Acts fuel starved after 10 minutes

[nkcarizona]

'29 roadster was running great, but with fuel leak at tank valve. Replaced interior fuel line and fixed leak, but a cheap rebuild on Tilly carb with brass inlet fitting failed. Replaced with another rebuilt Tilly that I worked over to get the two halves flat.

Now the car runs great for about 10 minutes or 5 miles. Speed doesn't seem to matter. Then it bucks and acts fuel starved. If I wait a few minutes it will run for a short distance then start bucking again. By stopping and waiting, I can get home again.

The coil is very hot, not sure if this is normal. I replaced the coil (mounted upside down) with another I had around, but this did not help. It doesn't seem to be a coil problem because it starts up and runs fine for a short while after waiting only a few minutes.

I have checked fuel flow to the carb and it is fine, no blockage from filter or valve or tank.

Have also gone through the carb several times to make sure all jets are clean, etc. Doesn't seem like jets are the problem since it runs great for the first 10 minutes. Also checked the float level.

Any thoughts???? I need some ideas.

[Mitch//pa]

Try loosening the gas cap
Make sure the fuel line is not extending to far past the ferrule on the carb line

[markyb]

how do the plugs look? If sooted up, maybe TOO MUCH fuel. at least it might lead you closer to the problem. I had a carb rebuilt by a shop and they installed the wrong GAV valve, was too short and allowed too much fuel, sooting up the plugs and at speed bucking and spitting. Since you've swapped carbs, probably not the same problem, although maybe carb related...good luck

[pooch]

Check points for correct gap and for burning .

Check charge rate of generator.

Check if you can or change condenser .

I had same problem and was sure it was fuel, but it turned out to be powerhouse putting out 18 volts to a 12 volt battery and burning the points.

By the time I dismantled the carb many times by the road, all had cooled down enough for me to drive off going great,and thinking it was a carb issue , until it kicked and bucked and backfired 10 minutes later .

I diagnosed it by plugging a timing light into the coil wire and driving it.

After 10 minutes, the light started flashing erratically .

[Purdy Swoft]

In hot weather, I am told that ethanol gas can cause vapor lock .

[Purdy Swoft]

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Originally Posted by pooch

Check points for correct gap and for burning .

Check charge rate of generator.

Check if you can or change condenser .

I had same problem and was sure it was fuel, but it turned out to be powerhouse putting out 18 volts to a 12 volt battery and burning the points.

By the time I dismantled the carb many times by the road, all had cooled down enough for me to drive off going great,and thinking it was a carb issue , until it kicked and bucked and backfired 10 minutes later .

I diagnosed it by plugging a timing light into the coil wire and driving it.

After 10 minutes, the light started flashing erratically .

A fun projects can style voltage regulator would have solved the overcharging problem. I also run 12 volts with an original generator and the Fun projects regulator is the only mod to the charging system.

[Mike V. Florida]

Sounds like a bad coil as it should not be real hot.

[700rpm]

Originally Posted by Purdy Swoft

In hot weather, I am told that ethanol gas can cause vapor lock .

Purdy, I've always been skeptical of the vapor lock phenomenon, but I may have experienced it today. 93 degrees and a 20-mile drive, and the coupe started to cut out like it was starved for fuel. I stopped, let it cool down, and went on for another 15 miles and then the same thing. I put some MMO in, and some non-ethanol gas, and got home the last ten miles, almost without trouble. A little sputter about three blocks from home.

I opened the hood, and both the coil and the condenser were very hot. I have a waffle-type manifold, but no cover, so I expect the condenser to get hot.

I replaced the coil, and we'll see what happens tomorrow, but it may have been vapor lock, or coil, or condenser, or gremlins.

[Purdy Swoft]

Ray, I too have been skeptical about vapor lock with model A's. They always told me that cars with gravity flow instead of fuel pumps couldn't get vapor lock. Its the ethanol that causes the fuel to boil at a lower temperature. Some have reported hearing the gas boiling in the carburetor. The waffle exhaust manifold can't help either way in summer heat. Good luck.

[37Benny]

here's a trick that worked on a '31 dodge brothers and my '70 valiant when i get bad gas, 1st take the idle air mixture screw out the carb with either a can of carb clean or compressed air (if you got an air compressor?) just spray inside that hole then put the screw back in, i usually screw it all the way in then back it out with 3 turns with the screw driver..then see if she fires off..Good Luck Benny

[johnbuckley]

as other have said - causes of overheating coil .... 1) possibly poor coil, 2) possibly poor condenser . 3) (and this has caught me out 2x in my life) condenser not earthed properly. 4) 12v through a 6v coil (or if someone's been messing , a ballast resistor is needed for this particular coil!). ...and since you have eliminated gas tank not venting and the carb/fuel supply I reckon ignition is probable culprit... after all it's gotta be one or the other!

[Purdy Swoft]

Not sure what the problem is but.. If it is running an A&L short proof condenser, the condenser ain't the problem. If it is indeed vapor lock, stick a few wooden clothes pins on the fuel line. The wood pins will help cool the fuel line like fins cool an air cooled engine. That is what we did with other cars with vapor lock back in the day.

[vermontboy]

You can also use a "cool can" around the fuel line filled with ice - a friend made a coiled fuel line (looked sort of like a still) that fit inside the can.

[Purdy Swoft]

The cool can was popular when drag racing in the 60s .

[nkcarizona]

Thanks for all the suggestions. I did not have a chance to get back to the problem until today. Loosened the gas cap, attached the timing light and took a drive. Turned out to be a short one. Within a mile it started acting up, no irregularities showing on the timing light. To get back I had to wait a minute, drive a bit,wait, drive, etc. I have practiced this many times now.

Definitely seems to be a fuel problem. I will make sure the fuel line is not too far into the carb tomorrow.

Any other thoughts? A problem with the float and inlet valve? I made sure the valve was clean the last time I had the carb off.

[29 Tudor]

Have you dropped the plug under the main jet and measured the fuel flow you are getting THROUGH the carb? That will quickly tell you how much fuel you are getting to the carb. A little math will allow you to determine if the flow will support the engine at given speeds. I did that with mine and wrote it all up a couple of years ago. I'm sure you can find my analysis with the search function. In my case, I had a bad needle and seat that would not flow nearly enough fuel to support the engine's need when climbing a hill.

Easy to measure and will give you a wealth of knowledge.

Steve

[Purdy Swoft]

My september 29 did that way back when I was a kid. Back then the stand up filters that fit in the gas cut off valve wasn't available. Horrie at City Welding and Machine took me aside and showed me how to install a stand up pipe in the gas valve under the tank and it solved my problem. Now that mesh stand up filters are available, I use them in my model A's. That may not be the problem but it sure can't hurt. A bad V8 or old original style condenser can cause the same symptoms.

[Tom Wesenberg]

Do you have a Zenith carb you can try?

If you had a Zenith carb giving trouble, I'd say check the screen at the carb inlet, but I'm not sure the Tillotson has the same screen.

[29 Tudor]

Oops... Didn't remember he was running a Tilly. I was referring to the main jet plug on a Zenith. I'm not familiar with a Tilly.

SD

[Purdy Swoft]

Tillotson carbs also have a plug under the bottom that will work the same way.