Shaking, id still look for a vacuum leak oil pressure will not cause this problem

My A body does the same thing, no matter what motor/carb etc it had on it. Its the crap they call gas these days is my guess..once it hits 190 +deg it starts, carb is barely warm to the touch otherwise will idle all day even with a cam with 82 deg overlap. Tried richening/leaning the idle circuits a million ways from sunday no effect.

 

Did you try more bypass air in the carb?

 

I bought the car in oktober last year and just drove it home to my garage for winter storage.
Had this issue all summer with better or worse days...

 

Choke is fully open, checked that.

 

Is the issue getting any worse?

Have you drained the oil and looked for metal flakes.

Losing oil pressure and knocking is usually not a good sign.

 

It is concistent with better or worse days, depending how hot it is outside.
That is why i`m gonna do a compression and valve check.
Oil looks good, previous owner did a crank and head overhaul.

 

Have you ever put vacuum gauge on it, and if so, what did you find?

I also could not find anywhere that you said what carb it is either.

What are all the timing numbers, at idle, vacuum disconnected, and total?

What do the plugs look like? Pull a couple out and post pics.

There are a some big brains here, the more info you can give them, the better chance of having the problems solved.

 

Maybe you're looking at it backwards. Maybe the oil pressure is changing because the idle rpm is changing, not vice versa.

 

That's my thought as well. Oil pressure commonly goes down a bit as the engine heats up. The correlation between hotter days and the idle issue is similar to issues I'm seeing with my 70 LS5. In my case, I lean to a fuel issue, possibly percolation. I too have an aluminum radiator, shroud, all seals in place, 180 degree thermostat, yet the temps reach 200+ when checking with a infrared thermometer. Problem shows up on hot summer days. Hence my question of how hot this fellow's engine may be getting. If not a fuel issue, is the ignition stock, points? Or was it converted to breaker less? Electronics sometimes begin to break down when warmed up. Possibly a coil problem?

 

these are all good sugestions, but I would also turn up the idle. I have the idle on
my 427 with manual trans at 950.

 

I bought my 71 late last year. The previous owner warned me about a rough idle when hot. Well, since I got the car I am unable to drive it due to the same issue. Mine was in the shop 3 times with no improvement, and I had it in my position a total of 3 days since I owned it. Very frustrating. The car is undrivable the way it is. Runs great when cold and warming up. Great on the highway. As soon as I get off the highway and hit a few traffic lights the **** starts. Very rough idle begins and then the car just dies. Usually in the middle of the intersection. Then very hard to start with lots of sputtering coughing and cranking over. Have to crank it allot and pump the pedal. eventually it will start, very rough, and the only way to keep it going is to rev the crap out of it. Let the rpms drop and she just stalls. Let the clutch out to get out of the intersection, and it dies. Totally undrivable. So its bin in the shop all summer. Now has a new rad, everything was checked over, does not get above 185 degrees bow, next step we are re building the carb, insulating the fuel line and isolating the carb from the heat. The mechanic thinks its fuel peculation. If this does not solve the problem I will probably sell the car. Can't handle the stress of blocking intersections and pissing every on off any more.

 

That sounds a lot like what I'm experiencing. I've had the same thoughts, fuel percolation, possibly a fuel pump. It tends to act as if it had vapor lock though I can clear it briefly by rev'ing the engine. Back to the OP's issue, sounds similar. It may be helpful to know if his problem came on suddenly. If so, what changed? I'm wondering if the formulation of modern gas, addition of ethanol, makes the problem worse?

 

Manifold vac is 15hg at idle.
New renovated Quadrajet, built by Kent, a reel wizard on this
Initial 14deg, manifold vac to distributor =24deg at idle, tried all kind of settings, this is the best.


As someone said here, mine was hard to start also, untill i changed my initial from 8 to 14 and set idlescrews at 1 1/4 turn out.
Now it starts like clockwork.


Plugs looks fine, exept cyl no 8, wich is slightly oily.
New plugs, HEI with new coil.

