help! 72 302 wont idle more than 10 seconds

[mcampbell26915]

I'm new to this forum and I am having serious trouble with my 1972 mustang 302, it starts up and idles well for about 10 seconds then rpms slow down and die almost instantly, I have replaced a lot of things on it so I don't know what could cause this problem. if anyone else has had a similar problem and could help me that would be greatly appreciated, I have tried everything that I know! thank you, if you need additional information I would be glad to give it out, just let me know what you need to know. ps: I've never used a forum before, so bear with me

 

[CZ-75]

Sounds like a fuel supply issue.

Could be many things... Fuel pump going bad. Carb not set properly. Fuel tank not vented properly.

Can you keep it running if you give it some gas?

Once it stalls, does it start right back up, then stall another 10 seconds later, or is it hard to start after it stalls?

 

[Jeff73Mach1]

I agree that it sounds like a fuel issue. It also sounds like it is running on the fast idle/choke cam for a moment and then dying. To me that is a signal that there is a vacuum leak somewhere, or the internal circuits in the carb aren't drawing fuel through the idle circuit.

Has the car ever idled properly during the time you have owned it?

 

[rutkak]

Remove the air cleaner and spray starter fluid in it when it starts to die. If it keeps running you have a fuel supply issue. If it dies then I'd look into a vac leak. I'd also make sure that your choke isn't wide open at cold startup.

If there are no leaks that you can find (use starter fluid to spray around the carb and vac lines) then I'd look at the timing.

 

[captthundarr]

All of the above. just do one at a time then move on. make a list and check them off.

 

[Wolverine]

Fuel...but make sure you have 6 volts at your coil....I believe that is 6 volts between the + side of the coil and a source for ground.

Could be worse. Consistent issues like this are relatively easy compared to a car that runs great in the driveway and peters out at 110 on the freeway.

 

[mcampbell26915]

Thank all of you for responding so quickly! To answer as many questions as I can, I just replaced fuel pump and filter, just replaced carb with a 500 cfm Holley, just replaced intake manifold and valve covers, relplaced exhaust ( just listing everything that I replaced) replaced spark plugs, replaced coil, 3 push rods that were bent , alternator, and re set timing . It runs for 10 seconds then dies, during those 10 seconds if I give it any gas at all it dies almost instantly. Also it will not start unless the choke is Completly closed, not even a hair open. If it is open at all then it will not start, and If I open it a little when it is started then It dies instantly. It ran before, it ran horribly rough but it ran, then it randomly stopped running ( I thought because of the carb) so I rebuilt the carb and it still didn't work so I replaced the carb and that still didn't fix it. So I tried all those other things i listed above and none of them fixed it so now I am here... Also I think it is noteworthy that when I set the timing I had it set at 30 degrees advanced which is crazy high, but that's where it ran best. It ran for about 10 minutes the other day no problem, but for some reason the very next day, after not touching it at all, it starts doing this. I thought I was extremely close a couple days ago, because it idled awesome but just died as soon as I put it in gear, so with a few minor adjustments to the carb screws I was able to take it around the block by 2 footing it. But now I can't even set the screws because it won't run long enough to do anything. I can't check for a vacuum leak because it dies too fast to spray around the intake. Alright so that's the end of my rant haha, thank you guys again for your responses, this car is really stressing me out that it won't run! So any ideas would be greatly appreciated, thank you very much

 

[rutkak]

I say vac leak as evidence by the choke. I'd still start with starter fluid to rule out fuel starvation.

I had the EXACT same problem with my 289 and it ended up being that the carb spacer was letting massive air in due to the shape. I used a stock 4 bbl spacer and fixed it by going with a cheapo 4 BBL spacer from Chinazone. I later went to an Edelbrock version due to hot start issues.

Check for air leaks @: transmission to manifold (modulator to metal tube & metal tube to manifold), any open holes on the manifold (my Edelbrock manifold came with 4 or 5 open holes to accessories), carb to carb spacer, carb spacer to manifold, brake booster to manifold, PCV to carb/manifold, valve cover to PCV, any open ports that needed to be blocked off on the carb (Edelbrock has one on the front for the PCV and one on back for accessory), manifold to block (front and back) and valve covers.

30 degrees is WAYYYYYYYYY too much timing at idle. Set idle mixture screws to 1.5 turns out and make sure your idle screw is around 3/4 in (as a start). For sh*ts and giggles, I'd try to back off timing a tad without starting it if you are confident your balancer & timing marks were right on.

KR

 

[JimNiki]

Are you sure the accelerator pump and the power valve are perfect?

The timing is wrong...

Maybe you're running on 6 or 7 cyl, check all leads for spark...

Worse case scenario, you've got worn lobe(s) on the cam.?

