1950 239 Flathead V8 Hesitation
 

EDIT:
I wanted to let people know on page 8/9 of this I found it was the condenser and/or points (both of which were new). Read initial symptoms/problem below and the rest of the posts... or skip to page 8/9. I found a forum where a guy was having the same problem and was chasing carb/power valve/fuel pump/timing issues just like I was and it ended up being the condenser and/or points. Very weird, but hopefully this helps someone out in the future! At least now my vehicle is running great after all the work I did trying to figure this out, and I learned alot from all the guys on this forum. I feel like I can actually diagnose issues now, since I pretty much went through everything!


Hey guys. Need some help.

I got the truck up and running after about 4 months. It had been sitting for 26 years. Replaced most things (wires/plugs/rotor/points/vacuum advance on distributor/all wiring/ignition coil/etc). I had it running well, but then all of a sudden it stopped running well. I would get hesitation when I gave it gas and especially under load (acceleration).

I changed out the power valve and jets to what is needed at my altitude (thanks to Ross!), checked plugs, and spark to wires. Everything seemed fine. So, i was thinking maybe the distributor... so i turned bolt and it broke. Ok, so then I had it sitting for about a month, and it was so hot i never worked on it. But I finally welded a nut on and got the bolt out, and replaced distributor back where it was.

So, that got it running again, but the hesitation started up pretty quickly, mainly after it got to operating temperature. It didn't run too bad actually when driving, but I came to a stop in driveway and it died on me. Then I guess it was flooded and wouldn't start (another issue and i need to figure out these old vehicle tricks). First time working with carb, etc.


Oh, one other thing. Could it be the gas? It was running great on 91 octane (non-ethanol), and I put 85 non-ethanol since it's closer to the house (I'm at 6800ft, so it's like the normal 87 everywhere else). Could it be the lower octane? Maybe just bad gas?

Any help appreciated. I just don't get what's going on.

I'd check the accelerator pump linkage to make sure it didn't come apart. Also verify that it's spraying fuel when you accelerate. It could be a bad vacuum advance canister on the distributor, but usually that won't make it die.

I run the cheapest gas (E-10) in my truck, no issues. 7:1 compression doesn't need high octane. But your fuel system may have deteriorated while it was sitting -- fuel pump, accel pump piston, or hoses.

I rebuilt the carb, new accelerator pump (unless you're talking about something else?), new vacuum advance thing on distributor, new fuel pump. I do need to replace the line from the carb to the vacuum advance, it's like a brake line with a different flare. Sorry, I don't know the terms, way new to all this.

I'll check the accelerator linkage and spray. Would timing do this at all? I haven't adjusted it at all but i guess i could try tuning distributor to see if it runs better. It runs really good at idle though.

Brian, the ignition and fuel systems on these old flatheads are extremely simple, and easy to diagnose once you understand how they work.

To begin with, it sounds like a fuel issue, as Ross has stated.

That said, if the truck idles well, I would go ahead and check the timing, just to get it out of the way. First off, make sure you have properly gapped the plugs (.025"-.028"), and that the points are properly set (.014"-.016" when at widest opening).

Easiest way to set the timing is to use a timing light. There is a small rivet on the crankshaft pulley that aligns with a pointer on the front of the timing gear cover (you can see the pointer as you look down past the distributor toward the crankshaft pulley) whenever cylinder one fires. Just clean the pointer and apply a little chalk to the rivet head, install the timing light (cylinder one is where you plug in the timing light lead, which is the first plug aft of the distributor), and start the engine. The light will flash when cylinder one spark plug fires. Point the light toward the crankshaft pulley. The rivet should be aligned with the pointer at every firing of the light. If not, loosen the distributor clamp bolt slightly, and twist the distributor till the pointer and rivet are aligned. Re-tighten bolt.

If you do not have a timing light, you just remove number one plug and ground it to the head somewhere. Grab the fan and turn over the engine till the rivet and pointer line up. Make sure you are on number one cylinder's compression stroke by placing a finger over the the open plug hole. If you are on the compression stroke, you will feel pressure building as you pull the engine over. Once the pointer and rivet are aligned, turn the ignition switch on. Then rotate the distributor to the right or left till the plug fires. At the point the plug fires, tighten down the distributor. This method isn't as accurate as a timing light, but gets you very close (close enough that the engine likely won't know the difference, and will run just fine).

If you have replaced the plugs, points, condenser, plug wires, cap, rotor, set the timing, and have a good hot spark, your ignition should be all set.

Now you state that the engine hesitates and dies. This sounds like fuel. If you have some issue with your vacuum advance, the engine will "sag" under acceleration, then pick back up, but usually not miss a beat. It will almost certainly not die.

From your description, it sounds like fuel starvation. Make sure you don't have any blockages in the tank, fuel lines, and in the pump. If you don't have anything blocking the outlet on the tank, and the lines are all clear, make sure that the fuel pump screen (located directly above the sediment bowl in the pump housing) is not clabbered up with gunk/dirt. If the screen is clear, disconnect the fuel pump inlet line (and the outlet line as well), then beg, borrow, or steal a vacuum gauge and connect it to the pump inlet. With all the spark plugs out, crank over the engine. A healthy pump will slowly pull to about 10 inches of mercury (or 10 inches Hg, vacuum gauges are calibrated in inches of mercury, although there isn't any mercury in most of them). Once you quit cranking, the vacuum should drop only slowly (go to zero in over a minute), or even hold. If the pump pulls around 10 inches, your diaphragm is OK, if the vacuum holds, the pump valves are good.

