240z overheating at idle in traffic lights and intersections

[Zed Head]

24 minutes ago, jalexquijano said:

At the streets, i can drive around nice until i get to a couple of traffic jams, lights and after 15 mins of driving temperature reaches to a Little less than 3/4 in the temp gauge. Idle becomes rough lowering from 1000 RPM to 500 or to 400 sometimes and rises back. Eventually car stalls and i have to crank it again.

When the car stalls, is your foot on the brake pedal?  If you weren't sitting in traffic, but instead were sitting somewhere with the parking brake on, and the brake pedal up, would the engine still stall?  Maybe you have a bad brake booster.  

I don't know how carbs would be affected by a bad booster, but EFI shows a noticeable change in idle RPM when the brake pedal is pressed if the booster is bad.

[jalexquijano]

Will need to check on this!

[siteunseen]

2 hours ago, Zed Head said:

When the car stalls, is your foot on the brake pedal?  If you weren't sitting in traffic, but instead were sitting somewhere with the parking brake on, and the brake pedal up, would the engine still stall?  Maybe you have a bad brake booster.  

I don't know how carbs would be affected by a bad booster, but EFI shows a noticeable change in idle RPM when the brake pedal is pressed if the booster is bad.

That's good thinking Zed! Mine went out on my 240 and it did lose rpms when applying the brakes. The pedal was a lot harder like a really old truck my dad had, no power brakes.

[Stanley]

Vacuum leak at brake booster or elsewhere is obvious thing to check, but it's been done according to previous threads. Sticking choke is possible but easy to check. Pull the choke lever and push it back. Then see if you can push either of the nozzles up. If so it's sticking and probably just needs some carb cleaner and spray grease.

Item #3 in the FSM carb tune procedure, is setting mixture adjusting nuts to 2 1/2 turns down (only if you're driving near sea level and the ambient air temperature is 68F, otherwise adjust preliminary setting according to the graph in the FSM) . Items 5 to 8 usually need to be repeated. When you're done, item #11, you check it with the Uni-sen (the "flowmeter" shown in FSM) or Synchrometer again, and if the air flow doesn't match you need to repeat items #5 to 11. So if you just do item 3, that's not it. Observing the tachometer at several stages is also part of the procedure. 

I thought you had to ask for the SM needles with the ZTherapy carbs, don't know though. N-27's are right for stock engine with stock air cleaner and exhaust. Modified engine (or just using K&N's, see official SU publications for in-depth discussion) may require different mix settings and/or needles. My car has some minor mods, and N-27's, even modded N-27's, didn't cut it. It's doing OK with heavier springs and SM needles, but it's a bitch to tune. The problem is the SM's (as stated in post above) are lean at idle. This is because they are British needles, and the first station is 0.099 inch instead of 0.095 inch like the Hitachi SU needles. So they have to be set richer to start, idle, or run at low RPM. This makes them even richer at mid-range and top end. There is a very narrow range of mix settings where my car will idle and not foul the plugs. 1/8 turn one way or the other can mess it up. I may try modding the SM's by making them thinner at stations 1 & 2, after I buy a spare set in case I it doesn't work.

Turn idle adjusting screws clockwise to increase idle RPM.

[Zed Head]

29 minutes ago, Stanley said:

Vacuum leak at brake booster or elsewhere is obvious thing to check, but it's been done according to previous threads

Actually, I believe that he tried to "check" vacuum and got zero.  Then never really followed up.  And checking vacuum won't tell you if the booster is bad.  The booster only leaks when you press the pedal.  The common symptom is "my idle speed goes up when I come to a stop light", but if you have a big leak or an edgy tune, it could go down.

One of this threads problems is that we're all talking over each other.  Simple stuff first, I recommend.

Edited January 16, 2016 by Zed Head

[Zed Head]

Never mind.  Breaking forum protocols, in general..

Edited January 16, 2016 by Zed Head

[munters]

I agree simple stuff first.

I would say Temp is fine Idle to low and thats it. The engine behaves like that, (jump from 400 to 8-900 and back down ) when idle to low.

Put the just idle higher to 900 and look how it behaves.

[bartsscooterservice]

On ‎13‎-‎1‎-‎2016 at 1:36 PM, Namerow said:

Carburetors have their charm, but after reading through this Nissan, 'how-to-make-it-run-sort-of-ok' document, it's easy to see why the industry embraced electronically-controlled fuel injection when it was finally ready for prime time.  Of course, if there were no emissions control requirements and no CAFE rules and we all lived in San Diego, carburetors would probably still rule.

 

I think fuel injection has prooven to have much more problems in reliability than carburated engines, their only benefit is fuel consumption. But simplicity carb is way better.

[Patcon]

Jalexquijano

You never answered my question about what happens if you try to rev the engine when sitting in traffic and the idle gets erratic. I still suspect too much fuel pressure or float levels. If it's a needle problem he will have a hard time finding someone to help get it right

[jalexquijano]

Zed Head,

Thanks for your advice, i think you nail it!! I tested the car with a mechanic and after performing all kinds of test we reached to the conclusión that the Brake Booster has an internal leak as the car idle becomes erratic and rough when you step on the brake pedal. Added to this the Petronix 40511 3 ohm coil was getting too hot. So hot you could not even touch it with your hands for more than 2 seconds. I had a spare one at the deposit so we replace it. However it does not get cool enough as to hold it with your full hands for more than 3 seconds.

Questions: SHould i replace the Brake booster and where do i get one OEM Nissan Booster? Can i settle for CARDONE Reman??

                  Should i get a Brand new pertronix 3.0 0hms coil or should i strive for a different Brand? I guess ill need to stick with this Brand as the ignitor module is the compatible one for this coil.

 

 

[Patcon]

 How long ago did I mention brake booster????

 

If the booster is bad the master cylinder is probably leaking too...

Edited January 16, 2016 by Patcon

[Zed Head]

Good luck with it.  The early model boosters are difficult to find, I think, and sometimes the remanufacturers send the wrong one.

The coil problem is a whole different issue.  2 seconds on a hot surface is pretty long.  That's only about 110 degrees.  Not really very hot.  http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20100020960.pdf

Edited January 16, 2016 by Zed Head