car misfires ,pops,etc after 10 minutes

[barryv]

hi,hope someone can help. i have a 72 cuda with a 440-4 speed after car is running for 10 minutes it starts to hesitate surge,pop etc.i ran a new fuel line from tank to filter,put aluminum spacer under carb thinking its a gas issue. im thinking maybe electrical.does any one know voltage reading at coil should be when its running,thanks barry

[dodge freak 2]

I had a crack spark plug boot that did only caused a misfire after 10 mins of running...shut it off for 20 mins it be ok for the first 5 mins...was leaking to the header pipe..why only hot I do not know.

Might want to look at each spark plug wire very good.

[MEK-Dangerfield]

Barry.

  It could be several things, but we'll keep throwing things at you. We are good at that.   

A clogged fuel filter? A weak fuel pump? The pushrod to your fuel pump could be worn if you are using a mechanical pump(I've been there). You wouldn't happen to have a fuel pressure gauge before your carb, would you?

As for electrical, when the car is running, you should have close to 9 Volts on the "+" side of the coil. If the problem is electrical, it sounds like something is overheating.

[barryv]

hi,it has a glass type filter thats clean,fuel pump has only been running a few hours,since installed.car seems to run fine at idle for exactly 10 min. then it hesitates,pops etc.i changed orange box from my other car ,it didnt help. i only have 5-6 volts at coil when running.engine temps are around 200 degrees using to temp guages. any hints,thanks

[Oldschool]

Borrow a known good coil and run it.  Sounds like either coil is heating up and losing power or the power supply going to the coil is faulty.  But if it runs fine for 10 minutes, then fails, I suspect the coil...        

[barryv]

i was wrong about coil voltage.its almost 12 volts when running. i have no fan shroud on car and noticed when car is approx.200 degrees gas in the glass type fuel filter starts to bubble then car really runs bad. i am going to take the shroud and flex fan off my 70 roadrunner and hopefully that will fix the problem or back to the drawing board.thanks barry

[Chryco Psycho]

check the gap in the dist , you need approx .008 , the pick up coil in the dist can break down with heat as well

[barryv]

my car has factory electronic ignition would the gap that you are talking about still aply,if so do i ccheck when running,thanks

[dodge freak 2]

i was wrong about coil voltage.its almost 12 volts when running. i have no fan shroud on car and noticed when car is approx.200 degrees gas in the glass type fuel filter starts to bubble then car really runs bad. i am going to take the shroud and flex fan off my 70 roadrunner and hopefully that will fix the problem or back to the drawing board.thanks barry

It should not matter, motor should run fine when hot...even at 220 degress...that isn't good for it but should not cause a misfire...the pick up coils can break down when hot..a common problem...I change mine before I found the crack plug boot.

[Chryco Psycho]

the gap is checked not running & yes that is the correct gap for the electronic ign

[barryv]

i am installing flex fan and hroud and will see if this help,then i will check for distributor,thanks

[71chally416]

Sounds like plug wires to me. Pick the hood up at night and see if spark is jumping anywhere when it's hot. My Ex had a 80's Olds Toronado that was doing that whenever it was hot or raining and it looked like Neon under there when I picked up the hood. 

[barryv]

tried that no arcs from wires etc. i am running car now past the 10 minute mark and it appears ok as of now.i lowered idle and put flex fan and shroud on from my other car . i will go back in 10 min. to see if its still running. hopefully i will be ok since this is my birthday,maybe ill have a good day.im crossing my fingers.thanks

[barryv]

well,im giving up for the day.car ran atleast 10 more minutes to approx 200 degrees.car starts to surge bad in idle then eventually stops. i will check distributor next.also i do not have a thermostat if that matters.atleast car is running cooler at idle longer until problem starts.thanks

[dodge freak 2]

Nope I threw my T stat out too (going to have to get one or block the rad with cardboard soon once fall comes)

What about higher rpms---a bad plug wire will show up at all speeds.

Do you have a spare carb to switch and see if the problem goes away. If not always good to have..get a cheap one off Ebay (once you straightened this out and put the spare carb on and tune it so it runs OK, then take it off and keep it for the next time)

Hard to  solve problems when you have no idea if its fuel or ignition