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1968 Ford Will not start and idle once at operating Temperature

The Vehicle:

1968 Ford ‘Falcon’ Ranchero

351 Cleveland 4 bbl. (5.8L)

3 Speed Auto.

Engine Mileage unknown- motor is not original to the vehicle. I’ve only owned it a few months…

The Problem:

The engine starts just fine and the electric choke works fine to bring the engine & coolent up to operating temperature. (195 F) Once at temperature I can drive around and “rev” the engine just fine. But if I turn the motor off- even for just a few seconds- once I try to restart it- the motor will die if I do not hold down the gas pedel. Sometimes I can very very slowly let off the gas and it will idle again, but usually it just dies. I have tried increasing the idle- and yes it will stay running then- but it makes it feel unsafe to drive because the car will accelerate to 30+ mph with out even touching the gas pedel. So I took the idle back down a bit but the problem still percists. I’m about ready to pull the motor and have it rebuilt since I don’t know it’s mileage anyways. Anyone out there delt with this problem before? Any suggestions? Thank you in advance! And please let me know if more information is needed. Thank you!

maybe vaporlock? try unscrewing the gas cap the next time it may not be venting properly.

I have noticed that every time I remove the gas cap it releases a huge amount of pressure. I have a '70 Chevelle and for that matter even my newer cars have a bit of pressure that releases- but nothing like this Ford. Would a new gas cap fix that? It’s the kind of gas cap that is on the driver side bed panel on the truck- visibal for all the world to see but painted to match the truck.

Well, it would be a cheap way to narrow down what may be causing the problem. less than 5 bucks.

My friend had a 69 chevy that did the same thing. get out and take off the gas cap and it would fire up and run fine.

There should also be a vent tube on the passenger side of the tank that runs underneath the truck (if it is like a chevy and the tank is behind the seat) make sure it isn’t stopped up.

I am leaning toward a blocked vent as well.  You might try a trick that was not uncommon back in the 60's and 70's.  Try drilling a small hole in the gas cap.

The problem doesn’t sound like a fuel tank venting problem to me, but it’s certainly easy enough to rule that out. You have a vacuum leak or a carb adjustment problem, IMHO. Or perhaps a timing problem. Are the vacuum and mechanical advance units in the distributor working right?

"…the car will accelerate to 30+ mph with out even touching the gas pedal."
That takes me back to the choke. Have you looked at the choke position when the car is acting up after it is warm?

The way I read the post, the self-acceleration only occurs when he bumps up the idle speed to prevent stalling.

Dirt in the carb idle circuit. Get a can of carb cleaner with the extender (like a skinny straw). Remove the idle mixture adjust screw from the carb. Spray the cleaner into the screw hole. Replace the screw, screw it all the way in then back out 2 turns. Start the car, warm it up. Might have to play with the screw to keep it idling. With the car fully warmed up find the screw position with max idle speed, then turn it in until the speed drops ~50RPM.

NYBo is correct. The self-acceleration was only a problem after I had turned the idle up to keep the engine from stalling. Last night I let the car warm up and then set the idle back to where it was previously.

I will play with the gas cap/ vent line theory when I get home from work this afternoon. The gas tank is under the bed near the rear of the vehicle. Remember- the Ranchero is more car than truck- it used the same platform as the stationwagons. But it does sound like this would be an easy and cheap problem to rule out. Thank you

What type carburator is on the engine? Why is a 195* thermostat used? MOst Ford V-8s of that period used an idle rebound device which slowed the throttle returning to idle for the reasons you described. Some used a vacuum powered fast idle servo incorporated into the throttle return.

The carberator is an Edlebrock. CFM is unknown. It has a 195* thermostat because that’s what Autozone looked up and said went with that engine. I have since bought a 180* thermostat and plan to put it in- but as of yet I have not installed the 180*. Should I get a carb rebuild kit and get busy? Thank you

Investigate the engine and the combination of after market parts involved, Malibu. The Cleveland 351 wasn’t available in 68. The 351 M is similar in appearence. Also, the “Falcon” Ranchero is not given much ink in the old Motors manuals but I didn’t think anything larger than the W engines were offered. However, vacuum choke pull-offs, vacuum spark advance, altitude compensators and PCV valves have all caused the problems you have. First, reconsider any advice from Mc Parts while you install a 180*thermostat. Check that ported vacuum is on the spark advance. Be sure that the choke is open fully and the fast idle screw is not hanging on the fast idle cam. BTW, the choke hot wire should be wired to the alternator “S” terminal and check the ground wire, also.

“Are the vacuum and mechanical advance units in the distributor working right?”

Is there a way to test this?