Help! Completely stumped on fuel or ignition problem

[KansasM715]

Hey everybody. I'm at my wits end on my 1968 M715. Here's the (long) history.

About a year ago I went out to the shed to fire up the M715 (works on our small ranch here) and I found the ignition switch on. Needless to say, she wouldn't fire, so a new coil (one of the chrome replacements from Vintage Powerwagon) and points and a condenser later, she would fire and run. But, I could never get her to rev up again very well. The timing was right where it was before (it wouldn't start when hot for awhile but it was because the timing was too retarded, fixing that fixed the problem). I have rechecked point gap.

When I parked it about a week before she was running perfect (other than a rear main that leaks like a sieve).

Sometimes she would get me part way around the section running OK then I had to come home on an idle, barely able to get above idle.

So, I noticed that the clear fuel filter between the pump and the carburetor was only partly full (as in about 1/8 inch in the bottom). This started a fuel system wild goose chase which has ended up with the tank out of the truck.

I took off the old pump and could hook up a hose into a gas tank and it would shoot gas 10 feet working it by hand, but when I put it back on the engine it would not keep the filter full at idle even when I was running from a hose into a gas can on the fender. So I figured, has to be the pump right, even though the manual pump test would not support that.

So, an $80.00 new pump later, I got it to fill the filter at idle, but she still wouldn't rev up. My brother recounted how he had a vehicle fall flat like that once and found a broken wire on the distributor. Sure 'nough, when I put in the new coil, I must have crimped the energizing wire from the ignition switch to the coil and it was grounding out I think. Some shrink wrap (2 layers) and a little coil bracket modification and we are back good. But doesn't seem to make a difference.

So since it was filling the filter at idle, I get brave and hooked the fuel pump back up to the stock fuel lines (hooked to a hose to the stock tank sitting on some boards on the floor) and it would not pull fuel. Just a trickle to keep the engine idling. So, I puit a clear filter between the steel line on the frame and the steel line on the engine. It wont' fill that filter either. I did notice some air bubbles in the fuel trickling into the filter between the engine and the steel line to the tank, and found that the short hose between the two steel lines on the tank had a hole in it and fixed that. So now no bubbles, just a trickle though.

Right now (as of 10 minutes ago) she is idling great and smooth. But open the throttle even a little and she falls flat on her face (I have tried two carburetors, each with a new kit, both act the same). Starts with just a touch of the starter. The accelerator pump is pumping fuel, and when I pull the carburetor (getting good at that) the bowl is full, even though the filter won't fill. This pump will shoot fuel a long ways pulling out of the tank on the fender (taking it off and operating it manually) but it won't fill the filter more than an 1/8 of an inch or so on the bottom of the filter at idle. If I open the throttle, with the choke at any position, she just falls flat and will die if I hold it there very long. I have double checked that the pump is properly engaged to the pushrod off the cam. I have even pulled the valve cover to make sure everything is still hitting there, but I haven't watched it run with the valve cover off.

I am about ready to give up and just repower it, but I have redone the seats and just put a new top on it (about 8800 miles). We are ready to paint this summer and it is 100% rust free, a really beautiful old truck. The 24 volt system still works well and i was hoping for a stock, restored truck to just drive around and show off, later I'll find one to hop up. I have brand new military tires on it and it will be really sweet if I can just get it to run again!

Is this just a junk coil?
Is is supposed to fill the filter at idle?

Any help appreciated.

Thanks!

KansasM715

[tnyankee82]

Hey Kansas, I'm going to watch your thread closely as I am having the same issue. Except that my fuel filters remain full. But it runs rough and won't accelerate either. If I figure anything out with mine ill let you know!

[fishtail]

The fuel in the bowl of the carb should be enough to keep the truck running for a bit. If your truck idles good, but drops off at acceleration, then you still have something wrong with the carb methinks. Acceleration won't empty the bowl that fast if you think the pump can't keep up.

What rebuild kits are you using? 45 year old NOS kits or new manufacture. Big difference there.

Scott

[brute4c]

First thought...the filter like "sock" on the end of the fuel tanks pickup tube...these tend to get nasty over the years and restrict or even, when they get bad enough, cut off fuel flow.

