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Vapor lock with my 79?

stevolwevol

Well-known member
Joined
May 28, 2015
Messages
239
Location
Michigan
Corvette
1977 light blue
Since the weather has been warmer, I have been getting some minor vapor lock with my 79 L48. I don't get it with my 77 though. They are essentially the same engine, but I have a performance cam on the 79, the only difference. Yesterday I had a difficult time getting it started after sitting 30 minutes.

I don't have fuel lines touching the engine, or too close to the engine. Is there anyone out there in corvette land that could point out what I may be missing? Both are Qjets by the way.
 

Tom Bryant

Well-known member
Administrator
Joined
Nov 9, 2000
Messages
7,197
Location
Edgerton, Ohio, United States
Corvette
1959 black 270hp (9/2/69) 1981 Beige L81(10/20/80)
Before you try to start it next time after setting 30 minutes take your air cleaner lid off and hold the choke open so you can look down inside, then pump your carb to check for a solid fuel squirt. If there is gas in the carb it isn't vapor lock. Vapor lock assumes there is no fuel getting to the carb. You could also check when you shut off the engine then check again before you try to restart in 30 minutes. If there is gas when you shut it off and none when it's time to restart you need to find out where it went.

Tom
 

stevolwevol

Well-known member
Joined
May 28, 2015
Messages
239
Location
Michigan
Corvette
1977 light blue
Before you try to start it next time after setting 30 minutes take your air cleaner lid off and hold the choke open so you can look down inside, then pump your carb to check for a solid fuel squirt. If there is gas in the carb it isn't vapor lock. Vapor lock assumes there is no fuel getting to the carb. You could also check when you shut off the engine then check again before you try to restart in 30 minutes. If there is gas when you shut it off and none when it's time to restart you need to find out where it went.

Tom

Yes, that would get me closer to what really is going on. The issue happens when the weather is warm, not during cool weather. I do have a rubber fuel line coming from the fuel pump, I removed it from the carb to reroute it away from engine heat. When I unclamped it no fuel leaked from the carb, or the hose. Could I have a bad fuel pump that's allowing the fuel to drain back? What say you Tom?
 

stevolwevol

Well-known member
Joined
May 28, 2015
Messages
239
Location
Michigan
Corvette
1977 light blue
Twice now I have ran the engine warm now. I removed the air cleaner and I'm getting gas from the float bowl. I believe I'm running too rich. I then discovered I need a 4.5 mm hex which I need to find. I'll buy one somewhere, and adjust the idle mixture with a vacuum gauge, and see if this does it.
 

Tom Bryant

Well-known member
Administrator
Joined
Nov 9, 2000
Messages
7,197
Location
Edgerton, Ohio, United States
Corvette
1959 black 270hp (9/2/69) 1981 Beige L81(10/20/80)
What have you found? What carb is on the car now?
 

stevolwevol

Well-known member
Joined
May 28, 2015
Messages
239
Location
Michigan
Corvette
1977 light blue
What have you found? What carb is on the car now?

Hi Tom, I figured I am running rich. I purchased the tool to fit the mixture screws BTW. I took the air cleaner off after I got the engine good and warm and I noticed fuel squirting out when I worked the throttle. I tried to adjust using a vacuum gauge, but it didn't seem to cooperate. I ended up turning in the mixture screws a quarter turn. Any leaner I get a hesitation from a stop. The weather has been cool lately, but when it gets in the 80's I'll see if it acts up. As I mentioned earlier I have an after market cam that was installed by the previous owner, but I don't know the specs on it. Maybe that could be why I don't get this with my 77 which has the stock cam. I get 5 psi of vacuum less with this engine than I do with the 77 with stock cam. Could the more aggressive cam cause finickiness with fuel mixture?
 

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