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Vapor Block?


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Hey everyone, if I leave my car for a bit to cool on a warm night mind you and come back and it won't start, does it mean the vapor is stuck in there until it decides to come out, or could it be something else? Last time I mentioned driving fine, shopping for 10 minutes, and then the car started. But when I pulled away, it stalled. This has been a recurring problem. I guess I'll wait until morning to see if it helps, along with the Stabil additive I put in. Dez

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Year? Carbed? Solex, Weber, sidedrafts, etc? Stock pump or electric? 

Inquiring minds want to know... we'll go have a beer while we wait. 😁

  • Haha 1

Hacker of many things... master of none.

 

Gunther March 19, 1974. Hoffman Motors march 22 1974 NYC

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Hi stock pump 73 base 2002 ,Weber,carbed, 

 

I’m sorry as I haven’t been on the forum in a bit.   The mystery stall is so random. It’s making me nuts. As I just went in my Chevy to a lonely parking lot to start it. No chance. 
still turning over. Strong start. But no cigar! 
 

I was instructed to leave it for a bit   And I did. But I guess I could try in the morning. Dez

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First step is to determine if it's no fuel or no spark.

Take the air cleaner top off, dribble a small bit of gas down the throat of the carb and see if it fires. If it does and stalls, you have a fuel delivery problem.

if no start, it might be loss of spark... or you could have both issues. Time for further diagnostics.

  • Confused 1

Hacker of many things... master of none.

 

Gunther March 19, 1974. Hoffman Motors march 22 1974 NYC

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I get the exact same issue occasionally with mine... same setup; Webber, stock pump.
I'm sure with mine it is vapor lock/boiled petrol. Mine will start then stall a few yards down the road and refuse to start.
But leave it a half hr or so to cool and it starts right away. 
I've heard a fuel pump helps or insulate the fuel line/pump against the under-bonnet heat... I've tried neither yet as UK summers aren't that warm! 
but I am intrigued to test when I do get a chance.  
 

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If it is vapor lock, try holding the gas pedal to the floor while starting it.  It seems counterintuitive to give it more gas, but you're also letting a lot more air in.  Sometimes that helps.

 

There are a lot of old discussions on the topic in the archives, talking about fuel return lines, Jeep fuel filters, fuel line routing, fuel pump type, one way valve installations, spacer plates under the carb, carb tuning, cool-air-intake (original) air cleaners, distributor timing, et-cet-er-a.

 

I've had the gas boil inside the carb bowl after sustained cruising at 4.5K rpm in 90 degree weather at high altitude.  I could hear it hissing inside.  I opened up the carb, while waiting for it to cool down and then got back on my way (and kept it at 4K for a while).

 

I even took a little video.  Have you been making any videos lately Dez?

 

 

image.thumb.jpeg.afd7f8c7df93af32e654d2ddda31f68f.jpeg

 

Tom

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Are you using a phenolic spacer between your intake manifold and your carb?  It isolates the carb from the heat of your engine and helps prevent vapor lock.

 

Mark92131

 

 

s-l1600 (3).jpg

1970 BMW 1600 (Nevada)

 

 

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vapor lock puzzled out. Fresh rebuilt, hot day drove fine going shopping. Came out to drive home, started right up, drove out of lot, stopped at congested rush hour traffic. Car died .would not restart. Police came / called to get me a tow . $200.00 to get 8  blocks to my house. Reduce heat soak with  spacer between 38/38 Weber and stock manifold. Utilize  carter fuel pump (P60430) to push fuel, to a fuel pressure regulator (Fuelab 515) and removed mechanical pump from hot block. One line in...gas splits... out to 2.7 psi to carb , (0 to 5 gauge monitors)... then  2nd line from regulator the left overs  returns to tank. No pressure left in line, gas keeps cool by moving not sitting blocked up next to the hot metal parts. My 74 , 2002  came with a return line running  from the bay under the car back to the tank, switching connections at the tank, I used that path with pump mounted under the car and not in the trunk. Pump is whisper quiet. So far ... no vapor lock this summer. This next week in the 100 degree range will tell for sure.

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Yup.an electric pump will take care of the vapor lock, but if you want to run the stock pump you need to make sure your fuel hoses are fresh and space the line away from the head move fuel filter to after the pump use a carb spacer and all that rigmarole, it can be done but it takes setting up and maintaining everything. 

If everybody in the room is thinking the same thing, then someone is not thinking.

 

George S Patton 

Planning the Normandy Break out 1944

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Good discussion, thanks everyone. I definitely have heard hissing (Weber 32/36, mechanical fuel pump, no return line) after a summer drive but thankfully I've never had it not start. Hard starts, but not no starts. I installed a phenolic spacer over the winter so hopefully that helps. I didn't realize the mechanical pump could cause issues but that makes perfect sense that this metal thing attached to a hot head would warm up the gas. Between modern gas evaporating out the bowl causing the car to take a while to start and vapor lock, I am starting to think electric fuel pumps are the way to go. 

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1 hour ago, popovm said:

I am starting to think electric fuel pumps are the way to go. 

Here's a sketch of an electric pump (pusher) installation using the steel return line as the feed, and the plastic line as the return. This (Rev 4) uses an inertia safety switch. There is a new type of safety switch that cuts the power to the electric pump when the tach signal is lost. When I get the details, a Rev.5 sketch will be available.

 

ElectricFuelPumpRev4.thumb.jpg.31d8b974863cb121ba163fdbb4984ed5.jpg

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Hi guys and gals. I don’t post much, but last year I got a 73. I built a fresh engine with a 32/36 and have been struggling with the exact same issue. I put an electric pump and damn, it still had a hard start problem after sitting hot for ten minutes. I searched every post regarding vapor lock on here. Finally I looked at the coil output when cranking. Seems the relay behind the coil had failed and so the coil was only getting something like 9 volts at crank instead of 12. Being a bit flooded compounded the problem. When cold it would start at 9 volts no problem as it wasn’t flooded. It still takes a few cranks when hot but the electric pump seems to have cured the vapor lock as it doesn’t stall after starting.

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4 hours ago, Whitesell said:

it still had a hard start problem after sitting hot for ten minutes

Are you pumping the gas pedal when trying to start the car? I have a '76 with a 32/36 and dealt with a similar hard start problem after sitting hot. Until, I read in the manual that you are not supposed to pump the gas pedal at all when trying to start the engine once the car is hot. When I stopped pumping the gas pedal the car turned over almost instantly when hot. Contrarily, even a single pump had my starter spinning for quite a while until the engine slowly turned over.

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4 hours ago, Whitesell said:

Seems the relay behind the coil had failed and so the coil was only getting something like 9 volts at crank instead of 12

Test at the battery terminals when cranking, it will be 9-10 volts.

Test the relay for function.

Fuel boilover is most likely a problem.  Floor the accelerator so the unloader function on the carb opens the plates and clears the flood while hot cranking.

A radiator shop is a good place to take a leak.

 

I have no idea what I'm doing but I know I'm really good at it.

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