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1972 240Z Fuel Percolation At Traffic Jam Or Long Idle Time


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#1 jalexquijano

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Posted 23 May 2017 - 02:44 AM

My 1972 240z is suffering from fuel percolation during traffic jams and traffic lights. In addition to the stock heat shield which was installed in the car by the Factory originally, i have mounted a two Stainless Steel heat shield extension that reaches the bottom of both 3 screws SU Carburetor float bowls. However, the fuel percolation is still present. The gasoline in my country, Panama, has no ethanol so this should not be happening. The heat comes directly from the manifold and thus there must be away of lowering that amount of heat so it does not affect the fuel that is inside the float valves and that will evaporize and consequently shut the engine down. Other owners only throw out ideas such as swapping metal fuel rail with 5 inch rubber hoses, i have already done this and the percolation is still present. how do i avoid the car idle becoming lumpy at traffic jams which leads to a sudden shut down of the engine? WOuld installing a 280zx injector cooling blower solve this? The heat in my country is 32°C and lots of traffic.

Heat shield SU CARBS
heat shield 1
Heatshield SU CARB rear
blower cooling engine
blower cooling engine 3
blower cooling
IMG 00003175

Edited by jalexquijano, 23 May 2017 - 02:45 AM.


#2 d3c0y

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Posted 23 May 2017 - 02:28 PM

Based on the other thread, percolation might not be your issue and it could be more to do with your plugs and mixture setup. I would get the the lean issue sorted first before trying to troubleshoot another issue.

Summer over here is regularly that kind of temperature and my cars didn't have that issue over summer when they had stock SUs


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#3 KatoKid

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Posted 23 May 2017 - 02:57 PM

Just a thought.....factory cast iron exhaust manifold will be a great big heat soaked source....would tubular headers dissipate heat better and not cause so much heat soak?



#4 chris240

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Posted 23 May 2017 - 07:48 PM

Carbs not heat..
Isnt percolation how coffee was brewed in the 70's ?

#5 dat2kman

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Posted 23 May 2017 - 10:47 PM

We ran into this problem with dirt rally cars,waiting at time controls in hot dry conditions.
We tried the insulation wrap, like you have, it made it much worse.

Remove that insulation wrapping, fit extensions onto the arms that the fuel rail is mounted to, to lift it higher, and bend it away from the rocker cover, and the heat rise from exhaust.
That worked OK, except on very hot days, then the problem came back. Increasing idle, speed helped, as it allowed more fuel flow.

We had to run a cast iron manifold, under Production Rally Car rules, we had it ceramic coated, to try to contain the heat.
Yes, a full length heat shield, that fitted as far into the spaces between intake manifold and exhaust manifold, and have that ceramic ( Heatproof) coated.
If you are using standard mechanical fuel pump, have the rubber lines to/from it, held further away from rocker cover.
We ran twin electric pumps ( one was a backup) at rear, and ran fuel line up to top edge of firewall, along, up into a fuel pressure reg,
and then, from inner left hand fender, into the carbs, with overflows running back along same route, this was all to keep it as cool as
possible. It worked.

Good luck!

#6 jalexquijano

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Posted 24 May 2017 - 01:46 AM

so installing the 280zx injector cooling blower will not dissipate the heat produced by the manifold which causes the fuel percolation at the bowls? WHich electric fuel pumps are recommeded? I have an airtex 8012s rated 5 to 9 psi but its really pushing only 3 psi  installed at the rear besides the gas tank. I cant believe i can only use my car when there is no traffic at nights or on sunday!! There must be a solution to this percolation!

IMG 00002257

Edited by jalexquijano, 24 May 2017 - 01:46 AM.


#7 jalexquijano

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Posted 01 June 2017 - 07:57 AM

We ran into this problem with dirt rally cars,waiting at time controls in hot dry conditions.
We tried the insulation wrap, like you have, it made it much worse.

Remove that insulation wrapping, fit extensions onto the arms that the fuel rail is mounted to, to lift it higher, and bend it away from the rocker cover, and the heat rise from exhaust.
That worked OK, except on very hot days, then the problem came back. Increasing idle, speed helped, as it allowed more fuel flow.

We had to run a cast iron manifold, under Production Rally Car rules, we had it ceramic coated, to try to contain the heat.
Yes, a full length heat shield, that fitted as far into the spaces between intake manifold and exhaust manifold, and have that ceramic ( Heatproof) coated.
If you are using standard mechanical fuel pump, have the rubber lines to/from it, held further away from rocker cover.
We ran twin electric pumps ( one was a backup) at rear, and ran fuel line up to top edge of firewall, along, up into a fuel pressure reg,
and then, from inner left hand fender, into the carbs, with overflows running back along same route, this was all to keep it as cool as
possible. It worked.

Good luck!

 

I had to fully remove my stock manifold in order to replace the 3 studs that bolt to the downpipe of the MSA Exhaust kit, as one of them was broken. Anyhow, during the reinstallation process I was wondering if replacing this stock manifold with a ceramic coated header will solve my fuel percolation issues? How much difference in temperature between the stock manifold and the ceramic coat headers? Any pros and cons? How about issues during traffic jams?
 

http://www.thezstore.com/page/TZS/PROD/classic19c/15-6012CH

This one looks amazing! Maybe it could radiate less heat than the stock manifold. Any cons??? Whats your opinión?? Just received that 280zx blower fan and it does not blow enough air to push the heat from the manifold away!



#8 Riceburner

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Posted 01 June 2017 - 09:34 AM

I agree with Jason (dat2kman) get rid of the mechanical pump and fit an electric type. You'll get consistent flow and it'll make starting much easier when the car is hot.

How old is the mechanical pump, could there be a pin hole in the diaphragm?

I ran a pierberg low pressure pump on my L28 with SU's and a 72 degree cam. It worked faultlessly.

Edited by Gareth. J., 01 June 2017 - 09:39 AM.


#9 jalexquijano

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Posted 10 June 2017 - 08:05 AM

My car has no mechanical pump. Only the Airtex 8012S electric fuel pump besides the gas tank which is pushing 3 psi.

 

Anyway, I was wondering if replacing this stock manifold with a ceramic coated header will solve my fuel percolation issues? How much difference in temperature between the stock manifold and the ceramic coat headers? Any pros and cons? How about issues during traffic jams?

http://www.thezstore.com/page/TZS/PROD/classic19c/15-6012CH

This one looks amazing! Maybe it could radiate less heat than the stock manifold. Any cons???






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