Running rough-need ideas

[Jim11787]

Trying to help a friend with his 1915 which has a perplexing problem. Car started running rough and lost power. This is both on 12v battery and magneto. Did the usual timer cleaning, plug check, etc. He checked the carb which he reported ok (float setting, air blown through it, installed Scott’s needle valve and seat) to no avail. He suspected fuel flow and we blew compressed air from fuel line back into tank. We did blow something metallic into tank which bounced around. Previous owner said he installed a screen type of insert which we probably blew into tank. Could not take apart sediment filter that’s why we tried compressed air. Started car and thought we solved issue- maybe some crud on screen but car ran great.

Then it didn’t a short time after. Switched out timer, switched to known good coils, no good. Still very rough on startup. Swapped carb from running car. No good. Couldn’t see any carbon tracks in coil box. Adjusted contacts in coil box to make sure good contact. Ran compression with all cylinders around 50 psi. Replaced timer, timer wiring, plugs and new plug wires. Adjusted timing. Started up great and ran great on 5 mile test ride. Celebrated and put in garage but didn’t know what fixed the issue. But it ran great.

Then 2 days later it didn’t. Hard start, started running rough and losing power. Did add new gas to tank on ride. This is where we are at. We did disconnect fuel line and fuel flowed pretty good into a bucket. Need some advice from people with more experience on what to look for. I’m thinking we may need to drain enough fuel and run through a coffee strainer to see if it could be clogging carb as I’m not sure where else to look. Any ideas next?

[Steve Jelf]

Dirt in the tank can drive you nuts if it's too fine for the sediment bulb screen to stop it. There was a loose baffle, which persuaded me to get a new tank. The dirt went with the old tank.

[Norman Kling]

Is it misfiring on one or more cylinders? It could be an ignition problem. If you swap coils in the coil box, does the misfire move with the coil or stay on the same cylinder? Has the coil box gotten wet? Sometimes a spark jumps to ground somewhere inside the coil box leaving a carbon trace which will cause the spark to jump though the carbon instead of going to the spark plug. Have you done a compression test to see if you have lost compression in one or more cylinders. Could be a stuck valve or a blow out of the gasket.
A lot of things other than the fuel system can cause the problem. But from your description, you might have blown something from the sediment bulb into the tank, however the gas would not flow freely if it was blocked. Just a few other things to check.
Norm

[Jim11787]

Is it misfiring on one or more cylinders? It could be an ignition problem. If you swap coils in the coil box, does the misfire move with the coil or stay on the same cylinder? Has the coil box gotten wet? Sometimes a spark jumps to ground somewhere inside the coil box leaving a carbon trace which will cause the spark to jump though the carbon instead of going to the spark plug. Have you done a compression test to see if you have lost compression in one or more cylinders. Could be a stuck valve or a blow out of the gasket.
A lot of things other than the fuel system can cause the problem. But from your description, you might have blown something from the sediment bulb into the tank, however the gas would not flow freely if it was blocked. Just a few other things to check.
Norm

Coil box has not gotten wet. Compression test was 50-52 all cylinders. Swapped in known good coils. Inspected coil box and did not see any carbon traces visible. I think we are going to try and hook up an external gas tank to try it. Can’t figure anything else out to check.

[Jim11787]

Dirt in the tank can drive you nuts if it's too fine for the sediment bulb screen to stop it. There was a loose baffle, which persuaded me to get a new tank. The dirt went with the old tank.

Thanks Steve. I think the next step is hooking up an external tank and see how it goes.

[FundyTides]

You can find anything and everything in an old tank. My second car when I was going to school was a 1939 Chev, just another used car then. A friend and I went deer hunting about 60 miles away. On the way home, the car started running out of fuel and dying by the side of the road. We would disconnect the gas line at the fuel pump and blow back into the tank. The car would run perfect for a few miles and then die again. Finally got back home and the next day we decided to remove the tank. After removing the tank and emptying it, we could hear something rattling around inside. Finally shook the tank enough that a burnt wooden match fell out the filler pipe. Many repeats later, we had collected 6 burnt wooden matches. I would like to know the story behind those wooden matches. Had the previous owner tried to dispose of the car before he gave up and sold it to me? Or maybe some neighborhood kids wanted to start a "bonfie" Who knows? Apparently it's not that easy to set fire to a tank full of gas

[600wt]

Early this century, I was on a tour with the Tennessee T's in my '21 Depot Hack, which was running great. Then it started running rough and it quit running. Had it not been for 2 "older" members (Larry Williams & Lynn Cook) I probably would have used the buzzard truck to get back to the motel. These guys had seen it all! They found that the baffle inside the round tank had come loose and fallen to the bottom of the tank, and was blocking fuel flow periodically.

