Car loses power and chokes out after going 80 MPH

[BoweP]

After changing out fuel filters, I thought that I had the problem solved. That is, until I took it for a half hour highway drive. After it started choking, I pulled over and shut it off. I popped the hood and immediately noticed a bubbling sound from my carb. and bubbling in my glass fuel filter (sits against the valve covers). I've never overlooked something so much before. Fuel percolation? I bet, especially given the hard starts after my car has set for about 15 minutes or so.

 

[will e]

Sounds like you found the problem. If you want to confirm I would suggest you go drive it with 1/4 tank full of gas until the problem starts. Then drive into the nearest gas station and fill the tank up. Take it out and see if the problem goes away. The very cool fuel from the underground storage should 'fix' it for a while.

Are you running your fuel lines in the stock locations? Have you replaced any of the metal line with rubber? How much ethanol is in your fuel (it has a lower boiling temp).

 

[BoweP]

Sounds like you found the problem. If you want to confirm I would suggest you go drive it with 1/4 tank full of gas until the problem starts. Then drive into the nearest gas station and fill the tank up. Take it out and see if the problem goes away. The very cool fuel from the underground storage should 'fix' it for a while.

Are you running your fuel lines in the stock locations? Have you replaced any of the metal line with rubber? How much ethanol is in your fuel (it has a lower boiling temp).

Well, the theory was nice. I did that test last night, and it starved all the way home (about a mile away from the station). When I went to take it to work this very cold morning, and it started to give me issues after a couple minutes. Hesitation and stumble at take off now, and starts to totally lose power right around where it shift into third.

 

[72HCODE]

if it is vapor lock (fuel boiling) then i would suggest a carb spacer, you want a thermal break between the carb and the intake manifold to reduce heat and fuel boiling in the bowls.

move the fuel lines away from the engine. you may need to fabricate a heat shield to protect the fuel from boiling inside the fuel lines

"glass fuel filter" take the filter off the car and put it in garbage, glass fuel filters are a fire hazard and banned from pretty much everywhere.

you can install a metal housing filter down by the fuel pump this allows you to restore original fuel line position and maybe keep the lines cooler and away from the engine heat.

 

[Jeff73Mach1]

There are a few possibilities that come to mind-

Often high RPM break down and inability to pull at higher speeds is an ignition problem. Check the cap for cracks, the rotor and contacts for being in good condition, the coil for possible failure, the condition of the wires etc. If your car is popping and backfiring under load, I would start here

your fuel could be boiling in the float bowls. Often a heat shield under the carb will eliminate this. A simple cheap way to test for this is to wad up aluminum foil and tuck it under the float bowls. If this works, you know a heat shield is going to help.

The other is fuel starvation. You may want to check the pressure developed by your fuel pump and it would not be a bad idea to remove the sending unit and check it's condition. The fuel filter/sock on the end of it could be clogged. If the pick up line is cracked inside the tank it will suck air. when you are below a 1/4 tank you can jack the driver side of the car up as high as possible, put it on jack stands and remove the sender without draining the rest of the fuel.

Also your car should have a vent line from the top of the tank, up to the firewall. Often the charcoal canister is removed. Some people plug the line which doesn't allow the tank to vent. If this line coming off the firewall and pointing to the passenger side is plugged, unplug it, open the gas tank and try and blow air through it.

 

[Carolina_Mountain_Mustangs]

Have you still not tried taking the gas cap off when this happens to see if it is vented? Takes a couple seconds.

David

 

[BoweP]

if it is vapor lock (fuel boiling) then i would suggest a carb spacer, you want a thermal break between the carb and the intake manifold to reduce heat and fuel boiling in the bowls.

move the fuel lines away from the engine. you may need to fabricate a heat shield to protect the fuel from boiling inside the fuel lines

"glass fuel filter" take the filter off the car and put it in garbage, glass fuel filters are a fire hazard and banned from pretty much everywhere.

you can install a metal housing filter down by the fuel pump this allows you to restore original fuel line position and maybe keep the lines cooler and away from the engine heat.

That's a good idea. I think that I will place the fuel filter at the length of rubber house before the fuel pump underneath the brake cylinder. There's too much hose between the hard line and the carb after the pump, so that's a good place to start.

Have you still not tried taking the gas cap off when this happens to see if it is vented? Takes a couple seconds.

David

I did take it off the first time that it did this and it gasped. After I filled up and drove home (when it started to do it again) I tried taking it off and it did nothing out of the normal.

There are a few possibilities that come to mind-

Often high RPM break down and inability to pull at higher speeds is an ignition problem. Check the cap for cracks, the rotor and contacts for being in good condition, the coil for possible failure, the condition of the wires etc. If your car is popping and backfiring under load, I would start here

your fuel could be boiling in the float bowls. Often a heat shield under the carb will eliminate this. A simple cheap way to test for this is to wad up aluminum foil and tuck it under the float bowls. If this works, you know a heat shield is going to help.

The other is fuel starvation. You may want to check the pressure developed by your fuel pump and it would not be a bad idea to remove the sending unit and check it's condition. The fuel filter/sock on the end of it could be clogged. If the pick up line is cracked inside the tank it will suck air. when you are below a 1/4 tank you can jack the driver side of the car up as high as possible, put it on jack stands and remove the sender without draining the rest of the fuel.

Also your car should have a vent line from the top of the tank, up to the firewall. Often the charcoal canister is removed. Some people plug the line which doesn't allow the tank to vent. If this line coming off the firewall and pointing to the passenger side is plugged, unplug it, open the gas tank and try and blow air through it.

My carbon cannister is still intact and hooked up everywhere except at the air cleaner, since I have an edelbrock. The fuel pump has good vacuum, it is new along with a new fuel sender. The problem seems to be getting worse for not much of a good reason, but I think you may be onto something with the "under load" thing.

 

[Carolina_Mountain_Mustangs]

I would put a vented gas cap on and see if it is ok. If it is then your vapor system has something blocking it. Did you blow through the line like suggested by another member? It would only show up when you have ran the car hard air would slowly leak in if you are driving slow. Getting a vapor lock without fairly hot weather is doubtful. Takes pretty good heat to boil the gasoline.

David

 

[barnett468]

After changing out fuel filters, I thought that I had the problem solved. That is, until I took it for a half hour highway drive. After it started choking, I pulled over and shut it off. I popped the hood and immediately noticed a bubbling sound from my carb. and bubbling in my glass fuel filter (sits against the valve covers). I've never overlooked something so much before. Fuel percolation? I bet, especially given the hard starts after my car has set for about 15 minutes or so.

Did you do any of the things I suggested?

What intake manifold do you have?

Did you block the exhaust cross over in the intake?

Do you have a carb spacer and if so, how thick is it and what is it made out of?

Your fuel level should be near the bottom of the sight glass immediately after you turn the engine off . If it is any higher, you may have a lot of probs including hard starting when hot.