Carb questions

Ok I bought my jeep from the PO with a offy intake and a holly 390 carb, the 258 engine is all stock and running really rich my plugs are smut black not wet with oil just smut. I can replace the plugs and its ok for a few days but right back to smoking at idle and plugs are just nasty, not to mention I cant let this thing idle in my garage even with the door open it will smell up the house and the garage for weeks if I do. I have been told that the carb is to big for a stock 258 and looking to down size, so my question is do I need to loose the intake to and start all over with stock intake and a different carb or can I keep the intake and buy a adapter? I also spoke with Weber and they said there carb want work with the offy intake and I spoke with Howell about the fuel injection kit and they make an adapter for the offy but its 1000 bucks. I also have a friend with a 84 ford truck with a motor craft 2 barrel not sure if it’s a 2100 or 2150 but its only 8 months old and he wants to swap carbs but will it work with the intake I have. Sorry for all the questions I don’t have a clue what I need to do and one person tells me one thing and someone else tells me another and im confused so figured I would talk to guys that actually have jeeps.

 

A Holley 390 cfm carb is not too much for a stock 258. I would say you have some jetting issues, a float level set too high, adjustment issues, etc. The Motorcraft 2 barrel may be too large if it came from a V-8. If from an inline 6 like a 300 or similar it should be ok as far as cfm goes. There are different sizes. Jetting could be an issue as well with those to match your engine's needs.

I'd start with your existing carb and do some checks on it. Also, the needle and seat could have some crud holding it open not allowing it to shut of fuel flow when the float bowl is full. I'd start there.

 

Blown power valve? Huge main jets?

Holleys are easy to rebuild and simple to tune. I suggest you get a kit and a book and try to repair and/or adjust the 390 you have.

I'm not a big fan of the street Holleys for a Jeep, but they can be tuned to work beautifully on the pavement. It seems to me that swapping for another carburetor without understanding what's going on, you'd likely be trading one set of problems for another.

 

Blown power valve would be my guess, too.

 

My jeep diid the same thing. if started in the garage it would make those in the house come out and say shut that thing off, your stinking up the house. I had about 3 people tell me my carb was shot. I even took it to a shop to have adjusted and they said it needed rebuilt or replaced. I have a 650 holley on a sbc, and knew nothing about carbs at the time. I bought a rebuild kit and gave it a try, I thought I cant make it any worse. It is very simple to do, and I am learning to tune it very well. Go for it, and just rebuild it. When you adjust your air/fuel mixture screws, bring them out about a turn to a turn and a half each. It was real simple, pretty much gasket replacements and unsrew the power valve, screw new one in, couple other little things. rebuilding saves you a tone of money... Oh, The gas fumes are gone, and it runs so much better. I do have a small vac leak at the throttle shaft, but still runs well enough not to buy a new carb.

 

Thanks for all the replies i will work on getting a rebuild kit and some instructions and jump in. Im also sure it has the factory 52 jets the PO wasnt that savy i have had all kinds of issues from him trying to fix things guess thats why they call them projects