VCCA Home Forums TECHNICAL - 1945 AND EARLIER 1912-1928 Engine cutting out problem

What would cause my engine to cut out at around 35 mph?

It starts fine, idles fine, revs up fine, and goes through first and second gears fine, even if I wind them out. Get up to 35 mph in high gear and it starts to cut out. No back firing at all.

Everything is new except the wiring. The carb was professionally rebuilt about 2 years ago. I just recently replaced the low speed jet tube in it as the one in it had a fracture running almost its entire length.

What brought that on was a problem with rust in the gas tank. The gas tank has recently been professionally cooked and sealed. I placed a clear plastic filter about 18" from the gas tank. It's not readily visible unless you crawl under the car but it does allow me to look for rust. I see nothing in it.

I also placed a sediment bowl just before the vacuum tank. This would allow me to see any water that might be in the fuel. There is none.

The gas tank work, fuel filter and sediment bowl, and carb work have all been done in the last few weeks. It ran ok for about 40 miles and started this problem again. I say again because it was doing it before.

I'm tempted to say it's an electrical problem and it may well be. A week or so back when all this started "again" it also at one point wouldn't turn over and blew the fuse to the headlights.

Long story short I concluded the problem was in the ignition switch, which needed to be wiggled to work anyhow. I made that conclusion because if I bypassed the ignition switch the starter would turn over. I took it apart, cleaned the contacts and reassembled it. It works better now then ever and even the headlights are brighter. But the engine still cuts out.

It's as if its running out of fuel as it does sputter but does not backfire.

I'm at a loss here. Any suggestions would be greatly appreciated. If I had some C4 I'd consider using it. I'm tired of chasing this gremlin. I want to drive my car, not stare at it and see a bottomless money pit.

The problem you're having where the fuel seems to run out,reminds me of the same trouble I had once.I had one of those disposable plastic filters in my fuel line,and suffered a similar problem.
I replaced it with one of the old style glass bowl sediment filters,and problem solved.I also put another sediment trap between the vacuum tank & the carb,and no more trouble.It's my guess(others may question this),that the modern filters are too restrictive in regards to fuel flow,as they are designed to work with either a mechanical pump,or have fuel forced through them by an electric pump.
But by all means,check the electrics to eliminate any problems there.

I would first look at the ignition system. Points first, then condensor and coil. The engine speed in lower gears is not effected as much by weak spark or mis-timing as high gear. The reason is fairly complicated to try to explain so I won't here.

Typically a lack of fuel or lean mixture will produce a pop or "backfire". It is not 100% but nearly so.

CJ, The problem was there before I put in the plastic filter. I put it in so I could watch for rust and other junk from the gas tank as I have heard too many horror stories about having them sealed.

Having said that, you do make a good point. But I don't think that's the problem. It would certainly be easy enough to remove it and place a piece of fuel line in there to see if the problem remained.

After I typed this in I thought about the points. Maybe they're not set just right. But as noted, everything is new.

I'll check the condition and gap of the points first chance I get

Replace the condensor just for the exercise.

Ok.

It's crossed my mind it may be a weak exhaust valve spring but I don't know how to check that under load. I can rev the engine and hold it at various rpms and not have a problem. Just going down the road and only in high gear.

Would it help if I hit myself in the head with a heavy hammer?

G Day Bill

Sounds to me like its in the fuel system as you have stated that all the electrics have been addressed. I had a similar problem with my 27 Coach and it turned out to be the brass petrol tank fitting was partly blocked and allowed enough petrol to start and idle and run up through the gears but once in top it would starve for fuel. I checked all the fittings on the vac tank and made sure the breather I even put a class bowl filter next to the vac tank to see that the vac tank was cycling through the fuel sucking process and yet the problem continued.
It was not until I took the tank back out that I found the brass fitting outlet on the tank blocked that I solved the cutting out at speed in top gear.
It makes the engine run lean and tends to make the car run hot which gives you mixed messages. One thing I have learnt from years of driving Chev 4's is that it is always very simple, like a blocked line or a spark lead falls off so don't go changing to many things.
Good luck
Dave

hi

- somewhere in the prior post on my choke issue on my 27 sedan someone suggested fill the vacuum tank manually(this should supply enough fuel to last a while I was told) and take it thru the routine see if issue gone, if gone all on engine side of vacuum tank ok etc.

