So car in question is an 83 berlinetta with stock 305. It's got the carburetor..... previous owner put edlebrock 1406 on it, I changed out the distributor..... other than that its all original, minus it being straight piped....

My question is why am I getting unimagiunimaginably shitty gas milage.... like I barely get 60 miles on a half of tank.... that's driving like a responsible person.....

I've done my a/f mixture, set total timing, ignition timing and now I'm lost....

Any ideas?

Thank you, Trey

 

Is the Edelbrock carb still on it? Hard to tell from what you said.

What distributor is in it? Specifically, does it have a vacuum advance on it?

 

Yup that sounds like the standard I put an edelbrock on it and got rid of that quadrajunk result.

How did you set the A/F? What did you set it to in Idle? Cruise? Power?
What distributor? Total Timing? Base timing + Vacuum advance?

 

You really need to figure out your mpg before deciding you have an mpg problem. "60 miles on half a tank" only means something if your gas gauge (40 years old by now) is VERY accurate. Not likely based on my experience. Make sure your odometer is accurate, then fill up several times and average it to determine your mileage. I bet it isn't far off from normal for these old cars, which never got good mileage even when new.

For reference, my 305 with Edelbrock 1406 gets around 16mpg city driving, 22ish all highway. 3:42 gears and a T5.

 

I had Edelbrock 1406 Carbs on my 71 Cheyenne 350.
I think they're crap.
I switched to the Holley Spreadbore/Quadrajet and couldnt be happier.

 

i set the A\F by turning them all the way in then going 1 and half out....hooked up vacuum to the carb and adjusted until vacuum hit the max reading (around 17)
idlde set to both 750 and tried 900 also
cruise but isnt hooked up
power....like power brakes and steering and stuff?
distributor is I believe is an accel and vacuum advance
set timing to 6 degrees total is 30-32 i think

from the math ive done i get like 7 mpg

Thank you for the help

 

the accel distributorand yes it has vacuum advance

 

well i thought it was a 12 gallon tank for some reason but looked up and it is apparently 16 (15.8) so with the math it comes out to 7 mpg,,,which jams better with what im experiencing. so yeah its way off from stock numbers

 

Reset your trip meter every fill up and divide how far you went by how much you put in. Don't rely on the gauge to calculate anything

 

I understand that the right way but my trip dont work.... and it cant be that far off....i ran out of gas and when i filled it i got like 15.4 in

 

You did not set the A/F ratio in cruise or power then. You need to use an A/F meter and tune the carb by swapping jets and rods to meet your desired ratio in all conditions.
Read this and use the diagram on page 17 it will help your decide what to swap in based on your A/F readings
https://www.edelbrock.com/mwdownload.../link/id/76969

Basically you need to redo all the stuff the factory carb and distributor where doing
Are you using ported or manifold vacuum for the distributor? What other timing settings have you tried?

 

Use a gps speedometer app on your phone that saves trip mileage

 

also it runs like ****....guy i bought it from cut a bunch of sensors out when he switched the air cleaner. What are the sensors ive GOT to have?

 

Ah yes the I'm gonna make it old school because I am too stupid to figure out a Q Jet method. I am sorry for your pain from previous owner stupidity.

If you are sticking to the Edelbrock you don't need any sensors to run but you will need a sensor for the oil pressure gauge and temp gauge.

If it was my car I would open the carb and see if anything was swapped inside then confirm float height and probably fuel pressure depending on the pump used. Then I would try 36 degrees total timing and manifold vacuum advance. Finally a ignition tune up so I could read the fresh plugs and see how rich or lean it is

 

LOL yes and the worst part is the stupidity is my father in law,,,,i highly and I mean HIGHLY doubt he opened up the carb...I mean he swapped carbs but not the distributor.... just to make sure for total i do that with vacuum hooked up and at about 3000 rpms right?

 

im new to the A\F adjusting...vacuum advance is hooked to the carb on the left side of carb if looking at it from the front

 

I prefer manifold vacuum so the right side looking at the carb. Total timing depends on the distributor but you want to disconnect the vacuum line and see how much it advance until it stops. It may be above 3000 depending on the curve on the distributor. I would shoot for 36 at Max advance no vacuum line hooked up and then go from there


What part number is the distributor? There is possibly a timing curve diagram in the manual online

 

This is useful information. If it runs "like ****" that would explain why it has "unimaginably shitty gas mileage". Forget your mileage and learn how to properly tune your carb with the advice above.

 

Although mentioned in a roundabout way, the best way to accomplish this level of carburetor tuning is to install an AFR gauge (AFR) and the accompanying wide band O2 sensor.
Being able to observe what the actual air fuel ratio while cruising down the highway (or anywhere else) will give the indications of what needs to be changed and in which direction.
Combine the AFR gauge with an in-cabin vacuum gauge and you'll have the instruments needed to tune with knowledge.
If the MPG is as crappy as you say it is, the gauge will pay for itself in a couple of tankfuls what with todays fuel prices.

