The Stovebolt Site Forums The Shop Area Engine Shop Ol' Roy Blew a Stinker / Busted a Grumpy / Cut the Cheese on the Drive Home

Just a thought would the vacuum advance be seized and not moving or leaking.

I did observe it moving.

When I’m trying to diagnose a suspected fuel issue, I try to test whether it is lean or rich problem. I’m not good enough to figure it out by intuition.

Testing for lean is pretty easy. Put the engine at the RPM where the rough running occurs. Add some sort of fuel (spraying something down carb) and see if it smooths out or gets worse. If adding the fuel smooths it out, I go searching for the cause of the lean condition.

If adding the fuel makes it run rougher, I presumably have a rich condition. Verifying rich takes a little more creativity. I’ve done it on small engines regularly but not on my Stovebolt. Either have to restrict fuel or create an intentional vacuum leak. Plan carefully as to not expose yourself to the lean backfire you might create. Someone here probably has a suggestion.

I am not altogether convinced you have a fuel issue. It’s easy to start throwing crap at the wall and seeing what sticks when you get into one of these frustrating diagnoses. I am still guilty of that approach even though I should know better. I get all confident I know what’s up and chasing rabbits down dead ends.

I would strongly suggest:

1) Verify that initial timing is somewhat close by the flywheel ball and rotor position. Dizzy might have moved and you didn’t know it. Might also run at idle with a dwell meter, if you have one. I get a better tune using dwell than I do with point gap.

2) Put a vacuum gauge on it at idle and report back with reading and needle behavior. Vac gauge can point out all kinds of goofy stuff. Sticky valves, timing, compression issues, all kinds of stuff.

Edit: Ignition issues can present themselves in all kinds of weird ways that can keep a guy thinking it’s fuel. My bet would still be on an ignition problem.

More thoughts:

1) Wonder if you could use the idle speed screw and kinda “sneak up” on the rpm where the trouble starts, but not so far that you kill it, or that it’s repeatedly backfiring.

Start pulling one plug wire at a time and see if RPM changes. A “no change” after pulling a wire is reason to suspect a miss at that cylinder. Bad wire. Valve issue. Something. I’ve located misses that way before.

2) Another check I’ve heard about but never personally tried: Run the engine somewhere pretty dark. Use a spray bottle to mist water around the plug wires and see if you can see arcing across wires.

Again, in your case, I think that might be best done at an RPM where it’s running noticeably rough. If it still idles fine it could be a problem that only presents once the distributor turns a bit.

If it is only doing it under load at higher RPM's have you thought about checking the the distributor shaft run out? A little movement would only get worse as the engine speed increases. I think JW51 is right, time to check the basics.

It isn't running at all now. Fuel pours out of the carb during start up so something happened to the needle valve.

Is all this related? Is it something else?

These are the symptoms the truck had before I bought and rebuilt a YF carb from Jon H over 4000 miles ago. The truck was running fine, then it wasn't.

I'm leaning toward bad gasoline at last fill up because it all started 5 miles after filling up - loss of power under load and backfire out the tailpipe, progressing to a bog/conkout when throttle is goosed with backfiring through the carb, to fuel bowl overflowing.

Whether water or debris in the gas is at fault, who knows? I have to get the carburetor sorted out first before I can do anything else.

Run a 2 gal sample of gas from the fuel line. Strain it through a cotton flannel shirt (got to be 100% cotton flannel... t shirt does'nt work.) If there is water in the gas then it will remain in the shirt when the gas strains out. Works every time. Then you can check "water in the gas" off your list.

You might have water in the gas contributing to poor running, but I’d struggle to understand how that would cause the “fuel pouring from carb” symptom. Debris definitely could.

Not sure how much gas is in the tank, but I’d consider draining and getting some fresh. I’ve done that preemptively in the past when I had some untreated sit in the tank over the winter and some weird coloration.

Agreed. Fresh gas and have that carb looked at.
This day and time ,its hard to imagine bad gas from a gas station.
Filter in line.

Here I am throwing crap at the wall, against my own advice….

Early in this thread you said you topped off the tank after it sat more or less idle since June. I think that’s probably more than enough time in a humid climate for ethanol to draw water and get weird. I’ve also had varnish-y looking deposits form (my suspicion is on the tank wall) in that sort of timeframe and show up in the clear filter under the cab.

–––––––

Getting way out of my league with the following, but here we go….

I know that a backfire can cause internal issues in some carburetors. For example, I think some of the 4 barrel Holleys can have their power valve blown out by a backfire(?).

Is there any sort of risk of internal issues a backfire could cause within a YF? From being inside of one…I don’t see how it would affect the metering rod or any of that main circuit. Could it blow out a pump diaphragm? That might be an ignorant thought. I’ve yet to experience a ruptured or dried out pump (from ethanol) in mine. Not sure if it causes just a lack of pump squirt or an internal leak.

The reason I bring that up –– you didn’t see to have the excessive fuel issue initially. If it was there to begin with, it certainly got much worse now if the truck won’t even run. Regardless of what caused the initial backfiring, I’m just postulating that the backfiring has caused some of the current issue.

How can a booming backfire FROM THE TAILPIPE have an effect on the carburetor?
Jerry

Has all the backfiring been through the tailpipe? He mentioned a couple pages ago a bog and the “pop” through the carburetor. I interpreted that as a backfire through the carb.

That's definitely a possibility. The family race car back in the early 1950s had a bad habit of collapsing the float when the engine popped back through the carb, but it had main jets drilled out to almost 1/8" in diameter and the engine was running on an alcohol/peroxide mixture. The carb was a Zenith 2 barrel from a BIG Mack truck 6 cylinder gasoline engine. Getting that much pressure back into the float bowl on a street engine would be difficult at best.
Jerry

Yes, water is unlikely but maybe debris or something got in.

Before getting started on it after work, I started it up and it ran for a few seconds before blowing fuel out the vent stack.

Anyway, the situation went from bad to worse. The fitting broke off the bottom of the tank and flooded the cab floor, garage floor and me.

I managed to catch about 10 gallons. Five gallons went everywhere else.

So, the tank has to come out and the carburetor has to be opened up.

Good times.

She’s angry!

Hey man, use the proper pronouns. Ol' Roy identifies as a male.

They/Them is angry!

I believe you mentioned in another post some time ago that you had a hard line from the tank to the fuel pump without any flexible connection between the tank outlet and the hard line. Possible cause of failure?

Yes. I'm sure that's why it broke.

I should point out that that's how the lines were when the truck came to me. When I ordered the new pre-bent tank to pump line it came with threaded fittings on each end - not a hose nipple flare on the tank end.

I naturally installed it all the way the old one came off.

How was the original rubber hose section installed?

That’s exactly what I was thinking! Here is that
hose from

Assuming the threads in the tank are ok, thread a new section of line into the tank that will go through the cab about 1-1/2" and slightly flare the end. Clamp a few inches of hose to the existing hard line (slightly flared.) Now you have a flexible connection between cab and frame to absorb vibration etc.

Jim Carter lists a rubber transition line from the tank to the hard line. I bought one for my '58, worked great.

The SKU for the part you need is: ME456

What was it that broke? The hard line connected to the tank? Or the pipe nipple that is threaded directly into the tank?

Otto,
Here are a few pics :
**Note I added the In-Line fuel filter to my set up*
Todd