driving around town it runs great. when it gets to about 50 mph or up hill at 45 acts like it is running out of gas it is a 73 with holly carb. could timing cause this? or carb?

 

Low fuel pressure or volume.

 

Is this all of a sudden or gradual over a long time?

Usual problems with low power under load are, fuel filter, timing, need a tuneup, clogged jets, too lean, fuel level wrong, weak pump, etc.

Does this truck have ignition points? Maybe dwell is off.

Good Luck,

Jim Henderson

 

no points. yes the timing could be way off, havent had a good day to put the light on it to see where it is. i thought about float level. filter is clear and looks good. this happened overnight. had it on highway one day 55-60 mph. the next day wouldnt go over 50mph

 

Overnite makes it sound more like it slipped a tooth on timing, or something is clogging the carb. Maybe a piece of junk is clogging the fuel inlet to the bowls or maybe the jets. Essentially sounds like you are not getting enough fuel or "fire".

Depending on how long it has been and what miles, it might be time to rebuild the carb, or check the timing and maybe replace the chain.

Also might check to see if the EGR is sticky. If you have a vacuum pump like the MityVac, you could attach it to the diaphram and see if the engine stumbles as you apply vacuum. Also you can usually move the vacuum with your fingers to check for stickyness.

Check the bolts on the intake manifold and carb just for fun. Once in awhile they will get loose and cause a vacuum leak.

Check the inside of the distributor cap for carbon tracking and make sure the contacts to the rotor(Do the 73 still have these?) are clean and actually making contact. Usually a carbon spring loaded button on the inside of the cap contacts the top of the rotor. I have had this wear out on other engines(not Ford).

Some distributors also require some oil once in awhile to keep the advance mechanism working. Not sure how the 73 disty is, probably all computer controlled but don't know. Most of the old disty's I have seen had a felt pad under a rubber plug inside the main shaft right under the rotor. Just pop the rotor off and take a look. If there is a plug and felt under there then it wouldn't hurt to put several drops of engine oil in there.

Plug wires in good shape?

And check vacuum lines. sometimes the rubber rots and you get a leak which dpending on which line it is, can cause all sorts of things to happen.

Good Luck,

Jim Henderson

 

Put a fuel pressure gauge on it before you do anything else. Classic fuel pump symptom. Should be over 4 psi at a quart or more per minute idling.

 

thanks for the input. the weather is not so good here for the next couple days, working outside. this weekend looks like sun. will be the day to try to figure it out. can i rent or borrow a furl press,guage from like advance or nottozone? more leaning towards timimg cause i tried to set dist. by ear and couldnt tell any difference no matter how far i turned it either way.

 

I'm stickin with fuel pump. I've had it happen just like you described several times. I have never had a timing chain jump just 1 tooth. They always spun all the teeth off or jumped so far the engine quits and dosen't refire. I have had the distributor gear pin shear and change timing but again engine quit wouldn't refire. You say it idles and cruises fine, then the timing is close enough not to be the problem.

 

well the fuel pump would be an easy fix but i dont really think it would be that cause there is no gas getting into the oil as far as i can tell. or atleast thats what has always happened to the ones i have had go bad.

 

Pumps don't always fail wih fuel into the crankcase, in fact that is the rarest failure because of changes in design.

 

tells ya how long it has been since i have had a mechanical fuel pump.

 

this thing is running really ric. where are the mixture screws on a holly 4 bbl carb? i found some screws on the sides that ook like mixture screws but they wont turn

 

They're on the sides and you should be able to turn them. They are a needle valve so if they get tightened they will wedge themselves in real tight. This can damage them and make it hard to adjust the idle mixture. Now you say its running rich, is that all the time or just at idle. With the idle mixture screw all the way in it will give you a rich idle then get normal as you open the throttle. I'm surprised it will idle, unless you have a vacuum leak. Hmmm original complaint is leaning out under load. Did you check your fuel pressure and volume yet?

 

not yet i am going to change the motor out in a month or so for another 460. i am going to be using the carb though i am thinking about getting another carb either new or rebuilt because this a daily driver. as far as running rich the exhaust pipes are coal black with lots of suet. when sitting idling there is a slight blue smoke and a strong smell of rich fuel exhaust.

 

vacume leak is a possibility