Hey i have a 1978 bronco with 400m and automatic transmission, all stock. My buddy drove it one day and said it broke down every 1/4 mile, and he limped it back to my house where it now sits.

It will turn over and idle on its own some times, other times it will idle for a few seconds and die, and when it idles on its own any throttle at all and it will die. Ive replaced gas tank, fuel lines, fuel pump, fuel filter, accelerator pump. And now I think its the distributor.

after poping the cap I noticed damage on the pick up coil where it had contacted the gear (not any more because it is slightly worn) also some corrosion on the distriuptor cap pick ups. So could this be caused by the pick up coil? please help i need the truck to drive to my next duty station in the marine corps in about 4 days

thanks as always, let me know if you need more information

 

not sure about the damaged pick up without seeing it but corrosion on the cap doesn't ever help. i would clean it up then check for spark at a few of the plugs. i would also check around for a vaccume leak. if all that checks out then you could have someone crank it over while you look down the carb with a flashlight and watch for fuel coming out in a good spray.

 

Okay so i put in a new distributor and all the goodies inside of it today, the bronco is idling much nicer now but still dies under any throttle and back fires out of the carb

I was slighting holding the choke open with a screw driver and had my buddy crank up the motor and the carburator shot out a lot of fire and then had a constant fire inside of teh carb, i quickly shut the carb and everyone is fine, what could cause that? i thought timing from the new distributor but it sounds right on, and I had the distrbutor line up prefectly with the marks of the old one.

any help please this is starting to get to me. Thanks

 

pull the coil wire then crank it over while looking in the carb if your getting loads of fuel then you probably have a stuck or bad float in carb

 

interesting, ill try that first thing tomorrow, how many reasons other than spark and fuel pressure would make a motor die under throttle? I hate chasing little problems like this

 

fuel, fire, and compression are the three requirements of internal combustion engines. take away one and it won't work. couple of questions. is the truck hard to start or is it poping right off, and when its running is it stumpling or hesitating and is it blowing any smoke (if so what color). oh have you checked the timing since installing the new dizzy if not i would double check it just to make sure you didn't get it a tooth off, but that shouldn't cause it to blow that much fire out the carb

 

thank you very much for the response

I have not checked the timing, I'll but piston 1 to TDC tomorrow and see where it lines up, but other than that im not sure how to check timing, im kinda a newbie,

when it runs it sounds good and there is no smoke coming out, however somtimes it will idle strong others it will idle for a few seconds and then die and have blow back come out of the carb, fire only happened 1 time, but after that i stoped, so it may happen more not to sure.

 

make sure #1 piston is on compression stroke when you set it to tdc. then if your rotor in the dizzy is pointing to #1 you should be close, but for fine tuning a timing light is best unless you can do it by ear. also you might double check your plug wires to be sure you didn't get one out of order(we've all done it atleast once). but it really sounds like a fuel problem to me, if its the original carb and its never been touched it could be due for a rebuild. is the choke opening when the engine warms? if not that could be it.

 

Backfiring through the carb, dying on throttle opening - sounds like it is way too lean. Fuel delivery or fuel mixture prroblem.

No matter what parts have been replaced, I would disconnect the fuel line after the fuel pump, put a length of fuel line on it, and with ignition disabled, crank the starter and measure fuel delivery into a can. Should get over 1 Pint in 30 seconds.

If that's good, and you have a fuel filter at the carb of the type that has a removeable paper filter element, remove the element and check that crud from before didn't work it's way into it. Remember, a cylindrical filter element has the flow coming onto the outside of the filter element, the filtered fluid flows out the inside of the filter, don't install backwards

Next I would try starting and running it at idle then a fast idle via a length of fuel line hose at the fuel pump INLET, with the other end in a gas can. This will take all of your new lines, tank, tank venting. etc. out of the picture. The cost to do this test is only about 6 feet of rubber fuel line of the right size.

If none of the above solve it, then I would pull the carb off and do a complete cleaning, blowing solvent through every little passage to be sure there are no blockages, then rebuild with a quality kit.

One other thought, this truck would have EGR, right? If the EGR valve is open at idle, even a little bit, it will lean out the mixture something terrible. Disconnect and plug the vacuum line to the EGR valve. Run OK now? If not, pull the EGR valve and look at its pintle. Is it held open by a chunk of carbon? The EGR valve needs to be completely closed at idle, and up to roughly 1500 RPM.

And vacuum leaks also. A good sized vacuum leak will make it real lean. Cracked/split hoses, etc. A good eyeball of every inch of them, with some squeezing here and there should find any hard as a rock crumbly rubber vac hose. I would start looking first at bigger diameter vac hoses at the intake manifold.

 

There are definitely some vacuum leaks in the carb due to missing and cracked lines. It has not been cleaned since op purchased the vehicle and before then it sat for a couple years outside. Before the fuel lines and tank were replaced the fuel filter would become clogged with crud almost instantaneously so I would assume some of the crap has made it to the carb.

I'm the buddy that has helped and had the fun of driving it then limping it back. Before the lines and tank were replaced it would die upon throttle then I would have to pull over and pull the filter. I would blow it out then crank the motor until fuel came out strong again which normally tool 10-15 seconds. The problem got progressively worse. At first it would make it a mile or two before dying but would run fine upon starting up again. After this happened two or three times I pulled off the fuel filter and cleaned it out. I started to go back to his house and it progressively got worse eventually getting to the point where it wouldn't make it 200 yards before dying. I kept pulling over and cleaning the fuel filter/turning it over until fuel came out and eventually limped it back.

 

ok now we're getting there. k i would try to make sure the lines are clean and blown out, also check the new filter to make sure no garbage that was in the lines pluged it up. then need to pull the carb to clean it, dip it, and rebuild it. also should go ahead and check for vaccume leak, use some carb cleaner, starting fluid, or i've even used break cleaner. while engine is running spray it around on the vac lines and intake (just not into carb) if the engine picks up then you have a leak and can narrow down where. if the lines are real old you should probably just change them all if you got the $$$.