75 Stingray bad gas mileage and stalling between shifts in automatic
07-23-2014, 08:48 PM
#1
Cruising
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75 Stingray bad gas mileage and stalling between shifts in automatic
Hi guys,
I have just recently purchased an automatic 75 l48 corvette that the guy claimed was a 4-bolt 0100 casting number. My gas mileage has been anywhere between 8-12 mpg and it appears that it smells rich to me. Additionally the car sometimes stalls when shifting from park to reverse and reverse to drive when its cold without giving the car gas. I fixed a large vacuum leak on one of the main lines which seemed to improve the stalling to only on the first startup instead of most of the time. The car does not stall once in drive or in park only between ***** without gas. I have a vacuum gauge on order as well as a timing light but I was wondering if anyone had any ideas as to what my issues might be caused by?
The headlights do raise up and down slowly left one first then right slowly after (post fixing large vacuum leak. There may be more but I did not hear any).
Stock distributor with new cap and plugs/wires
stock headers and 2.5 inch true duel exhaust not cats
The car has the following mods:
670 holley carb
new aluminum intake manifold
port and polished 305 heads
rv cam and lifter kit
double roller chain set
oil pump
accel engine coil
new plugs and wires (march 2014)
water pump and hoses
new fuel pump
push rod and rocker set
I have just recently purchased an automatic 75 l48 corvette that the guy claimed was a 4-bolt 0100 casting number. My gas mileage has been anywhere between 8-12 mpg and it appears that it smells rich to me. Additionally the car sometimes stalls when shifting from park to reverse and reverse to drive when its cold without giving the car gas. I fixed a large vacuum leak on one of the main lines which seemed to improve the stalling to only on the first startup instead of most of the time. The car does not stall once in drive or in park only between ***** without gas. I have a vacuum gauge on order as well as a timing light but I was wondering if anyone had any ideas as to what my issues might be caused by?
The headlights do raise up and down slowly left one first then right slowly after (post fixing large vacuum leak. There may be more but I did not hear any).
Stock distributor with new cap and plugs/wires
stock headers and 2.5 inch true duel exhaust not cats
The car has the following mods:
670 holley carb
new aluminum intake manifold
port and polished 305 heads
rv cam and lifter kit
double roller chain set
oil pump
accel engine coil
new plugs and wires (march 2014)
water pump and hoses
new fuel pump
push rod and rocker set
07-24-2014, 11:02 AM
#2
start from the begining by checking the timing.
then check the choke to see if it is properly adjusted, closed when fully cold and fully open when hot.
then check the idle speed and idle mixture screws.
exactly what cam is in the engine and do you have sufficient vacuum to keep the power valves in the carburetor closed at idle.
then check the choke to see if it is properly adjusted, closed when fully cold and fully open when hot.
then check the idle speed and idle mixture screws.
exactly what cam is in the engine and do you have sufficient vacuum to keep the power valves in the carburetor closed at idle.
07-24-2014, 04:12 PM
#3
Drifting
If your expecting better gas milage you bought the wrong car. Ive never got better than 10mpg in my 76. But hey I have a heavy foot ,its a Corvette.Good luck.
07-24-2014, 07:24 PM
#4
Cruising
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I will get the vacuum reading off the intake manifold/car tomorrow and post it up. I think it may be running very rich just by the smell. When my timing light comes in I will make sure its set at 36 degrees total and see if this helps.
Meanwhile I will hunt for more vacuum leaks.
Thanks for the replies. Any other input is greatly appreciated.
07-27-2014, 09:14 PM
#5
Cruising
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A minor update:
Did not have a whole lot of time to work on the car this weekend as I was out of town but I did some poking around.
1. My vacuum gauge from summit came in Vacuum off the carb to the dizzy is steady at 19 in-Hg(this is without all other vacuum lines coming off manifold/carb plugged).
2. I found what I believe to be my positive electric carb choke wire (green electric wire coming off of passenger side by coolant overflow bottle?) not hooked up to the choke and welded to the passenger side header
It appears previous owner tried to splice it to a shorter wire as it would not reach the carb and then gave up and left it hanging. Choke is permanently stuck at roughly 3/4 open. Not sure if this is my issue. How bad is a 3/4 open choke for cruising around with?
3. The fuel levels is sight glasses are at about 1/2 in the rear and 1/2-3/4 in the front.
I wont mess with the mixture until I get my timing light in from harbor freight and can confirm timing.
I apologize for my newbness. This is my carbed car and first vette. Pictures to come soon.
Did not have a whole lot of time to work on the car this weekend as I was out of town but I did some poking around.
1. My vacuum gauge from summit came in Vacuum off the carb to the dizzy is steady at 19 in-Hg(this is without all other vacuum lines coming off manifold/carb plugged).
2. I found what I believe to be my positive electric carb choke wire (green electric wire coming off of passenger side by coolant overflow bottle?) not hooked up to the choke and welded to the passenger side header
It appears previous owner tried to splice it to a shorter wire as it would not reach the carb and then gave up and left it hanging. Choke is permanently stuck at roughly 3/4 open. Not sure if this is my issue. How bad is a 3/4 open choke for cruising around with?3. The fuel levels is sight glasses are at about 1/2 in the rear and 1/2-3/4 in the front.
I wont mess with the mixture until I get my timing light in from harbor freight and can confirm timing.
I apologize for my newbness. This is my carbed car and first vette. Pictures to come soon.
Last edited by 75Rayvette; 07-27-2014 at 09:45 PM.
07-28-2014, 08:23 AM
#6
Melting Slicks
Choke does exactly what it says so if it is not fully open it will have some effect on your mixture. Your idea to get the timing sorted first is good. I would suggest blocking off all vac pipes from the engine while you get the engine running correctly, don't ask how I know!
If the choke wire is welded to the manifold you will likely find once you have repaired it that there will be a blown fuse in this circuit. Was the harmonic damper replaced when the engine was rebuilt? You need to make sure it reads true TDC on the timing marks when setting your timing, mine had spun and was telling me full advance was 52 deg BTDC when it was really 36 deg.
Vac leaks at least in my case, lead to lean running in cylinders 7 & 8.
If the choke wire is welded to the manifold you will likely find once you have repaired it that there will be a blown fuse in this circuit. Was the harmonic damper replaced when the engine was rebuilt? You need to make sure it reads true TDC on the timing marks when setting your timing, mine had spun and was telling me full advance was 52 deg BTDC when it was really 36 deg.
Vac leaks at least in my case, lead to lean running in cylinders 7 & 8.