Misfiring And Affecting Acceleration After 10 Mins Traffic Jam On My 240Z

[jalexquijano]

Just installed a coolant reservoir tank to my champion 3 row radiator. It´s working better now. Anyway, the car is still presenting some sluggish acceleration when stuck on a 5 to 10 mins short traffic. Can someone explain to me why if i pull out all the NGK BP6ES spark plugs and brush the carbón off, the car accelerates fine? I have both of my carbs set to 3 turns clockwise. If i lower it more, i start loosing power at 1st gear.

[1600dave]

If you stop, wait the same amount of time that it takes to remove the spark plugs (but not actually remove and clean them), how does the car run after you start up again ?

[KatoKid]

/\ /\ /\ This man knows!

[1600dave]

Reason I ask is that I used to have a similar issue with SU carbs (admittedly on a 1600, not a zed).

 

The fix in my case was to insulate the fuel rails leading from the mechanical fuel pump to the carbs, it seems the issue was heat related from sitting in traffic idling away. Not so much actually "overheating", the engine quite happily sat at its normal operating temperature, just that the underbonnet heat soaked into the fuel rail / carbs / etc.

 

It may be that stopping to remove the plugs is giving everything enough time to cool down, it may not actually be removing the carbon off the plugs that is fixing it, just giving it a chance to cool off a little.

Edited October 3, 2017 by 1600dave

[24 Dat]

Sound like it might be fuel vaporisation in the fuel lines, you might need to insulate them and also the factory heat shield between the exhaust manifold and the bottom of the carbs is not very effective try a sheet of ACL heat sheld or similar  http://www.autoxcel.com.au/product_info.php?products_id=140 

[Enzo]

Sounds like your just running rich if the plugs are carboning up at idle. You state that if you wind down any further the car loses power. Dial it back to lean off at idle. What needles are you running. You should be able to get a good idle regardless of the needle as long as it is not adjusted out too far.

Make sure both needles are installed to the correct height in the damper and back the dial off to 1-2 turns out. A vacuum guage is always a handy tool when setting idles. Adjust the needles to give the highest vacuum reading. As the revs increase, back off the idle screw and keep adjusting the needle heights for the highest vacuum. At your chosen idle speed you should have the best vacuum reading.

Give it a try.

David

[AndBir]

Dejavu?

 

http://www.viczcar.com/forum/topic/16353-sluggish-acceleration-misfiring-after-5-to-10-mins-traffic-jam/

http://www.viczcar.com/forum/topic/16146-1972-240z-fuel-percolation-at-traffic-jam-or-long-idle-time/

[AndBir]

Have you checked you are getting enough fuel flow back along your return fuel line - maybe it is blocked / restricted?

[jalexquijano]

Reason I ask is that I used to have a similar issue with SU carbs (admittedly on a 1600, not a zed).

 

The fix in my case was to insulate the fuel rails leading from the mechanical fuel pump to the carbs, it seems the issue was heat related from sitting in traffic idling away. Not so much actually "overheating", the engine quite happily sat at its normal operating temperature, just that the underbonnet heat soaked into the fuel rail / carbs / etc.

 

It may be that stopping to remove the plugs is giving everything enough time to cool down, it may not actually be removing the carbon off the plugs that is fixing it, just giving it a chance to cool off a little.

 

1600 Dave,

 

Thanks for your kind advice. I already insulated the metal fuel rail with header wrap and besides of the stock metal heat shield that is fastened to the intake, i added additional heat shield extensións that covered the 3 screws Su Carburetors fuel bowls. However, the problem persists, ngk bp6es spark plugs get fouled in traffic and once fouled car acceleration becomes sluggish and misfires. Please find attached pictures of my engine with the shields and the wrapped fuel line. THis problem needs to be solved in someway. I am using an AIRTEX 8012S fuel pump and my cam is a Schneider 274F. Motor has been overhauled to 2.6L with oversized pistons.

 

[jalexquijano]

Reason I ask is that I used to have a similar issue with SU carbs (admittedly on a 1600, not a zed).

 

The fix in my case was to insulate the fuel rails leading from the mechanical fuel pump to the carbs, it seems the issue was heat related from sitting in traffic idling away. Not so much actually "overheating", the engine quite happily sat at its normal operating temperature, just that the underbonnet heat soaked into the fuel rail / carbs / etc.

 

It may be that stopping to remove the plugs is giving everything enough time to cool down, it may not actually be removing the carbon off the plugs that is fixing it, just giving it a chance to cool off a little.

Any other opinions asides from adding more heat shield or wrap? How come some users do not suffer from this issue.

[jalexquijano]

Reason I ask is that I used to have a similar issue with SU carbs (admittedly on a 1600, not a zed).

