Holy Vapor Lock Batman!

[Nunyas]

Ok, I've double checked my coolant level and checked my thermostat and they're both good. The only thing I haven't done to my cooling system yet is completely flushing it out. I'm positive it needs doing, but I'm not sure it's going to solve my recent high temps problem.

A side effect of these high temps is the carburetor is also getting pretty hot, and as a result I'm 99% sure I'm experincing full on vapor lock. It nearly happened to me on the Malibu run on Monday. It most certainly happened to me twice today. The first time was at a stop light after having driven 20 miles. The car stalled, and wouldn't restart. Fortunately, I was at an intersection with a gas station. I managed to push the B in to the water/air station and check things out. To which, I found nothing broke, and all _appeared_ ok, except the under bonnet fuel filter was empty. After my poking around for 30 minutes, I found the fuel filter was full again and the car would run again.

Fast forward to an hour later. On I-5 heading home, 70MPH, and blam vapor lock hits me again. I hit my right turn signal, and carefully cost off to the side of the road dodging traffic as best I could under no power. I get to the side, and notice in my rear view a full-size Chevy pulled over behind me and hit his hazards too. I thought maybe he was there to help. I pop the hood go up front look around a little; started to pop the radiator cap and immediately notice it still has plenty of fluid, but the under bonnet fuel filter is empty again. At this point I decided that I have vapor lock, and I go back to talk to the driver in the Chevy.

Turns out the Chevy was LA Metro Transportation Safety folks. I chatted with the guy about cars for 20 minutes and a tow truck shows up at which point the fellow asks if I want a tow off the freeway. I told him I planned to wait 30minutes and then attempt to start the car and since it took 20 minutes for the tow truck to get there I wanted to wait the last 10 minutes and give it another go. So, we chat out the last 10 minutes and I go back to the car and it started right back up like nothing happened. I told the guy I'd be able to finish my trip under my own power and thanked him and the tow truck driver.

Erm.. I guess I got a little carried away there. To the point, I'm 99% sure I'm getting vapor lock when the engine gets as hot as it does in the late afternoons (mornings the engine never goes over mid-way on the Temp gauge). The first thing I notice when the engine stalls and won't restart is the fuel filter is empty. The second thing I notice is the carburetor is pretty dang hot (darn close to being too hot to handle), hotter than I *think* it should be. During these 30-minute cool downs, the fuel filter refills (with the ignition OFF), and the carb cools down *a lot*. I know for a fact that my fuel line runs across the bottom of the heater core box, between the heater box and the engine. My clutch line runs the same route. I have the stock ZS carburetor converted to manual choke. Is there anything I can or should do that will eliminate this highly irritating vapor locking problem?

 

[Steve_S]

Do you have a heat shield? Does it have heat resistant material attached to the underside? It makes a huge difference!

 

[Nunyas]

I have the late B fiberboard like heat shield thing in place. I also have the chunk of sheet metal that's supposed to let the carb suck hot air when it's cold out, and cold air once the engine is warmed up.

I don't know about the late model B's having those pads on the shields though.... /ubbthreads/images/graemlins/confused.gif

 

[Mickey Richaud]

Do you have a heat shield on the fuel line - where it passes at the rear of the engine?

 

[vping]

Steve,
Do you have a heat sheild on the fuel line in the GT? If so any pics? The reason I ask, is that I may have been experiencing the same problems as Nunyas. I do not have a sheild covering my gas lines and I notice the same thing with my filter.

 

[tony barnhill]

Overheating engine won't cause vapor lock....somehow, your gas itself is getting hot....Mickey touched on 1 thing that might be causing it...other would be either lack of the heat hield or missing carb spacers (the big black things) or fuel lines routed too close to engine/exhaust.

I'm guessing its the late heat shiled..try putting the earlier metal/fiber shield back on.

But, a question: every time it 'vapor locks', is the fuel filter empty? If not, it might not be a fuel issue but, instead, could be an ignition issue.

 

[Steve_S]

I have the stock heat shield behind the carbs with the padding on the back. No other heat shields that I am aware of.

 

[wkilleffer]

My car's experiencing some heat-related issues as well, especially in the afternoon. It doesn't stall while moving, but if the temp gauge is between the N and the danger area, it idles roughly and slowly. Also, when it's hot and I've had to shut it off to go in somewhere for a few minutes and come back out to start it, it's very hard to start, runs badly, and sometimes stalls unless I keep my foot on the gas.

Is this a vapor-lock situation? Most, but not all, of the insulation material is on the back of my heatshield.

Thank you,

 

[DrEntropy]

Rob, are you SURE the pump is okay? Reason I ask is: I've *rarely* seen fuel vapour lock in an MGB... just seems odd to me.

