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Alioli77

Sputtering, coughing and misfiring during first 15 mins

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My 240z is sputtering, coughing and misfiring during the first 15 minutes since cranked. Is this normal? I have to run it with the choke lever pulled until the temp reaches to half of the temp gauge. After that it runs rough. I have cleaned all the plugs to see if it solves the problem. Airtex 8012sx electric fuel pump is just pushing 3.2 psi. Coud this be the cause of the symptoms addressed?

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Welcome to the forums, it looks like you posted in fuel delivery, than in model specific. I moved both posts to the trouble shooting/general engine section as that seems to be perhaps a better fit.

 

You will probably want to supply more information.

 

Was the car running ok before you installed the pump?

 

Has it always been running this way?

 

Did you install the pump recently?

 

With the fact it is a 1972 Z, the assumption will be you are running SU carbs. Have they been matched? Are both carbs getting fuel and filling the bowls?

 

You mentioned you pulled the plugs and cleaned them, what did they look like? Were they fouled?

 

Without the answers the basics come to mind. Did you check the timing? How old is the gas? Do you have good gas flow? Where is the regulator plumbed in? 

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I just have an airtex 8012sx pump installed at the back next to the gas tank.

 

https://www.summitracing.com/int/parts/atx-e8012s/overview/

 

This pump used to push 4.2psi before and now it only pushes 3 psi (maybe this is inmaterial as i am within the limits. Please confirm) My car is a 1972 240z which has been overbore making it a 2.6Liters. I also has a Schneider 274F camshaft and both 3 screws su carbs were  remanufactured by Ztherapy on November 2014. Pertronix ignitor module with pertronix 1.5ohm flamethrower coil.

 

Spark plugs were fouled when i returned home. Should i buy a new set of NGK BP6ES and start again? Gap them at .32?

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Well the plugs indicate you are running rich. Whether that is caused by inconsistent fuel delivery, or incorrect mixture is yet to be seen.

 

The drop in fuel pressure is interesting. I believe the SU carbs want something in that neighborhood. Would you entertain us with a picture of your setup with the location of the fuel regulator and the gauge? We've seen people put the regulator before the rail before, it should be on the return side of the rail.

 

The drop in pressure could mean a fuel restriction meaning even with the pump working at adequate levels the amount of fuel behind the pump is inadequately supplied. That can mean inconsistent fuel delivery which can mean at some points you are running real rich, sputtering, coughing, putting out black smoke, and at other times running lean enough to be ok.  The first 15 minutes is a bit of a kicker as that is a bit long for the engine to warm up, indicating maybe that is the time it takes for sediment in the tank to settle down or something of that nature.

 

Assuming this is still a fuel problem.

 

Pop the return line off the fuel rail and run just the fuel pump. Time how long it takes to put out say a gallon while watching the fuel flow, it should after the pump pressurizes the rail be a pretty consistent flow. 

 

If the fuel flow, volume, and pressure are good, then you would check the basics, mixture screws on the carbs, spark plug wire firing order, compression, flow, etc.

 

If the fuel flow, volume, or pressure are inconsistent, then you have a clogged hose, plugged filter, holes in your pickup, etc etc etc.

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THis is really strange. In order to sort this out faster i decided to accomplish the following:

 

1. Purchase, gapped at .032 and  install a new set of 6 NGK BP6ES spark plugs

 

2. Cleaned the distributor cap and  rotor with deoxit d5.

 

Once concluding the above steps, i cranked the engine and left it warming up with the choke lever pulled for 3 minutes,  and drove the car. No more sputtering, coughing, misfire whatsoever. No more rough acceleration.

 

What could have been the cause?? Do the plugs become useless if fouled? Is it normal for them to get fouled during traffic jams?

 

My car has an airtex 8012sx fuel pump with no regulator as it just pushes 3 psi.  

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They can have a much weaker spark if they are fouled, the spark would have to transmit through carbon deposits so it would be weaker.

 

Cleaning the rotor and cap could also have helped if there was debris.

 

If this solved your issue then it means either you fouled them up by running it with the choke for too long, or your mixture screws were on the rich side which caused the plugs to foul. Do you also drive around at low rev? The SU's tend to lean out the higher you push them, assuming you had them tuned for your application that usually means a fairly rich idle if you want to stay safe in the upper rev range. As a side effect that means if you don't rev the engine in the higher RPM's you are staying quite rich all the time, I believe this is what people call the "italian tune-up."

 

You should have a regulator, my memory is failing a bit, but on a stock 240z one side of the fuel rail has a restriction which causes the fuel pressure to remain raised. 

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Is it oil fouled or fuel fouled? Care to share a picture?

 

Did they put in different needles? Or did you tell them you had a bigger cam in your motor? 

 

Did you set the idle mixture screws and adjust idle? Or did you just install them and go?

 

Running rich would be my guess. I had SU's on my L28 and I had to adjust the low RPM mixture way down to keep the car from leaning out on the top end. According to some charts I've seen the stock needles are kind of made for the stock car, you would want to look into maybe SM needles depending on how modified the motor is to kind of flatten the fuel curve.

 

Without a way to measure AFR you are kind of just guessing at it, and if you haven't messed with them before you are really guessing. Some older shops or shops that deal with older cars have a service where they will adjust your idle and your mixture for you using a wide band sensor clamped to your tail pipe. I'm guessing you need that type of service.

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