Hey Guy's, I have a earlier 70z.I needed more Z power so I put in a F54 block, w/ N42 head ,w/ non-EGR F.I.,w/ 79 dizzy, w/ E12-80 ignition.I put in T-5 Brg/wrner and a 88 300zx se Visc/LSD. My concern is when I start the Z ,this black wet bubbley soot shoots out my tailpipe about 3feet or so. It happens everytime i start the Z. It's all over my drive-way it's a dirty mess the guy next store to me his wife's white Mercedes benz my Z shot out a nasty mess all over her car... anybody have a simuliar experience with this black soot shooting out PLEASE tell me whats going on here. Thankx Guy's

Mine does that also, although not as bad. Running the carbs too rich perhaps. I'm guessing you have a large exhaust, 2.5 inch or so, as that seems to make it worse. Bigger pipe equals lower velocities, and more black soot settles in there, then when you give it some, it all gets blown out in one ugly hit. Cheap fuel makes it worse too.

Mine does that also, although not as bad. Running the carbs too rich perhaps. I'm guessing you have a large exhaust, 2.5 inch or so, as that seems to make it worse. Bigger pipe equals lower velocities, and more black soot settles in there, then when you give it some, it all gets blown out in one ugly hit. Cheap fuel makes it worse too.

^^that's what i was thinking, but he doesn't have carbs..... maybe the FI is too rich.... anyway, it's pretty normal for performance cars... nothing to be too concerned about

I just went out tofire up the Z and lots of water also & soot

Unless you the car has been sitting for a long time in the rain (high humidity), check your radiator. You might be leaking radiator fluid into your combustion chambers when your car is off.

Black soot is excessively rich mixture. If it is only during startup, you might have a leaky injector or cold start valve.

I did disconnect the cold start valve to try & eliminate the soot. my injectors are new .the radiator i don't exactly know what you mean by leaking ,can you narrow down what would cause such a thing. I drive the Z every day for at least 1 hour a day. good combustion. I will go & check my radiator it's been a month since last i checked

Back in the olden days (when I was a lad) they talked about talking a rig out and blowing the carbon out of it. Sounds like that's where you're at today. When the car gets driven, does it get driven far enough to get fully warmed up, I mean fully warmed up? The exhaust needs to get hot enough to burn that accumulation of condensation out or you'll just make you neighborhood exhaust guy happy.

It does sound like things are rich, and you might also want to take a look at a set of hotter plugs.

You could have a bad head gasket, warped, cracked or corroded head. All could let coolant into the cylinders when the engine is off. Next time you start your engine after its been sitting overnight, remove all the spark plugs and crank the engine over. Watch the spark plug holes for the one spraying out the coolant.

This is good info guy's. I allow my Z a 10min warm up, then go for a drive for an hour or so. So i can blow out the carbon & have some fun to.I go from 70mph to 100+ mph very quickly with the help of the , Ld28 crank ,w/late 73, 133mm -9mm 240z rods, using 240sx 89mm flat pistons w/ 0.120" over bore (I did'nt for-see pistons would hit the head)but a friend suggested i use a HKS 2mm head gasket that solved a costly oversight on my part. I do drive the Z hard & it never gets hot. However mentioning my head gasket could be going by curtis 240z has got my curiousity looks like i'll be pulling plugs tomarrow ..Thanks again guy's I was at a loss I will post my findings in the am hours

Hey guy's , well it's been raining here in San Diego ,Ca so i have'nt gone out to do anything with the Z maybe tommarrow.

The water from the exhaust is more likely to be from condensation than a coolant leat, especially if you are in a humid area. A compression test or leakdown test can help rule this out. Easier than pulling off the head for nothing. I would think that with a stroker, the mixture would be lean rather than rich. Seems strange.

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I would think that with a stroker, the mixture would be lean rather than rich. Seems strange.

When running an engine for Max Power, mixtures are set rich. This enables the engine to run cool, avoiding excessive cylinder head temperatures.

Aero engines have an advantage in that mixture can be manually set from lean to rich, handy when your flying, perhaps not such an advantage with both feet firmly plated on the ground....