 

[mcampbell26915]

thanks again guys for the help,

the starter fluid idea is a good idea however i wouldnt be able to test it because as soon as i would open the choke to spray the fluid into the carb it dies, so i couldnt really check that unfortunatly, are there any other ways of testing if its the fuel delivery problem? I thought about getting a fuel pressure gauge to check if i am getting pressure but let me know what you think. the float could possibly be stuck which would cause it to not get very much fuel and explain why it dies every time, but it shouldnt be stuck because it is a new carb and it ran the other day pretty well, so it would have had to have gotten stuck within the past couple days so i dont think that is it. i have a spacer on it aswell, it is a 2bbl though. maybe the spacer is upside down or something, but i doubt it. it has brand new gaskets so there shouldnt be a leak on the carb spacer, do you recomend i take out the spacer completley and see if it changes anything? a couple other things worth mentioning is when i replaced the intake manifold and gaskets, i had a bad oil leak so i took manifold off again and re put it back on but i used the same gaskets, which i heard is not a good thing to do. the oil leak stopped, which is good but apparently using the same gaskets could cause a vacuum leak. i also took out the AC compressor and pully to take weight off the front and to have more room in the engine comp, i dont think that matter just letting everyone know. im not sure how i would check for any air leaks in any of those places you mentioned because i cant keep it running long enough to do a test with the carb spray, are there any other methods of checking for vacuum leaks without the car running? and the carb screws are already 1.5 turns out, im not sure about the idle though, i just tuned it untill it sounded best for those 10 seconds and left it there. i will try to retard the timing a little bit and see if that fixes anything, the way it is now, at 30 degrees, was when it ran the best however and didnt backfire at all so if i move it back i have the feeling it will start to backfire again, but i will give it a shot. thank you so much for your help, to answer jimniki ,

the accleerator pump should be good, it is pretty much a brand new carb, only used for a couple weeks before i bought it. im not sure what the power valve is exactly , sorry :/. also how would i check if I am only running 6 or 7 cylinders? these seem like dumb questions so i apologize ... thank you so much both of you for helping me with this

 

[CZ-75]

Get a spray can of starter. As soon as you start it, spray some starter fluid around the base of teh carb and around the intake manifold. If the RPMs go up, that means you have a vacuum leak, and starter fluid is bsiing sucked in at the leak.

Regarding timig... Are you at 30 with or without vacuum advace? Being at 30 WITH vacuum advance isn't too bad.

 

[mcampbell26915]

Alright I'll give that a shot, I'll have a friend start it for me so I have more time that way. And that is with vacuum advance I beleive, are you talking about the hose that connects from the vac advance to the carb? The vacuum advance is te thing attached to distributor with 2 screws and it's kind of circular , if so then I have a hose Hooked up from there to my carb, there is also a little nozzle on top of that thing and that nozzle is capped off, I'm not sure if I need it because it ran ok before and it was still capped off

 

[Wasagachris]

Everyone seems to be ignoring your statement regarding the three bent pushrods. You may have stuck valves or the timing chain may be so worn out that the timing is so far off that the piston is hitting the valve and bending the pushrods.

I would pull the valve cover again to inspect those replaced pushrods in case they have been bent again.

Maybe that's why it ran fine for a while and suddenly the problem appeared.

Someone who is an expert engine builder may be able to help you diagnose this further.

How long had the engine sat before you tried to get it running and exactly what did you do to the motor before starting it for the first time?

 

[72HCODE]

sounds like a massive vaccum leak on the surface.

might seem stupid since the choke has to be closed for the engine to run but maybe get a piece of cardboard and cut it so it fits over the carb air intake then duct tape it seal it off and go start the car if it runs for 10 seconds again then you have a massive air leak somewhere might even be able to hear it or see it with the air intake closed off.

at least that would rule out vaccum leak, next would be fuel.

one way to test the fuel getting to the carb is disconnect the hose to the carb and install a long hose and put it in a bucket, then disconnect the coil and crank the engine over with the starter.

there should be a good amount of fuel going into the bucket. that would tell you the pump and lines are working and not clogged.

next focus on the carb.

does the holly have a inline brass fuel filter inside the fuel inlet fitting. i had a issue were i didn't know holley put a little thimble looking brass filter with a spring inside the fuel inlet tube and i installed a AN fuel fitting and it crushed the brass filter and clogged the entire inlet on the carb, i had to replace the fuel bowl from the damage it caused.

at least that would let you zero in on if it is the carburetor.

now it could be electrical, a bad coil can run bad and kill the ignition a couple of seconds after start up.

it heats up internally and the ohms shoots to the moon and the engine dies.

do you have electronic ignition that can go bad even new.

the problem is even when something is new doesn't mean it is good.

the wrong ignition wires can blow out a new electronic ignition or coil, same with some types of aftermarket spark plugs.

