I've had my 1986 460 powered E350 cutaway camper van for about 10 years now and all the while it's had a bit of a lump at idle and a big flat spot right off the line.

The secondaries seem to come in at about 3,200 RPM and it runs up to 4,000 RPM fairly quick under heavy throttle. It doesn't want to go beyond 4,000 (seems to run out of air) but that doesn't bother me 'cause I never really push it beyond 3,200 RPM anyway.

I generally get about 8 MPG and it doesn't seem to matter whether I'm towing a 3,000 lb boat or not, and I think I got closer to 10 MPG before the E10 fuel came along...

Other than the lump at idle (more pronounced now that I've replaced the motor mounts), and the flat spot off the line, I'd say it runs fairly well.

I suspect an idle mixture adjustment would help the lump at idle but since the mixture screws are blocked off/plugged (which seems a bit of overkill since they're pretty much impossible to get at with all the stuff that's in the way anyway) that's not an option.

It's got 90,000 miles on it and I know I've never touched the carb for the 10 years I've owned it and looking at the thing I'd say it's never been touched.

The carb is a Holley 4180 and it has the following stamped on the air horn:

E5HE-9510-ED
List -50260-3

I found another carb at the junk yard with identical numbers and I've been slowly cleaning and rebuilding it.

Part of me says "if it ain't broke, don't fix it" and to leave well enough alone, but another part says "with a rebuild I'll be smokin' the duallies off the line and getting 15 MPG!" (every man should have a fantasy LOL).

The junk yard carb that I'm rebuilding has the idle mixture screw plugs removed and I'm particularly curious where I should start with those. As I said, since the mixture screws are in the throttle plate (not the metering block) it's gonna be tough trying to adjust them once it's on the vehicle and I'm hoping to get it right the first time. FWIW the mixture screws were out three turns when I pulled it off the donor vehicle...

So what do you guys think? Should I bother? Any advice for a fella rebuilding his first 4 barrel Holley?

 

You will definitely see an improvement with a carb rebuild. The junk gas they sell now is really hard on carb parts, and the newer kits come with upgraded rubber to handle the alcohol in the gas(so I am told).

I would turn the idle adjustment screws in till they stop, and then back them out 1 1/2 turns each and start from there. They make special tools to adjust these hard to get at screws, maybe you can try a local Napa and see if they sell one. They are usually a flexible looking screwdriver with the correct tip on it.

Do not take the old carb off and plop the new one on right away. Mark all you lines carefully, and get ready to replace some of them if they look old and squishy or hard and cracked. Keep going and pull off the EGR plate if yours is setup that way(a spacer plate under the carb). These things are famous for rotting out and burning out the gaskets. We had a guy on here with the same setup as you, only his was a RV. He found his spacer was burnt out, and had to build it back up with JB weld and file it down so it would seal again.

This is the great thing about doing something like this yourself. You can take your time, and really go through this thing, checking everything out to make sure it's ok. Don't get in a hurry.