First off, It's has been toooooo long since I've been here. My van has been neglected sitting in the covered car port for yeaaars. This was partly due to medical issues and driving, and a leaky "freeze" plug but that's been remedied and no one called Van Protection Services on me.
I need some advice on troubleshooting what may be a carb issue. This carb was replaced years back, but still, didn't drive the van much after. As a newbie on engine troubleshooting, I'm not going to try to explain, rather here are some youtube links of the issue.
Prior to firing this van up again the oil / filter and fuel filter have been changed. I can't rule out the fact that the van has a little old gas then new gas mixture and i added fuel preservatives. But I do recall this problem before the van went in to "hibernation" though.
Maybe a valve not closing. The ignition is off, the cylinder compresses but the intake valve is not fully closed allowing it to blow back through the intake manifold like that. I would try a compression test and see how you get on. i would also check the timing is on point
Disclaimer- I do not know what I am talking about and on average it takes me about 6 months to figure out and fix what is wrong with my vehicles
Thanks for the reply KogonDodge, I'm way late on posting an update.
So it dawned on me- The van is running @ 1500 varying to almost 2000 RPMs while in park. I know this can't be the RPM's to have when idling in park. Looking on line I learned of condition called "Dieseling" in which best described the issue I was having and how high RPM's can cause it.
Turned out that the carburetor linkage was sticky and was not fully relaxing onto the Idle screw.