hot starting issue

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modelaguy

New member
I have a 47 Ford coupe and really need some help with very hard starting when the engine has been run and is hot. I have a rebuilt carb, distributor, new plug wires, fuel pump, fenellic block under carb and I still have a major issue with very hard to impossible starting after running it. When cold, it starts very well. Frustrated to say the least, not sure what to do.
 
i've been struggling with a similar issue, although my symptoms run just a bit different:

when cold, engine starts up instantly and runs smoothly. i then drive it for ten to thirty minutes and turn it off. possibly to get gas or something. then it won't start at all because there is no spark. and the coil is hot. very hot. the engine temp gauge shows a little above the mid point.

then coil cools down after i open the hood and let it sit for fifteen to thirty minutes and it starts right up just like it does on a cold start. i've verified that the hot coil is the issue, as i now carry a second coil that sits at ambient temp in the trunk and swap it in within a couple of minutes when this happens and the car will start right up without waiting.

OTOH, it could be heat soak associated with the ballast resistor under the dash if you're still running one. that was a classic problem BITD. on a hot day the engine heat would keep the ballast resistor hot when the engine was turned off and should have been cooling off so as to aid starting.
 
here it is:

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hueyhoolihan said:
OTOH, it could be heat soak associated with the ballast resistor under the dash if you're still running one. that was a classic problem BITD. on a hot day the engine heat would keep the ballast resistor hot when the engine was turned off and should have been cooling off so as to aid starting.
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Add a intermittent push button switched wire that bypasses the resistor. Push the switch button in at the same time you start. I have this setup on my '32 and works very well.
 
Both the coil and condenser will often work fine when cool, then start to deteriorate when warm from operating producing a weak spark. Spark may be good enough when engine running, but when starter steals some of the available voltage that weak spark gets weaker. To diagnose weak spark, pull a plug wire with pliers and hold near ground. Good spark is 1/2 inch long and blue, weak is short and yellow.

If weak spark is found, I would start with the condenser because it is cheap and easy to install.
 
The ignition resistor under the dash rarely fail. They are robust little animals. Most original resistors still operate as designed. Of course, the connections at the resistor need to be clean and tight.
 
If you are going to your FLAPS for a new condenser, buy several, as they have a reputation for being bad out of the box. One of the H.A.M.B. members dissected one of these failed condensers and found that the lead wire is not connected internally, just laying there, counting on the crimped cap to keep it in electrical contact.
 
modelaguy said:
I have a 47 Ford coupe and really need some help with very hard starting when the engine has been run and is hot. I have a rebuilt carb, distributor, new plug wires, fuel pump, fenellic block under carb and I still have a major issue with very hard to impossible starting after running it. When cold, it starts very well. Frustrated to say the least, not sure what to do.
Click to expand...

I'm thinking coil as the "usual suspect".
The resistor can be the issue but that would be a distant "third" place for me.
Alson, for most of '47 the resistor was atop the coil.
 

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I use a voltmeter to measure the voltage in the circuit at different spots when it's hot and cold to try and find the problem. Make sure the points are open to check the voltage otherwise you won't get the correct readings. I think you guys are on the right track, either the resistor which you could momentarily bypass to see if it starts or the coil. At work we stocked all that stuff, so it was easy to just swap parts out. At home it's not so easy.
 
Flathead Fever said:
Make sure the points are open to check the voltage otherwise you won't get the correct readings.
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If points are open, there is no current flow thru the ignition circuit. It's like closing the nozzle at the end of a garden hose; with no current flow there will be constant pressure everywhere in the hose. With points open, you will just see battery voltage everywhere, before and after the resistor.
 
Test for spark when no start first as that is easy to do without disassembly with an inline spark tester between the plug and the wire. If you have good spark I bet you have fuel issues. Pop the top off the carb and see if it is dry. If it is it is because modern gas has low vapor pressure and evolves easily with the heat. The gas moves out of the carb and down into the intake giving first a flooded condition followed by no fuel delivery until it fills back up.
 
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