Vapor Lock in a C3
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Joined: Jul 2003
Posts: 95
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From: Davenport FL
Vapor Lock in a C3
I have an black '81 with almost new everything and I still can't trust it to get me back home after a cruise. My mechanic says its vapor lock. I have the new engine, new fuel filter, new fuel pump and I am using braided lines with my Holly carb. After about 30 minutes it goes from super great to dead. One minute later, starts right back up and runs great until it dies next time. I keep thinking one day it will not start up again and I will be stuck.
What does NASCAR do to prevent vapor lock on all those big hot carb cars?
Thanks.
What does NASCAR do to prevent vapor lock on all those big hot carb cars?
Thanks.
Burning Brakes
Joined: Mar 2006
Posts: 793
Likes: 1
From: Houston Texas
I suppose you have an HEI distributor?
If so try replacing the module in the HEI. Bad modules will do the same thing as you vapor lock theory. When old one's get hot they stop keeping the spark plugs happy.
Dan
If so try replacing the module in the HEI. Bad modules will do the same thing as you vapor lock theory. When old one's get hot they stop keeping the spark plugs happy.
Dan
Drifting
Joined: Aug 2005
Posts: 1,372
Likes: 4
From: Springfield VA
When it won't start have you sprayed fuel into the carb to see if it is really a fuel issue?
I also agree test the IM. Advance and AZ use to test for free. Make them run the test 3 times. I have seen plenty pass once but the 2-3rd time they are warm and fail.
I also agree test the IM. Advance and AZ use to test for free. Make them run the test 3 times. I have seen plenty pass once but the 2-3rd time they are warm and fail.
Burning Brakes
Joined: Mar 2006
Posts: 793
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From: Houston Texas
EDIT: Hey Carl914, I'm not laughing at you or your Holley, I'm laughing because I'm stuck with more than one of the little buggers!!! There is an element of truth to what Mike is saying.
Dan
Last edited by jetjockey; May 31, 2012 at 02:52 PM.
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Joined: Jul 2003
Posts: 95
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From: Davenport FL
My HEI is old, not 15 years old maybe. I have changed the cap and rotor in the last ten years, but not the coil. I think its one of those dark grey Accel ones. Someone said to check the cap, that those HEI can arc the cap and leave a carbon trail. I have changed the module, also to an Accel if I remember correctly, but that has also been a very long time. All if that was working well right up to the time the original engine went boom.
I have two shows I want to go to Saturday, but I think I will get up early and check out that whole HEI system first.
Thanks everyone!
Safety Car
Joined: Aug 2001
Posts: 4,883
Likes: 11
From: North Easton Mass
If you have a stock intake manifold and a heat riser valve (I think that's what it's called) in the exhaust system make sure it isn't stuck so it is always ducting hot air under the carb. The valves corrode and stop working - these cars weren't intended to last 30+ years.
Rick B.
Rick B.
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Joined: Jul 2003
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From: Davenport FL
If you have a stock intake manifold and a heat riser valve (I think that's what it's called) in the exhaust system make sure it isn't stuck so it is always ducting hot air under the carb. The valves corrode and stop working - these cars weren't intended to last 30+ years.
Rick B.
Rick B.
Maybe this stalling is caused by the fuel hose resting on top of the valve covers. I have a new chrome hose hanger somewhere and maybe its worth that shot too. Maybe also I need to reroute the fuel hose in from the back instead of the front where it won't touch the engine. I would think that a braided hose would be cooler than a factory metal hose, but I could be wrong about that too.
Last edited by Carl914; Jun 1, 2012 at 01:43 AM.
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Drifting
Joined: Jul 2002
Posts: 1,944
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From: The only Corvettes in Highett Victoria
I'm inclined to agree with Mike now that you mention your current pump. GM spent millions designing a fuel system that would discourage vapour lock, and there is no way they would have fitted a pump with a return fitting if it wasn't needed.
Maybe you could fit a pressure regulator after the pump with a return line to the tank. I hope this helps.
Regards from Down Under.
aussiejohn
Drifting
Joined: Jul 2002
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From: The only Corvettes in Highett Victoria
[QUOTE=Carl914;1580958332]
Maybe this stalling is caused by the fuel hose resting on top of the valve covers.
Carl,
That would be a good place to start, as rocker covers get pretty hot when the engine's running.
Maybe also I need to reroute the fuel hose in from the back instead of the front where it won't touch the engine.
I don't think that's worth doing. Millions of Corvettes and other Chevs have the fuel line coming up the front of the engine, just make sure that it's spaced away so that there is an air gap between it and the engine block.
I would think that a braided hose would be cooler than a factory metal hose, but I could be wrong about that too.
Maybe, but the best way to keep the fuel line cool is to make sure it doesn't touch any part of the engine.
