Carburator switch

[guardianfyre]

Got a question for everyone who has more knowledge of engine components than I do (which probably includes everyone on this forum...). I have a '79 Chevy 1/2 ton. The motor is not the original (original was 305, current is 350) but the carburator is. I'd like to find out how difficult it would be to switch from the 2 barrel (?) to a 4 barrel (?) and if anyone knows if there is a throttlebody system available for my year of truck. How would changing to a larger carburator affect my gas mileage? Is there anything else I should know? Please consider me a complete n00b when it comes to working on vehicles. The most I can do is check and add fluids and give my truck a tune-up (filter changes, oil change, radiator flush, spark plug change, etc.). I'm willing to learn, please teach me.

If you need more information than I've given, please ask. I'll do my best to answer any questions.

~Fyre

[Srubydo1986]

2 to 4 barral: tou will need to remove r the carbrator and the intake replace the intake with a 4 barrel intake. (you can go stock but i would edelbrock) and the install the 4 barrel carbrator. (Again you can go stoc i went edelbrock)

if anyone knows if there is a throttlebody system available for my year of truck OK not to shure i know if you after market then yes edelbrock had a kit but it like 2000.00 dollars so yea. and then there is a stock one but youll need alot f stuck computers wires the engine (catty corner head bolt + the cam)

How would changing to a larger carburator affect my gas mileage? OK id say about 1-2 mpg if you keep your foot out of the gas.



I think that it but heres a picture of my set up to give you an idea

[Ivan D.]

Actually with heavy vehicles it ain't uncommon to notice an increase in fuel economy when upgrading to 4bbl carb, provided of course new carb is tuned decently well.

[72C203503ONTHETREE]

If you use a good quadrajet(quadrajunk, lol), you will increase gas mileage if you stay out of the secondairies since they use even smaller venturies than the stock 2 barrels. The Edelbrock carb is a good one, stick with a 600-700 cfm version and you may want to buy a cheap plastic spacer since Edelbrocks(Carters also, same carb) tend to heat soak and flood the engine with the gas that pukes out the vents. You can reuse the same linkage and PCV hoses, brake booster line, etc. While your that far into the engine you can get a nice cam to, lol. It never ends.

[Srubydo1986]

i guess ill get a spacer for my truck.

[ron350]

Fyre are you looking for more power or better mileage?

Both the Qjet and the Carter carbs have good and bad points but you can save lots of money if you can find a good used Qjet.
If you can find a Qjet that will idle smooth you can make the secondary’s do any thing you want.


Srubydo
That engine compartment sure looks good.
Not over done but just right.

[Ivan D.]

Originally Posted by ron350

If you can find a Qjet that will idle smooth you can make the secondary’s do any thing you want.

Dayum strait - I fooled with the secondaries of my double-pumper, I got it to the point where at 2k rpm cruise I'm running the primaries at like 1/4 open and the secondaries ain't even close to budging open. Pulling 18-20mpg freeway steady, opening the secondaries brings me down to like 4-5mpg or so So yeah, get a 4bbl spreadbore carb, then stay out of the secondaries unless you really need to haul.

[Srubydo1986]

Originally Posted by ron350

Srubydo
That engine compartment sure looks good.
Not over done but just right.

Thx for the complement ive been think a single belt setup would be nicer though i keep throwing my power steering at high rev. Also thought about puting ac back in the truck i may loss mpg but man life is much sweeter with some ac.

[Ivan D.]

meh, with A/C you lose fuel economy only when compressor clutch engages, as long as you use yer vent doors and windows smart you'll be just fine - that, and A/C sure is nice to have when stuck in a traffic jam.

[Srubydo1986]

its been hot and ive been missing it

[guardianfyre]

*blinks* A/C...What's that? Just kidding. I don't have A/C installed in my truck. It's never had it. Started it's life as a bare bones farm truck in Illinois. I prefer having the windows down and the floor vents open anyway.

ron350: I'm looking more for mileage than power. My truck has enough power for what I use it for (daily driver, camping, etc.). That power was enough to haul a fully loaded Uhaul trailer from Cleveland to St. Louis no problem, so I'm set in that department.

