My 61 International Harvester is backfiring threw the intake

[Jmpaulin44]

Hello I’m new here I currently own 61 international Harvester C1 20 three-quarter ton pick up with a 3.9 L in-line six and when I go to accelerate when the truck is warm it is backfiring and popping seems like through the intake and it’s blowing it out to top the carburetor anyway to fix this is it an air fuel mixture issue I’m at wits end my first antique vehicle that I’ve owned any advice or help would be great thank you I will post a video with this so you can hear it 

It won’t let me post the video 

[carbking]

Do a compression test, then an ignition test before throwing rocks at the carburetor

 

And while there are some really sharp folks here, and we are glad to have you; there is a site specifically for the I.H.C. that might have folks that own similar vehicles.

 

IHC website

 

Jon

[Jmpaulin44]

Thank you for the reply from my understanding the ignition is ran by points which I understand is slightly different is that true

[carbking]

Unless someone replaced the points with an electronic whizbang, then yes, points would be in the distributor. If the points go out of adjustment (wear, burn, etc.) that throws the timing out of adjustment. Improper timing can cause an intake valve to be open when a cylinder fires, creating a backfire. 

 

Jon.

[JamesR]

My experience is that an idle mixture that is set too lean can sometimes cause backfiring. It's something that can be fiddled with before more invasive or permanent remedies, anyway.