ZCar Forum banner
Status
Not open for further replies.
1 - 10 of 10 Posts

·
Registered
Joined
·
650 Posts
Discussion Starter · #1 ·
well, i ran my 71 at the CMI races this sunday and i got a weird problem. when the rpm hits around 5k the car spits out black smoke, i checked the spark plugs and it doesnt look like its running to rich (according to the book) which leads to another question... how do you know if its running rich or lean. but does anyone have any ideas.
 

·
Registered
Joined
·
1,544 Posts
Ed I told you to cut down on smoking!

I think when you smoke you hurt your car, as well as yourself hehehe, and stop throwing cigarattes in your exhaust! your car doesn't want to smoke cigarettes;P hehehe just kidding
Zya
yuichi
p.s. why don't you get a ninja special?? hehehe
 

·
Registered
Joined
·
1,826 Posts
RE: Ed I told you to cut down on smoking!

get a air fuel meter to monitor the ratio at full throttle. o hook up a good digital meter to your oxygen sensor. Tie negative to ground and the positive lead into the oxygen sensor wire. Shoot for .850 volts at full throttle. Anything richer will read higher, leaner will read lower. Below .780 at full throttle is dangerously lean. Ignore the reading at anything but full throttle for your purpose. I doubt if you car is running that rich at full throttle to cause black smoke, but it sure sounds like it. You probably won't blacken the plugs on such a short run. What carbs are you running? And what type of fuel pump/regulator if applicable.
greg
71 240z
 

·
Registered
Joined
·
996 Posts
I don't know what your smoking but it shouldn't be black, imagine what your lungs look like, and what about the kids watching the races? What kind of example is that?

Seriously, what has been done to your engine? If it is fairly stock without the bottom end built you could have a little blow-by, which keeps your fuel from igniting and burning cleanly causing loss of power and smoke. Check the fuel pressure at the carbs or what type of fuel system are you running? If carbs there are numerous tuning issues. If your car has points type ignition are they adjusted properly and is your coil hot enough. Stock Z engines make very little power over 5500 rpm and the stock ignition makes a very weak spark over 5000 rpm. A weak spark could easily cause a rich condition and at low rpm's this wouldn't seem like a problem.

Just some ideas, It really depends on how your car is setup.

Later
Matt
 

·
Registered
Joined
·
650 Posts
Discussion Starter · #5 ·
basically the engine is stock. im running a mild cam that came with the head so i dont know the specs. duel dgv 32/36. im using a zx turbo elec. distributor with an accel super coil (yellow boxy one) and accel 8mm wires. i never noticed this prob when i was running on splitfires, but i swapped to NGK's 2 days before the race and now it shows up. gapping them at .032

as for the O2 sensor, i guess thats what that hole in the pacesetter 6-2 headers is for, huh? =) guess i need to get one of those now.

im running a carter 7psi fuel pump and fram high perform. fuel filter. i havent put the holly fpr in yet, because i was planning on rebuilding the engine anyways, and i just ran it to get some timeslips to compare with. but i would really like to solve the mysterious black smoke problem so it doesnt show up after the rebuild. =) thanks guys for your help.
 

·
Registered
Joined
·
650 Posts
Discussion Starter · #6 ·
hey yuich

the ninja special is sitting in the garage waiting for a BTM. you wanna buy it for me. =)
 

·
Registered
Joined
·
107,695 Posts
<b>RE: black to the smoke prob</b>

I bet it's the cam. Mine did the same, so I rebuilt engine(was using oil too) and problem continued. I just think some cams allow so much fuel at high rpm that we can't burn it all. Correct me if I'm wrong, but I'll bet your smoke was more of a real dark brown, that actually black, right? If so I would say it is just unburned fuel from the cam. I don't worry about it, plus it gives someone something to choke on after i beat their ass from a stop light!!
 

·
Registered
Joined
·
1,826 Posts
RE: no way

Too much cam causing black smoke?? Too much cam will kill your torque and make your car a dog, but it won't cause your car to run too rich. I'd go ahead and put that regulator in since you are running an electric pump, especially since it's a carter. I've always had to run regulators on Carter pumps to keep the pressure under control. Check the new plugs and make sure they are the right ones for your car. You might have got a set that was to "cold" by accident. Check plug wires and connections since that's the last thing done to the car. maybe the secondaries in the DGV's are jetted too rich and you only notice it under prolonged full throttle at the track? I'd stick to fuel and ignition problems.
greg
71 240z
 

·
Registered
Joined
·
650 Posts
Discussion Starter · #9 ·
i think greg may be right on this one guys

like i said, i didnt have this prob when i was running the split fires. how about a smaller gap to cause faster firing? or can i increase the spark power?

im ready to drop a direct draw carborated turbo into my Z, so i would like to get this prob out of the way... now if i could only find some money for my BTM =) anyone wanna buy an extra center consel for a 72, good condition =).
 

·
Registered
Joined
·
996 Posts
Try a few things

With a mild cam and those webers you have some tuning issues possibly. As Greg said the secondaries are probably to much and causing a rich condition. I am sure the cam doesn't make the car rich and smoke however it will let more air/fuel into the combustion chamber which if the carbs are jetted wrong will make this problem very apparent. As for the ignition it sounds like you should have a decent spark but the plugs may be to cold.

This really sounds like a carb tuning issue to me I run sidedraft webers and just had them tuned by someone who really knows them, he rejetted them based on my cam specs and displacement. I also had a hot coil hooked to the factory ignition box, which was replaced with a MSD 6AL and the car has really woke up. No smoke and the torque curve is almost flat. Hope this helps.

Later
Matt
 
1 - 10 of 10 Posts
Status
Not open for further replies.
Top