[ron350]

I would try the Qjet for fuel economy and lower price than the Carter.
Like I said if the Qjet will idle smooth you can make the secondary come in really late or remove the secondary rod and temporally turn it into a very efficient 2bbl.

For tune-ability the Carter is hard to beat but I’m not crazy about the dual floats and dual needle and seats.

Lots of factory aluminum and cast iron intakes in salvage yards for the Qjet cheap.

Years ago Holly tried to market a replacement for the Qjet but I don’t know what ever happened to that.

[jebenger]

These guys are right about the carbs. Hell even if you have a decent Qjet a rebuild kit is between $13-26 and its not that hard to do. Or Summit has rebuilt ones for $239-269.

As for fuel injection. If you wanted to go with a stock set up, the most common type around is the 1986 and up setup. The only problem is that you'll have to change the intake and heads because they changed to bolt arrangement. On top of that, all the wiring and the ecm needs to be installed.

Let us know how it goes for you
John

[Pyrotechnic]

I have a Holley Remanufactured Q-Jet and it runs great. Idles very smooth and has great power.

Make sure the choke mechanism on the carburetor matches the manifold you get. If you get an electric choke carb, it does not matter what manifold you use. If you get a carb with the divorced stovepot choke, you need the stovepot that sits on the passenger side of the manifold next to the carb.

[Ivan D.]

Originally Posted by ron350

Years ago Holly tried to market a replacement for the Qjet but I don’t know what ever happened to that.

I got one, it's #4165 which is a double-pumper, believe #4175 was the vacuum-secondary one - mine came with the dual power valves so that's another thing you can tune, and I'm fairly happy with how it works. Currently #4175 is available both in mechanical and vacuum version, #4165 seems to have been discontinued. There are few particular 4165 lists tho (such as 6499) that are really sweet, they not only have the dual power valves but also externally-adjustable floats and also sight plugs, which are not options available on most 4165s - throw in two blow-out protection kits and you got yerself one darn nice carb.

[72C203503ONTHETREE]

I never used chokes on my carbs when I lived in Iowa, lol. Had a 66 Chevelle SS396 I drove in the winter with a Holley 750 double pumper, couple pumps of the gas pedal and it would start up in zero degree weather. Dont know why it worked so well but it did. Now that I am in Alabama it hardly ever gets lower than freezing.

[guardianfyre]

When I replace the carburator, will I also need to switch out the air intake/breather? Please remember that I'm new to this. I had to have my dad and my brother translate about half of what was typed above.

[Srubydo1986]

yes the hole on the bootm parts is smaller then that of a 4 barrel.

[72C203503ONTHETREE]

Just go to Autozone or wherever and get the cheap 30 buck Edelbrock air cleaner, will fit and four barrel but be careful on the edelbrock(and Carters) carbs, the fuel inlet on the rear passenger side will hit most dropped base air cleaners. There is a part that takes care of that but buying a short spacer to go on top of the carb is cheaper and theres plenty of room under the hood so it wont hit. Holleys and Q jets will wrok fine without a spacer.

[Srubydo1986]

Originally Posted by 72C203503ONTHETREE

Just go to Autozone or wherever and get the cheap 30 buck Edelbrock air cleaner, will fit and four barrel but be careful on the edelbrock(and Carters) carbs, the fuel inlet on the rear passenger side will hit most dropped base air cleaners. There is a part that takes care of that but buying a short spacer to go on top of the carb is cheaper and theres plenty of room under the hood so it wont hit. Holleys and Q jets will wrok fine without a spacer.

LOL that reminds me I beat mine out with a hammer to get it to fit. Good call forgot about it after all this time.