AJ/FormS
68 Formua-S fastback clone 367/A833/GVod/3.55s
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- Jan 19, 2014
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a 2-3 minute warm-up at the current ambient temperature is not nearly enough for a carburated car, especially if the choke is not set right. I shouldda mentioned that. So I would do the test again, but with a fully warmed up engine; the first test was relatively meaningless, except to point to a possibly faulty choke or choke adjustment..
I think there are plenty of relevant posts so far, that the solution is imminent, lol.
Most of the guys are pointing to the fuel system; and I agree.
But since the engine flat quits with no recovery, Ima thinking more along the lines of a load-induced ignition failure. Like a faulty coil or coil wire, or perhaps one or more faulty spark plugs. Or even a too-tight valve lash.
So if it was mine, I'd go back to the basics with a valve adjustment and compression test. Followed by assessing the timing and ignition system. If the timing is frozen at a very low number and Not advancing, this kind of thing will happen, because peak cylinder pressure will never occur at or near the optimum crank position, nor will it be very high, and the engine either misfires or just runs out of power very early. On a 6-banger this is very important, because there are only three ignition events per revolution, and they are 120* apart.
When you test the accelerator pump in the usual way, it may be just fine. But there is a second/third/fourth test for the A-pump; It has to begin spraying and not dribbling, at the slightest throttle-movement. And it has to do this from any point in it's travel, not just at idle. and as soon as the throttle stops moving, the spray also has to stop.
So say you come to that hill, at an rpm above stall, and with the throttle fixed at say 30% (I'm just guessing). Lets say the A-pump is 70% stroked out. When you begin the climb, the engine might run out of power and begin slowing. And so you increase the throttle to say 50%. Well when you do that, the pump better supply enough small-particle fuel, for the engine not to go momentarily lean. If it goes goes just a lil lean, then it may just hesitate then go. But if it goes very lean, it could misfire, and the engine suffers a 1/6th power loss. But if the misfired mixture is on fire and finds it's way back into the intake, now you have a pressure pulse in the intake!
When you get a missfire into the intake, all forward air-flow will stop, and the next several cylinders will get nothing until forward flow resumes. And if the pressure pulse went backwards thru the boosters, the mixture for the first few cylinders will be very rich.
At low rpm, the engine will just stall.
But if it doesn't stall, and you increase the throttle opening some more, it may be that the pump is fully stroked out, Now the assist has to come from the power-valve....... But with the near total loss of air movement in the intake... the engine is forced to try and stall, and at low rpm, only a heavy flywheel will prevent it.
IDK if this applies to your situation, but I thought it was worth mentioning, because it points to the importance of having a properly set up A-pump.
Another thing is to have a fully warmed up engine. The slanty is particularly sensitive to this on account of the long horizontal intake runners. On a cold engine, those runners will collect fuel on their surfaces, which will just hang out there until too heavy to stick anymore, then tear off move along. The choke is there to do two things; 1) to enrich the AFR to compensate for that fuel monkey business, and 2) to increase the rpm so the engine doesn't flood when the fuel tears off the cold walls.
In the meantime, there is a carb-heater right under the carb, whose job it is to get that plenum warm enough to evaporate the cold fuel, and put it back into the airstream. Later model carbs also have heated intake air to help with these same issues.
Somebody already mention some of these things, but they have to be collectively considered.
And finally, the coolant thermostat sets the minimum water temperature, and helps with setting the rate of warm up. If your cooling system is up to to snuff, I like to run it at around 200*F, as measured by an Infra-Red gun, on the hot-side of the stat housing. If yur running 160, good luck with trying to make that work. If all your systems are working correctly, you might get away with 185. But my slanty's have always run 195s.
Somebody mentioned the manifold heat control valve. This device does all it's work on a cold engine. If it has failed, then you lose the carb-heater, so that's a bad thing. Once the engine gets up to temp, this device is no longer useful, unless the ambient temp falls sufficiently to cause icing in the throttle bores, then you would really miss it if it wasn't there. Oh and just cuz the counterweight moves freely, does not mean that the valve inside the manifold is still there,lol. They can burn out. But maybe not on a slanty......