One way to confront that is to blow strong compressed air into the fuel line thus blowing the sock off the pickup tube or blowing it open enough to let fuel flow again. Then put a fuel filter between the tank and the pump...the see through kind are my choice for that task.

Second thought...there have been issues with the points being installed incorrectly at times...there is a leaf spring arm that puts tension on the points to keep them closed...idle is ok if the leaf spring is installed wrong, but as rpm's rise, the points wont stay closed and there is no spark.

Since you do have limited fuel flow, I would work on the fuel end first...the points thing, just something to check while you are in there...


Whatever turns out to be the issue, please let us know...this is how we learn about new gotchas too!!

[kwai]

After all you have already done, I would swap another coil in.

[Don Cavey]

I have never seen a "full" fuel filter. It is not unusual for them to only be partially filled. I have been down that chrome coil path as well. Started OK. Drive for a while. Shut off, then try to start. Starter spins the engine just fine. But it just will not fire off.

Installed a used coil... No problem and that is with the truck living in Florida now. Just my experience...

[KansasM715]

Thanks everyone. I will recheck the points and go back to the online manual to make sure they are correct. I actually bought two new sets, so will swap in the other just for good measure. I just bolted the spring on the points to the tab where the wires from the condenser and the coil goes.

Questions:

How do I check if the coil is good?

Will my old dwell meter I used to use on my 64 nova with a 283 work on this engine? Seeing the dwell change as I rev it up would tell me a lot

How many volts actually goes to the coil on these? I know on 12 v points engines (all experience was small block chevys and old straight sixes) we had a resistor that cut the 12 v down to around 6-7 volts to the coil, correct?

I took pictures of how things are set up so will see if I can post those.

Thanks

KansasM715

[Pineyguy]

24v to the coil.

I had a problem with similar symptoms. After fighting with the fuel system (I could keep it running for a while by pouring gas down the throat of the carb so I was convinced it was fuel), an older guy I know told me to change the condenser. I had put a new one on when I rebuilt the distributor not long before, and already checked for spark, but I was at the end of my rope and gave it a shot. It fired right up and ran perfect with what was probably the original 40 year old condenser. Hope you figure it out.

[KansasM715]

So, a little history on this M715. I bought it on the GSA auction from the Kansas Forestry Service (yes, we have a forestry service in Kansas). They are the ones that supply the used military vehicles to the Kansas Fire Depts. This one came out of the Army in 1975 and spent until about 2008 in the Astoria, KS Fire Dept as a range truck. Here it is being pulled out of the Kansas Forestry Dept. in Manhattan, KS on 4-22-2011. (Slashed front tires and not running).



And here it is in the driveway at home getting ready to be drug off to a new home. My little tractor could lift the front, but I had to go get my wife to hook up to the back of the tractor to drag it off since all the weight was on the front. She used my 1984 1 ton 4x4 chevy with a bigblock and it came right off.



Put in a couple of used batteries around the place, fired it up, replaced all of the wheel cylinders, bled it out, and swapped on some new military treads. The top was trashed so pulled it off. Took off the front and rear platforms. Here she is doing a little work hauling brome hay to the shed with my sons working up a sweat.



Here she is with the new hood, repro bumper (from vintage powerwagons) and a new top. That creature to the side is a 1940 something Clarke Trucktractor aircraft tug that was used to drag B29s around at the bomber training base in Greatbend, KS. My Dad had that in the shelterbelt, so it is one of the next projects in line. Number one son hit an owl between home and his girlfriends place in the M715 so it has a new windshield. Luckily the windshield was up.



Here's a picture of how I have things installed in the distributor.



I'll go mess around with the points again.

[Don Cavey]

Does it have a ballast resistor under the coil? (#4 in the diagram). Now that I have replaced the coil in my ignitor with a used coil (and it works fine) I wonder if my used coil is the newer type that has the built-in ballast. Just more confusion unfortunately! Maybe someone knows if the early and late coils are different lengths. Hopefully, the later coil with a built-in ballast will be too long? I do know that the NOS ignitor that I have has no ballast. I will check that out today.