FTR, my overcammed 355 would knock down better than 20+ MPG(US) in highway cruise. That's close to 400 miles on a full tank. That engine wasn't built for economy but I wrestled with it until it delivered decent results.
Equally as important as the AFR is the ignition timing. Typical SBCs can swallow up a lot of advance under light load cruise conditions. Especially if the AFR is tuned to the lean side. 45° isn't an unreasonable amount

 

Okay so here goes.....I'm an idiot...Some how when i dropped in the distributor I got it 180 degrees off....not only that I somehow hooked up the spark plug wires just enough screwed up it would start and drive. Also I have a GPS speedo on my stereo, also an app to determine mpg. After going back to the beginning, pulling the distributor and finding TDC (on compression) then timing it fires up so much easier.And Im about at 15-16 mpg....That's without even touching the A/F mix....I plan to do it tomorrow with a vacuum gauge...total timing and everything...I appreciate the help guys.....I LOVE 3rdGens, but this one has me close to the edge lol....I Would Have burnt it to the ground already without you guys.

 

I will go check to see if i can get part number on distributor....Now I came off the left (standing at front of car)...I thought I want the vacuum that isn't constant for my vacuum advance. I hooked my vacuum gauge to the right side of the carb....I was told that I should be around 32-36 total running at 3000 rpms....Is that what you're saying?

 

Generally, yes.

That would of course be without the vac adv connected at all.

Problem is, timing marks are NEVER accurate. I have yet to see EVEN ONE in all my days in this hobby - near half a century now - that was ANYWHERE NEAR right, except when it had been individually measured and calibrated; and EVEN THEN, it was only right for a relatively short time. Reasons for inaccuracy are, mismatch between "mark" location on the damper and "tab" location on the block, due to parts that are simply designed different; and, the "mark" on the damper IS NOT on the damper itself, rather it's on the outer inertia ring, which is only connected to the crank by A BLOB OF SPOOGE. There are 3 common "tab" locations on various common iterations of the SBC: the most original one was at 1:30, essentially directly in line with both the keyway and the #1 crank throw; about 1:00, which obviously is about 15° RETARDED from the original; and the one that came on these cars, which is right close to 12:00, yet ANOTHER 25 - 30° RETARDED. Virtually ALL aftermarket timing covers have the 1:30 mark, which is USELESS in these cars due to the PS pump location. If you use a typical such cover, especially a "krome" one, in conjunction with a stock damper, then EVEN IF THE DAMPER IS INTACT, you will end up setting your timing about 40° RETARDED from where it needs to be. If the inertia ring has broken loose from its BLOB OF SPOOGE, then all bets are off as to whether even that is an accurate estimate of how messed up you can be.

Bottom line then is to simply set it to where the car runs the best. You can begin to get an idea of where that is by simply advancing it to where it starts pinging, then backing it off slowly until it quits. No guarantees that that's "right", but if you discover that you have to advance it 45° to get it to ping, then at least you have a good idea how far off it was.

Then, as repeatedly stated, learn to tune the carb. I'm not a fan of Vic's carbs AT ALL, butt they can be made to work OK enough, although other kinds are "better" in various ways IMO (Holley will outrun it, QJet will be more efficient, etc.)

For vac adv, back before emissions became The Thing that dominated factory tuning, it was ALWAYS connected to hard manifold vacuum. The ported (non-full-time) connection was introduced in the late 60s in the first wave of emissions compromises. Engine will usually run better with full-time vac, butt it's eeeeezzzy enough to try it both ways and see which you like, ONCE YOU GET THE RIGHT STATIC TIMING (twiddle the dist housing). Typical vac adv for a street car should begin advancing at 10 - 12" of vac, and be "all in" by about 15 - 16"; and should add 12 - 15° of advance. Its purpose is to give the material in the cylinders more time to fully burn when the mixture is lean and the cyl fill is incomplete, which occurs at relatively high speeds and low loads, aka "cruising". It should drop out when any significant power is being demanded because the mixture conditions detailed above no longer apply.

"If it RUNS good, it IS good".

Doesn't matter what "number" you come up with using "light" on "mark" and "tab". "Spec" in "book" doesn't apply in any case since you no longer have the factory setup, and even if you did, it's heavily compromised in favor of emissions, and in NO WAY "the best". Set your timing to where the car runs the best - which YOU get to decide, based on YOUR preferences, how YOU drive YOUR car in the place(s) YOU drive it on the fuel YOU can buy in the weather YOU live in - based on some combination of best power, lowest fuel consumption, coolest water temp, crips throttle response, and so on. "Number" is USELESS for any of that. Make the car run the best it can and EFFFF the "number".