Hard Hot Starting.
Thread Starter
Cruising
Joined: May 2018
Posts: 13
Likes: 0
From: Ridgeville S.C.
Hard Hot Starting.
Hi, I have a 79 L48. Its all original, as a matter of fact I just replaced the original plugs, wires, cap and rotor and fuel pump.. I've had a problem surface recently with hard starting after driving a while. I can drive say 30 min. after trying to restart after say 20 min. its very hard to start again. I changed the fuel pump because of hard cold starting which solved that issue. ever since its hard hot starting. I pulled the fuel filter to see if it was blocked but i could blow through it. one thing i am puzzled about is when i pulled the fuel filter i figured it would spill gas everywhere but didnt. It was dry as a bone after sitting for around an hour waiting to cool down. I'm one of those old farts that can build an engine but apparently not so bright when trying to diagnose fuel issues! Any help would be greatly appreciated.
Drifting
Joined: Apr 2017
Posts: 1,377
Likes: 282
From: Bedford New York
Thread Starter
Cruising
Joined: May 2018
Posts: 13
Likes: 0
From: Ridgeville S.C.
Holding the pedal to the floor it starts. Runs rough and then evens out until i stop again. Forgot to say its the original Quadrajet with 68,000.
Ran perfect until changing the fuel pump.
Ran perfect until changing the fuel pump.
Last edited by GoldenC5; Jul 9, 2018 at 03:49 PM. Reason: mis spelling
Race Director
Joined: May 2006
Posts: 18,735
Likes: 2,582
if the new pump is putting out more pressure than the original it may cause the float level to be too high?
do you know what the pump manufacturer states for fuel pressure?
after you turn off a hot engine and look down the carburetor throat do you see gasoline dripping?
do you know what the pump manufacturer states for fuel pressure?
after you turn off a hot engine and look down the carburetor throat do you see gasoline dripping?
Drifting
Joined: Apr 2017
Posts: 1,377
Likes: 282
From: Bedford New York
The theory: fuel boils off from 'heat soak' while the car sits after getting hot. When you go to restart it, the fuel bowl is dry and needs some cranks for the pump to refill the bowl. Once the fuel level rises, it fires off.
Seems to be the prevailing theory on hot restart issues. My LS5 suffers the same way.
Seems to be the prevailing theory on hot restart issues. My LS5 suffers the same way.
Drifting
Joined: Aug 2009
Posts: 1,346
Likes: 160
From: new iberia la
The theory: fuel boils off from 'heat soak' while the car sits after getting hot. When you go to restart it, the fuel bowl is dry and needs some cranks for the pump to refill the bowl. Once the fuel level rises, it fires off.
Seems to be the prevailing theory on hot restart issues. My LS5 suffers the same way.
Seems to be the prevailing theory on hot restart issues. My LS5 suffers the same way.
Racer
Joined: Sep 2013
Posts: 284
Likes: 16
From: St Louis MO http://1972corvetterestomod.blogspot.com/
does sounds like fuel boiling in lines, fuel filter, and carb while parked. If that's the case, insulating fuel lines (Earls has their Flame Guard wrap) and/or insulating the carb itself with a heat shield (Holley's heat shield kit for carbs) could help. Anything you can do to keep the fuel in the lines and carb cooler.
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
Top 10 Most Expensive Corvettes Ever Sold on Bring A Trailer
Brett Foote
10 Things Every Corvette Owner Needs (2026 Edition)
Michael S. Palmer
8 Most "Only Corvette Owners Understand" Quirks and Problems
Pouria Savadkouei
10 Reasons the C6 Z06 is Still A Performance Benchmark After 20 Years
Joe Kucinski
How Much Horsepower Every Corvette Engine "LOST" in 1972
Joe Kucinski
Top 10 DOs and DON'Ts for Protecting Your Convertible Top!
Michael S. Palmer
Top 10 Most Explosive Corvettes Ever Made: Power-to-Weight Ratio Ranked!
Joe Kucinski
150 hp to 1,250 hp: Every Corvette Generation Compared by the Specs That Matter
Joe Kucinski
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
Safety Car
Joined: Sep 2013
Posts: 4,355
Likes: 2,633
From: Draper Utah
I spent two years chasing my hot hard starting problem. I solved it by insulating my fuel line with a Heat Shield Products Fire Armor 210040 Sleeve.
