Author Topic: Vapor lock?  (Read 1667 times)

ThinkSS

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Vapor lock?
« on: June 26, 2017, 05:18:05 AM »
1968 L48
Headers
1965 #461 heads (1.94's)
Comp cam XE262H
Cast iron intake, Q-jet
180 thermostat

Temperature outside was 93... although this has happened at lower temps also... in the 70's

Car runs fine for about five miles and then when you come to a stop it stutters and stalls out.

Opened the air cleaner operated  the throttle no fuel, only a little vapor.... poured some gas into the carburetor and could hear it sizzle!!

Fuel pump was hot to the touch, so I got a bag of ice and set it on there for about 20 min. Car started after that and I was able to get home. This is happening more than one occasion

Insulated the fuel line near the rear tail pipe with high heat tape, had no impact. Thought that was a problem because it was only a half of an inch away

Here are a few shots under the hood, I have the steel fuel line from the fuel pump to the carburetor and you can see the distance from the rubber hose to my radiator hose, and my steel fuel line to my headers.

I'm not sure what to do here other than perhaps and electric fuel pump. I do not know what temperature the engine is so I will put a gauge on it this week and see if it's running crazy hot. But the car did not overheat at all.

Any ideas suggestions comments?

Thanks everybody in advance

ThinkSS

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Re: Vapor lock?
« Reply #1 on: June 26, 2017, 05:21:19 AM »
Here is the fuel line at the radiator

TRLAND

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Re: Vapor lock?
« Reply #2 on: June 26, 2017, 11:23:50 AM »
Your carb is too hot and it sounds like the fuel is boiling. You don't say what intake you have but make sure you have the right gaskets between the intake and carb.  Here's a post on the subject from the Corvette forums:  https://www.corvetteforum.com/forums/c1-and-c2-corvettes/1978466-q-jet-carb-base-gasket-tech-info-the-hot-slot-manifold-problem.html
Mike in Northern Illinois
1967 RS 327

Stingr69

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Re: Vapor lock?
« Reply #3 on: June 26, 2017, 12:44:14 PM »
Carb is hot.  Not the fuel line.  You are cooking the carb.

bcmiller

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Re: Vapor lock?
« Reply #4 on: June 26, 2017, 03:06:51 PM »
I agree. Does not sound like a fuel line problem. Hopefully if you get the correct gasket setup that will solve the problem.
Bryon / 1968 Camaro SS 396 - now 468 ci, M21, 12 bolt
Looking for 68 Camaro with body number NOR 181016

67 RS Ragtop

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Re: Vapor lock?
« Reply #5 on: June 26, 2017, 03:44:39 PM »
JMO make sure your exhausts heat riser valve is not stuck in the closed position, and it opens fully when at operating temps (if you are still running one). One other issue that was supposedly recalled many years ago due to fire issues, was blocking off the exhaust passages at the intake below the carb. - simply remove carb., tap the ports and install pipe plugs, reinstall carb., etc..

ThinkSS

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Re: Vapor lock?
« Reply #6 on: June 26, 2017, 04:53:49 PM »
Ok... got a break from the desk!!

Stock cast iron intake... the exhaust crossover it is unmodified.
Attached is the gasket set-up.

Are you speaking of the heat Riser valve in the air cleaner?


L78 steve

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Re: Vapor lock?
« Reply #7 on: June 26, 2017, 05:37:11 PM »
There is no heat riser valve in a header system. Is your Ign. timing correct and not retarded? I would also heat shield the metal fuel line where it passes the header tube.
You could also block the heat riser passage in the intake but with this set-up it should not be necessary.
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Stingr69

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Re: Vapor lock?
« Reply #8 on: June 26, 2017, 06:18:38 PM »
I would plug that exhaust gas passage on the non-choke coil side of the intake manifold. Heat is flowing thru there.

ThinkSS

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Re: Vapor lock?
« Reply #9 on: June 26, 2017, 07:13:08 PM »
Have you ever tried any of those tin block off plates that come in some gasket sets?

Just got this thing put back together to!

ThinkSS

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Re: Vapor lock?
« Reply #10 on: June 26, 2017, 11:21:33 PM »
I could try and Advance the timing a bit, right now I believe I'm eight degrees before top dead center on the marker... but it could be less than that I would have to check again

How far Advanced would you suggest I go?

L78 steve

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Re: Vapor lock?
« Reply #11 on: June 27, 2017, 05:21:46 PM »
I could try and Advance the timing a bit, right now I believe I'm eight degrees before top dead center on the marker... but it could be less than that I would have to check again

How far Advanced would you suggest I go?

Go with 36 degrees total. Disconnect and plug  Vac. advance before setting total then reconnect.
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ThinkSS

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Re: Vapor lock?
« Reply #12 on: June 27, 2017, 08:13:48 PM »
Thanks for the tip.

I will get this done in the next few days and report back

Thanks again

z28z11

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Re: Vapor lock?
« Reply #13 on: June 28, 2017, 03:28:55 AM »
Seat a 7/16" freeze plug in each end of the heat transfer slot under the carb - it will block the heat from under the carb bowl and keep from frying the gas and the carb. It'll also save you from having to pull the intake and blocking the heat passages until you need to do a tear down. First thing I did on the Pace Car L48 when I redid the carb a while back - effortless, and will save the carb and gas from cooking. Use the stainless heat plate you show, or a composite gasket with the plate sandwiched in. Works for me -

Regards,
Steve
1968 Z28 M21/U17 BRG/W
1969 Z28 X77/M20/VE3 LeMans/W
1969 L78 X66/N66 Cortez/BVT
1969 Z11 L48/M35/C60/C06

ThinkSS

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Re: Vapor lock?
« Reply #14 on: June 28, 2017, 04:42:54 PM »
Great idea. Was hoping to not habmce to pull the intake!

Did the plugs seat into the manifold well?
I also think i can advance the timing by a few degrees...