I have a 1970 with a 240 inline 6 with 83,000 miles: It's an old farm truck seeing light duty: I've installed new plugs, plug wires, distributor rotor, and cap., water pump had gone -- and has also been replaced.

Engine will start - and run without a miss while not under a load: When placed in gear -- truck bogs down, and the engine coughs as if starving for gas. I've replace the fuel filter:

After running for a short period on the road -- the engine has overheated.

Initial thoughts were that I have problems with the timing -- the engine was running so rough, and what I throug was a miss. -- while not in gear & higher rpm -- the engine smooths out. then placed in gear driving -- the engine will boug down, as if starved for gas.

Any thoughts how to flush out the problem - fuel pump, carb., and or timing?
In the past when I've seen a bad fuel pump - I'd see a leak around the pump indicating problem with the diaphram.

 

You did not mention new points - did you put all the rest of that stuff in new and leave old points? Was the distributer moved/rotated at any time?

Overheating is a tip that it may be a timing problem or running lean. Did all this start when you did the work, or was it coming on before hand?

Any backfiring through the carb?

 

rough running was in advance of all of the new parts:

didn't replace the points - didn't have my set of feeler gauges with me:
no rotation to the distributor: yes some back-firing thru the carb when under a load:

would the back-firing suggest timing is off: cylinder is firing slightly in advance of the intake valve seating.

if my material is correct - the 240's don't have a timing chain: just gears - and with only 83,000 miles wouldn't expect a problem with the timing gears.

being that I could get a smooth run without a load -- just didn't associated the rough running with the points:

 

OK - more facts to sort out:

If your rough running was in advance of all of the new parts, then you probably did not cause the problem. (I do not mean to insult you, but some "other people" have caused their problem and then proceed to cause more & more problems, instead of taking things back where they started.)

You didn't replace the points, but a weak spark can fire well enough for smooth running under no load. When there is a load and the throttle is opened to meet it, the cylinder pressures go up and a better spark is necessary to jump the plug gap. This does not seem to be your case. Can we assume that the points are not seriouly burnt?

Ther was no rotation of the distributor, but a quick check with a timing light would still be a good idea.

Some back-firing through the carb when under a load could be from a lean condition or an ignition or cam timing problem. It is obvious that if a spark occurs while the intake valve is still open, then the flame will travel back into the intake manifold. Another less obvious way backfiring can occur (especially in lean conditions), is that the mixture is so lean that it does not burn completely during the whole cycle and manages to set off the incoming charge of the next cycle.

Would the back-firing suggest timing is off? Cylinder is firing slightly in advance of the intake valve seating? YES this is one possibility. Have you double-checked that your plug wires are properly connected? There are a few combinations of mis-wiring that will allow the engine to run enough to act as you are experiencing.

You are correct - the 240's don't have a timing chain: just gears. With only 83,000 miles you actually are entering the "zone" problem with the timing gears if you have a plastic cam gear (likely) AND oil changes have not been done often enough. Timing chains can "jump" and the engine will run, but less well. Gears usually will "eat themselves" once the first tooth fails, so I doubt this is your problem.

I still cannot give you a simple cure-all answer, but do the checks on your ignition system: timing light, wires in the right place, points look OK (or replaced). Then I recommend you look at the fuel side of things.

You can test your fuel pump for volume flow by running long enough to make sure there is gas in the carb. Then shut down and hook a long hose up onto the line on the pressure side of the pump. You should be able to observe a steady (pulsing) flow out of the hose into a container (do not want to waste any expensive gasoline). Locate the container outside of the engine compartment for safety. The engine should run long enough on the gas in the carb to do this test. There is an volume that a good pump will pump per minute (& a pressure number as well), but a really bad pump will be obvious, only making a dribble instead of a serious stream. (One thing to try is to fill the behind-the-seat tank full. If this makes a difference, you definitely have a pump problem.)

After that, it is time to look at the carb.

 

Thanks for the comments: Point looked OK: I have a new set, and will replace the next time I back at the old home place - it'll be a couple of weeks.

I'll have my timing light, and vacuum gauge to use.

Friend of mine -- had said odds were the carb was the problem: That the 240's had a reputation of problems -- not sure of that:

If timing and vacuum check out - and new points - and fuel pump is OK: any specifics to check on the carb? other that just making sure the throat is clean, and no gunk?

Thanks

 

If your truck sat up for a while, it would probably be a good idea to pull the top of the carb and see what is living in the float bowl. A carb kit should not be too expensive for this carb and it will have pretty complete directions. If you have never done a carb before, be sure to take great care when taking it apart to observe where there a ***** and other small parts are. Look at the diagrams to see what to expect before you take it apart. You can buy a gallon of carb dip, which will be useful for other projects as one carb will only deplete 10% of its cleaning ability. Others may recommend using a spray can of carb cleaner, but over the years safety concerns have made them less & less effective. (Read & follow safety instructions - this stuff takes little care.) Rinse with a lot of water & blow out all the passages with air. If you pay attention, you can learn a lot about how the carb works, especially if you read a textbook on how a carb works at the same time. I have a '68 240 carb I can look at to answer any questions you might have.

P.S.: I am always amused by people who say that "they all do that" or "such & such model has this problem". While there is always some truth behind these generalizations, they often distract you from the real problem. Every case is an individual and the best thing is to trouble-shoot what is in front of you based on its unique symptoms. More than one thing can be wrong, so keep your eyes open - you're doing fine so far.