 

[Nunyas]

William- My car's carburetion system is a bit different from yours, but my car behaves how you mentioned on long drives. If I continue to drive the car will eventually stall and I have to wait 30 minutes before it'll run again.

Mickey & Tony- No heat shield on the lines where they pass nearest the engine; if there's supposed to be one there it was gone before i got the car. The rest of the fuel line routing puts the fuel line as far away as possible from the engine. Everytime it stalls the filter is empty. It's gone empty in the past, but I've always reached my destination before it got to the stalling point. Recently I've been pushing my luck and driving longer distances on really hot days in bad traffic, therefore the stalls have caught up with me.


Is there a specific type of foam I should get to fill the gap between the radiator and the support shroud? While I was under the hood I notice how big the gap is between the two and that certainly can't help the temp at speed.

 

[Steve_S]

Next time it does this, disconnect the fuel line and see if fuel is still flowing. Just be extremely careful where that fuel goes around a hot engine!

The other consideration is fuel tank venting. Have you tried removing the cap and then attempting to start the car again?

If you need a spare fuel pump let me know, I have one for my '67 that should work in your car.

 

[DrEntropy]

I'd say prep for the test by keeping a four foot piece of fuel line in the car with a one gallon gas can... swap the line for the one to the carb and end it in the can, hit the iggy. Quick 'n dirty emperical test! /ubbthreads/images/graemlins/grin.gif

 

[jlaird]

Duh, why did I not think of that.

Might have saved me some time a number of years ago.

 

[DrEntropy]

"We here at Chaos & Mayhem PTY., LTD. are dedicated to making life easier through dissemination of Quick 'n Dirty solutions to your technical problems." /ubbthreads/images/graemlins/wink.gif

 

[Nunyas]

I've done this before in the past (a little over a year ago.). I had good flow rate back then. If it happens again, I'll be sure to re-check.

I snagged up some lime green foam (matches Doc's pool noodle pretty well /ubbthreads/images/graemlins/jester.gif)from "Joan's Fabrics" earlier and stuffed it into the gap between the radiator and support. I didn't see any 'temp' ratings for the stuff. It's ugly under there, but no one but me has to know about it. erm... and you all I guess. heh

 

[DrEntropy]

At sixty MPH nobody will notice! /ubbthreads/images/graemlins/grin.gif

 

[swift6]

I know that I am just a "rumfie" over here in MG land but I have not heard of vapor locking occuring on a running engine. As the fuel moving through the system should keep stuff cool enough to prevent vaporization. (I've seen the results of an MGB that was left running with the manual choke fully set on a car with a catalytic converter, the cat was glowing cherry red and all the plastic bits in the engine bay began to melt but the car kept running because the fuel flowing through the carb was keeping it cool enough to finish the destruction).

I was always taught that vapor lock occured after an engine was shut down and the pump and line would be soaked through with heat and fuel would vaporize and cause a sort of vaccum which would block the flow of fuel.

The cure for most older cars that would vapor lock would be to add an electric pusher pump to the fuel line or get rid of the mechanical pump and use solely an electric pump. That being said, I don't believe it's vapor lock. I would be looking to the fuel pump and the tank vent.

I don't recall whether or not you mentioned that after it stalls if you can still hear the fuel pump or not. You should be able to hear it ticking away trying to pump fuel. Especially if your fuel filter is empty. If you can hear the pump furiously pumping away but no fuel is flowing, then you have a problem other than vapor locking. That would point more to a vaccum lock in the fuel tank. Not a vapor lock at the carbs.

Just my "rumfie" two cents worth though.

/ubbthreads/images/graemlins/cheers.gif

 

[Nunyas]

hmmmm...that sounds like a possible suspect. Could that be related to the fact that I can NOT pump fuel into my tank full bore (full squeeze)?

 

[swift6]

[ QUOTE ]
hmmmm...that sounds like a possible suspect. Could that be related to the fact that I can NOT pump fuel into my tank full bore (full squeeze)?

[/ QUOTE ]

We might be getting somewhere now!

Is this a "new" development? Does your B have a charcoal canister with a vent line from the tank? Is it supposed to have one (my Triumph bias now shows through /ubbthreads/images/graemlins/grin.gif). If so, they were often a hard plastic line that can melt and block it.

On second thought, I can't fill my TR8 very quickly either but I have no venting issues. That has to do with the angle of the fill tube sometimes and ultra sensitive pumps.

/ubbthreads/images/graemlins/cheers.gif

 

[DrEntropy]

Shawn!!!! NEVER apologise for pappin' up! More info from more peeps is what this thing is all about!

Rob, I'd be lookin' for blocked vents, etc.