Anyway, it's lunchtime!/ gotta go
I think there are plenty of relevant posts so far, that the solution is imminent, lol.
Most of the guys are pointing to the fuel system; and I agree.
But since the engine flat quits with no recovery, Ima thinking more along the lines of a load-induced ignition failure. Like a faulty coil or coil wire, or perhaps one or more faulty spark plugs. Or even a too-tight valve lash.
So if it was mine, I'd go back to the basics with a valve adjustment and compression test. Followed by assessing the timing and ignition system. If the timing is frozen at a very low number and Not advancing, this kind of thing will happen, because peak cylinder pressure will never occur at or near the optimum crank position, nor will it be very high, and the engine either misfires or just runs out of power very early. On a 6-banger this is very important, because there are only three ignition events per revolution, and they are 120* apart.
When you test the accelerator pump in the usual way, it may be just fine. But there is a second/third/fourth test for the A-pump; It has to begin spraying and not dribbling, at the slightest throttle-movement. And it has to do this from any point in it's travel, not just at idle. and as soon as the throttle stops moving, the spray also has to stop.
So say you come to that hill, at an rpm above stall, and with the throttle fixed at say 30% (I'm just guessing). Lets say the A-pump is 70% stroked out. When you begin the climb, the engine might run out of power and begin slowing. And so you increase the throttle to say 50%. Well when you do that, the pump better supply enough small-particle fuel, for the engine not to go momentarily lean. If it goes goes just a lil lean, then it may just hesitate then go. But if it goes very lean, it could misfire, and the engine suffers a 1/6th power loss. But if the misfired mixture is on fire and finds it's way back into the intake, now you have a pressure pulse in the intake!
When you get a missfire into the intake, all forward air-flow will stop, and the next several cylinders will get nothing until forward flow resumes. And if the pressure pulse went backwards thru the boosters, the mixture for the first few cylinders will be very rich.
At low rpm, the engine will just stall.
But if it doesn't stall, and you increase the throttle opening some more, it may be that the pump is fully stroked out, Now the assist has to come from the power-valve....... But with the near total loss of air movement in the intake... the engine is forced to try and stall, and at low rpm, only a heavy flywheel will prevent it.
IDK if this applies to your situation, but I thought it was worth mentioning, because it points to the importance of having a properly set up A-pump.
Another thing is to have a fully warmed up engine. The slanty is particularly sensitive to this on account of the long horizontal intake runners. On a cold engine, those runners will collect fuel on their surfaces, which will just hang out there until too heavy to stick anymore, then tear off move along. The choke is there to do two things; 1) to enrich the AFR to compensate for that fuel monkey business, and 2) to increase the rpm so the engine doesn't flood when the fuel tears off the cold walls.
In the meantime, there is a carb-heater right under the carb, whose job it is to get that plenum warm enough to evaporate the cold fuel, and put it back into the airstream. Later model carbs also have heated intake air to help with these same issues.
Somebody already mention some of these things, but they have to be collectively considered.
And finally, the coolant thermostat sets the minimum water temperature, and helps with setting the rate of warm up. If your cooling system is up to to snuff, I like to run it at around 200*F, as measured by an Infra-Red gun, on the hot-side of the stat housing. If yur running 160, good luck with trying to make that work. If all your systems are working correctly, you might get away with 185. But my slanty's have always run 195s.
Somebody mentioned the manifold heat control valve. This device does all it's work on a cold engine. If it has failed, then you lose the carb-heater, so that's a bad thing. Once the engine gets up to temp, this device is no longer useful, unless the ambient temp falls sufficiently to cause icing in the throttle bores, then you would really miss it if it wasn't there. Oh and just cuz the counterweight moves freely, does not mean that the valve inside the manifold is still there,lol. They can burn out. But maybe not on a slanty......
Anyway, it's lunchtime!/ gotta go
