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or... put the old pump back on if its not broken. I'll be at the baseball field at Broward College in Ft. Lauderdale Friday from 4-9 PM. If you bring your car by I'll be happy to give you a hand.
I think it's time for you to pull the jets out and make sure they're not clogged. You can do this by removing the brass plugs, reach in with a screwdriver to loosen each jet (don't remove it yet), then reach in with a wooden tooth pick and use that to draw the jets out the rest of the way. That way you don't have to pull the top of the carb off to get to them.
You might also want to check the filter screens under the banjo bolds where the metal fuel lines attach to the top of the carb. Could be an obstruction there.
About that SE fuel pump; I'm not sure if a regulator will be capable of toning down that much pressure. I'm also not sure if the standard plumming can withstand those pressures. I would recommend that you go back to a stock pump and continue troubleshooting from there.
Nikki carbs on the 12A motors need around 3 psi. GSLSE 13B FI pump puts out 50-70 psi. Did you replace the 12A fuel filter with one for the 13B? IF not, try that first.
i have not tried this, i will. i cannot make it friday i work at 5, but i appreciate it.
Originally Posted by Kentetsu
I think it's time for you to pull the jets out and make sure they're not clogged. You can do this by removing the brass plugs, reach in with a screwdriver to loosen each jet (don't remove it yet), then reach in with a wooden tooth pick and use that to draw the jets out the rest of the way. That way you don't have to pull the top of the carb off to get to them.
You might also want to check the filter screens under the banjo bolds where the metal fuel lines attach to the top of the carb. Could be an obstruction there.
About that SE fuel pump; I'm not sure if a regulator will be capable of toning down that much pressure. I'm also not sure if the standard plumming can withstand those pressures. I would recommend that you go back to a stock pump and continue troubleshooting from there.
I really dont think the jets are clogged, will check but don't think so, because i can clearly see that the problem is fuel starvation into the bowls because when i go wot, i will eventually turn off and when i immediately check the bowl levels they are empty even if i have the regular set to 4.5 psi, it just runs out of fuel even with a more powerful pump. right now i put the regulator at 5 psi and the levels are pretty high and when i went wot it did not turn off, but i think i did not run it long enough to use everything in the bowls, thats why it did not happen. i am out of ideas, a more powerful pump is supposed to keep fuel in the bowls not let it go dry, i am running out of ideas. will let you know about the 13b fuel filter and the banjo bolt screens tomorrow. by the way the tank has been dropped and the screen inside the tank cleaned and the whole tank insede was cleaned off rust, just to clear that up.
kentetsu i checked the banjo bolts and the jets, they are not clogged. the problem is not that the se pump is putting to much pressure, but that the fuel is not getting inside the bowls fast enough at wot
@kutukutu1 did you ever figure it out? I am having nearly identical symptoms that you described in your first post. I just changed out my stock OEM Mazda fuel filter for a new Mazda filter a few weeks ago. I’ll change it again today and cut open the new-old filter and see what it looks like. I’ll also inspect the banjo bolts and screens and see what i find.
I’ve already checked the igniters, and gave her a tune up which really smoothed things out but still this power loss issue lingers.
Tune up = new coils, ignition wires, cap, rotor, spark plugs, air filter, checked timing, oil change.
I even replaced the fuel pump with a brand new Mazda unit.
I have checked and adjusted the throttle cable within spec per FSM.
Maybe I need new vacuum tubing to replace my worn out ones (although no visible cracks but some are quite easy to pull out).
My idle is great at 750 RPM so i’m not sure about vacuum leaks… adjusting the idle fuel mixture made it run noticeable better too (leaned it out and then richen by 1/4 turn).
checked the accelerator pump is functioning which it is.
Carb was cleaned and rebuilt around 2010 iirc. Maybe it is time for me to do it again. Hopefully gas tank is not rusty but yet to be determined as well.
i would be interested in knowing what the AFR is when you are experiencing this phenomenon. i'd be interested in the timing, too, but i this is likely a fuel supply thing. since your main parts (pump and filter) are new, maybe try seeing what happens if you wire the pump directly to the battery. if it makes a difference then, find a way to re-do/rebuild the stock circuit.
Here's a few pictures of what my 3 month old fuel filter looks like. Some sediments from the tank, looks like paint chips or rust flakes.
The mesh screen on each banjo bolt and they were clean. Drove the car some more and when it started to not climb RPM any more under load I turned off the engine and ignition so fuel pump is no longer running and coasted to a stop. Saw the front bowl was nearly empty and the rear bowl was good. So that explains why I feel only half the power and no acceleration under load. Of course in order to get to this condition I need to be WOT and accelerating with secondaries opened; at least this is how I can reproduce the issue quickly.
