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Discussion Starter · #1 ·
So after replacing head gasket and timing belt and all that good stuff. I decided to put a header on while I was at it since the catifold was visually clogged anyway. So I deleted all the egr lines and just blocked them off at the air cleaner. I'm running about 9 degrees btdc timing. So it doesn't do it the whole time while driving but it will load up it will buck and carry on and my fuel mileage is completely gone. I mean I went from like 25-30 to 10-15 at best. I used original carb. I actually left all the vacuum lines on the carb I just layed it over upside down ish or on its side. Any help in any direction on what to do or what. Anyone else ever have this issue? Can you run a stock carb with the headers? Do I need to just go to a Weber and will that fix my headache?? Any help you guys would be awesome.
 

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As I mentioned in your previous thread that you started on Nov. 21st.......your stock carb is probably in limp mode (overly rich condition) from the adjustments that you have made to the truck. You won't get very good fuel mileage while in limp mode......I would buy a Redline Weber carb kit and install it on your truck's engine, then you can eliminate all of your stock emissions stuff, including the O2 sensor and the computer behind the passenger side kick panel, inside the truck's cab.
 

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1992 Mazda, B2200 ext cab
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ABE
I have a 92 carbed model, stick shift. and i have a 92 injected model, stick shift.
I know the injected model has limp home, but have never experienced that on the carb model.
are you sure the carb model has limp home mode?
Bobmo
PS mine runs like crap when the cold weather sets in and the carb plate sticks. only time, lots of Kroil, and heat helps. I guess I should take it apart, but thats another day.
 

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Discussion Starter · #4 ·
Well it's just weird that it doesn't run like that constantly. But you can tell it loads up. You will be cruising along and then it will start bucking a little bit and I leave off and then back on and it clears up. But mileage is just completely gone. I figured it was the carb and vacuum stuff with me getting rid of the lines from the exhaust catifold.
 

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ABE
I have a 92 carbed model, stick shift. and i have a 92 injected model, stick shift.
I know the injected model has limp home, but have never experienced that on the carb model.
are you sure the carb model has limp home mode?
Bobmo
PS mine runs like crap when the cold weather sets in and the carb plate sticks. only time, lots of Kroil, and heat helps. I guess I should take it apart, but thats another day.
The Mazda feedback carb has two phases that it operates in, Open Loop and Closed Loop. The Electronic Control Module (ECM) holds the carb in "open loop" when it is warming up, and/or, the ECM sees that the engine needs a rich fuel mixture. Once the engine is at operating temp, the ECM will put the carb in Closed Loop and start monitoring the sensor signals, and start adjusting the carb fuel mixture.

So, most feedback carburetors like the one that was stock on the B2000 and the B2200, send info to the ECM during the "closed loop" cycle only......which is after the ECM gets info from the engine sensors (Air & Coolant temp. sensors, O2 sensor(s), Barometric Pressure sensor, etc.) and then sends voltage signals to one or more carburetor "actuators" that in turn limit the fuel and/or air delivery to the engine. In the Mazda feedback carbs, the actuator is the "Mixture Control Solenoid" (MCS) which is located in the center of the carb.....where the 2 wires enter the top of the carb at the front. I have cut/taken these MCS's apart and have studied them before, and I can assure you that if the truck has sat with today's gas in the carb for a lengthy amount of time, the MCS has become "sticky" inside of it, and it probably won't work to it's designed potential after that.

NOW, don't go and take your Mazda feedback carb apart and try to clean the MCS! You probably won't be able to totally clean it well enough for it to work like new.......best thing to do is replace it with a new one.......there are a lot of small parts inside of it that can become gummed up and sticky. They are also expensive!

ALSO, if the carb has been messed with any at all, you could go through the trouble and expense of replacing the MCS and cleaning everything, and still have a bad performing feedback carburetor.......ask me how I know this! I've learned this lesson more than once!! So now, I never mess with the stock Mazda feedback carb......I buy a Redline Weber carb kit, and toss the feedback carb!

So, the main thing I wanted to convey here is......it is possible for the ECM to keep the carb in Open Loop and therefore an overly rich fuel mixture condition. It really is a tedious job to get one of these carbs to perform like they are supposed to if and when they start having issues.

