Changing to quadrajet

[MrSony]

Do you have an aftermarket intake? If a magnet sticks, it's cast iron, no stick, aluminum. That effects whether or not you can swap carbs. If it's the factory intake, it probably has a square bore carb (front and rear barrels are the same size) with an adapter. All quadrajets are spread bore, the front barrels (primary) are smaller for economy and the rear barrels (secondary) are fekkin yuge for "power".

 

[DoubleV]

Do you have an aftermarket intake? If a magnet sticks, it's cast iron, no stick, aluminum. That effects whether or not you can swap carbs. If it's the factory intake, it probably has a square bore carb (front and rear barrels are the same size) with an adapter. All quadrajets are spread bore, the front barrels (primary) are smaller for economy and the rear barrels (secondary) are fekkin yuge for "power".

If it's a factory intake it will be a spreadbore and may also be aluminum....🤔

 

[MrSony]

If it's a factory intake it will be a spreadbore and may also be aluminum....🤔

afaik no 305s had factory aluminum intakes with a carb. 307s did, depending. someone correct me if i'm wrong tho.

 

[airboatgreg]

It might be a bad cannister prurge vale. Disconnect the top carb vent hose. If it has vacuum or gas the valve is bad

 

[olds307 and 403]

afaik no 305s had factory aluminum intakes with a carb. 307s did, depending. someone correct me if i'm wrong tho.

Up here almost no Olds 307's pre 85 had aluminum intakes. I had to get a A4 from the US. After 85, they were all aluminum and tiny ports.

 

[Bonnewagon]

afaik no 305s had factory aluminum intakes with a carb.

I had a 1978 305 with an aluminum factory intake. It used a 2GC carb. Last year for that carb, not sure about the manifold. OP: an O2 sensor at the collector may be too far away to work right. They are usually as close to the exhaust valves as possible, that is why they are on the exhaust manifold. Just another downside to headers.

 

[565bbchevy]

afaik no 305s had factory aluminum intakes with a carb. 307s did, depending. someone correct me if i'm wrong tho.

My 83' Monte which is not an SS came with a factory 305 with a factory spreadbore aluminum intake and a Quadrajet but my Monte did come fully loaded and had the F41 suspension and was also sent to ASC for a power sunroof.

 

[1bad79]

my 1984 z28 has a 305 ho and a factory aluminum intake with a qjet

 

[pagrunt]

The '86 parts car 305 had a aluminum intake.

 

[CopperNick]

Okay. Things to consider here, First is that the existing Q-jet, distributor, and computer come as a matched set. The computer is a primitive OBD 1 unit that is set up only to monitor and tweak the timing advance to optimize mileage and maintain the factory lean burn settings. The power leads for it are attached to the battery stud on the starter solenoid. While the engine will start and run without the computer, getting the timing right so that it doesn't diesel when you turn it off can be a monumental pain. As noted, you can go with an older version of the Q that is tuneable and mate it to a similar generation of HEI distributor. Be careful if you go second or third hand for your timer as the bushings in the shaft housing can and do wear which can mess up the advance. New might be the way to go here if you plan to stay with this system for the long haul. Another option is to score a Holley 650 Spread bore instead of the Q-Jet. Ran one on my old 85 motor and liked it. They do come with an electric choke so a little wiring needed there.

Next, Forget the 02 sensor. Your computer never did have it to begin with and neither has the harness or the software on board to do anything with it. Depends on where you are located but you might be able to lose the cat as well. California is absolutely rabid about having them still in place and functioning but other states are not so psychotic about them for vehicles over twenty five years old. Anything you do do to the carburetion/fuel system is likely going to result in you having to retune the engine to some degree simply because it came from the factory tuned lean for best fuel consumption/mileage and your tweaks may have to include a few degrees of timing more or less to just to get back to the best vacuum and idle.

Agree with keeping the canister. it is attached to the vent line on the gas tank and traps fumes from the tank as well as helping to keep its internal pressure stable so that fuel will flow from the pickup to the pump and north from there.

That multi-ported fitting that is screwed into the thermostat housing is a heat operated vacuum distribution unit. The engine feeds it vacuum via one of the ports and, as the coolant warms up, a bi-metallic strip inside the unit acts to expand/contract to open the remaining ports in a specific sequence in order to allow the inbound vacuum to be sent out to the various vacuum operated switches and sensors that it feeds. Most of them are tied in to the smog/lean burn factory tune and they come and go in order to allow the engine to warm up and run/idle while doing so as well as reacting to part throttle and demand down shift situations. They, like that cat, are all about compliance with Cali DOT and the EPA collective fantasy that having all this quasi-useful junk attached to a motor actually makes a difference to air quality there. You can delete that whole x-mas tree of vacuum tube simply by unplugging it all and blocking off the vacuum port on the intake that feeds the vacuum switch to begin with or you can go a step further by either draining the coolant below the level of the thermostat housing and swapping out the switch for a simple brass pipe plug, or changing out the entire housing for an aftermarket unit that has no provision for switches at all.

Last thought on the distributor. The vacuum advance canisters attached to the advance mechanism are not one size fits all. There are different versions of them that came as OEM depending on the year and model of vehicle. They are also available as aftermarket with built in adjustability using a hex key stuck down the vacuum delivery tube.

Nick