So I'm thinking that the needle is sticking. Okay so today I took the carb off and took a look at the needle and floats. Floats are measured to be adjusted in spec so I didn't need to mess with that. I just cleaned it with carb cleaner and replaced the gaskets between the main body and air horn, secondary vacuum diaphragm where it attaches, fuel bowl vent solenoid, sight glasses, and between the and vacuum plate and throttle body section. Now I have a very small vacuum leak right under the accelerator pump but it's between the vacuum block and carb. Thinking of sealing it with some black gasket maker rtv that I have. The power loss is still there so the mystery continues. Thinking of adding seafoam to the gas tank when near empty and then running it for a few minutes and then turn off engine and letting everything sit over a few days. Of course I didn't do a full thorough deep cleaning but just spraying carb cleaner through all the passages and blowing out with compressed air. The bowls did have some what looks like red color fine rust sediment so that was wiped away. Also new crush washers were used on the banjo bolts because I did see fuel leaking from the top of the bolts and I think fuel was leaking from between the air horn and main body, it was hard to tell but clearly only on the front right side of the carb. Time to study up the carb manual on foxed.ca. I wish Sterlings website was still up! Thanks for the read and tips. This is more of a journal entry for me because earlier today I was reading up on my carb related posts back in 2011 on this forum and was amazed at how I forgot a lot of things in 10 years.
Fouled my new spark plugs and then engine would run really rough and barely idle. Swapped back to my previous set of plugs and that brought the engine back to life again. I think I was trying to compensate for the vacuum leak and richened the idle way too much to bring the RPM down but that was because it was way too rich and even saw some black smoke coming out of the tailpipe. Lesson learned.
Ordered some more parts to address the vacuum leak. It is still good to know that Mazda sells new isolator plates - the black plastic with the rubber gasket built in which sits between the intake manifold and throttle body - along with some vacuum tubing and cork-rubber gasket material and set of hollow punches to make my own (thicker) gasket between the throttle body and the main body. If I pull up on the throttle linkage (I am referring to the area where it contacts the dash pot), the idle will drop to 600-750 but I think I am compensating for the vacuum leak and blipping the throttle will make the engine idle back at 1500-2000 RPM. Waiting for this haul of parts to be delivered soon.
Took off the carb again to see if I can address the vacuum leak. When I put the carb back on the throttle body I missed the accelerator pump linkage/threaded rod and boy was that fun to reattach from where the cotter pin goes because I didn’t want to take off the carb again after connecting up all the linkages and cables. Another lesson learned. Took it for a drive still with the vacuum leak there - yep didn’t fix anything really - and ran into the loss of power issue. So right away I turned off the engine and coasted into a gas station to inspect the bowls. Both front and rear bowls were empty this time which corroborated with complete lack of power this instance rather than the typical 50% power I have been experiencing. Turned on the ignition to let the bowls refill and drove her back home.
Since the fuel tank level was nearing the red block area, I emptied a full can of Seafoam in the tank and let it run through the fuel lines, carb, and engine as indicated by the slight smoke coming out of the tailpipe. Turned off engine and let it sit for a few days. Drove her around today just to see if that helped but I ran into the 50% power loss again (this time watching the speedo I could not go faster than 60 MPH) no matter what gear I am in (tried with 3rd, 4th, and 5th gears). Turned ignition to off and let it coast to a safe spot and inspected the fuel bowls. Now this time it was the rear bowl that was empty and the front one is correct at the halfway point. So I have experienced three cases so far: front empty rear good, both front and rear empty, and rear empty front good. Dumped another can of Seafoam in the gas tank because why not? It seems like the needles could be sticking closed if the bowls are not filling up is one possible cause. It doesn’t have a flooding issue as I have never seen the bowls over-fill past that halfway point on the sight glasses and confirmed that the magnetic fuel vent solenoid is working with 12V power. Also confirmed shutter valve is operating normally as well and not leaking as I know that will cause a lot of running engine performance issues. Checked the anti-afterburn valve hose is not cracked but I ordered a new one just to replace it.
I shall check the volume output from the fuel line going in to the carb next. Maybe my premix (I use the SuperTech TC-W3 stuff) ratio of 1oz to 2 gallons of gas is too high since I can feel the oily-ness when rubbing the fuel between my fingers and can see the blue colored tinge. Maybe that is causing my needles to stick since I didn’t use to regularly fire up the engine (but now I surely do since I have been troubleshooting since last October). Appreciate the read and advice. I’ll continue to scour previous threads for more information.
