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Item Posts    Sort Order

stalling after hard run rough idle

 
Classic65
User
Posts: 87
Joined: 11/08
Posted: 09/21/12 11:10 PM

So I have a 66 coupe with 349 stoker, Mallory distributor demon carb. for the past two years all is well. I changed the thermostat and all of a sudden, it would not start so I replaced the distributor and then she was good to go, Now after I get on it hard then slow down she wants to die and I throttle it and the car just sit no revs or anything and mind you I have foot on the throttle the hole time, just sits barley running then all of a sudden its back. everything seems fine revs and all good......

Could it be a float sticking , since the car does sit for long periods of time?
I checked the plugs timining and float levels all good.

I am at a lost thought it was just the disturtor, now I am not sure again.  

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waynep71222
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Posts: 455
Joined: 04/12
Posted: 09/22/12 07:44 AM

you could have a multitude of issues....

let me cover the tests... you will want to PRINT this ... carry it to the car..  

required tools are cheep.. a circuit tester... and a timing light..  a screw driver and an empty soda bottle...  a remote starter button would be nice but a friend to turn the key would work just fine..


with the circuit tester...   hook the clip end on the coil positive terminal.. the other end to ground in a location where you can see the circuit tester light from the drivers seat...
get in.. slowly turn the key on.. you should get a moderate bulb brightness.  turn the key farther and you should get a bright bulb.. release the key to the run position.. it should return to the moderate brightness .. this shows that the power to the coil seems to be getting there through the wiring and the ignition switch... warning.. if you have some aftermarket ignition box like an MSD.. the test is different as the wiring to the coil has over 300 volts..


next...   hook the timing light to the coil to distributer cap wire..  lay the timing light under the wiper arm... close the hood so you don't crush the wires.. take it around the block .. if the flashing changes.. when you get under load and the engine starts to run rough..  then you might have narrowed the issue down...   not all timing lights will like the coil wire speed of flashing.. you might need to change it to one of the spark plug wires..  and another trip around the block..

lets you know if the ignition high voltage is failing..


lets look at the fuel system...

with a cold motor.. disable the ignition system so it cannot make a spark...  this is usually removing the positive wire from the coil...

disconnect the fuel line at the carb... extend the fuel line into a clean clear 2 or 3 liter plastic soda bottle... while you watch the end of the hose... have a friend crank the engine for 15 seconds..  each pulse of fuel should be nice and full.. equal to the others..

if the pulses of fuel from the end of the hose get smaller till they are just a drip.. or are reduced in any way... you have a restriction in the fuel lines..  could be under the drivers floor pan.. along side the rocker panel under the door... a kink in the fuel hose at the tank.... debris blocking the fuel inlet in the tank..  i don't know if you have ever had the sending unit out.. replacement strainers are available.. several versions of sending units are available..  all come with new strainers..

i have shoved a brand new universal speedometer cable core all the way through the fuel lines with both ends disconnected... then spun it with a variable speed battery powered drill.  don't say its impossible. it just takes 2 people.. one with thick palmed gloves pushing it in.. the other holding the cable core snug and straight as the drill spins it..  the twist in the wire pulls it in..  i have some skills as i used to do some plumbing and sewer cleaning.. but it does work.. the reason for the NEW core is to avoid any stiff or broken strands in the cable.. that will not only leave  pieces possibly in the fuel line.. but also rip right through your leather glove and into your palm and fingers.

yes.. i know that new pre bent fuel lines are available.. this is just to clean them or verify that they are NOT CRUSHED FLAT or clogged with sediment...

coat hangers will only go so far..

going farther...  if you don't have a fuel pump pressure test gauge...  place thumb over the end o the hose...   have the friend crank it again for a second or two.. hold the pressure..   the fuel pump should hold pressure for a long time..

there are a lot of Red dUST problems in gasoline today...  clogs fuel filters.. on fords those are usually at the carb.. is yours clogged??? but it also gets into the fuel pump check valves.. limits their ability to pull fuel up from the tank.. and hold the pressure on the carb side...

you might want to wave a magnet around the bottom of the soda bottle..  you should have about 1/2 a quart of fuel in there from 15 seconds of cranking..    see if the magnet attracts any sediment.. i have been sticking big strong magnets to the bottom of fuel tanks.. and little strong ones inside the fuel tanks when i have the sending unit out..   must verify they get to the bottom.. tricky devils.. will fall upward and stick to the opening ..

dirt effects some electric fuel pumps also... must have a strainer or a filter before the pumps.. it can hold the bypass valve inside the pump open and drop the pressure to ZERO.. then come right back....

warning.. these are just the beginning of the diagnostic process... its really important that you kinda follow the steps...  you won't believe how simple they are when you have finished them.

spark...  or fuel.. which is the problem..  