Here is a couple of pics from a bad MCS that I cut/took apart......the MCS also has O-rings, one at the top & one at the bottom......if either is letting fuel pass by them, you'll have an overly rich condition as well.

Cylinder Gas Font Engineering Auto part


Gas Cylinder Electric blue Engineering Metal


Circuit component Sky Line Electrical wiring Electricity


Gas Font Engineering Nut Electric blue


Gas Auto part Electric blue Cable Metal
 

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1992 Mazda, B2200 ext cab
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AH HA!
Thanks ABE.
I leaned something today.
My carbed version runs like crap and I always blamed the choke plate. However, my injected version has a true limp home mode.
When limp its in control you truely LIMP, no power, and one is encouraged to pray that you can catch all the green lights home.
Whereas the carbed version just runs bad, as in running rich. ie open loop. A lot of shake rattle and roll, but still will run at 60+
Might be time for santa to treat me to a new weber.

Thanks and Merry Christmas!
Bobmo
 

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Discussion Starter · #7 ·
Ok. The carb was not messed with other then a couple lines taken off to move it to the side while I was doing my head gasket. And took pictures to put the lines back on. It did sit on its side for a bout a week or so til I was able to finish the head gasket. So do you think something could have happened being on its side? Dirt knock loose or anything like that? And I'm gonna reset my timing as well I have to have my distributor turned the whole way counter clockwise and I'm at 9 btdc. So any ideas? This all started after doing head gasket and header install. I did just see a video on YouTube where Mazda Mitch deleted everything off the carb and the truck actually ran.
 

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Check to make sure the timing belt installation is not off a tooth, and then make sure that your distributor is installed correctly, so that the rotor tip is pointing to the 9:00 o-clock position when it is fully seated, and the engine is at the number 1 cylinder's top dead center. Your distributor hold-down bolt should be close to the center of the adjustment slot on your distributor when your timing is at 6° BTDC.......more than likely your distributor is installed, one tooth off.

Let us know what you find out.
 

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Discussion Starter · #10 ·
I did recheck the belt 2 weeks ago or so and the marks were still were they were supposed to be. I'm more on my distributor being off at least a tooth or two. Being I have to have it turned so far forward. I'm hoping to have time to do it tomorrow. And then the carb will be getting tackled. If it doesn't help then I guess a Weber it will be.
 

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Discussion Starter · #11 ·
Ok. So I got the distributor in it was off one tooth. The timing is perfect! Now the carb is still messy.. still running rich and it actually burned thru a set of plugs in about 2 months from being so rich... So I watched what Mazda Mitch did and unhooked everything on the carb unplug everything and capped it all off. It ran better this morning and then on my way home it was back to normal running kind of crappy and rich af... So I'm thinking after Christmas I'm just going to get a Weber. And I'm hoping I have time this week to take valve cover off and put in another new set of hydraulic lifters in. Brand New and they have tapped once warm since then... So I got better ones to try this time... Maybe this summer I will find a wrecked Miata and just swap everything for fuel injection... Any idea how to adjust the air fuel on these stock Nikki? Is it that screw behind the pin?
 

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Good about finding the distributor "stabbed" on gear tooth off.

Most of us who have switched feel that you'll be happier with a genuine Redline Weber kit.

There are things you'll likely need to do:
Most important: Make Weber adapters flat perfectly flat, sand them flat using wet/dry on a sheet of glass.

Use a thin coat of Permatex Aviation or similar used on all the gaskets for the adapters and bottom of carb
Torque the mounting screws and bolts correctly? Did you use blue Loctite on their threads?
Plug the electric choke of the Weber into the rear of the alternator. If the bi-metallic spring doesn't get heat from the choke heater to open up the choke butterfly, the fuel:air mixture will be richer than it should be for a warm engine.
Cap off all the vacuum ports capped off with GOOD quality caps (or pieces of vacuum tubing and golf tees)
Get a stronger throttle return spring.
 