Edit: I also removed the catalytic converter when I was having the bogging issue with the fouled plugs thinking I had melted my cat and I also was way lean as seen by the glowing red hot cat because I was trying to compensate for the crappy running fouled plugs. No clogged cat, the mesh screen inside looks fine and I can see through it. So I put on the bonez straight pipe for now and engine definitely breathes better
Also I’ve noticed that lately the larger hose on the charcoal canister seems to blow itself completely off attachment on the canister. Too much back pressure in the canister or maybe weak hose? I also have considered if these areas of pressurization can cause fuel supply issues. For example when taking off the gas cap there is pressure escaping (positive pressure in the fuel tank) but I have always had this for many years before the power loss issue.
You need to fix your tank vent - there shouldn't ever be pressure or vaccuum in the tank if your vent (which goes through the charcoal can) is hooked up properly. If it's blocked or hooked-up wrong, the pump will have a hard time pulling fuel from it. Because air can't get in to replace the volume. It's supposed to be free-breathing.
Suck through a straw. Now put your finger over the end and suck. Hard to get air, right?
So there are 3 hard lines that run under the car, from the tank to the engine bay. Biggest is fuel supply, middle-est is fuel return, and the tiny one is the vapor vent to the charcoal can. This line needs to be free-breathing so gas vapor can escape the tank, and air can flow back to the tank as fuel is used. The small line on the charcoal can is the tank vent and the large line goes to the nipple on the center iron (near the base of the oil tube).
How the charcoal can works:
As said, when the gas in the tank is warm it vaporizes and the pressure needs to escape. It passes through the tiny line up to the charcoal can and is trapped in the layers of charcoal inside. **The bottom of the can is actually open to atmosphere so it can breathe in and out, but the gas vapor hangs in the charcoal layers**
When you start your engine the rats nest allows vaccuum to suck the vapors out of the charcoal can (through the big tube), through the engine and into the intake (via the small tube on the oil pipe). It gets those gas vapors out of the can and sucks oil/gas/water vapors from the engine at the same time. Like a PCV system on a piston engine.
Under normal running conditions the gas tank then breathes-in through the filtered hole on the bottom of the charcoal can. So that the fuel pump can easily suck gas and send it to the carb.
I strongly suspect this is why your fuel flow is tapering off a few miles down the road. It gets increasingly difficult for the pump to suck-n-send fuel as the vacuum in the tank builds. Some guys drill a hole in the fuel cap to overcome this but if you have a charcoal can, why not just hook it up correctly? Especially if your subject to strict emission inspections.
You need to fix your tank vent - there shouldn't ever be pressure or vaccuum in the tank if your vent (which goes through the charcoal can) is hooked up properly. If it's blocked or hooked-up wrong, the pump will have a hard time pulling fuel from it. Because air can't get in to replace the volume. It's supposed to be free-breathing.
How the charcoal can works:
As said, when the gas in the tank is warm it vaporizes and the pressure needs to escape. It passes through the tiny line up to the charcoal can and is trapped in the layers of charcoal inside. **The bottom of the can is actually open to atmosphere so it can breathe in and out, but the gas vapor hangs in the charcoal layers**
When you start your engine the rats nest allows vaccuum to suck the vapors out of the charcoal can (through the big tube), through the engine and into the intake (via the small tube on the oil pipe). It gets those gas vapors out of the can and sucks oil/gas/water vapors from the engine at the same time. Like a PCV system on a piston engine.
Under normal running conditions the gas tank then breathes-in through the filtered hole on the bottom of the charcoal can. So that the fuel pump can easily suck gas and send it to the carb.
I strongly suspect this is why your fuel flow is tapering off a few miles down the road. It gets increasingly difficult for the pump to suck-n-send fuel as the vacuum in the tank builds. Some guys drill a hole in the fuel cap to overcome this but if you have a charcoal can, why not just hook it up correctly? Especially if your subject to strict emission inspections.
Much appreciated for the detailed and clear post! I drove her around with the gas cap off (loose and not sealed, gas filler door closed) and this did help since I was able to not get bogged so early on meaning I was able to make it to redline in third gear but then shortly after it suffered the lack of power fuel delivery issue quite badly and pulled over with ignition off and peaked into the sight glasses. Both the front and rear were empty. Wait like 5 seconds to get the pump to refill the bowls, engine always starts right up, drove her home.