[Norman Kling]

On one of the "California Dreamin" tours, about half way from the hotel at Buelton to Pismo Beach we passed an intersection with two gas stations. Many of us stopped to fill up our tanks. I went a few miles and the engine quit. I drained the sediment bulb and water ran out. The car ran farther. After a few such episodes it ran fine again. I found out that every one who used that gas station had similar problems, but the ones which used the other station were fine. Sometimes a gas station has a lot of water or sediment in the underground tank. That was the case at that time.
Norm

[nicklm]

After a rebuilt motor was installed our car ran good on bat and when on mag would run bur falter. Went thru as many checks that we thought possible and found the wood block on the firewall had a loose connection that was not consistent. Check for loose wire connections and make good contacts as well as high and low tension wiring. Maybe even looking at the running in the dark for visible sparking between the wiring may help.
Nick

[Jim11787]

Early this century, I was on a tour with the Tennessee T's in my '21 Depot Hack, which was running great. Then it started running rough and it quit running. Had it not been for 2 "older" members (Larry Williams & Lynn Cook) I probably would have used the buzzard truck to get back to the motel. These guys had seen it all! They found that the baffle inside the round tank had come loose and fallen to the bottom of the tank, and was blocking fuel flow periodically.

Thanks. I’m suspecting something similar- something sometimes blocking flow.

[Jim11787]

After a rebuilt motor was installed our car ran good on bat and when on mag would run bur falter. Went thru as many checks that we thought possible and found the wood block on the firewall had a loose connection that was not consistent. Check for loose wire connections and make good contacts as well as high and low tension wiring. Maybe even looking at the running in the dark for visible sparking between the wiring may help.
Nick

Thanks Nick. We did run through a lot of the wiring. Replaced the timer harness and spark plug wires ( and plugs). Checked and cleaned coil box connections. Will run through them again. I wonder if the ignition switch could also be a possibility. Might try to bypass it.

[TXGOAT2]

I would check the ignition switch. Also, if the coil box has wooden parts, they can carbon track internally and cause trouble, especially in humid weather or after the car has not run for some time.

[Jerry VanOoteghem]

You stated that with the fuel ine diconnected from the carburetor it flowed "pretty good". What exactly does that mean? It should flow outwards from the fuel line in a decent arc, and not just a stream falling nearly straight down. Which was it?

Do you have a small lawn mower gas tank, or something similar, that you can hook up as a test, and run gas directly to the carburetor?

[tom_strickling]

Loose or leaking intake manifold?

[Jim11787]

Loose or leaking intake manifold?

Sprayed starting fluid around it and no rpm difference. Thanks.

[Jim11787]

You stated that with the fuel ine diconnected from the carburetor it flowed "pretty good". What exactly does that mean? It should flow outwards from the fuel line in a decent arc, and not just a stream falling nearly straight down. Which was it?

Do you have a small lawn mower gas tank, or something similar, that you can hook up as a test, and run gas directly to the carburetor?

It appeared to flow unrestricted- with an arc and not falling down straight. Still suspect to look into as there may be a baffle loose or other moving blockage that could potentially restrict flow and then clear up again. A friend has a lawnmower tank we may try.

[Jim11787]

I would check the ignition switch. Also, if the coil box has wooden parts, they can carbon track internally and cause trouble, especially in humid weather or after the car has not run for some time.

I’m thinking to jump the ignition switch out of the circuit to eliminate it. Weather here on Long Island has not been high humidity. Can never rule out carbon tracks unless we can see them, but it ran great on a 5 mile test and then 2 days later didn’t want to start and ran rough again. Weather didn’t change in that time period so I’m thinking probably something else.

[Moxie26]

Remove the four ignition coils, check the internal coil box terminals for cleanliness and proper curve spring tension.....also wire brush terminals on the four ignition coils. May need "wood shingle wedges" to snug up coils to insure electrical contact.

[Jim11787]

Remove the four ignition coils, check the internal coil box terminals for cleanliness and proper curve spring tension.....also wire brush terminals on the four ignition coils. May need "wood shingle wedges" to snug up coils to insure electrical contact.

Thanks we had done that. New update. Last night my friend fired it up in the dark and saw plug #1 was weak compared to others. Moved plugs and coils but stayed weak on number one. He leaned against side cowl lamp and got a jolt. Shut things down and looked closer in coil box. He saw one of the mounting head bolts had fractured the wood underneath and penetrated it. He is ordering a coil box rebuild kit. Hopefully the issue.