Join Date: Sep 2017
Location: cincinnati, ohio
'69 351W Holley Carb Jet Sizing
I have a relatively stock 351W in my my car. The only mods to it are a Holley 750cfm vac secondary carb, Edelbrock dual plane intake, Ignitor II igntion and dual exhaust. I was, and to some degree am still having problems with it heating up on the highway. I have replaced the t-stat, upgraded to 3-core ACP radiator, has good fan clutch, has fan shroud, etc. A guy was trying to help me and recommended I pull the plugs to see how it was running thinking that it running lean could be causing it to get hot. I pulled the plugs and the porcelain was white, no color at all. The carb had 70 jets in it. I've since upped the jets to 75s and the plugs are still pretty much white; they have a little color to them but not much. The car is getting kind of crappy gas mileage I think, anywhere from 8-14mpg and to get the 14mpg I had to baby it pretty good. The 8 was from when tuning, setting timing, and accelerating moderately aggressively on the highway, running 65-80.
For some reason it seems this engine just loves to drink fuel despite it not being built up much. When I put the carb on initially it would stumble, pop up through the carb, or stall if you stabbed the throttle from a stop. It ended up needing the 2nd biggest accelerator pump to correct this.
I was thinking about swapping the Edelbrock 600 off my Jeep onto the car to see if mileage increased but I almost hate to do that since the driveability is great on the Holley and it's dialed in for the most part.
My question is: do you think I need to step up to the 77 jets based off my spark plug readings or is there something else I should be looking at to determine if it's running too rich or lean?