I'm replacing the 305 in my 85' Pick-up this week-end. It currently has the factory Electronic Q-Jet on it which I plan to swap and run on the new 350.

Anything I should do to the carb or would it act alright with the factory settings?

350 combo is

Vortec heads
Flat tops = close to 10:1 comp.
Comp XE262
GMPP Vortec Q-jet Intake
GM HEI

Thanks

you should be good

you'll need to change out the primary jets, but they're not standard Q jets , they have a long tube sticking out the top to guide the rod. My personal experience is that a 305 computer Q won't pass enough fuel for a 350. maybe for idling around it might work, but if there's any load and throttle opening at all it'll go full rich but it won't be enough and the car will run bad and on the SES light. Why not trade in the carb for a rebuilt 350 computer Q for a similar year and vehicle? Use a NAPA or Holley brand rebuilt.

oops I thought it was another 305.

Dwayne.
I took the tired 305 out of my 85 Blazer at about 140k miles and replaced it with a 350 I built. New engine had hydraulic roller cam and flat top pistons for a little more compression.

I took everything right off the 305 and bolted it on to the 350 and drove another 100k miles before I sold it. Ran absolutely perfect. I would not change anything unless you actually have a problem after the swap.

By the way, the 350 actually got a little better mileage than the 305 and had a lot more power.

Thanks fellows.

I think I will at least try it first to see how she acts. No use fixin it if it ain't broke. If it does not have the throttle response I think it should, I will prob. go the NAPA rebuild jobber for a 350 mode. I'm not looking for balls out performance as it is my daily driver. But, I do want it to be able to put a smile on my face when I want it to. ;)

And Bill, I hope I have the same fortune with the gas milage. I've always said the lil 305's were too anemic for these heavy trucks and I bet they use more gas trying to get em rollin than a 350 would.

For the combo you are talking about, the carb has enough adjusting range that the ECM can manage it. It'll work fine.

About the only thing you MIGHT want to do, is loosen the air valve spring a bit (305s like 3/4 - 7/8 turn, 350s tend to like about 5/8 turn); and MAYBE get different sec metering rods. But, try it like it is, and see what you get, before making any changes. It might be OK as is.

OK,

Got the engine installed and runnin...and runnin she is! Very nice combo with plenty of low end torque and mid-range power.

The Q-Jet seems to be runnin fine...but, I checked the plugs last night and the porcelin is snow-white indicating a severe lean condition.

Look like I'm gonna have to start tweaking it a bit. :D

if you have a dwell meter you can manually check the duty cycle of the mixture control solenoid, see if it's in the range at steady state cruise.

there should be a green wire connector near the carb, use a dwell meter on it. NOTE: set the scale to 6 cylinder, not 8. Don't ask, that's just the way it is. Tell us what reading you're getting at cruise. Obviously, this might mean taping the meter to the windshield or something. I lengthened the wires on mine so I could run it in the passenger window.

if it's off the scale lean but close you can jack up the fuel level to ragged edge. there's a couple tricks to popping the top off these carbs but no killers.

Dwayne,if the motor is running well not seeming to be running lean but plugs look to be lean send me your email address and i will send you some good info on reading spark plugs when running todays unleaded fuel that doesnt color the plugs near as fast /quickly as fuel ofthe past and it includes photos too.

For ex,my basically stock 69 396 thats stock except for mild cam would not color the plugs for 300-400 miles af6ter putting in fresh AC's that were 1 heat range colder then req for that motor in stock form & thats also with going up 1 step over stock on primary jetting too.

I am running stock ex manifolds with stock pipes & flowmasters.

I thought it was todays fuels not coloring the plugs as quickly which i verified when i asked Sean Murphy (SMI) and he stated the same thing including that the 73 prim jet with 45b prim rods was just the right fuel claibration for a q-jet on my mild 396.

The motor ran fine and didnt show signs of running lean in its performance but the 1 heat range colder then stock plugs (r44's to r43's) stayed white for hundereds of miles which was concerning me too just like it cincering you.

Then i also found the plug reading info that also stated todays fules dont color the plugs much in some cases so i stopped worrying about it sine the motor rans well showing no signs of running lean in its performance and didnt detonate nor showed any signs of detonation with black speckles or aluminum speckles on the plugs either.

So i am leaving well enough alone because i know 73 prim jetting w/45b rod is senceable prim fuel calibration for a mild 396(now 402) BBC and the R43 AC plugs are 1 step colder then rec for stock setup and its running well so i know the plugs arent too hot too.

Scott

OK,

I checked the plugs last night and the porcelin is snow-white :D

D,
Unless you hear it pinging, dont sweat it. Snow white is pretty much normal on any modern vehicle. I bet if you run it for a while out on the highway, and then get a plug reader and really look down in the plug at the porcelain, you will see it is ok. The 350 does not need that much more fuel than the 305 and the MC solonoid should adjust for it. If you are not getting any check engine codes set, then it is not running lean or rich. A good scanner would verify this.

I have a '78 Q-Jet on my '72 Olds Vista Cruiser. I'm told by '78 the carbs were set up lean, and the plugs are absolutely white, but the 4600 lb wagon will get 20 mpg at 55mph.

Thanks fellows!

The truck really is runnin very, very well :D.

I was suprised to see the plugs so white. But, I do only have 350 miles on her now (probably just less than 300 when I checked the plugs).

I believe that since this is my daily driver, and seems to be getting better gas milage now than with the 305...I'm just gonna run it as is and leave well enough alone.
I've got a really good tech article on Q-jets written by Lars Grimsrud. It explained that the truck carbs made after 1981 had .036 dia. tip primary rods in lieu of the .026 rods on the older Q-Jets which would make it a little leaner than most. But like I said, she is runnin fantastic, so, I'm not gonna mess with it.

Scott, I would like to see that article on reading plugs if you don't mind. Email is dwayne@tqmroofing.com

Dwayne,i sent the info to your email.

scott

Dwayne,
that info from Lars doesn't apply here at all. Computer Qs have metering rods but they don't operate like the old style vacuum controlled at all.