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240Z 72’ wants to die once it gets to op’ temp


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Car runs sweet until it gets to a specific temp, basically operating temp, then judders, RPMs slowly drop and it want to die unless I start giving it high RPMs. Even then it can be hard to keep alive. This problem happens like clockwork. If the weather is really cold and it takes longer to get to op’ temp, it will run longer. So it is nothing to do with distance or time, just temp. I’m thinking the water temp switch is supposed to operate with the EGR at op temp. So maybe it’s not working? 

I installed a lower temp water thermostat and as long as I kept driving and didn’t gun it or sit in much traffic, the issue could be avoided. I thought I had sorted the issue with refurbishing the carbs and changing fuel hoses, and adjusting valve clearances, so I put the standard water thermostat back in, lo and behold, the problem was still there. It occurs when the temp gauge gets to the half way point. 

Using the choke to try prevent a stall, doesn’t really work. Maybe helps for a few seconds only.

Will want to stall when I come to a set of lights. And if I keep it going by playing the gas peddle, it will barely pull away. Feels like fuel starvation. But I don’t see how it could be as it’s so temp dependent. Temp dependent. I don’t think it’s the coil as the issue would be less temp precise.

Any thoughts? 

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Thanks for response. It makes no difference if air filter is on or off. The warm air / winter setting is not hooked up to receive manifold heat. The original manifold has been removed and the exhaust is stainless. Filter is nearly new. This is an operating temp issue. Besides, taking the air filter box off does not allow for cooler air into the carbs. It allows for less restricted air. The air box gains air from the front of the car while the carbs without the air box would be drawing in air from above the hot manifold/exhaust header.

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I made my own heat shield. Two sheets of 1mm metal with a 5mm gap between them.  However, I don’t think it’s a heat management issue as the issue starts on the dot when temp gauge gets just before mid point. Opening the hood doesn’t really make any difference. 

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2 hours ago, jonbill said:

got a pic of your spark plugs? 

One was running rich and sooty another a little sooty, and these where the valves that needed the greatest amount of adjusting. All plugs good colour now. (Dry and clean-ish) 

Edited by jas
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There is a single wire coming from my water temp switch and it looks pretty unhealthy and under tenstion. Wire goes up to the coil/ relay. (see diagram) It is suppossed to affect timing when car gets to operating temp. Its resistance changes with temp.


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