- I have a 6 volt electric fuel pump with regulator, i never installed it as I do not desire modification, but was going to use as diagnostic tool as I am not sophisticated enough to troubleshoot it any other way, I also think fastest way to find issue, In my situation I would assume that continued backfies thru carb after electric pump would most likely eliminate supply problem and point to the valves or leaky head gasket (i sprayed carb cleaner around seam of head and block no change) but because all works good enough to have fun drives with son during day I have saved this project for later.

-I have also decided to take up carb rebuilding and vacuum tank rebuilding as my new winter hobby, gotta get some cores.

-never give up you will find problem

Ken45145

If you do decide to use a 6V elictric fuel pump I suggest you place it near the fuel tank (mount it on the frame behind the right rear tire) I used an AC electric pump that fuel will freely flow through when it is not running. A self cancelling toggle switch (spring loaded) under the left side of the dash can be used to fill the vacuum volume tank. I mounted a diesel truck fuel filter with a replaceable cartridge BEHIND the electric pump. It will catch any rust of crud in the tank. then I mounted a glass settlement bowl with a WIC paper filter on the firewall where the fuel line comes up to the vacuum tank. I used a couple of brass ells the in fuel line goes up to the settlement bowl and the out line to the vacuum pump goes up to the vacuum pump, it works fine. I drain the vacuum pump, carb when I store the car for winter, then when I want to start it up I run the vacuum pump with the glass settlement bowl removed and catch the old gas in a small coffee can, I run the electric pump to clean out the fuel line, then replace the glass bowl and a fresh Wic filter and run the electric pump to put some gas in the vacuum pump and then start the car. I planned to only use the electric pump to fill the vacuum tank on a long up hill climb when the manifold vacuum is low, however I have never had to use the electric pump, as my vacuum pump handles the fuel delivery to the carb fine. When I start to work on the 28 (lube and oil change) I will try to get some pics.

I would check for fuel flow at the carb and also from the main tank. Pull off line and slip on a rubber hose that fits and let it syphon. do that for both the vac tank and the main tank. It should flow a stream the size of the tube for a long time from the main tank and till the vac tank emptys. You could have some crud in a line that doesn't let the full amount through, or a kink in a line and possibly crud build up at the kinked spot, BUT if you say it isn't backfiring at the carb then a lean condition right before it dies may not be the problem. Listen to it real close as it may be hard to hear it backfire at the carb at that speed and may be just a light pop. I just say that because my hearing isn't what it used to be and it may just do it once at that speed before it dies, May help to have a good set of ears ride along if yours are like mine. Another possibility, Weak spark. A weak coil may not have enough juice to jump the gap when the cyl pressure is higher. Remember air is an insulator and high cyl pressures with throttle open = more air, more air = higher resistance. Another possibility is if you have the small diameter vac tank, not the fat one like on some 28s but the skinny stewart tank there was a special fitting used where the vac line goes into the intake that had a tube that went down a couple inches into the air stream from the carb. Might be something to look at but I would think vacuum is vacuum and the tank would still pick up the gas. Anyway Chevy did put those in some cars with the skinny tanks for some reason. For another reason they didn't use them in cars with the fat tanks. You might also fill the vac tank and then hook up a vac gauge to the fitting that goes to the main tank and see if it is pulling vacuum good. It should pull about the same as it will at the intake fitting! What ever the problem is you sure will feel good when you find it! My 24 Olds ran like crud for 9 years and the problem turned out to be a weak coil and the wrong plugs in the engine. (Needed long reach plugs and it had short reach) It would start better with the coil change, And the plugs took care of the low power and rough idle and running. I didn't change either for all those years because they were new parts when I got the car. Just didn't think they were bad so I did everything else and nothing worked. Last year at the Newport Hillclimb it ran 112 seconds, This year with only the plug change it ran 59 seconds. Much better!

Mack, here's my sediment bowl.

sounds to me the fuel tank may not be venting,this is when the fuel level drops, in the fuel tank ,and it is causing a vacuum in the fuel tank and this is fighting the vacuum from the fuel pump,check the vent hole in the fuel filler cap that it is not blocked up with dirt or crud,or easy test drive with cap loose,or off,so it vents tank.

I would try running the vehicle without the inline fuel filter installed. You're asking a lot of the vacuum fuel pump to operate correctly with the filter installed, especially up so high in the system.

Here's what I've done so far.

I checked all the electrical connections and cleaned them. That didn't help.