Oh yeah by the way the car is 100% completely stock.
I will try driving her again with the smaller tube disconnected on the charcoal canister and also the gas cap loose/off. I did unplug it and tried driving her around like that a few weeks ago but I recall that didn’t make much difference either. I took a peak into that tiny restriction in the small inlet and saw debris so I took a staple, straightened it out and poked it through the restrictor to hopefully clear up that blockage.
Saw you posted in another thread that helped another member solve their fuel delivery issue by replacing the check&cut and fuel vaporizer valves. Can’t seem to buy them new anymore so I need to post up on the marketplace or call some shops.
Last edited by boyee; 03-13-22 at 12:19 PM.
Reason: add note that car is 100% stock
Well, it's a start. I'll assume you've checked/changed your fuel filter. I saw another recent thread "Covid Restoration" or something like that...... Where he found his pump was only putting out half the flow it was supposed to. He cleaned all the wiring terminals on the pump and it was back up to full flowing. Just a thought.
Good to know! It sounds like a lot of the wiring is basic such as the power window switch contacts not transferring all the electrical load to the motors if they get dirty.
Also forgot to mention that I took a compressed air to the fuel return line to see if the restrictor valve on that was clogged. Before I used compressed air I tried blowing through the tube by mouth and could not feel any air pass through. After using compressed air I could hear a small “ping” or “pop” noise in the tank so I assume that means the restrictor is not clogged and the air is making its way back to the tank.
Fixed the vacuum leak with the insulator replacement. I made a thicker gasket for between the throttle and main bodies but ended up not using it for now to see how it'll run with just the new insulator. Currently holds idle at 750 RPM even down to 600 RPM. I need to change plugs to new ones and take her for a drive to see if the power loss issue is still there.
Oops.. posted on the wrong thread because I was doing it on my phone. It was meant for the thread "power loss at 5k?"
I did get to drive around after fixing the vacuum leak and the power loss/fuel starvation issue is still there, even with disconnecting the fuel vapor vent hose at the charcoal canister. Narrowing down… I bought a new fuel cut and check valve and also a new fuel vaporizer valve. I should just take my tank off to have it chemically cleaned as well and sealed inside.
Progress update!
Performed a fuel volume test and after 60 seconds I got about 850cc. So that is a bit under what the FSM states that typically it should get 1100cc within one minute. And this is a brand new Mazda fuel pump too. One month old Mazda fuel filter as well with less than 500 miles on it.
Yesterday I installed new spark plugs and adjusted the idle mixture and speed. Also check ignition timing for leading and trailing to be exactly at 0 and 20 degrees advanced, respectively, with the vacuum lines attached at 750 RPM, referencing the emissions sticker on the hood. If I hadn’t mentioned this before the car is all factory stock with full California emissions equipment all hooked up.
Today I inspected the fuel lines underneath the car and none looked kinked. I then installed the fuel cut valve and took it around for a test drive. Still the familiar power loss fuel starvation issue after WOT in third gear around 5k RPM. So it was not the fuel cut valve.
Next I change the fuel vaporizer (vent) valve. I think this solved 90% of the fuel starvation issue!
The reason why I said 90% is because I am still experiencing fuel starvation at the top end but I am now able to get past 3rd gear at WOT and shift into 4th gear WOT and then start experiencing some fuel starvation around 5-6k RPM in 4th. And my shift point is at 7k redline for each gear for the testing. If I let go of the throttle for a second or two the bowls are seeming to refill faster than before because I am able to accelerate without the power loss feeling within those 2 seconds. So maybe this is how a factory 12A Nikki with stock fuel system behaves with a little bit of fuel starvation? Can anyone confirm this? I have read in other threads that even an optimal fuel pump still performs quite mediocre and have seen Kentetsu’s mod where a second fuel filter is added to improve fuel flow, and the factory fuel filter is quite restrictive. I haven’t really driven her this way with WOT for all the gears (although it is quite fun) so I am not so sure if fuel starvation is normal. Normally I drive her without this many redline pulls throughout the gears, but rather with the occasional first or second gear redline and then immediately back off and cruise. Also to note, before I installed the hoses to the valve, I took my air compressor and blew air through all of the tubing. I did not find any blockages, or at least if there were any blockages in the tubing then they were blown out.
I observed after changing the fuel vaporizer valve that after parking and immediately opening the fuel cap, I still hear a whoosh but it sounds more gentle now. I also tested with WOT redline first to fourth pulls with the gas tank vent line disconnected at the charcoal canister but that made no difference. I was trying to see if there was a clog in the charcoal canister that was blocking flow of venting of the tank.
