"Stumbling"

The truck (1939 D-2) had been running fine, however lately, once the engine has warmed up, it "stumbles" going up hill. Feels like a loss of power related to fuel, so the first thing I did was to check the fuel filter, which is a Durex unit with a porous brass mesh element. There was quite a bit of sediment in the bowl, and I also cleaned the element with carb cleaner and compressed air.

Got back out for another test drive - same thing.

Then I remembered that I had a similar thing occur with my '53 R-110 and it was the coil going bad. I had a new coil I was going to install anyway, so wired it in and took another test drive - same thing.

So it would seem it is either a fuel delivery issue (haven't checked the fuel pump and fuel flow yet - flow should be 1 pint per minute and pressure between 2 and 3.5 PSI) or an ignition/timing issue related to the distributor. Without completely taking the distributor apart, I checked the points gap and set at 0.020" (specified range is 0.018" to 0.024"). Still stumbling.

It is my understanding that the vacuum advance only comes into play at idle and very low RPMs and the mechanical advance regulates timing for higher RPMs. I would have to tear the distributor apart to get at the weights for the mechanical advance - point plate held in by 4 bolts at 90 degree increments around the distributor, which is a Delco-Remy 622R.

Am I headed in the right direction on this or am I not considering something else that I should? Trying to tackle from simple to more complex, so before I take the distributor out to investigate further, I thought I'd check in here.

Don't give this old shade-tree mechanic too much guff if I've missed something obvious! LOL

John

Had the exact same problem on my D2 with a rebuilt fuel pump, put an electric fuel pump close to the fuel tank, problem solved. I do have a spare rebuilt
fuel pump that I'll drop in one of these days but for now its running so good I don't want to mess with it.

--George

In my shop I'd try to figure out if it was ignition, fuel or internal engine.
Ignition miss tends to repeat and nearly always feels the same. My customers call it "pulling" or "tugging".
Popping through the intake is one sign of lean mixtures.
Can you choke the motor slightly and change the problem?
Does the engine crank evenly? Uneven cranking has to be looked at first and backed up with a compression test and vacuum gauge.
Once I get a vehicle past the "even cranking, good vacuum" tests I start looking for vacuum leaks, hoses or wires off.
Using carb cleaner to find vacuum leaks is risky. You can certainly set things on fire. Even a spray botlle of water (hose down the wires while you're at it) is better. Just squirt water where a vacuum leak might be.
I'm spoiled in that I have a infrared analyzer next to a dyno. I just load the dyno and "climb" while checking emissions and or the ignition scope hooked up.
Things reveal themselves QUICKLY.
People who poo-poo ignition scopes have never learned to use one. They work great and are becoming a drag on the market. Very inexpensive.

I'll throw my hat in the ring. It can be as simple as an almost bad ground or even low voltage. Bad timing, bad tank of fuel. Do another road test and post a video of that road test showing/hearing what she's doing. The only thing we can really do here is point and shoot at a long list of might be's. Fuel, air, electrical. Or like the doc says when you tell him it hurts when I do this..... Then stop doing that. Find a road with no hill.

Point gap: On used points it is almost impossable to get an accurate setting (by gap) after they have some time on them. Dwell angle is the way to set points once they are in service.
You can check mechanical advance with a timing light. Even if you don't have an "advance" type light. dis connect the vacuum advance (for the test) and rev the engine while using the timing light. You should see the timing advance on the mark as the speed increases. It will not tell if it is to spec, but will show that the weights aren't stuck.
I had a badly worn distributor that would cause 9 kinds of hell when it tried to advance, essentially, the dwell would drop out (points would stay closed) as the distributor tried to advance. New bushing in the distributor and all was well
Almost impossible to diagnose over the .net could be so many things, and stuff MM or I would pick-out just looking at, you may think is OK. Hard to think of everything.
If you can, put a dwell meter on it and take it for a spin and watch the meter while it is acting up, that will not ellminate the ign, but will tell you if the primary side is functioning.
Could even be a partially plugged exhaust.
To an experienced mechanic Ignition problems tend to "feel" different than a fuel problem, but it is hard to describe how or why that is.

Yankeefan150,
Your electric fuel pump testimonial warms my heart. God bless you, sir!

I am in the process of acquiring an older dwell meter that will work for the 6V positive ground system (I have heard that new digital multi-meters also work, but many need to be connected to a 12V battery for power). I am also upgrading my old timing gun (doesn't have a 6V switch like my really old one did) with a self-powered timing light that should work on the old truck. Then I will know more.

If it comes to it, I'm not sure whether I'll go electric on the fuel pump or not - no strong opinions one way or another, except that I am trying to keep the truck as original as possible.

Thanks for the input guys - will be playing with this more on Thursday...

John

I'll throw my hat in the ring. It can be as simple as an almost bad ground or even low voltage. Bad timing, bad tank of fuel. Do another road test and post a video of that road test showing/hearing what she's doing. The only thing we can really do here is point and shoot at a long list of might be's. Fuel, air, electrical. Or like the doc says when you tell him it hurts when I do this..... Then stop doing that. Find a road with no hill.

Roads with no hills are not an option (for very long) in south-central WI Posting a video is a good idea, though, and if the wife brings her fancy new camera home for the weekend, I may just do that!

John

Still getting my ducks in a row for the weekend - I like to know exactly what Parts I a man dealing with and to what extent they are replaceable or not. The fuel pump is an AC Delco Type 502 mechanical advance unit, #15201011. I have a backup fuel pump, but it needs rebuilding - and I was fortunate enough to come across a rebuild kit for this very pump at "Then and Now" Parts. The rebuild kit price seems high to me at $47, but it has been more than a few years since I've purchased a pump rebuild kit. I will likely buy it and rebuild the backup pump so it becomes just that - a viable backup

John

12V timing light will work fine on 6V vehicle if you connect to a remote 12V battery. Like another car.
I use Snap-On Vantage for dwell. overkill.
Prices are sometimes in the hundreds for a tool that was originally $2500.
Vantage is half repair manual and half Digital Graphing Meter. It is OUTSTANDING.