someone had the same problem, switched something not so obvious and fixed it.
When the problem first developed, it was only a momentary problem, the car would pick up power again and run fine for a few minutes. Eventually the problem just stayed consistantly. It happened over about 30 minutes of driving on the way home.
If the solenoid fails, does it stay stuck open or shut. I think it stays shut but I need to look at my other carb again.
I was hoping someone had the same problem, switched something not so obvious and fixed it.
06-24-02, 07:23 AM
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The solenoid does'nt fail. More likely would be the power source to the solenoid. The valve closes when no power is going to the solenoid. Usually the only problem is that people fail to reconnect them, not realizing that it's the only vent to the float bowls.
I know these carbs pretty well, and unless you've been monkeying around with different jets and airbleeds, and you've checked all the other things about the carb out, then I don't think it's a carburetor problem.
How's your fuel tank vent situation? Sometimes the canister will become full of sludge from water, fuel, and oil vapor that gets sucked up into it if there's any problem with the system. (excess water in fuel, excess water in crank, oil overfilled, ect)
One of the results is that the fuel tank does'nt vent. If the tank can't vent, then the pump is dealing with an input pressure that is constantly fluxuating high and low as the fuel expands and contracts with temperature.
Can cause all sorts of problems, but its presence is usually easily recognized as either an inward or outward "whooosh" as the fuel tank is opened.
You can check this as a possibility simply by removing the line to the canister that comes from the fuel tank. Blow thru that line to see if it is obstructed. (Theoretically, I suppose it could have water or fuel in it, but I don't know.) Leave it disconnected, and drive.
But you can't leave it that way indefinitely. Fuel vapors will be escaping into your engine bay while the car sits all day in a hot parking lot or driveway!
Also, had you given any thought to a bad coil or ignitor?
I know these carbs pretty well, and unless you've been monkeying around with different jets and airbleeds, and you've checked all the other things about the carb out, then I don't think it's a carburetor problem.
How's your fuel tank vent situation? Sometimes the canister will become full of sludge from water, fuel, and oil vapor that gets sucked up into it if there's any problem with the system. (excess water in fuel, excess water in crank, oil overfilled, ect)
One of the results is that the fuel tank does'nt vent. If the tank can't vent, then the pump is dealing with an input pressure that is constantly fluxuating high and low as the fuel expands and contracts with temperature.
Can cause all sorts of problems, but its presence is usually easily recognized as either an inward or outward "whooosh" as the fuel tank is opened.
You can check this as a possibility simply by removing the line to the canister that comes from the fuel tank. Blow thru that line to see if it is obstructed. (Theoretically, I suppose it could have water or fuel in it, but I don't know.) Leave it disconnected, and drive.
But you can't leave it that way indefinitely. Fuel vapors will be escaping into your engine bay while the car sits all day in a hot parking lot or driveway!
Also, had you given any thought to a bad coil or ignitor?
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