 

I have had this issue many times on all of the BB cars. The one I currently own is a 69 coupe with a .070 over 1/4 inch stroked 454 so basically a 500ci engine. Mine is pretty stock with factory exhaust, and intake manifold (aluminum) the cam is a hyd. roller but very streetable, and pump gas compression. The problem first off is the mechanical fuel pump is too hot mounted to the engine, and too small. Even my BB stock 396 Camaros run out of fuel half way through 2nd gear on the on ramp. Your fuel system is turning your fuel into vapor as soon as the fuel hits the carb, or sooner in the fuel line leading to the carb which will cause all of the problems described. It will not idle if there is no liquid in the float bowl.
1.I run the biggest mechanical fuel pump you can buy without having to run a pressure regulator, and put a filter just before the pump, a big free flowing one. Even though running the filter before the pump is taboo, it is necessary on these type of pumps because the tiniest amount of dirt will kill the function of this type of fuel pump.
2. A return line is a must. The fuel in the tank is the coolest, and the return line keeps it constantly flowing that cooler fuel right up to the carb. If you are idling on a hot day with no return line the fuel is moving very slowly, and is being super heated in the fuel line, and pump, and then it flashes to vapor before it gets to the carb, hence the rough idle, and or the car dies, and is very hard to restart if not impossible until it cools down.
3. Insulate the fuel line from the pump to the carb for obvious reasons to keep even more heat out of the fuel going to the carb.
4. If this still does not fix the problem then run a thicker insulated base gasket under the carb, and if all else fails put a small electric fuel pump as close to the gas tank as possible to feed the mechanical pump. Fuel pumps are great at pushing fuel, and suck (pun intended) at sucking it. So a small push of fuel from the rear goes a long way.

 

Wondering if there isnt something to the fuel pump/heat bit
My eng compartment unlike a vettes stays pretty reasonable (temps) in comparison, carb is barely lukewarm at full temp fuel lines arent hot either. Maybe a return is the answer..never could figure it out myself (and run a large mech pump)

15 yrs ago it didnt matter what motor/carb or gas was in it (and there were a bunch of em)would go all day any day.

 

I have found the aftermarket auto parts store mechanical fuel pumps aren't worth a darned because they are using thick (and stiff) Chinese-made valves that don't seal so the pressure drops off real bad after they get warm. Buy a quality Holley or Edelbrock or Chevrolet Performance fuel pump from Summit Racing.

 

When i pop the hood i can easily lay my hand on both carb and fuelline, it`s not that hot.
Restarting when hot is no problem for me.

 

Even my small block car has the factory fuel filter with the return line out of the side of it. GM knew it was a problem clear back then even with the old leaded gas. I have been doing this for 30 years and have owned over 200 (not a typo) c-2 and c-3 corvettes, plus when you do it for customers it has to work.
It is your choice to make the necessary changes or live with the car as it is.
Also what is the condition of your fuel tank? can you shine a flash light in there and see rust, and crap?

How does the fuel sock look on the fuel line pick up in the tank? Is it torn?
Is the carb (even though it is rebuilt) full of rust and scale from a dirty fuel tank?
Is the tank end of the fuel line half rusted shut?
These issues are on every one of these cars.
When you wash the car and the black cup around the gas cap fills up with water because it can't drain fast enough so you have a puddle around the gas cap, guess where some of that water ends up, in your gas tank.

 

Ignition coil is bad ... I wont say why I come to that conclusion but put a new one in and check all ignition components . . Replace any suspect items like points cap and rotor if you have done all that I am betting you have not put a new coil in her.

 

Hey all, so over the last few months we worked diligently on solving this hot non running issue. First we insulated the fuel line and re built the carb. Re installed it with a thermal insulating plate. As a result, the situation got better, but the thermal readings from the manifold and the base of the carb remained very high. In and around 250 degrees. So the decision was made to remove the intake manifold and block off that exhaust bi pass circuit that channels hot exhaust gasses through a opening in the manifold and directs the gasses under the carb. This bi pass it there for winter and cold weather operation of the choke. This circuit was supper heating the carb and percolating the fuel in the idle circuit causing that awful symptom. The choke was also modified to work with less heat. ( I don't know exactly what the mod to the choke was ) Well now the car runs so so good. Carb temps are down to a pint that you can rest your hand comfortably on the carb at full engine temps. I am very relieved and can start to love my Vette again.

So if your car is having this hot running issue, go straight to the exhaust bi pass circuit and plug it up. A new intake manifold gasket is what you will need. one that does NOT have the "cut outs" for the ports. Its the steel gasket that plugs the ports up. Easy Peesy Japaneesie.