1969 427/ 390 stalling once warmed up.
06-24-2013, 04:20 PM
#1
Heel & Toe
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1969 427/ 390 stalling once warmed up.
Hi all,
This is my first question as a new member. I recently bought a 1969 427/ 390 ( My life long dream car). First thing i did was have the carb (4brl holley) rebuilt as it was leaking and for general good measure. Installed carb and she fires right up (hasnt been fired in 5 years). After a couple minutes of warm up the engine runs real smooth and sounds tight. Rev it up a little at a time and she purrs like a kitty, no stumbling. Then after about 10 minutes of idling (around 1000rpm) once the car is really warmed up, the idle starts to get rough then it just dies and kind of lets out a big gasp. Upon trying to restart it, it just cranks over and over and periodically burps and blows flame out of the carb. Is this because of gas getting too hot? I've heard of people blocking the port on the intake manual, beneath the carb., that was meant to originally warm the carb. Is this the correct move here? Is this because gas is different than the old days? Lower boiling point? Is this classic vapor lock? Thanks in advance for any feedback. Viva La Forum
This is my first question as a new member. I recently bought a 1969 427/ 390 ( My life long dream car). First thing i did was have the carb (4brl holley) rebuilt as it was leaking and for general good measure. Installed carb and she fires right up (hasnt been fired in 5 years). After a couple minutes of warm up the engine runs real smooth and sounds tight. Rev it up a little at a time and she purrs like a kitty, no stumbling. Then after about 10 minutes of idling (around 1000rpm) once the car is really warmed up, the idle starts to get rough then it just dies and kind of lets out a big gasp. Upon trying to restart it, it just cranks over and over and periodically burps and blows flame out of the carb. Is this because of gas getting too hot? I've heard of people blocking the port on the intake manual, beneath the carb., that was meant to originally warm the carb. Is this the correct move here? Is this because gas is different than the old days? Lower boiling point? Is this classic vapor lock? Thanks in advance for any feedback. Viva La Forum
06-24-2013, 04:36 PM
#3
The car never came with that Holley. Hopefully it was rebuilt properly.
How about your fuel delivery system? Screen clogged on the tank pickup? Does the car have a vented gas cap...especially now that the fuel return line from the filter is not being used. How about the filter? How about the metal lines? How about the pump?
You need to make sure about these things before you go messing with the intake manifold.
How about your fuel delivery system? Screen clogged on the tank pickup? Does the car have a vented gas cap...especially now that the fuel return line from the filter is not being used. How about the filter? How about the metal lines? How about the pump?
You need to make sure about these things before you go messing with the intake manifold.
06-24-2013, 04:43 PM
#4
Heel & Toe
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Thanks for your reply. The Holley was rebuilt by a very reputable carb guy. I'll have to check the screen, filter and pump pressure. All the lines are non-kinked. Not sure about the vented gas tank cap. I hadn't thought of that. The tank cap looks original. I guess I could test this by running car again until it dies out, then open gas tank and listen for pressure releasing?
Side note, fuel delivery in general (screen, pumps, filter, lines) seems fine because she runs like a dandy for the first 10 minutes. Seems like a temperature issue or maybe the suction building in gas tank like you mentioned.
Side note, fuel delivery in general (screen, pumps, filter, lines) seems fine because she runs like a dandy for the first 10 minutes. Seems like a temperature issue or maybe the suction building in gas tank like you mentioned.
06-24-2013, 05:12 PM
#5
The stock 427/390 manifold allowed exhaust gases to pass underneath the bowl of the Rochester Q-jet...for winter operation.
Being in Florida, I installed threaded plugs in each side to block the gas. I also installed a stainless plate along with the carb base gasket to further prevent heat transfer to the fuel bowl. Do you have the stock manifold on the car?
Why not show a picture of your setup...the fuel pump, filter and line to the carb.
Being in Florida, I installed threaded plugs in each side to block the gas. I also installed a stainless plate along with the carb base gasket to further prevent heat transfer to the fuel bowl. Do you have the stock manifold on the car?
Why not show a picture of your setup...the fuel pump, filter and line to the carb.
06-24-2013, 08:44 PM
#7
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Yes it is the original manifold. It has that open cavity that allows exhaust to contact carb base. I will take some pics of the fuel set-up.
You mentioned you used threaded plugs to block the holes. I'm assuming you tapped the threads into the manifold.?.? I don't remember seeing threads in there. Are there other alternative solutions/ plugs you've heard of?
My gut is telling me this is hot fuel. Seems like similar symptoms I had with my 55 chevy, which has a glass fuel filter and you could actually see the gas boil. Fuel line was too close to manifold. But it wasn't a problem years earlier with exact same setup. Heard people say today's gas is different than 10-15 years ago. I'm assuming lower boiling point. Anyway, I appreciate your help 'faster rat' and I'll work on geting some photos up. I'm a forum newbie, still can't figure how to get photo in my profile box. ttys
You mentioned you used threaded plugs to block the holes. I'm assuming you tapped the threads into the manifold.?.? I don't remember seeing threads in there. Are there other alternative solutions/ plugs you've heard of?
My gut is telling me this is hot fuel. Seems like similar symptoms I had with my 55 chevy, which has a glass fuel filter and you could actually see the gas boil. Fuel line was too close to manifold. But it wasn't a problem years earlier with exact same setup. Heard people say today's gas is different than 10-15 years ago. I'm assuming lower boiling point. Anyway, I appreciate your help 'faster rat' and I'll work on geting some photos up. I'm a forum newbie, still can't figure how to get photo in my profile box. ttys
sorry that photo is so big... still figuring this out..
06-24-2013, 10:42 PM
#10
With the manifold off the motor, I tapped the holes to match a piece of threaded rod, hack-sawed to length, ground flat and then notched one end for a straight slot screwdriver. Used loc-tite to make sure they would not come out. No harm...no foul.