now you could also have had some type of mechanical failure inside the motor.

start with a major vaccum leak somewhere, try my idea of blocking off the fresh air and if she still runs then you will have a good chance of finding this leak, could be the Carb spacer. could be a bad seal from the intake manifold to block.

sometimes a motor is rebuilt and they plain the decks and then somebody goes and buys a new intake manifold and guess what it no longer fits correctly due to the decking and you have a massive massive air leak through the lifter valley.

basically you mentioned the engine ran well before. you want to back step and figure out from point A to B what changed.

if you made a lot of changes like you outlined that makes the job harder.

check vacuum leak first.

you can do that simple fuel test to just make sure the pump is doing its job.

after that things get more involved.

you may also want to do a compression test on each cylinder just to make sure mechanically nothing happened.

you said you changed the plugs, what did you gap them to. start with .035" if you left them as is from the box then installed them in the engine they could be .060" and the engine will not run.

you can use a timing light to check for spark put the pick up on each wire and crank the engine and watch the strobe if you get some wires where the strobe is out of rythem or will not light then you know you have a dead cylinder causing problems, and you need to check the wires or trigger for the spark.

the idea is to keep testing things until you can isolate it to one area.

then break it down from there.

with all the work you did, i would double check firing order and your initial timing might be completely wrong. if you used after market 9-12MM ignition wires, rip them off the engine and return them for a refund and buy OEM carbon filament wires and start over. you have no idea the pure hell those spiral core MSD i add horsepower BS wires can cause.

 

[marks73]

And that sir is why he's our TECH ADVISOR!

 

[rutkak]

72HCode is the man.

Great thought on firing order. I would definitely double-check to make sure your spark plug wires are in the right sequence. Never telling if you have 2 or so swapped.

 

[mcampbell26915]

rutkak, I tried your idea with the starter fluid down the choke to see if it was a fuel supply issue. I started it up, and I waited till it was going to die and I sprayed starter fluid on the choke plate and it kept running, if I keep spraying more and more starter fluid it runs but as soon as I stop then it dies. this makes me think it is a fuel supply issue, what are your thoughts? I still wasn't able to open the choke at all, it had to be 100% closed in order to start the car, but when it did start I sprayed the fluid over the closed choke plate and some of the fluid was able to make its way into the carb without me having to open the choke, and that is what kept it running. so maybe it is a mix of both vac leak and fuel supply? because it just does not start with the choke even a millimeter open, but when its all the way closed it starts then dies soon after, unless I manually supply it with starter fluid. let me know what you think about that, thank you for the good idea.

wasagachris, good point, I will pull the valve covers and see if they got bent again. the car, when I first bought it in august, had been sitting for about 10 to 12 months, and when we first fired it up after those 10 months it fired up, took a little bit of adjustments on the carb and then it was able to drive home 30 minutes.

72hcode, wow thank you so much for your in depth response. you are very imformative and I will try all of the things you mentioned, and as soon as I do that I will post my outcomes. thank you again for all of your help guys

 

[rutkak]

rutkak, I tried your idea with the starter fluid down the choke to see if it was a fuel supply issue. I started it up, and I waited till it was going to die and I sprayed starter fluid on the choke plate and it kept running, if I keep spraying more and more starter fluid it runs but as soon as I stop then it dies. this makes me think it is a fuel supply issue, what are your thoughts? I still wasn't able to open the choke at all, it had to be 100% closed in order to start the car, but when it did start I sprayed the fluid over the closed choke plate and some of the fluid was able to make its way into the carb without me having to open the choke, and that is what kept it running. so maybe it is a mix of both vac leak and fuel supply? because it just does not start with the choke even a millimeter open, but when its all the way closed it starts then dies soon after, unless I manually supply it with starter fluid. let me know what you think about that, thank you for the good idea.

wasagachris, good point, I will pull the valve covers and see if they got bent again. the car, when I first bought it in august, had been sitting for about 10 to 12 months, and when we first fired it up after those 10 months it fired up, took a little bit of adjustments on the carb and then it was able to drive home 30 minutes.

72hcode, wow thank you so much for your in depth response. you are very imformative and I will try all of the things you mentioned, and as soon as I do that I will post my outcomes. thank you again for all of your help guys

Sounds like fuel supply. However, I would not rule out a combination of many things. If you can fuel it by a spray can then she's gotta be getting starved out. I wouldn't rule out a vac leak entirely but fuel sounds like the problem. First thing I would check would be the fuel filter. You replaced the fuel pump and those things hardly ever go bad so that's probably not the issue. A fuel pressure gauge will tell you if you are okay, but I'd think generally you probably are. On the carb I'd check the float levels first and then think you may have some junk in the needles.

 

[marks73]

Are you sure you put the fuel pump arm in correctly against the cam?