Jets For A Holley 390

OK you altitude guys, setting my new fourbbl for Colorado. I think carb comes stock with a 5i. What jet works for the Colorado high country?

Fltfndr

 

The jets from the factory will undoubtedly be too rich for your altitude.But the factory configuration will typically run without changes.

Jets should be available at your local speed shop. It's got to be a 2-digit number, say 51. Run it and look at the plugs. Too rich, go a couple of steps smaller to 49s. Rinse and repeat.

The alternative is to get a wide-band O2 sensor like the Innovate Innovate Motorsports Wideband Air/Fuel Ratio Tuning and add a bung to your exhaust for the sensor. Then you can dial in the mixture very easily.

 

Right you are Tim, factory configuration will do fine. I've had my Holley for years. From negative elevation at Salton Sea to over 10,000 Ft in the Sierras or White Mtns. I tried 51 jets and 49. Both are in the neighborhood.

 

It's better to be too rich than too lean...I live at 6500 ft and all the trails I run are much higher than that. There's a couple of trails in Colo that top out on 14000 ft peaks. So, my jetting is never "right".
Another important thing to consider is timing....you need at least 6-8 dergees advanced over the stock setting, more if it'll take it. IIRC i'm running at 18 degrees initial timing.

 

I took my 66 cj5 to the Rockies last summer. The guys here helped a lot do some searching for mntbuggy and you can find the links. Mine is a v6 with a offy 360 , Holley 390, mild cam fresh build. I cranked up the advance as recommended above and ran 49 jets. The worked great except for going over trail ridge road 12,183 ft. Seemed to Get flakey around 11,000 feet. Was able to keep it running but had to have my foot in it. If I was going to do it over I would probably put 47 jets in it and maybe not put as much timing in it. Good luck

 

Might add I was staying at Estes park 8,000 ft then went to black hill SD, 3-7,000 ft. The Jeep did fine in these lower elevations.

 

Not to add more confusion but my distant memories of running Holley's at high altitude also include changing the power valve.
Not remembering the numbers but it seems to some Holleys came with power valves that would open in the 12" vacuum and up here we only start with 15 or 16" where sea level is 20+".
The result is dumping gas in with the slightest load. Seemed like something in 8" range was the magic trick.

 

The 0-8007 Holley comes stock with a 6.5 power valve.

 

I figured you'd know.