Terrible gas Mileage on 1986 Monte Carlo!

[Lorenzo]

Hey guys wondering if you could help me on this. The car has the 305 v8 with a 4 barrel carb.Ive done a full tune up on it aswell as new cap and rotor coolant flush oil change all the bells and whistles. The most ive gotten to a tank is 300km and i was pretty happy about that. But now it seems its just drinking my gas! Last tank i only got 195 km outta a 52 liter fill up and today i noticed i only went 42km and from a full tank im almost at 3/4 left!!! This is insane! It really hurts too when i gotta dish out 70$ every 5 days or so. Please can someone give me some info on this! Thanks!

 

[84cutlass383]

Does it run good? when running do you smell alot of gas in the exhaust? if so, tune your carb. Check ur fuel lines make sure u dont have any leaks. check ur fuel tank top to bottom, last change ur gas cap. ill bet its ur carb tho. hope this helps

 

[Lorenzo]

Well just last week i replaced the carbs base gasket because it was broken and it seemed to run better. I was going to adjust the carb but couldnt find the screws! My teacher told me they were on the base but both were covered with some big metal circle. We tried drilling threw them but nothing would work. Also my car has a dual exhaust system and i notice more smoke out of the driver side pipe when the car is idling and reving then the passenger side. Thanks!

 

[bill]

Well just last week i replaced the carbs base gasket because it was broken and it seemed to run better. I was going to adjust the carb but couldnt find the screws! My teacher told me they were on the base but both were covered with some big metal circle. We tried drilling threw them but nothing would work. Also my car has a dual exhaust system and i notice more smoke out of the driver side pipe when the car is idling and reving then the passenger side. Thanks!

You have to remove the carb to remove those plugs. I hate to say this, but its possible that you drilled a hole where it shouldnt be...and you may have really messed up that carb...only way to know is to remove the carb and remove those plugs. They are plugged because they are set at the factory and really dont need to be adjusted. I would check the gasket and the carb mounting bolts..make sure everything is tight and the gasket hasnt gotten pinched or torn. Good luck!

 

[khan0165]

I have to agree, those metering screw plugs are not the issue. I once had a Carter 650cfm 4bbl carb, with those plugs. They were very tricky to remove.
And even if you removed them and adjusted your metering screws, this would only effect your idle characteristics, and have no improvement on your gas consumption.

I think there are more than a few issues at play here. Before you start pulling the carb appart, start the car and look inside the carb. Keep your face at a distance and just peek in. See if it's pouring too much fuel in. Rev it a few times and see how the fuel flow changes. Then shut it off, go back to the carb, see if there's fuel sitting at the bottom of the carb. If not, open the throttle all the way, and see if there's a puddle of fuel sitting at the bottom of your intake.

if fuel is overflowing, it is likely a fuel bowl issue. It's common for a float to get stuck inside the bowls, and this may cause an overflow of fuel. Corroding or broken gaskets, debris from dirty fuel or the air, all these factors can play in disrupting the proper flow of fuel and air vacuum thru your carb.

Check all your vacuum lines, check if your choke is operating properly (not opening to soon? or too late?)...

if all these options don't show what's wrong, you should take the carb off and rebuild it with a gasket kit.

 

[Lorenzo]

Well just last week i replaced the carbs base gasket because it was broken and it seemed to run better. I was going to adjust the carb but couldnt find the screws! My teacher told me they were on the base but both were covered with some big metal circle. We tried drilling threw them but nothing would work. Also my car has a dual exhaust system and i notice more smoke out of the driver side pipe when the car is idling and reving then the passenger side. Thanks!

You have to remove the carb to remove those plugs. I hate to say this, but its possible that you drilled a hole where it shouldnt be...and you may have really messed up that carb...only way to know is to remove the carb and remove those plugs. They are plugged because they are set at the factory and really dont need to be adjusted. I would check the gasket and the carb mounting bolts..make sure everything is tight and the gasket hasnt gotten pinched or torn. Good luck!

Well where we were trying to drill the holes they were where the screws are and it didnt even make a hole so im not to worried about it. The gasket is fine as it has been replaced and we made sure not to break it. I really think that over the time when it had no fuel filter in it, all the jets got clogged up and thats my problem.

 

[Lorenzo]

Ok so last tank of gas i got 320km on it which i was happy about, but i now that i can get more out of this car! Do you guys think the carb can be an issue with this? Whoever had this car before ran it without a fuel filter so do you think that gummed everything up?

 

[Clone TIE Pilot]

Have you tried checking your m/c dwell with a dwell meter?

 

[Lorenzo]

Have you tried checking your m/c dwell with a dwell meter?

Im sorry i have no clue what that is lol.

 

[Ribbedroof]

For the USA folk that's 186 miles to 13.74 gallons...or 13.5 MPG for the 300km/52 litre tank or 8.8 MPG on the 195 km tank

I suspect that the electronic components of the CCC quadrajet are in need of attention....assuming it still has one on it.

Tough to diagnose without knowing a lot more about the situation.....driving style/type of trips/idling time/state of tune/overall engine health.

My personal experience with the OEM QJ on my 83 Bonneville was that after almost 30 years, it had deteriorated to the point that I was getting about 9/10 MPG. The TPS and the idle solenoid were both dead players. After installing a completely remanufactured unit, MPG went to 16 on my daily commute.

Are there any codes stored? Even if there is no check engine lamp on, there may be codes being generated/stored...some people (like the previous owner of my Bonneville) seem to believe that removing the bulb will "fix" that annoying light

And BTW, "clogged jets" would make the car VERY lean, assuming it would run past idle at all.