 

The fix in my case was to insulate the fuel rails leading from the mechanical fuel pump to the carbs, it seems the issue was heat related from sitting in traffic idling away. Not so much actually "overheating", the engine quite happily sat at its normal operating temperature, just that the underbonnet heat soaked into the fuel rail / carbs / etc.

 

It may be that stopping to remove the plugs is giving everything enough time to cool down, it may not actually be removing the carbon off the plugs that is fixing it, just giving it a chance to cool off a little.

Do you have pictures of your engine bay to see how you solve this issue???

[1600dave]

No pictures, sorry. This was 25 years ago when the Datsun was my only car, I still have the car but its been sitting in the shed for 15 years and the carbs were removed long ago.

 

Looked pretty much like yours does, with heat wrap around all the fuel piping.

[nizm0zed]

your location says Panama?
How hot and humid is it there? are you using an ethanol mix fuel?
Reason I ask is ethanol fuels absorb moisture, particularly if its been sitting in a tank for a while, if the moisture content is high in the fuel it'll be more likely to 'boil' and creste a vapour lock in the lines.
Is there possibly another way you can reduce underbonnet heat? Vents maybe? or drive with it popped open? (but still with the saftey latch)

IIRC the 280zx had a fan setup to blow cool air over the injector rail, maybe something like that coud help.
not sure on your location or what the local cops would think, but if you can consistently get it to fault, maybe try replicating but with the bonnet removed completely, temporarily of course. Im thinking that if it still does it with the bonnet off completely its going to be a deeper issue than underbonnet temps.

Your heat wrapped rail is usually a good working solution, the extra heat shields are definitely not going to hurt the process either.

[GregTas]

If I recall correctly the factor fuel line wrap was shiny on the outside to reflect the heat. That insulated wrap you have used could just slow the heat absorption but not eliminate it.

 

Perhaps you could wrap all the lines to aluminium cooking foil and see if that reflects the heat any better. It would be a no cost thing to try and only a few minutes work.

[jalexquijano]

This is a picture of the 6 spark plugs in the following order of cylinders 6-5-4-3-2-1. This ishow they came out after long idle time during traffoc jam last saturday. I have already lowered the mixture knobs on both carba to 2.5 turns and have installed new spark plugs to test.

Edited October 5, 2017 by jalexquijano

[aircobra]

but the  electrodes look white, which is a sight of TOO LEAN a mixture? unless its the reflection of the flash

[Agno]

http://www.crankshaftcoalition.com/wiki/Reading_spark_plugs

 

Looks like you're too lean and too much timing.

[jalexquijano]

Yesterday i cranked my 240z and drove with the choke pulled for 5 minutes until i reached to normal temperature as otherwise the car misfires and stumbles. Once on the speedway i pushed the choke lever off and when accelerating the car started to pop or backfire at the intake. In order to avoid this i had to add some choke so i could reach back home. Is this a symptom proving that the Airtex 8012s electric fuel pump is failing? I had this problem 2 years ago, replaced the pump and never had this again.  What is the mínimum PSI that i need in order to avoid this problem? Both of my carbs are set to 2.65 turns clockwise and have been balanced.

 

https://www.amazon.com/Airtex-E8012S-Universal-Electric-Fuel/dp/B000DT7Y7A

 

[d3c0y]

Could just be a blocked fuel filter. You know how in all your other threads we all said you were running lean.... 

 

According to main ole FSM the static fuel pressure should remain within the following limits: 3.41 to 4.27 psi

[my_mad_z]

As d3c0y suggested, check the fuel filter; If it's ok, check timing components or for vacuum leaks as they can also cause backfiring through the intake;

[jalexquijano]

everything was checked, i guess its the new system which is less restrictive and its of a different material than stock.

 

Its weird as when i recently purchased the car, it carried a twice pipe system and it did not backfired when releasing the gas pedal at any gear:

 

http://www.thezstore.com/page/TZS/PROD/classic19i/15-6031

 

the one i installed is made from aluminum and has no reduction or glasspacks:

 

http://www.thezstore.com/page/TZS/PROD/classic19j/15-6304

[jalexquijano]

i was recommended 12 btdc

[jalexquijano]

I live in Panama where temperature rises to 33 degrees Celsius. Both of my 3 screws roundtop SU carbs were fully rebuilt by Ztherapy who recommended to use ATF as damper oil. However, after 3 years i am still struggling with the car during slow traffic situations. Should i consider changing to better Brand of ATF or just settle with 3 in one motor oil SAE 20?

[1600dave]

Depends what problems you are having. The damper oil really only has much of an effect when accelerating. Using a thicker oil will slow the rise of the piston due to vacuum, resulting in a slight "enrichment". Under constant vacuum (ie when not accelerating), weight of the oil has no effect.

[d3c0y]

No.