In my 87 305, my stock Q-Jet 4bbl seems to be going bad. It runs, but smells sickeningly rich, stalls at half throttle, and the electric choke does not seem to be working. Also, after checking to tune it, the screws appear to be "detached" and turning them does not affect idle or anything else.

I bought a cheap rebuild kit at a local Auto Zone, but I also recently began researching parts for a 355 build.

My question is this; could I find a new carburetor that can run well on both my 305 and eventual 355 down the road? This 355 is a casting from a '70 Caprice which is bored .030 over, with Vortec heads. I've heard since the Vortecs need a different intake manifold, the carb might need an adapter or not fit at all.

I just want a carburetor that I can run on my 305, then swap to my 355 when it is ready.

I was thinking the 650 CFM range, which I know due to airflow restrictions the 305 cannot utilize it all, but would it still work? If not, should I just stick to looking to rebuild my Q-Jet? Sorry for the loaded question.

Thank you

 

qjet will work fine on a 350 and there are several manifolds available for the vortecs that are also spreadbore.

 

You're probably going to get a lot of different opinions on carburetors as it's been brought up a few times before with similar results. IMO, you're going to have to decide if you still want/need emissions and/or the computer involved. If you ditch the computer, the auto trans will need to be modified. Then you can add whatever carb and will need a non-computer distributor.

If you keep your carb you may have to get the throttle shaft bore fixed, because if it is worn it can cause excess air to enter the manifold leading to driveability issues. I have posted about this a few times so if interested search "throttle shaft bore scorpner."
Here:
https://www.thirdgen.org/forums/carb...ml#post5806931

The choke may be allowing too much fuel into the manifold and can sometimes wash the cylinder walls and then end up in your oil. So check your oil for the smell of fuel.

(BTW,IMO, either Q-Jet or Holley is fine.)

 

Emissions are completely deleted on this car already. After reading one of the links you provided, it looks like the throttle shaft bore may be the culprit, but I had no clue the trans and carb used a computer together.

How would one modify the trans to accept a non-computer carb? Or are there any carbs out there that are a plug-and-play replacement with the computer, besides other Q-Jets?

I really appreciate this response, thank you!

 

The factory style CCC Qjet is the only carb that will work with the computer. If your building a vortec headed 355 I would go ahead a swap over to full non computer.

$90 Large cap HEI dist.
Edelbrock 600 cfm carb (or holley, but I like edelbrocks better for street use)

The 600 cfm will be alittle much for the 305 but will still work fine, and the 600 will be perfect for a milder 300-400 HP 355 (I ran a modded 600 cfm carb on a car that went 11.40's @ 118 with a 355 engine). You will get alot of folks telling you to run a 650, 670, 750 cfm carb on a 350.. That is not right, yes for a race car that works, but on a street/strip car thats too much. People tend to over carb, over cam, under gear, and under stall their cars.

Your stock intake is a spreadbore design, and most likely the intake you get for your vortec 355 will be a square bore carb mount... The edelbrock carb has the mounting holes to fit both intake designs and if you use a good thick gasket you can get the edelbrock carb to seal to your stock intake with out an adapter plate, and then of course it will fit the intake you use later on your 355.

The transmission is just the torque converter lockup. You can leave it as is, no mods and it will not harm the trans and tras will still shift right and all, but you will loose the lockup of converter which will cost you about 5% fuel mileage..

Or you can buy a lock up kit, (go to summit racing and type in torque converter lockup kits...they have them for $64 for basic kit, up to $200 for more advance kits) or make your own and have the torque converter locking like normal. Do a search on here for "torque converter lockup" and you will find the info on how to make/wire it up your self

 

This is perfect. I don't care much for fuel efficiency as I park it 8 months out of the year. As long as my transmission functions without the computer that is all I care about. Thank you so much. But the distributor must be non-computer as well for it to work?

Also, you're saying I should get the square bored carb with an adapter for the 305 use, then bolt it straight on to my vortec's square bored? Just clarifying, but this is really helpful.

 

Yes you need a non computer distributor.. Summit brand or skipp white $90 new HEI works perfect.

The edelbrock carb is sorta both spread bore and square bore.. The base is square, but prim. bores are smaller than sec. bores. They also have 8 mounting bolt holes, 2 per corner so it will bolt up to the square and spread bore intakes. I have used the edelbrock carbs many times on stock spread bore intakes with out the need for an adapter.

So yeah put it on your 305 now, and for some reason if you have to then get a $25 adapter plate and run it, then just bolt it over onto your 355 w/o the adapter later.

Yes the only computer control on your transmission is the torque converter lock up, and like I said before you can run w/o the lockup with no harm to anything.

If you do go edelbrock or holley carb you will also need to buy a TV (throttle valve) adapter bracket kit to hook up your transmission's TV cable to carb

 

running without lockup will increase heat build up within the transmission. I'd recommend an alternate method of lockup. another option is a secondary transmission cooler.

 

Yes I do recommend an add on trans cooler.. for all performance uses.

I do not fully agree with the non lockup building too much heat though as all of the power glides, th-350, th-400, etc from the 1950's through late 70's was non lockup, and also non lock up torque converters are sold for the 700r4..

But yes an added on extra trans cooler is never a bad idea.

 

there is plenty of experience that the 750 is the proper carb and can be tuned easy to run fine temporarily on the 305. holley is more easy to understand and tune to me, i have a 400hp 350, and a 4150 holley, with a huge cam and very good street manners. my wife drives it sometimes. its all in the tune. and there is a million right ups on it, there is a good one in the sticky section here.

https://www.thirdgen.org/forums/carb...-equation.html

 

Go to guaranteed carburetors you can get a rebuild for like 175. Get it caliberated for the L69.
And then when you go to put 350 in swap to a L69 or ZZ4 prom.