I am looking for someone who can tell me what could cause my latest symptom.

My 66 F-100 240 6 cylinder, 1 BBL carb studders when I am accelerating.

When I get up to speed it smooths out.

It does it in every gear.

I took the fuel filter canister off, and the fuel of course drained, and the problem disappeared for a little while. Once the fuel filter filled again it came back.

I took the Air cleaner off and drove it and the problem was less obvious.

I put the Air cleaner back on and it got worse again.

I think I am getting too much fuel and the air just can't keep up. This is semi confirmed by my getting 7 mpg. I don't know but I assume this is a bit on the bad side for a low end 6 holer.

I adjusted the screw at the bottom of the carb all the way in and the truck almost died, I loosened it a little and then drove it. It seems a little better.

I am considering a fuel regulator. Has anyone used one of these and could it solve my issue?

My 2 primary issues are the studder, and the fuel economy. Any help would be appreciated.

 

G'day mate.

My guess is that the accelerator pump plunger may be on the blink.

To be honest, I've never had one of those carbys apart, but it looks similar to plenty of others I've done. My 240 wasn't in my 65 F350 long enough to require a rebuild.

The issue may stem from the plunger (or plunger bore) becoming worn, so that when you put you foot down, it don't give you that immediate fuel shot, yet the bores open up resulting in a lean, no fuel, cough splutter, in every gear as you try to accelerate.

The extra or excessive fuel consumption might be because you're trying to compensate by planting the foot further.

If the old girl was a sweet runner up till now, that's where I'd start.

Cheers, Ron.

 

I agree it sounds like you are running to rich.Do you have a electric fuel Pump? If you do I would say yes to your Fuel regulator. Not saying this is your problem. Just most electric fuel pumps put out to much pressure for your needle and seat to handle.If you turn your idle mixer screw all the way in and its still runs, either your idle is set to high and your out of your idle circuit or your dribbling fuel. At idle look down the throat of your carb and look for dribbling fuel. You should see none. If you do I recommend a carb overhaul. I am unfamiliar with the 1 BBL carb But I would look for a bad needle and seat, saturated float,or brass float that has fuel in it, bad power valve if it has one, and of course clogged passages. good luck be safe

 

I really tried to remember everything, but you guys brought up the one point that I forgot. I bought this truck 18 months ago, and rebuilt the carb myself once about 8 months ago. I mucked it up so I paid a Mechanic at a local Ford dealer to rebuild it. He apparently didn't get it boiled out well enough because it was pouring fuel into the engine when I took it to another Mechanic. He suggested rebuilding it again. I took it to a place here in Denver called the Carburator shop. He boiled the Carb out for 24 hours, and rebuilt it. That was 1 month ago. I am beginning to think this Carb is beyond help.

I also do not have an electric fuel pump. I am trying to stay as stock as possible. I replaced the Fuel Pump but it is the stock type.

Ideas based on new info? Thinking bad carb??

 

Yep Thinking Bad Carb, But why? most of the times you replace a carb because it has worn throttle shafts and bushings causing more of a lean condition not because it plugs up. Fuel tank and lines dirty also? At this time I would consider replacing the carb also since it has been gone through so many times recently.

 

So you know where I'm coming from, I'm a journeyman mechanic of 35 years and cut my teeth on pre electronic ignition and carberated engines.

In as much as there are no definitive test procedures for carbs, the first thing you always do is eliminate any other posibilitties. So you start with the ignition. The most practical way of doing that is to go through the reg tune up procedures checking points, plugs, condenser, plug wires, cap rotor and coil. Because it takes more current to fire the plug under load than it does at idles an ignition system issue can show up under acceleration. Timing static setting and advance are very signivicant when it comes to hesitation off idle. Real important that you check the operation of the vacuum advance, a very common source of hesitation on acceleration. Use a vacuum pump to ensure no holes in the diaphram and smooth movement through the advance. You also want to check that the mechanical advance is working properly. Generally a twist of the rotor to see that it move forward and springs back of it's own accord will suffice. Once you've assure all those things are correct check the timing with a light. Running a few degrees on the advance side will improve economy and performance. If driving it advanced that far gives you pinging, pull it back a bit. If you have to pull it back further than the tuneup spec to get it to stop pinging, you've got another problem.

So now you've done all that and you still have your hesitation. Now we move to the other side. If this has a heat riser valve in the exhaust below the carb check to make sure it is moving freely and the spring is returning it to the closed position. Make sure the stop is not rusted off and the flap going past it's normal closed position. Heat risers are also important in hesitation complaints, especially if the complaint came up as the weather cooled.

