First, I couldn't think of a better title for this post. Second, I put a 86 300 in my 79 bronco....I bought a new '79' duraspark distributor, rebuilt the non-emission 1bbl carb (off a '78' 300)put that on with no EGR, manual choke, kept the 86 coil w/pigtail wires, added on '89' EFI exhaust manifolds w/ walker downpipe & 2.5" exhaust out the back w/ 1 muffler. I still used the C6 and NP203, w/3.50 gears and 265/75/R16 tires on 16" aluminum wheels. I have no emissions sticker on the valve cover since it's an 86, so I timed it to the '86'year spec in my chiltons @10 BDTC. However, with the '79' dist. doing the work, and that there's no emissions whatsoever, I believe the timing should be changed to the year of the dist., which my chiltons only says to go by the emissions sticker....which there is none. So my question is what should the timing be set at? I'm getting 13 mpg on the highway @ 55 mph, and after reading about most guys getting towards 20 mpg, I figure something must be wrong. I also plumbed the vac. advance to the manifold tree, since the carb. port didn't show vac. on the gauge til you redlined it. There's no hot-water plate or cover on the intake manifold either, as this was tested at about 10-25 degrees F. Any suggestions would be greatly appreciated.

 

From the factory, the distributor used ported vacuum, meaning the vacuum port you use for vac advance, should NOT have vacuum at idle. Running full advance at idle can affect mpg.

10 btdc is about right.

 

I have no vacuum on the gauge from the dist. port(it's labeled that on the carb) until I hit about 2700 rpms. It goes from zero to in the green instantly, even though I only gradually increase the throttle. But on the intake tree, it increases smoothly with the pedal. I know, it doesn't make sense to me either. That's why I was wondering if having no egr or no plate/cover under the intake(where the old stock exhaust man. fit) made a difference or not.