The problem was the crappy ethanol laced fuel was boiling in the fuel line.
Next time you have the issue pop your hood and grab your fuel line and if it's really hot that might be your issue.
Since then I've found reasonably priced non-ethanol gas nearby which I noticed also helped my problem. Either fix works, but both together and it's never even a slight issue.
Hope that helps someone else as I spent a lot of time chasing my hot start problem.
The problem was the crappy ethanol laced fuel was boiling in the fuel line.
Next time you have the issue pop your hood and grab your fuel line and if it's really hot that might be your issue.
Since then I've found reasonably priced non-ethanol gas nearby which I noticed also helped my problem. Either fix works, but both together and it's never even a slight issue.
Hope that helps someone else as I spent a lot of time chasing my hot start problem.
Drifting
Joined: Apr 2017
Posts: 1,377
Likes: 282
From: Bedford New York
you need to insulate the fuel from the heat rising from hot engine after shut down to stop the percolation .. to continue to run it this way is doing harm .. you are fuel washing the oil off the cylinder walls every start.. not to mention the fuel runs past the rings while sitting and dilutes your oil ..
Thread Starter
Cruising
Joined: May 2018
Posts: 13
Likes: 0
From: Ridgeville S.C.
So I've found other posts with a similar situation. The gas is actually boiling out of the carb and fuel line? I guess that can explain the dry fuel filter. Can it be showing up now because of the new fuel pump is not siphoning the fuel back from the carb? I will insulate and try. Thank God for fuel injection on my C5! Thanksfor everyone's input. Much appreciative.
Drifting
Joined: Aug 2009
Posts: 1,346
Likes: 160
From: new iberia la
actually its both.. you shut down, heat rises thru manifold into carb. , fuel boils out of bowl ,over into engine leaving bowl empty. engine is now flooded..hard to start... if you wait to start til next day or longer, it has evaporated, no fuel to start.. you have to spin the engine to refill bowl. .. a phenolic spacer under carb, insulate all fuel lines and filters from pump forward with heat wrap, , also heat shields are available to go under carb .... still not a believer? next time you shut off engine, open your hood immediately and leave open . .. I ll bet it starts right up later .
Intermediate
Joined: Feb 2018
Posts: 49
Likes: 14
From: Lugoff South Carolina
I am having hot start issues with my '79 but mine is slightly different. My car will start easily cold or hot but on hot starts it floods as soon as it starts causing a rough idle and a gassy smoke cloud out of the tail pipes for about the first 20 seconds. It runs great after about 20 seconds though. If I open the hood when I park it doesn't do it. So far I have installed a heat shield, a 1/2" plastic carb spacer, rebuilt the carb and insulated the fuel lines and nothing has helped. I'm sure the fuel is boiling inside the carb because it gets really hot after being parked for a little while but I can't figure out how to stop it.
Safety Car
Joined: Oct 2007
Posts: 3,729
Likes: 267
From: Austin Texas
Corvette of the Year Winner 2017
2016 C3 of Year Finalist
if you are Not running the original type 1/4" isolation gasket under your carburetor,
you will have these problems. the fuel literally boils away, from the carb. being too hot.
you will have these problems. the fuel literally boils away, from the carb. being too hot.
Last edited by 69Vett; Jul 11, 2018 at 11:29 AM.
Intermediate
Joined: Feb 2018
Posts: 49
Likes: 14
From: Lugoff South Carolina
I'm using the 1/4" gasket plus a heat shield, a 1/2" phenolic spacer and heat shield on the fuel lines and still have heat soak issues when it's above 85 degrees.
Race Director
Joined: May 2006
Posts: 18,735
Likes: 2,582
So I've found other posts with a similar situation. The gas is actually boiling out of the carb and fuel line? I guess that can explain the dry fuel filter. Can it be showing up now because of the new fuel pump is not siphoning the fuel back from the carb? I will insulate and try. Thank God for fuel injection on my C5! Thanksfor everyone's input. Much appreciative.
Thread Starter
Cruising
Joined: May 2018
Posts: 13
Likes: 0
From: Ridgeville S.C.
You stated you didnt have the problem until you changed the fuel pump, your gasoline didnt change all of a sudden. I asked you further up in this thread about the fuel pump manufacturer and part number to determine the amount of fuel pressure the new pump puts and now need to know if it has an anti-drain back valve.
Thank you for your help Mike