Don't get too hung up on the fuel pump. It's role in driveability is very minor. The float/needle/seat is what determines the fuel level which in part determines mix. The fuel pump should have around 5 psi with a gauge on it and should fill a container with a steady stream of fuel, not bursts of bubble and spurts. There is a spec for how long it should take to pump a quart of fuel, but I can't remember it.

Now look down the throat of the carb. As you push the throttle open (engine not running) you should see a stream of fuel pumped into the throat of the carb by the accelerater pump in the carb. If the stream only appears at the very end of the stroke the acc pump is defective. It may not start to squirt as soon as you move the throttle, but shouldn't be long after. If the pump is defective an o'haul is in order which will then deal with any other carb issues.

Steve g

 

Steve, frankly you are exactly the type of Mechanic I want to talk to. The only "Mechanics" I can find are actually "Technicians" They hook up a computer to the car/truck, and the computer tells them replace __________ and they do that. They don't know about the feel the turn a screw and listen technique.

On the tuning side, the last guy at O'Meara Ford that put the rebuilt carb on it also checked the points and the timing. He said the points were slightly out. Something like I had it set to .04 and it should have been .038. Not enough to keep it from running but enough to make it not run as well. He also checked the timing, and said it is set to 8 degrees past TDC. I assume that was the right setting. He also told me the coil was cracked. Could that cause this??

I replaced the plugs, points, condensor, cap, rotor, and wires about 10 months ago when I was trying to get it running.

I have had suspicions about the vacuum advance for some time. The tube that connects it to the carb has a rubber section that is clamped with pinch clamps in the middle of it.

So let me explain what I think happens when you accelerate, and anyone who wants can correct me, so I can properly diagnose this.

You press the accelerator, and the vacuum advance moves the distributor a little forward, so that it can speed up. Once you get there the advance pulls back again which could explain why once I am at speed my truck settles down, no matter the speed.

The strange thing is I see no symptoms sitting still. Hit the gas, and it revs right up. No studder!! Weird.

I may have to find an old time knuckle buster Mechanic here in Denver to help me with this.

The fuel part still bugs me. I will check the dripping while running and the squirt when not. (I do have reservations about the squirt considering I know the accelerator pump is new.

 

First off, replace the coil. What appears to be a crack may in fact be a carbon trail. A carbon trail is what it sounds like, a deposit of carbon left on the surface from electrical current arcing across it at some point. What happens is if you have an open in a plug wire the coil will raise the voltage to it's max to try to overcome that resistance. It also is always seeking out it's shortest path to ground. So it jumps across the coil. Doing that long enough leaves the carbon trail. Eventually the wire is replaced and as long as the voltage requirement stays low it will not follow the carbon trail, but rather, fire the plug.

As I mentioned the higher the load on the engine the harder it is to fire the plug. The coil and ignition system create as much voltage as they need to fire the plug (to their max limit). As that requirement increases the voltage in the system increases until it reaches the point where the carbon trail is the shorter route to ground. This would also explain why it does it driving, but you can't simulate it sitting. You can't get the load high enough to cause it to arc. With cars with auto trans we would sometimes put it in gear and build it on the brake and have someone watching the ignition system for an arc.

Gotta run. I'll give you the skinny on the advance when I get back. Removing the body from a 69 427 Corvette this a.m for a restoration/detailing. Halfway through it and want to have it off by lunch.

Steve g

 

I copied your quote so I it would be convenient to refer to.

At 8 degrees past TDC it would not be timed right. In order to work properly, the lean mixture at idle must have the 'fire lit' earlier, so the spark must be advanced. In order to do this properly, 8 degrees before TDC would work, although 10-12 would likely be better. Get out your timing light to check with the vacuum advance disconnected. Also, make sure the vacuum advance is connected to manifold vacuum, not ported vacuum. You can tell because when idling the vacuum advance line should have suction.

Since you say you replaced the wires only 10 months age, I tend to discount the coil carbon trail explanation, but if the coil is cracked, replace it.

The symptoms describe a classic accelerator pump problem, and you can check it as advised by Steve g.; however, since the carb has been rebuilt twice, I would doubt this is the problem and I would verify the timing issues.

Good luck there, bum

 

Just a thought? might try replacing the condenser in the and the points, or go with a pertronix set up! put one on my 65 and smoothed out the engine performance to a whole new level'' and I agree that the coil could be the culprit....hope you get her straitened out...can't rest untill my slick is slick runnin..

 

Huck, I appreciate the idea on a petronix, but I am nearly a purist when it comes to my truck. I know that electronic ignition made things work smoother, but it's not the way they were set up. I don't want to put anything in my truck that was not an option in 1966. I have actually never heard of a condensor going bad, and considering I only have about 500 miles on the truck since changed them I will wait on that thought.

