I've got an 85 van that came with a 305. It has a Rochester Quadrajet with numbers 1708226 and 905 HLY stamped on the identification column. From doing some research it looks likethe same 4 barrel carb used on 80s camaros.

The problem is that it idles WAYYY too high. I would guess 2-3k rpm.

I have my suspicions about vacuum leaks causing this. Would it be possilbe to just plug off the 1/2 dozen or so vacuum ports coming out of the carb to narrow this down? Or does plugging EVERYTHING off cause other problems?

What about the electrical crap on these carbs? Would disconnecting everything cause drivability problems? I dont care about emissions, performance or terribly aweful gas mileage at this point. It is simply a vehicle to haul my F-body around. Thanks!

 

Does the choke work?

 

Is that the flapper on top of the primaries? It was wide open today when I took the air cleaner off to have a look. As far as I know it is open all the time.

 

Yeah, it's the flap inside the choke tower over the primaries. When the choke is closed, the fast idle cam raises the idle speed, but if yours is staying open then chances are that's not the problem. Have you tried turning the idle speed screw out?

 

NO I haven't. But there is a story behind this problem. The engine in the van is a donor from my Camaro. THe van engine had a spun bearing so we replaced it with this working engine from my Camaro (same engine size btw). The van was idling and running fine before the swap. But the engine swap required swapping the intake manifold and unhooking and rehooking up all of the little emissions stuff, which I'm sure was not done right.

My buddy just gooped some RTV on the engine instead of using a real intake man. gasket so I am very suspicious that there is air creaping in where the manifold meets the engine.

I'd like to do a vacuum test, but I don't even know what port on this Q-jet would give me a full vacuum reading.

Thanks for the help so far and I'm open to any ideas you guys have!

 

To start with you might want to reinstall the intake properly before you even bother looking at anything else. An intake gasket set costs all of maybe $10, so I don't know why anyone would only use RTV.

 

Ok I just went out and hooked up the vacuum guage to the brake booster port. It read a solid 20 inches - perfect.

All vacuum ports are plugged too, except for the brake port. Any more ideas? Thanks.

 

The linkage is all free? Nothing binding?

 

Since the engine swap has it always ran at 2-3K rpm? If so, I'd also check to make sure the primaries are closing all the way by disconnecting the throttle linkage from the throttle bracket allowing the primaries to close completely.

 

It seems to be fixed now. All we did was back out the idle stop screw.

The new 305 from the camaro had ported/polished heads, a roller camshaft, and the camshaft was a 350 truck camshaft (a little more agressive than the stock 305).

Maybe all of the combined mods bumped up the volumetric efficiency and it idled faster.