Rough Idle, RPM drop and stalling at intersections

[tr8er]

Whatever you do, don't drive it around without the hood on.

[DaBlist]

Whatever you do, don't drive it around without the hood on.

because it's free and free is an American thing

 

And have the radiator flushed again

[jalexquijano]

Datzenmike,

 

I decided to add some additional heat shield extensions convering the bottom of the carb fuel bowls and thus isolating the percolation or vapor lock even more. Drove it a while, got stucked in traffic and got home. After minutes of sitting on the sun on traffic jams. Idle started to drop from 900 to 200 rpm. However, the car did not stalled. Tended to but not. Now i see the heat shield extensions on the rear and front carb are helping. Got home and quickly opened the Hood. I could notice that the fuel filter was less tan half full and the car rpms tended to drop and raise again. so i left the Hood open. Result: heat came out of the car and idle became stable at 900rpm. SHould i also replace the metal fuel rail that is attached to the cam cover with some sort of braided fuel hoses to lower the fuel temperature thus avoiding the fuel supply to evaporate and affect the idle?

 

 

[G-Duax]

Being in S. Texas I understand the hot fuel/vapor lock problem.

 

I run my fuel hose from the filter, around the front of, and below the radiator, all the way up to the left fender, before going strait over to the carb.

I also use the vapor return line that my 620 came with, and allow a little fuel to return to the tank.

 

And one of the first things I do to any vehical, is eliminate any hot coolant passages/hoses going to the intake manifold.

Enough heat transfers through the intake manifold flange.

Down here, the winters are mild, seldom freezing, and have never had a problem with carb icing.

Now I can sit in rush our trafic on a 100+ degree day, and not have vapor lock problems, even if my engine temp goes way too high (220+ at times!)

 

And yes, leaking brake booster can cause idle issues, but only if you have the brake pedal depressed.

[jalexquijano]

still battling with this fuel percolation issue! Everytime the car is at idle sitting in traffic the idle becomes lumpy and at sometimes the engine will shut off. I was recommended to change the original fuel rail with rubber hoses and re route it differently away from the valve cover. Is this reasonable??

[datzenmike]

Did you try taking the hood off, yet????This would either cure the problem, indicating under hood temperatures ARE the cause or maybe something else?

[jalexquijano]

Ok. If Hood temperature affects then should i simply swap the original Steel fuel rail with rubber hoses or is there something else i need to accomplish?  

[datzenmike]

You describe a problem similar to vapor lock. I suggest taking the hood off to test this theory and you want to replace fuel line. 

[jalexquijano]

Okay. Just to let you know i still have not replaced the Steel fuel rail that is fasten to the Valve cover of my 1972 240z. Anyway, recently hired a retired Panama Canal Commission mechanic who used to repair the locomotives that pull the vessels in transit in the Panama Canal and who owns a Corvette with holley carburator. He arrived to the same conclusión: Too much heat affecting the fuel inside the 3 screws round SU CARBURETOR Float Bowls which eventually causes the fuel to evaporate during traffic jam and shuts down the engine. He argued its a bad design and that the manifold should have been placed on the other side of the car and not under the carburetors. Should i remove the stainless Steel heat shield extensión and wrap it also in header reflective tape or insulator?

[flatcat19]

Why are you avoiding taking the hood off?

 

 

This seems like such a simple way to verify a condition.

 

And it's free. Stop spending money until you k ow for sure that you need to.