Backfire from down draft tube.

[Noah H]

I have pin pointed my backfire/popping noise is coming from my road draft tube

 

when I start the car/once it’s running few seconds it pops then runs fine after it’s little hiccup.

 

Is there something clogged in there? I have stuck my hand underneath and can definitely feel the movement of air coming out when it pops. 

[Sniper]

You have a serous issue if there is enough gas getting into the crankcase that it will ignite.

 

Do a compression test and look at your carb to make sure it's not dumping fuel.

[TodFitch]

As @Sniper notes, you have a very serious problem if there is that much gasoline vapor in the crankcase. In addition to the checks suggested by @Sniper take a look at your fuel pump: A bad diaphragm in the pump can leak gas into the crankcase.

 

Whatever the cause, fix it ASAP as sever damage to the engine and car could occur if you have an explosive mixture in the crankcase.

[knuckleharley]

Check the oil to see if it looks thinner than usual and/or smells of gas BEFORE you try to start the car again. If either is the case,I would suggest the first thing you do is pull your oil pan and thorougly clean it before putting it back on and filling it with oil.

 

The second thing I would do would be to check the carb to make sure it is shutting off the fuel when the engine isn't running. You can best do this with the carb held in a vise and a bucket under it to catch any gas.

 

Finally,have you modified the fuel system with an electric fuel pump? If so,how much PSI does it put out,and is it adjustable?

[Noah H]

On 10/2/2021 at 6:16 PM, knuckleharley said:

Check the oil to see if it looks thinner than usual and/or smells of gas BEFORE you try to start the car again. If either is the case,I would suggest the first thing you do is pull your oil pan and thorougly clean it before putting it back on and filling it with oil.

 

The second thing I would do would be to check the carb to make sure it is shutting off the fuel when the engine isn't running. You can best do this with the carb held in a vise and a bucket under it to catch any gas.

 

Finally,have you modified the fuel system with an electric fuel pump? If so,how much PSI does it put out,and is it adjustable?

 I have not modified the fuel system at all. 

[Noah H]

On 10/2/2021 at 6:16 PM, knuckleharley said:

Check the oil to see if it looks thinner than usual and/or smells of gas BEFORE you try to start the car again. If either is the case,I would suggest the first thing you do is pull your oil pan and thorougly clean it before putting it back on and filling it with oil.

 

The second thing I would do would be to check the carb to make sure it is shutting off the fuel when the engine isn't running. You can best do this with the carb held in a vise and a bucket under it to catch any gas.

 

Finally,have you modified the fuel system with an electric fuel pump? If so,how much PSI does it put out,and is it adjustable?

While I look down carb throat immediately after I shut down I see vapor with the throttle closed. My oil smells normal with no gas smell. 

[keithb7]

Consider performing a search for a local oil lab. Take an oil sample into them. Costs about $15. They can tell you if you have fuel dilution. Also the oil viscosity. Also if there is coolant, iron, tin, lead, chrome, copper, whatever, in your oil. Then you'll know whats getting into your crank case.  Left alone, bearings and cylinder walls can be wiped out.

Edited October 4, 2021 by keithb7

[allbizz49]

Check your timing. Points too. I have to think if you have fuel getting into your crankcase, your oil level would be high, thin and/or smell like gas. I had a 218 that backfired and blew the oil fill cap off due to wrong timing. I bet it blew out of the draft tube too but the cap was closer to my head so that's all I was paying attention to at the time.

[Adam H P15 D30]

Old mechanical fuel pump leaking into the crank case?