I was wrong it seems. The fuel starvation issue is still 100% there as I just took her out for a drive and the same symptoms are still there; not the 90% improvement like I thought. I wonder if temperature plays an effect since this is night time driving and air temp is cooler. Current air temp when I was experiencing the issue was 59F and I drove the car all day Saturday for a good two hours at least with some hard pulls through the gears and not once did I feel any hesitation from fuel starvation and ambient temps that day were around 70F.
Guess the next thing to do is to drop the gas tank and have a look inside.
Small update: finally got ahold of a camera scope tool and stuck it down the filler neck and did confirm there is some rust inside the gas tank. Some areas do not look so bad but some areas definitely have that cancer. So time to drop the tank and try to refurbish and seal it.
I finally took care of the rust in my gas tank. Removed the tank, took it to a local radiator shop to have them boil, flush, seal, and add a drain plug. Here are some before and after pictures. Unfortunately the fuel starvation is still there after reinstalling the tank with new hoses and new Mazda fuel filter however it feels as though it's faster to recover. Next plan is to remove the carb again and this time soak it in chem dip carburetor parts cleaner, fully disassembled. Thought process is that the alcohol in gas these days plus not driving the car that much over time cause corrosion and parts sticking like the float needle, at least this is my current theory. I need to get an inline fuel pressure gauge as well.
Before. Rust on the bottom panel of the tank. After. Not sure what product that they used to seal which is a red color.
Confirmed fuel pressure by hooking up a gauge to the fuel in line right before the carb. The pump out pressure is measuring 5.1 to 5.2 psi and when the engine is running the needle on the gauge is fluctuating between 3 to 4 psi rapidly. Then when flooring the accelerator pedal to rev it to redline the fuel pressure can go as low as 2 ish psi. Fuel flow volume test in 60 seconds got around 750 to 800cc which is under FSM spec of 1100 or higher cc.
Confirmed fuel pressure by hooking up a gauge to the fuel in line right before the carb. The pump out pressure is measuring 5.1 to 5.2 psi and when the engine is running the needle on the gauge is fluctuating between 3 to 4 psi rapidly. Then when flooring the accelerator pedal to rev it to redline the fuel pressure can go as low as 2 ish psi. Fuel flow volume test in 60 seconds got around 750 to 800cc which is under FSM spec of 1100 or higher cc.
Yes I'll look into getting another new fuel pump to see if there's any improvement with the flow rate.
Also I'm disassembling the Nikki again but this time soaking it in parts cleaner. I found little mesh screens in the needle seat assembly once I took off the seats. Is this standard? I was only aware of the screens that go over the banjo bolts. I looked up the exploded view in the carb manual and there's no mention of this part. It sure looks restrictive.. mine is a stock 1982 Nikki.
Looks like I wasn't searching hard enough and I found the answer to my question in the last post about the little screens right before the needle valve assembly in this thread here answered by Carl. https://www.rx7club.com/1st-generati...inlet-1157549/
Well I'm slowly getting there with OCD cleaning all the parts of the carb including all the miscellaneous hardware. Ordered another carb rebuild kit from rock auto and will start to put it all back together once I get it delivered. Then need to order another fuel pump which I shall do now.
Carb is finally assembled and back on the car. I haven't done any testing yet. After leaving the carb main body soak in parts cleaner for over a week I think it removed the finish coating off it.
Got a chance to drive her today. No fuel leaks at all after reassembly so that's good. I'd say after a deep clean of the carb, it runs even smoother than before and throttle response is real nice. However the fuel starvation power loss was hit hard after I floored it in second and then into third gear and all of a sudden no power. Put it into neutral and the engine died so I pulled over to the side of the road to let the bowls refill before starting the engine right back up and driving back home. She pulls really nice though. Idles alright... I probably need to make my own thicker gasket that goes between the throttle body and main body instead of that super thin paper one that comes in the rebuild kit. Also the diaphragm connected to the bi metal choke assembly doesn't seem to work because when I manually pull the diaphragm lever when choke is engaged, the engine speed increases and becomes less brappy (although I do like the sound of the brappy braps!)
Another brand new Mazda factory fuel pump arrived last week so I'll install that next and do a fuel volume test and pressure test on this one. Good thing I read on racing beat that the stock fuel pressure is 4.5 psi and it shouldn't drop more than 30% pressure. Seems like the stock fuel pumps can't keep up with the pressure when the engine is demanding a lot of fuel.
10-14-09, 09:17 AM