See where I am going with this? We are systematically eliminating parts of the ignition and fuel systems till we reach the problem.

IF the pump checks out, the fuel lines are all clear, and there isn't any varnish/rust/or grunge blocking the tank outlet, the issue is with the carburetor. At this juncture, I would suggest you doubly check your fuel tank. I let my truck sit for a number of years, and had the devil of a time getting all the old dried fuel varnish flushed out of the tank. Truck would run well for varying periods, then lose power, hesitate, and ultimately die. Grunge kept plugging up the line at the tank outlet. You may also wish to replace the flexible fuel line that connects to the pump if you haven't already. Occasionally the inside of the rubber gets soft, and will collapse under the vacuum of the pump, thus starving the engine of fuel.

If you have ruled out everything above, you have carb. problems. You say you overhauled it. Did you soak it in a good carb. cleaner? Blow it out well with compressed air, including all the little holes and ports? As Ross said, is the accelerator pump connected? The accelerator pump is connected to the linkage, and is the downward pointing shaft on the side of the carb. When you actuate the linkage, you will see the shaft get pulled downward as you pull back on the throttle rod (throttle rod is the thingie that attaches to the carb. at one end, and the pivot on the firewall on the other end). On the accelerator pump, there are three holes that the pump shaft can go into. The middle one is generally the one you connect the shaft to. One position is for summer, the middle hole is for all-around operation, and the last hole is for winter. In 46 years of driving my truck, I have never seen the need to use any of the holes except the middle one.

I suggest your checking every thing out except the carb. Once you have done that, get back with us, and we will walk you through a two-barrel Model 94 carburetor to line out any problems it may have.

Adjust your carb with a vacume guage. Tune each side for max vacume

Ross, the linkage was connected and it is spraying fuel in carb when I pull it. And sounds like the octane is probably not the issue, could be bad gas but I doubt it. Also, I put on a new vacuum advance thinking that was the problem as well a month ago. I do think the line at the carb that goes to the vacuum advance was not seated properly, so that could be the hesitation... I need to replace the fittings (and got them at NAPA, part 6100x3) as the original are stripped badly. I saw in another post you don't need to flare the 3/16" line? How does it even keep it seated at the carb? I guess I'll find out.


Gertie, that's the name of my truck too, we named it as kids 30 years ago! FYI, I have a new tank, fuel hose, pump, and all that works and obviously no varnish. Fuel glass bowl is full, fuel in carb at float. Used good carb cleaner and have new accelerator pump (carb rebuild kit).

I did the finger compression on cylinder 1 and lined up the timing marks already, but I'm going to borrow a timing light and verify. Maybe it's off a bit, even though it seem to idle fine. I'm also going to adjust screws for maximum vacuum as suggested. And, I think I'll plug the wiper vacuum port. My wipers aren't working really anyway, and I don't know which direction is off!

After I do all this I'm hopeful! Thanks!

The "tube nuts" clamp down on bare line as they are tightened into the fittings on the carb and distributor. Push the new tubing into the fittings until it bottoms, then tighten down.

Huh. Well, I definitely did not do that when i put it back on after rebuilding the carb in the first place. I have a feeling this is my main problem now... I've done brakes, and fuel fittings, this is a bit weird. Thanks again! I'll update if and when I fix this!

Since you have a vacuum gauge you should check your engine using this "old school" diagnostic chart. I works well on "old school" trucks.

https://cimg3.ibsrv.net/gimg/www.for...5297ccc0d7.jpg

Let us know what you find.

So, is this just with vacuum gauge attached to where the windshield wiper tube is? That's what I was going to use and the only vacuum point I know of besides the one that goes to the vacuum advance (which I don't want to use for this I woudn't think).

Thanks, I'll see what it reads.

You don't want to hook it where the vacume advance hooks up. Slide the rubber tube over the spot where the wipers hook up.. that vacume guage will unzip most of the secrets of your engine. A forgotten valuable tool in my mind

That is correct. You need full manifold vacuum not ported.

Sounds like the power valve.
Aftermarket power valves can be flakey, and in the rebuild kit, there is a choice of gaskets for different carbs, you may have picked the wrong one for the power valve.

Kirk

Little embarrassing. I couldn't get it started even after sitting for days. Decided to check the fuel pump, and there's no bubbles when cranking in the fuel bowl. So, i unhooked at the carb, and nothing is spraying out when I crank ( I assume it should).

I had put on a new mechanical fuel pump and had some issues with getting the arm on the rod that goes up and down at first. I finally got it on but I wonder if it broke off already or maybe just slipped off or something? Anyway, I'm pretty sure it died because of the fuel pump, glad it was in the driveway!

The hesitation is another problem probably unrelated (or maybe related?). Either way I have all the tools ready to fix that. First order of business is taking off the fuel pump AGAIN and figuring out what's going on.

Brand & type of fuel pump please . Where made ? Make sure you are getting full action w/ fuel cam mechanism . When you have it off look inside the little dome on the pump . The cam arm doesn't have a lot of throw.Check the cap on fuel pump arm . Found a POS china pump arm cap on one I had Measure the fuel pump rod against spec. May need to look at the condenser & inside the dist. for worn wires . This problem has me curious as to the cure . Please report back when found .