The Hurst is my daily driver. I recently moved and my commute went from 1.2 miles to 17 miles (work). My trips since sunday= 85 total miles. 17.1 gallon tank/2= 8.5 gallons. Grand total 10mpg..

Stats: 100k on the clock. OD tranny, 3:73. Headers (pass. collector has a leak).

Am I naive in thinking I should be getting more than 10mpg on sunoco 91? Fresh Oil change, plugs are 6 months old, KandN filter was recharged 5 months ago, 160 thermo.

I am not a carb expert. Cold start yields a VERY high fast idle. Any tips on adjusting the carb to relax the choke would be helpful.
*Note I know what I signed up for at the gas pump driving a 30 year old 4bbl GM daily.
Thank you

 

Cold idle is on the left, if you look from the front. Hot idle is on the right. Little screws if I am correct.

 

Hot idle is on the passenger side, which is the car's RH side. Whenever possible, try to use THE CAR's left and right, because the observer's left and right will vary as they move. You wouldn't say the tail lights are on the "front" of the car just because you are looking at the car from the hood area, would you?

Study up on the carb operation. Surely there are youtube videos explaining the operation of all them links and stuff. Can you get a spare carb and go over it w/o it being on the car? Once you get a good look and move them a little, it's easy to understand how all that interacts.

But, yeah, basically, the screw near the primary [front] throttle shaft controls the idle. Driver's side is in contact only after the choke opens and allows the passenger side one to come off the fast idle stepped cam.

10mpg?
That's good engineering!

Also, immediately after the engine starts, the choke pulloff vacuum canister is supposed to force the choke open just the right amount, which should then drop the fast idle screw to the 2nd step of the FI cam... and bring the idle down to faster than hot idle but less than ridiculous high.

 

Still has the CCC setup? That seems about the mileage on a CCC in limp mode.

 

I'm getting about 12 to 15 mpg in the 91 k5 with od. And 3.73 gears but the 35 in. Tires help the mpg on the road. Engine is a stone stock tbi 350

 

A 160 degree tstat on a computer car is too cold. Things like TCC won't even kick in until the temp reaches about 180. The system is designed around a 195 degree t-stat that should give you a running temp of around 205.

 

I get 20-21 MPG on a stock '71 350/350 combo and a 2.56 rear. Only things changed are a '77 Q-jet and an aftermarket HEI. I'd dare say you should be getting even more with an OD tranny.

 

What is the commute like? Are there alot of stop lights? Are you jumping on it at every stop? 10mpg could be good or bad depending on the trip. If there is 30 stop lights between you and work your mileage will suck no matter what you do.

Larry

 

My 455 is getting 14 mpg. You should be doing better unless you are doing a lot of stoplights. Why are you running 91 octane and what's your timing set at?

 

Sounds low so may check the math also. Did you start with a completely full tank and then refill to get actual gallons used for the miles driven? Kinda sounds like you estimated a half tank and gauges are inaccurate.

 

Timing is set to factory (20deg advance, I believe). Anything less than 89/91 octane and it pings/diesels. I put in 8.5 gallons on purpose as I knew the milage for the trips would by 85 (got home last night, resting on the E). No more than 5-6 stop lights and I ease out of them. The car still has the CCC. Rear tires are 24565R15.

 

If it's not something obvious like a gas leak, I would say you should do a full CCC diagnostic as per the service manual.

 

Re: pinging. Is your EGR system working? Replacing a bad EGR valve solved the pinging problem I had on an 86 Regal 307Y. The only way to accurately check mileage is to start with a fill-up and end with a fill-up, preferably at the same pump. I've heard individual nozzles' shut off points can vary quite a bit.

 

Cooper I get the same mileage with my 94 Z71. I calculated 13-16 imperial mpg on the highway, same gearing. Short trips, it is awful like any truck. I have 32" tires and the TBI Olds 350 in it will kill that swirl port turd power wise.

 

If I had my say I would have stuck a cummins 4bt in it. But the fiance is half owner and she has had this truck since 16 and does not want to convert it to diesel. Atleast the bowtie 350 is the 4 bolt hd package. According to the original owner who was a heavy duty mechanic he speacial ordered it with all kinds of stuff. Like the block heater , posi, and little things like that.

 

Block heater is standard equipment up here. Whatever genius ordered this Z71 without posi should be kicked. I threw a gov bomb in it. As said,go through everything, swap the thermostat and sure you are accurate with the amount used and miles. My mileage is with ethonal blends, that also lowers mpg.

 

I get around 12mpg on my cutty with 355, get 8-10mpg in my 69 chevelle with 454 FI, 15 -17mpg in my caddy with 4.6 northstar

 

An 83 Olds should be low compression and run fine on 87 octane. I think there is another problem if you are pinging with 87. That car is lighter than mine has a smaller motor and has the overdrive trans. I would expect closer to 20 mpg.

 

Pinging in these 307's is usually caused by carbon build-up in the EGR passages and those tubes under the carb.

Those tires you have are taller than stock. Not sure if it really makes a difference or not but it may effect the signals to the ECM speed/RPM wise. So the ECM may be providing you with fuel/timing based off of what it thinks your driving conditions are but in reality your driving conditions are different. Again I'm sure this isn't really much if any of a problem, but it may at least be contributing to whatever the main problem actually is.