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Discussion Starter · #13 ·
So my truck ran crappy this morning but when I got to work I noticed I still had a single wire plug still plugged in. It went from the base heater thing at the bottom of the carb to the choke. I unplugged it and it ran Amazon my way home. And I think I actually got my old fuel mileage back also. I used to get around 30mpg. What do the Weber's get?
 

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1991 Mazda B2200
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So my truck ran crappy this morning but when I got to work I noticed I still had a single wire plug still plugged in. It went from the base heater thing at the bottom of the carb to the choke. I unplugged it and it ran Amazon my way home. And I think I actually got my old fuel mileage back also. I used to get around 30mpg. What do the Weber's get?
I picked up 3-4 mpg when I switched over to a Weber, headers, and knocked the last cat out. Seems like once those Mazda carbs start acting up, just toss it. Prior to putting the Weber on, I actually bought a rebuild kit for mine. Started taking the carb apart and got so frustrated with it, I threw it on the ground and that was the end of that. Wasted the $ on the rebuild kit. I have rebuilt many a carb over the years, but that carb was not simple at all.
 

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I picked up 3-4 mpg when I switched over to a Weber, headers, and knocked the last cat out. Seems like once those Mazda carbs start acting up, just toss it. Prior to putting the Weber on, I actually bought a rebuild kit for mine. Started taking the carb apart and got so frustrated with it, I threw it on the ground and that was the end of that. Wasted the $ on the rebuild kit. I have rebuilt many a carb over the years, but that carb was not simple at all.
I hear ya!
Been there, done that!
 

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So my truck ran crappy this morning but when I got to work I noticed I still had a single wire plug still plugged in. It went from the base heater thing at the bottom of the carb to the choke. I unplugged it and it ran Amazon my way home. And I think I actually got my old fuel mileage back also. I used to get around 30mpg. What do the Weber's get?
Hmmm.....not sure what wire was running from the PTC heater under the carb, to the choke.

Your choke should have a yellow wire with a blue stripe on it that runs down, and plugs into the rear of the alternator. The choke wire is even soldered onto the choke assembly, and nothing else plugs into it, from the factory........sounds like someone has been messing with that factory carb.....before you bought it.

On the air mixture screw at the base of the carb (on the passenger side).....yes, the roll pin has to be removed (or carb casting broken) to adjust the mixture screw behind it. You are supposed to remove the carb and tap it out......but some people just bust the carb casting that's securing the roll pin.
 

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Discussion Starter · #17 ·
I will take a picture of it here tonight for your to show your which wire I'm talking about. I've messed with a lot of Holley and demon and many other but nothing like this with all these insane vacuum ports.. so you guys are still getting the same if not better fuel mileage with the Weber 32/36?!?! Some people said they got worse.. not sure how.. but yeah I have no cats and a header. There is a 38/38 kit on Amazon someone is selling but it seems like these trucks do not need that much carb. And I want my fuel mileage back. Here in PA the price is anywhere from 3.50-4 or more.
 

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Discussion Starter · #18 ·
And that air fuel mixture screw. Richer inwards or run screw out for richer? I need to try and lean it out as much as possible. Until I can get a Weber which won't be for like 2 weeks or so.. it sucks. Christmas. 4 kids. Only income.. shit gets tight this time of year.
 

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The choke plate wins.
I'll have to do some routing around on mine to see if i have a wiring problem too. I've always been thinking the plate was stuck from age and gunk.
Merry Christmas all!
bobmo
 

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With the choke wire plugged into the red lead coming off of the PTC heater, you have no power going to your electric choke. So......the choke is staying closed way longer than it is supposed to, therefore causing the engine to run very rich.

The heat from the motor getting to operating temp will eventually fully open the choke plate/flap, but prior to that happening, your running rich!

Drop the choke wire down between the cylinder head and the intake manifold, and plug it into the rear of your alternator......that is as long as you still have the correct Mazda alternator on your engine. There is a electrical "port" on the Mazda alt. that the choke wire fits into.......I have a pic below that shows the back of the alternator and "my" wire that I rigged up to operate the electric choke, on a remanufactured factory carb that didn't come with the full length choke wire.......so I made my own!

Automotive tire Motor vehicle Automotive fuel system Vehicle brake Rim
 
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