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Classic65
User
Posts: 87
Joined: 11/08
Posted: 09/22/12 03:16 PM

Wayne,
So I checked the fuel pressure I do have a Gauge while cranking I have about 6 to 7.5 lbs of pressure and even flow from my manual pump.

I am kinda lost on the timing light issue.
Do i hook the light onto the battery and the coil wire and then prop it under my wiper blade and test drive?  I would assume this would be correct so we have power to the light.    
 I was testing the car after fuel check , and it was doing it in the driveway were it won't rev more then 1000 it I take my foot off it dies.......
I will have more feed back after I test the circuit.

Thanks
little at a time, I am doing this alone.  

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Classic65
User
Posts: 87
Joined: 11/08
Posted: 09/22/12 03:47 PM

So I did the circuit test, Hard to tell, but the light seems to just be the same brightness thu-out the turning of the key to the run position.  

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waynep71222
Enthusiast
Posts: 455
Joined: 04/12
Posted: 09/22/12 04:55 PM

how much fuel did you get out of the fuel system in 15 seconds of cranking..

you should have gotten almost if not more than a pint... half a quart... half a liter... as i don't know which part of the world you live in..


if you rev the engine up and it seems to run out of fuel.... and you get good full pulses of fuel from the pump when the full flow test was performed...  then you could have clogged fuel inlets in the carb... you could have debris in the carb...

let me relate a story from 20 years ago...
i redid the top end on my families 78  E350 with a 351W 2bbl.. i built the carb.. left it on the work bench.. did a friends carb also...

when we went up the los angeles side of the grapevine.. it took 8 hours of struggle to get to bakersfield..  kept running out of gas.. clogging the fuel filter.. but even when the filters were brand new.. sometimes it would hardly run....  it might go 15.. it might go 25.. it might run a 55 like an electric motor..  it was really strange...

i finally got to the point where it would not go... so i unpacked the cab of the truck.. pulled the inner cover.. ripped the carb off.. pulled the top...  found 3 dead med flies floating in the fuel..   they would sometimes sink and plug the main jets... removing the floaters fixed it..   when i got back from that trip .. my other friend was awaiting me..  i could not get a word in edgewise...  he kept saying how great it worked.. then sometimes it would go 45 and 25.. i managed to get in.. you probably just  have some bugs in the carb...  when i pulled the top off that quadrajet.. and pulled tweezers out of my pocket.. removed real DEAD bugs from his carb.. he was laughing so hard i thought he was going to die..

seems the county dropped off buckets of sterile med flys  to wipe them out..  they were everywhere.. i just never figured they would crawl down the bowl vents..  

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Classic65
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Posts: 87
Joined: 11/08
Posted: 09/22/12 07:52 PM

Guess I will have to take the Demon carb apart and see, there bowls are on front and back. I live in So cal I am gonna have to check another day tomorrow I am going to Mustangs at the Queen Mary show. I will update when I can perform a new check.
Thanks again for your help.  

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waynep71222
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Posts: 455
Joined: 04/12
Posted: 09/22/12 08:51 PM

so cal?    near ktla??  

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Classic65
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Posts: 87
Joined: 11/08
Posted: 09/23/12 06:58 AM

down near the 605 Fwy & the 5 Fwy meet  

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Classic65
User
Posts: 87
Joined: 11/08
Posted: 10/07/12 12:40 PM

After doing the fuel pulse test I am getting plenty of pressure little more then a pint or so was in the bottle.

I will have to remove the bowls and see whats in there I have a Demon carb, this will be my first try at repairing a carb or seeing if it is clogged, any advise ?  

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waynep71222
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Posts: 455
Joined: 04/12
Posted: 10/08/12 05:37 PM

check messages..  

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Classic65
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Posts: 87
Joined: 11/08
Posted: 09/04/13 04:08 PM

Coil was bad and so was Distributor  

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