Sputtering, coughing and misfiring on 1972 240z

[jalexquijano]

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?

[banzai510(hainz)]

ck the distributor for water and make sure ytour fire order is correct.

 

timming? Use a timming light?

 

also is this SU carbs?  we need more information. was good good before your you just buy it? Was soemes project?  cam timming good?

 

Points, condensor?

[Doctor510]

Back to basics and check the float level along with ALL the other suggestions.  Whem you pull on the choke. it pulls the fuel nozzles down, may times they will not go back up.

[datzenmike]

Check the damper oil. If leaked out or low the slides will raise too quickly causing a lean condition. Good for a backfire through the carb when cold. I imagine in Panama it isn't very cold so I'm surprized you need the choke for so long.

 

Twin carbs need to be synchronized to run properly so that one isn't working harder than the other.

[racerx]

Same guy with the same issues since 1901. You still have ur MSA exhaust?

[jalexquijano]

Twin SU Carb. Float level was already set to .55 inches. Pertronix Ignitor module with pertronix flamethrower coil. I am even getting intake backfire with the both idle mixture knobs set to 3.70 turns clockwise. No vacuum leaks.

[jalexquijano]

Float level set at .55 inches.

[datsunfreak]

 Airtex 8012sx electric fuel pump is just pushing 3.2 psi. Coud this be the cause of the symptoms addressed?

 

In my experience, this is too much fuel pressure for stock Hitachi SUs. They'd be a lot happier around 1.5psi (2psi at most). 

[jalexquijano]

The FSM states 3.4 to 4.2 psi.

[I'm BLUE]

Twin SU Carb. Float level was already set to .55 inches. Pertronix Ignitor module with pertronix flamethrower coil. I am even getting intake backfire with the both idle mixture knobs set to 3.70 turns clockwise. No vacuum leaks.

Pertronix ignition module. I had one installed in a 73’ 240z when I purchased it 10-Years ago. I had a random miss-fire that turned into a bad somewhat consistent miss-fire on the way home one hour away. It ended up being a LEAKING wire from the module itself that at some point vibrated/cut through the wire itself ever so slightly causing an obvious electrical arc. The grommet that held it in position to prevent this inside the distributor was positioned a bit off.

 

Have no clue if that’s of help , but that scenario happened on my Z.

 

Stick a timing light on your car and see if the Mark jumps around. Timing Chains can stretch. Harmonic balancers fall apart over time as well , so keep that in mind when checking timing.

 

Distributor advance plates are KNOWN TO FREEZE up or fall apart. Check operation of everything inside of it...clean and lubricate. Depending on the humidity in your environment you may just want to keep changing out your distributor cap. I’ve had them fall apart whilst driving...

 

 

On another note to keep an eye on....the valve seats in the early heads (US?) were SOFT. Which doesn’t leave much room if any adjustment for valve lash. Ran into this quite a bit.

 

 

Flat-top or round top SU’s ? SU carbs need to be taken apart and reworked top to bottom. No cheap easy long term fix. You get the quality of the work you put into them.... Needles have specific profiles as well...easy to bend or fuck them up ! (People tightening down hard on them).

[datsunfreak]

The FSM states 3.4 to 4.2 psi.

 

Alright. But every one I've ran over 3psi ran like shit, then they all ran better closer to 2psi. Just offering my experience. If you trust the book, you trust the book.  :thumbup:

[I'm BLUE]

Alright. But every one I've ran over 3psi ran like shit, then they all ran batter closer to 2psi. Just offering my experience. If you trust the book, you trust the book.  :thumbup:

100% my experience as well ^^^ !

 

+1 !