ClassicOldsmobile.com - View Single Post - L69 Tri-Carb vs. Pontiac Tripower

aliensatemybuick · 03-05-2008, 06:01 PM

I'm no expert on Pontiac tri-powers, but I am surprised to hear that they would use a vacuum source from the front carb. My understanding is that on the Olds setup, the vacuum source for the dist. advance is above the throttle butterflies (i.e. "ported"vacuum) so that unlike manifold vacuum, it is lowest at idle and then when the throttle plates are opened acts more like manifold vacuum. So if using a ported vacuum source, I would expect it to be from the center carb. On the Olds setup, the outer carbs don't even kick in for a significant portion (something like 60%?) of accelerator travel / throttle movement on the center carb, and I'd expect the same to be true for the Poncho. So I would wonder how vacuum from an outer carb (front OR back) would help regulate dist. advance.

Are you sure its not the power brakes and not dist. advance. that draw vacuum from the front carb on the Pontiac setup?

03-05-2008, 06:01 PM	#2 (permalink)
aliensatemybuick Member Join Date: Jul 2007 Posts: 45	I'm no expert on Pontiac tri-powers, but I am surprised to hear that they would use a vacuum source from the front carb. My understanding is that on the Olds setup, the vacuum source for the dist. advance is above the throttle butterflies (i.e. "ported"vacuum) so that unlike manifold vacuum, it is lowest at idle and then when the throttle plates are opened acts more like manifold vacuum. So if using a ported vacuum source, I would expect it to be from the center carb. On the Olds setup, the outer carbs don't even kick in for a significant portion (something like 60%?) of accelerator travel / throttle movement on the center carb, and I'd expect the same to be true for the Poncho. So I would wonder how vacuum from an outer carb (front OR back) would help regulate dist. advance. Are you sure its not the power brakes and not dist. advance. that draw vacuum from the front carb on the Pontiac setup? Last edited by aliensatemybuick : 03-05-2008 at 06:39 PM.