Regards from Down Under.
aussiejohn
Maybe this stalling is caused by the fuel hose resting on top of the valve covers.
Carl,
That would be a good place to start, as rocker covers get pretty hot when the engine's running.
Maybe also I need to reroute the fuel hose in from the back instead of the front where it won't touch the engine.
I don't think that's worth doing. Millions of Corvettes and other Chevs have the fuel line coming up the front of the engine, just make sure that it's spaced away so that there is an air gap between it and the engine block.
I would think that a braided hose would be cooler than a factory metal hose, but I could be wrong about that too.
Maybe, but the best way to keep the fuel line cool is to make sure it doesn't touch any part of the engine.
Regards from Down Under.
aussiejohn
Melting Slicks
Joined: Oct 2003
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From: Chapel Hill NC
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vapor lock
I believe today's gas is formulated for EFI and not carbs. I fight vapor lock issues every spring in a non Vette vintage car when the weather warms up but the gas companies have not switched to their summer formula. Pay close attention to the fuel line from the tank to the fuel pump. You may have to insulate/shield it.
Melting Slicks
Joined: Apr 2001
Posts: 3,399
Likes: 278
From: Olmsted Falls, Ohio
I had a MGB that did the same thing. Ran good for 20-30 minutes, then you could hear the fuel pump quit "clicking" and the car would stall.
The previous owner had put a non-vented gas cap on the tank and when I finally figured out that the electric fuel pump was not the cause I opened the tank cap right after the problem and you could hear the pressure being relieved. Changed caps and never had the problem again.
The previous owner had put a non-vented gas cap on the tank and when I finally figured out that the electric fuel pump was not the cause I opened the tank cap right after the problem and you could hear the pressure being relieved. Changed caps and never had the problem again.
Had a 1976 L-82, 4-sp
Joined: Mar 2011
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From: Some days your the dog and some days your the hydrant.
Royal Canadian Navy
I guess those brilliant GM engineers decided to put a Holley on the L88, ZL1, 302 Z/28, etc to keep the HP down for insurance purposes or they ran out of QJ's on the assembly line. I can't imagine how much of a performance boost these engines would have had if they had put QJ's on them. Hey, any owners out there replace their factory Holley with a QJ?
Burning Brakes
Joined: May 2008
Posts: 1,116
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From: Middleburg Florida
I'm not going to get into the Holley vs Qjet thing again, Lars dispelled the myth that Holleys were better performance carbs with actual testing on a dyno and posted the results for all to see. GM put Holleys on for a whole host of reasons, mostly for sales. That being said, before I'd go chasing down a vapor lock problem, I'd verify it. When the car stalls or doesn't start, simply pull the air cleaner and look into the carb and see if it shoots any gas when you throttle it. If not, it's likely vapor lock or a bad pump. If there is gas, probably and HEI problem.
Tech Contributor
Joined: Aug 1999
Posts: 14,379
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From: At my Bar drinking and wrenching in Lafayette Colorado
Mike is absolutely right: The non-return fuel pump with your setup is a huge problem when it comes to vapor lock. I install fuel return systems on every car & engine I build now due to this problem, and it's essential to have a good return system if you intend to run a carbureted car on today's pump gas in warm climates.
The Holley carb makes a return system very easy to install. Here are 2 different systems that I typically use to cure the vapor lock issue:
This first one is the most basic. It uses a small drilled oriface in a restrictor fitting at the rear carb inlet "T". This works just like the GM return-fuel filters with the 3 connections (simple bleed oriface for return fuel) that GM used with Holley carb systems in the 60's. Fuel bleeds through the restrictor and keeps cool fuel circulating past both carb inlets:
The better system, but a little more compicated, is to use a return-style regulator. The regulator is simply set to a pressure slightly below the pump oulet pressure, and it continuously bleeds fuel back to the tank to eliminate any vapor lock issues. Since your car has the return line installed down on the frame, it's an easy tie-in to create the return system - no excuse not to use it and fix your problem:
Lars
The Holley carb makes a return system very easy to install. Here are 2 different systems that I typically use to cure the vapor lock issue:
This first one is the most basic. It uses a small drilled oriface in a restrictor fitting at the rear carb inlet "T". This works just like the GM return-fuel filters with the 3 connections (simple bleed oriface for return fuel) that GM used with Holley carb systems in the 60's. Fuel bleeds through the restrictor and keeps cool fuel circulating past both carb inlets:
The better system, but a little more compicated, is to use a return-style regulator. The regulator is simply set to a pressure slightly below the pump oulet pressure, and it continuously bleeds fuel back to the tank to eliminate any vapor lock issues. Since your car has the return line installed down on the frame, it's an easy tie-in to create the return system - no excuse not to use it and fix your problem:
Lars