In my friends 81 f150 the motor will fire but wont start. The carburetor is not flooded and the timeing has not jumped. Its getting fuel and spark so I cant figure it out. Is there anything wrong with the duraspark that could cause this? Also the coil was warm after cranking the motor. We have tried chokeing the carb starting fluid and pedal to the floor. This has gone on for days now and just cranks and you can hear it fireing but the motor wont start up. The carb is you average 2bbl carter and when you crank it you can see a light mist comeing out of the ventura. The accelerator pump also works. It ran perfectly a few days ago and we have done nothing to it.

 

Did you pull the spark plugs to see if they are wet? Would it run at all with starting fluid?

 

I am confused - fires but won't start? What does that mean? What is fires?

The ignition system should provide battery voltage to the coil with the key in START and then ~7V when in RUN. Two different circuits; could this be your problem?

 

We have not pulled the spark plugs yet and with starting fluid it wont fire at all.

 

When the motor cranks it trys to start but wont. Were gonna change the coil tomorrow and see what happens but ive never seen one act like this.

 

OK, so it cranks but won't start.

Attach the positive lead of a voltmeter to the positive lead of the coil; attach the negative (of the meter) to a good ground. Measure the voltage in START and in RUN. It is the job of the OEM ignition module to vary the voltage (and ignition timing) in these two modes.

If that shows weird results, try measuring on the other coil lead; I'm pretty sure it's the positive lead that varies but am not 100% certain.

I wouldn't go replacing parts without having done some diagnostic work and found a fault in a component.

 

Put dry spark plugs in it first. You have flooded it out. Smell your dipstick for gas in the oil, you probably have washed the cylinders and now have contaminated the oil, the gas has to go somewhere.

 

He said he has spark, but it could be a weak spark. Pull the coil wire out of the distributor, hold it close to a good ground. Crank the engine and see how far it will throw the spark. You should get a blue spark that will jump 1/2" or so. You should do the same check at the end of a spark plug wire or 2 also. It wont be as strong of a spark but should be close.

 

Or, he could have spark at not the right times.

 

Or he has spark, and everything is flooded, and won't fire

 

The first thing I'd do is making sure the timing is right.

Then, check the firing order on the plugs.

Check the accelerator pump to make sure it's working.

Make sure there are no vacuum leaks.

Is the carburetor bolted down tight?

New fuel filter?

Make sure ALL of your connections are good.

Once you've got the easy stuff out of the way, then you can start checking the coil, the distributor, the ignition module, and the carburetor.

You say a light mist pops out of the venturi when it tries to fire?

Check your timing.

 

Pulled the plugs today and they were black as coal so I would assume its flooding out, dident think it was flooding but im just a rookie lol. We tried to start the truck after sitting for 24 hours, dident pump the gas at all it still trys to start but wont. Tried a little bit of starting fluid and no change. Which way do you turn the dizzy on a 351M to advance it? Im used to working on chevys. I checked the spark on the coil and plugs and they have a nice blue spark. Not sure of what the fireing order is but its kinda acting like it jumped time somehow. We turned the dizzy to the left a little and it fired 6 times and then quit. Curse ford and their backwards engineering

 

Pull #1 plug, and put your thumb over the hole. Have someone bump the key until the compression blows your finger off the hole. That's Top dead center. See where the mark is on the damper, then open the cap, and see where the rotor is pointing. should be on #1. if not, open the valve cover, and see if #1 cyl has both rocker arms closed.

 

Do just like the post above mine stated, but try and see if you can see the piston through the spark plug hole and turn it over by hand until it reaches the top of the compression stroke. That is the true TDC, not when it JUST starts to blow air by your finger. You want it at the top of the compression stroke.

The plugs are black because of all the starting fluid you've been spraying. That's why I don't like starting fluid.

It does sound like the timing is too advanced though.

IIRC, on the V8's it's clockwise to advance it and counterclockwise to retard it.

 

When the #1 piston is at TDC of the compression stroke, the harmonic balancer should be reading 0° at the pointer.

If it's not, your balancer has slipped and this could be causing you to errantly set the timing.