I am going to get the coil replaced, and I still suspect there are issues with the Carb, and possibly the Vacuum advance. The carb is the most suspect since the mileage on my 240 6 cylinder is worse than my Dad's 7.3 powerstroke.

 

I've been giving this some more thought and think a little clarification is in order. The term studdering isn't one that is used in the field to describe a condition so let's go over the symptons.

We use the term hesitation or bog to describe the situation where you step on the pedal and nothing happens. All cyls cut out momentarily. Backing off on the pedal brings them back. This can vary from very mild where there is just a momentary pause to where the engine will quit altogether unless you back off on the pedal. This is what you will experience if you have an accel pump inthe carb issue, a timing advance issue or a heat riser problem. All of these things affect all cyls more or less equally.

The other condition, which I suspect may be more like what you're experiencing is when you step on the pedal and the engine does not bog or hesitate, but runs rough and has a shudder. It will continue to accelerate, albeit at a slower rate than normal, with this shudder until you reach cruising and lighten on the accelerater at which point it smooths out. This condition is caused by one or more cyls cutting out under load. The remaining 5 cyls continue to pull normally which allows you to pickup speed, but the engine is rough with a somewhat rythmic shudder. If this is the case you want to be looking for something on the high voltage side of the ign system,a plug, plug wire, cap, rotor, coil.

One other thing. Although the points were changed only 10 months ago you should recheck them. It seems few people today know how to properly install them and they fail to put a film of lube on the cam and a dab on the leading edge of the rubbing block. Dry points will wear the block out in no time. Also, if you put 10,000 miles on in 10 months you could be due.

Steve g

 

Steve,
Thanks for the clarification on different things that could be described as studdered. This feels kind of like when you have an engine choked past when you should have pushed the choke in. I can make this symptom worse by half choking my truck. This truck also has one of the shortest choke times I have ever seen. You choke to start on a cold day, and either push the choke half in to let it warm up or it will die in 30 seconds or less. Once you want to move, shut it off or you will kill it. This along with the fuel consumption, and the fact the truck runs better without an air cleaner is why I keep drifting back to air fuel ratio.

I know I have at least a couple issues here, but I would like to figure out which to tackle first. I think I will go for the coil first because it is easy and cheap. Then I can scratch that off the list and work on.

As for mileage, I have not even used 18 gallons of fuel. At 7 MPG that put me at less than 126 miles.

As for installing point correct, I did all the things you describe as I was taught years ago. I was only told one thing was wrong by the technician I took it to, and that is I had the point gap to tight. He reset it to proper according to Ford.

 

Something doesn't sound right about the air cleaner thing. A clean filter will flow 10 times more air than the engine could ever use. If it's an oil bath air cleaner they never plug up, they just get less effective. So I can't see the air cleaner causing a restriction. Secondly, a plugged air cleaner doesn't effect fuel mixture very much. This is because the carb works on a pressure differential. When you have a restricted air cleaner the pressure drops in the throat, but it also drops in the bowl vent. That's why bowl vents are in the air horn and above the choke plate and not just vented to atmosphere outside the intake system. What a plugged filter will do is generally slow the thing down off idle rather than give you that rich black smoke effect.

If you haven't already done it, check that all screws on the carb body are tight and that the weight of the air cleaner isn't moving the carb body parts.

I would also pull all spark plugs keeping track of the holes they came out of and ensure that they all appear to be burning similarly.

Steve

 

Back again.

As I said earlier. I still think you have an accelerator pump issue.

As I see it,you have a couple of choices.

1. Replace the dodgy, cracked coil. Replace (not rebuild again) the carby.

2. Give the truck to another (old school) mechanic to fix and throw him the money,, no fix,, no pay.

3. Find a mate with a similar truck, a good runner. Swap his coil first, ( or any other suitable coil for that mater) try it. If it's fixed, job's done.

4. Same mate. Swap carbies, and try it. Only do one thing at a time, so you can figure out the culprit. That way you can let us all know,,, lol.

5. If 3 and 4 work. Give your mate a slab of beer, then sit down and help him drink it. 3, 4, 5, would be my choice. Cost? Some gaskets and a slab of beer, (and maybe a hangover the next day).

Good luck.

Cheers, Ron.

PS.It's still rainin cats and dogs here in Queensland. It's about 4.30 am here and the rain's keeping me awake. We're OK, but the last I heard was 860,000 sq/kms under water. Bigger than Germany and France put together. That was about 4 days ago, and we've had a lot more rain since.
I'm gearing up now, truck, pumps, wet/dry vacuums, water tanks etc, (and my gumboots), to go help with the cleanup when the water drops. They say about 3 weeks in some places, if the rain stops.