From Carter BBD to Holley 350 cfm

[Deerhunter30]

I did the carb swap from the stock Carter BBD to a Holley 350 cfm two barrell. I had rebuilt the Carter, but was still not happy with it. It would load up and stumble on climbs. The idle was also bad (some days it would die at idle). It had a surge below 1100rpm and another surge around 1600rpm and a serious dead spot at 2000rpm. With the Holley series 2300 350cfm two barrel, the idle is awesome, there is no surges or dead spots, and it will motor up a steep hill at 900rpm in 4L0 and 1st gear. The motor also has more power now under hard acceleration.

By adjusting the power valve using a air/fuel gauge and a vacuum gauge in the cab I was able to get the power valve to stay closed under normal highway driving circumstances. Here are my gas mileage numbers:
Carter Carb: City 13.6 mpg
Hwy 14.4 mpg
Holley Carb: City 14.2 mpg
Hwy 16.6 mpg
That means a .6 mpg increase in the city and a 2.2 mpg increase on the highway.

 

[Tug-n-pull]

Tell me where you got it the modle number and if you will the cost! Did you have to have an adapter plate? Thanks tug

 

[Bounty__Hunter]

Nice, good to see the results of the upgrade.

 

[Deerhunter30]

Tug,

I did use an adapter. I bought it from Summit Racing (Item # TRD-2086 Large Holley 2 barrel carb to small Rochester 4-bolt, t barrel intake manifold, carb adapter) for $12.75. I think you started a Motorcraft carb change and I am pretty sure that the Motorcraft carb has the same pattern as the Holley so you probably already have the adapter that you need. The carb itself is a Holley Series 2300 350 cfm two barrel from Jegs (Item # 510-0-7448) for $239.99. I also bought a few extra power valves, jets, fuel hose, etc for a few dollars. The total (with shipping) for the carb and adapter was around $270.

I bought a 4.5, 3.5 and 2.5 power valve to help improve gas mileage. Right now I have the 4.5 in, but if I tow a small utility trailer while heading hunting or camping I might use the 3.5 or 2.5. You probably already know this, but the power valve lets in extra gas under a load. The way I selected the power valve was to run a vacuum line inside the cab and hook a vacuum gauge to it. I then got the Jeep up to highway speed (70 mph) and read the vacuum under slight acceleration or a slight incline which was about 6 or 7. Then I took a little off and put in that power valve. The theory is that under normal cruising speed the power valve is always closed. This optimizes gas mileage. If you want more instant throttle response you go higher and if you don’t mind giving some throttle to get acceleration you can go lower.

I also installed an Air/Fuel gauge from CB Performance (http://www.cbperformance.com/catalog.asp?ProductID=598) for around $100 with shipping. My Jeep had an O2 sensor that controlled the Carter BBD so this was a simple install for me. The gauge is not quite as useful as I had hoped. It did help me dial in the correct jets, but I could have probably done just as well by looking at the plugs. I looked at the plugs as I changed jets and would have ended up with the same jets even if I did not have the gauge. Just for information, I discovered by contacting Holley that their carbs are jetted for sea level from the factory, which in my carb was a 61. I live at sea level and ended up with a 60 so it was VERY close from the factory. I also found somewhere that for every 2000ft of elevation increase you should jet down one size. Using that information you should be able to get close to start with.

Next, installing a new three core radiator to replace my wore out two core, and fixing some rust in the driver's side floor board.......it never ends, but sure is fun!

 

[Tug-n-pull]

Thanks Tug