I have a 79 f100 longbed single cab, 300 standard. Pretty much stock just switched to a holley 500cfm carb 1442-2 no choke yet. Offy c intake, dual efi exhaust manifolds now I cant get the truck to idle under 2500rpm. Main jet size 65, power valve is 6.5 the screw is all the way out on the curb idle, adjustable screws on side are all the way in, I adjusted float according to rebuild kit, fuel pressure reg is at 5psi. Any thoughts on what im doing wrong? Carb came off a ford 2300 racing motor off one of my mini stocks. Any suggestions on jet sizes?

 

Is the throttle linkage set up in such a way that it won't let the carburetor's throttle arm return fully?

 

Vacuum leaks? And verify with the Holley Techs what the float setting is supposed to be.

 

The linkage is not hooked up and it is closed all the way. Just checked no vac leaks checked with carb cleaner. Only vac line goes to distributer

 

Check for vacuum leaks with WD40 or carb cleaner. Go slow. You must be leaking air at a pretty good rate for a 2500 rpm idle. Are there fittings manifold or at that base of the carb that could be leaking?

This is a 2bbl on an adapter, right? Check those seals, you have more gaskets to worry about. I used to have to use two gaskets to bridge the imperfections on my 289 2v.

 

At 2500 RPM your idle screws are useless , you are running on the main system . Take the carb off and check throttle blades to insure correct transfer slot adjustment . I think they are open to far could be bent , loose , not centered or because of its racing history have holes drilled in the throttle blades . for some reason your pulling air / vacuum

 

Ok there is a 1/8th in hole drilled in the blades and backs are bent up. I figured it was common for the carb I used to have a carb guy he could tune the **** out of them now im just having to learn what I didn't pick up then

 

Those modifications might be great for racing but for street use, not so much.

 

Thanks a bunch ill change those out and see what happens. Never would of figured that out been staring at it for a week.

 

Glad you got it , stock jet size for a 4412 =500 CFM Holley is 73 ,nozzle [squirter] is .028 .Let us know how you make out

 

Swap it for an Edelbrock.

 

Got an eddelbroc 600 4 barrel laying around to any reason you suggest going to that.

 

Edelbrock carbs generally run well enough out of the box and are so simple. I've been running a 500 cfm on my 300 for years and it's reliable as clockwork. The primaries on the Edelbrock 600 are probably smaller than the bores on a 500 cfm 2v, so maybe even a little crisper off idle and better fuel economy too.

 

Went ahead and switched to the edle 600. Twisted off a bolt in the holley. Fired right up idle at 500 rpms but falls on its face when I rev it. So im off to search the internet to learn how to play with the 600. Never had one opened up this one has been on the shelf for 2 years I tend to stick with what im used to so im out of my zone on this

 

First thing, look down into the primaries and work the throttle linkage to confirm the accelerator pump is giving a good shot. If not it may need a new plunger. Moving the linkage to the top hole in the pump arm will give the biggest shot.

Try going richer on the idle mixture screws as well. Keep backing them out 1/4 turn at a time until the idle speed stops rising, then tighten down 1/4 turn.