Hard Start after Warm looking for suggestions

steve-cook

steve-cook

Member
I am having a problem starting my 1940 Ford after it is warmed (not overheated) it starts right up when cold no problem it cranks fine.

It seemed as if it was not getting spark I originally thought it was the timing verified to the best of my ability it was correct replaced points condenser still had the problem, replaced coil and plugs/ plug wires same problem after that I rebuilt the carb I notice the new accelerator pump leaks slightly and needs to be repaced but no change in the problem, in frustration most reciently I started pumping the gas while adjusting the choke it started up and then ran, drove home from the gas station shut it off and of course waited a minute or two and it would not start.

Any suggestions would be greatly appriciated.
 
Two things come to mind. First, what is the replacement coil? Even new ones can go bad, and NOS are even worse; condensers are the same. IMHO, the only sure thing is a coil rebuilt by Skip Haney and an IH-200 condenser.
Second, check your ignition switch--the contacts may not be making a good connection. JMTCW:)
 
Bad electrical conections? on my 36 it would crank right up when cold then
it would start very hard when hot. ther was a bad conection on the starter switch
cleand tightend them all up and it would start right up.
 
So many things could cause hard starting when hot.I have seen the following causes over the years:Carb leakdown,bad coil,starter fields swellinhg when hot,loose ignition connection,distributor not properly grounded(caused by freshly repainted,rebuilt engine,distributor not grounded,same with coil.Many items can cause your problem.Don't panic,work one thing at the time till the problem is gone.
 
Corrosion, causes resistance and increases heat, heat causes more electrical resistance, snow balls till failure. May need to slightly retard timing. Try cleaning all connections and apply dielectric grease or anti oxidant compound to all critical connections of electric conduct. This will of course also apply to the grounding system. Ionic return to the battery is critical.
 
Steve it takes three main things for the engine to start, air, gas and spark. Check the spark when the condition occures by jumping a spark from the plug wire to ground NOT to a spark plug connector. Jump the spark to a head nut or the grounded base of the plug. You could also do this test cold to see if you have a good spark and what a good spark looks like. It should jump a 1/2" be steady and show a crisp blue spark. When it's hot and the problem starts do this same test and if it has a good spark then the problem is a blocked air filter, spark plugs or gas. If you flood the engine with too much gas it won't start or even try to start. When checking the spark when hot if the spark becomes weak, don't jump the 1/2" is yellow in color then it is the coil or low voltage to the coil due to bad wiring, resistor, ignition switch, low battery, wires and connections or bad ground. Most stock old Ford coils when hot the spark will get weak and the hotter they get the more the insulation leaks and the weaker the spark. The sparks gets down to a fuzzy little yellow ball. This type spark isn't strong enough to jump across the electrodes of the plug with the air from the compression blowing it out like a candle. Always carry a can of starting fluid which will start with a weaker spark. If you have a good spark and it will only fire on either then you have to check the gas supply. G.M.
 
If you have checked out all your connections etc, try shorting across the resistor for the coil when the engine is hot. Often time, it will start right up.

When the resistior gets hot, there is too much voltage drop across it and the coil is not getting enough voltage during cranking to produce a hot enough spark.

When everything is cold, there is little voltage drop across the resistor and the coil will get enough voltage.

This is not uncommon, even in the "Old Days" if your electrical system, coil, starter or battery were at all marginal.

My experience, Chris.
 
I appears that the spark starts out strong and weakens as the temp increases (it does not take long) I will take a look for a bad ground this week and follow up with what I find. The replacement coil was a china replacement from MACS I do not think that is the problem I will play with it this week and follow up with what I find. I believe I will also purchase a new coil resistor.
 
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Steve,
Skip Haney...Punta Gorda Florida the coil guy, get one of his coils.
If the china coil isn't the problem today it will be very soon when
least expected.
Charlie ny
 
Before you waste a lot of time measure the voltage at the wire from the resistor at the top of the coil. Turn the switch on and measure the voltage from the wire terminal to ground. If the points are open it should read close to the battery voltage 6.2 to 6.4 measure across the battery before you start and make sure it is over 6.3. Now you need to get the points closed, when closed the voltage will drop and should be in the 3.5 to 4.2 range. Jog the starter until the voltage drops and then the points are closed. If the battery is 6.3 and the coil voltage is in the 3.0 or less range when the points are closed there is a loose connection in the switch and resistor line. A dirty arced ignition switch will cause a voltage drop. Also the battery shut off switch with the green knob go's bad in time and causes a voltage drop. WHEN YOU ARE TESTING THE COIL VOLTAGE AND THE POINTS ARE CLOSED NEVER LEAVE THE SWITCH ON LONGER THEN 2 MINUTES. When the points are closed and the engine isn't running the winding of the coil becomes a resistor dead shorted across the battery and in about 7 or 8 minutes burns the insulation off the wire and melts the tar or potting material in the coil. G.M.
 
I have found that Mac's ignition components are bad when sold. I replaced a couple of new condensers to find all were bad.
 
If you are giving it gas you maybe flooding after a hot start.If you think its a coil problem something to try.
Mopars don't seem to have starting problem,you may want to try a old plymouth dodge 6 volt coil no resister is needed.
 
The wiring on this car is scary I did the voltage drop test at the wire on the coil at one point I was able to get battery voltage but it appears when the points are open then I get almost nothing would this be the condensor not holding a charge?
 
Hello Steve:

Re-check GM's post above. Full voltage should be seen at coil terminal when points are open. Seems like a coil problem. But another unlikely possibility is that a point arm or spring is somehow touching a ground when the points are open and warmed up.

Jack E/NJ
 
Steve you will get battery voltage with the points open. If the points are shorted to ground or adjusted so they don't open you get a 3.5 to 4 volt reading all the time. I don't get the part where you said you don't get nothing?? If that means you don't get nothing at the coil wire when the points close that would indicate you had voltage to the coil when the points were open. There is no amperage draw when the points are open. When the points close then there is about a 3 amp load. If you have a REAL BAD connection or a realy dirty, arced switch this bad connection would make the volt reading at the coil wire drop very low. Leave the POS side of the meter grounded and check the the voltage at the coil side of the resistor with the points closed it sould be in the 3.5 or 4 range. Move the probe to the ignition switch side of the resistor and it should be 6, move to the ignition side of the switch and should be 6 now go to the battery side of the switch and it should be very close to 6.3 or the battery voltage. If you have 6.3 on the battery side of the switch and 5 volts on the ignition side of the switch the switch is dirty and arced. Anywhere the voltage drops below battery voltage before the resistor indicates a bad connection between where you are testing and the battery. These tests all need to be made with the points closed. Remember not to let the switch on longer then 2 minutes with the points closed or the coil will have a melt down. A one to three tenth of a volt drop across the switch is normal. G.M.
 
Mine will percolate gas out of the float bowl when it's hot and flood the engine. Checked float level when hot, and tried lowering it to no avail -- new gas? Since I have an electric fuel pump, I tried shutting off the pump before turning off the ignition in order to lower the fuel level in the float bowl so that it couldn't percolate out and flood the engine. Worked for me, but of course no guarantee for your problem -- particularly if you are running a mechanical pump or electric with no switch.
 
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