I removed the bowl from the carb and found very small amounts of a very fine dirt that appeared to be metal as it was shiney. I removed the carb and sparyed everything down with B12.

I then disconnected the fuel line from the modern filter by the gas tank. I allowed the fuel to flow through the filter. It flowed quite freely.

I then disconnected the fuel line from the vacuum tank on the gas tank side. I wrapped a clean, white, cotton rag around the other end of the fuel line and using a compressor blew it out. I did not find any dirt on the rag. I then moved the rag to the other end and blew the line out again. Still, I did not fing any dirt on the rag.

Then I removed the inner tank from the vacuum tank to look for rust or dirt. I saw none but did take note that there was very little fuel in the lower chamber and none in the upper chamber.

This is the 4 screw vac tank. The shut off valve on the bottom of the inner tank looks to be no more than a fiber board. It moved freely but only a little. I have no idea how much it is supposed to move.

I went to clean it out, using B12, and noticed that the B12 would flow very slowly out and sometimes not at all. I tried to clean it and free it up some but could not.

Fortunately, I had another. The second one allowed fuel to flow freely passed the fiber board valve.

I sprayed liberal amounts of B12 on the mechanisms that attach to the float in the vacuum tank and gently wiggled them hoping to remove any dirt that may be there. I then reassembled it and reattached the fuel lines to it.

The gasket appeared to be very old and thin so I made a new one from paper gasket material about 3/32" thick.

Then I removed the lines from the vac tank to the carb amd also blew them out.

Meanwhile, an older mechanic suggested the coil was overheating, even though it is a new one. The coil sits on top of the oil filter. He told me that the next time it quit to put hands on and see how hot it was.

The car started and ran fine, until I took it down the road. Again it sputtered out. The coil was very hot to the touch. Hotter than the oil filter. So I raised it about 1/4-3/8". This would allow air to flow between the coil and filter.

Then I removed the bowl from the carb and found more, but not as much, of the same shiney "dirt" I had found there before. I cleaned it out, replaced the bowl, and drove away.

No problems this time. After 30 miles I removed the bowl from the carb again and again found more, but even less of the dirt. I drove about 40 miles with no problems and again removed the bowl from the carb. This time I found only a very tiny am't of the dirt in the bowl. I have now put 90 miles on it without it sputtering out.

What was the problem? I'm not sure. It may have been a combination of things.

Where did the dirt in the carb come from? Damifiknow. I have trouble imaging it getting past a brand new modern filter as well as the sediment bowl, which shows no dirt at all.

Could it have been the gasket in the vac tank? Maybe. It was rather thin and old.

Have I fixed it? Let me drive it another hundred miles or so before passing final judgement. Meanwhile, it seems to be doing just fine.

Having said that, I'll wake up tomorrow only to find all the fenders have fallen off, the tires will be flat, the seat fallen through the floor, the steearing wheel in pieces, and gremlin poo all over everything.

I think you corrected the problem(s) as much as the gremlins will allow. Seems that the shiny contamination was the majority of the problem and slow draining of fuel from the internal vacuum tank contributed. Popping back is a common symptom of lean gas mixture. Weak or incorrectly timed spark is the other common cause of "backfire". The best advise I got was to do the simpliest and cheapest first and then move to more difficult and expensive. You will kick yourself all the way to the bank if you replace expensive parts needlessly.

The question begs, where is that shiney contamination coming from? I went about 60 miles today without a problem. I haven't checked the bowl yet but before I left I did and there was just the tiniest bit there. Every time I check there seems to be less and less.

I do agree, that regardless of the source, that contamination was most likely the problem.

I don't have a clue to the source of the shiny stuff. Have had four calls from a VCCA member in Georgia that is finding teensy shiny particles in his '31 carb bowl. Rebuilt carb in May, cleaned and sealed gas tank, new or cleaned fuel lines and rebuilt fuel pump. Everything ok until a short while ago. Then noticed hesitation and popping and lack of acceleration. Checked and accelerator pump worked sometimes and others did not. Has removed the carb several times and only found some really small shiny particles. Blew out, cleaned out carb, lines and getting improved performance but still not back to fresh rebuild. Wonder if it is something in the gas you SE US folks have gotten post IKE?

We don't have any E gas here....yet, but it is coming. Just the same, you may have a point. I think just for the heck of it, I'll try another station for awhile. The one I use has a large amount of gas customers. I'm going to assume they have a lot of deliveries, which may keep sediment stirred up in their tanks.