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jmarwill

Gas evaporating from Carburator

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I’m new to this forum and would appreciate any advice you can offer. I have a ‘72 240Z that is pretty much all original. I’ve owned it for about 2 years (my father-in-law was the original owner). I’ve noticed that if I don’t drive it at least every 1-2 weeks, the gas seems to evaporate from the carburetor. The only way I can start it is to put gas directly into the carburetor and the rubber lines leading to the carbs. This is more than just a hard to start carberated engine...there is no fuel in the carburetor or fuel lines and the fuel pump is not bringing gas to the engine when I’m trying to start it.

 

If I drive it once a week, the Z starts up pretty easily. And the Z runs very smoothly when warmed up with plenty of power.

 

Is this normal?

Thanks,

Jeff

 

 

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Yes it can be. Some people add an electric fuel pump to use as a priming pump

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Jeff, I guess it's possible, but I'm wondering if maybe your float levels are a low contributing to the problem.

I'm thinking that if it only takes two weeks for the bowls to evaporate that far down, then there wouldn't be so many people with gummed up stinky gas left in the bowls of cars that sat for a year?  LOL

Also, do you have the stock air cleaner and stock vent tubing in place?

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I agree with Patcon. An electric fuel pump, with or without the mechanical pump, would be a cheap fix. Personally I'd run both pumps.

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Jeff, I guess it's possible, but I'm wondering if maybe your float levels are a low contributing to the problem.
I'm thinking that if it only takes two weeks for the bowls to evaporate that far down, then there wouldn't be so many people with gummed up stinky gas left in the bowls of cars that sat for a year?  LOL
Also, do you have the stock air cleaner and stock vent tubing in place?

Yes- stock air filter. Im not sure about the vent tubing but I’m pretty sure it is stock. Thanks to all for the feedback and ideas


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Jeff is your choke lever working. I have always had to choke mine in the morning or after it sat a few days. The other day I decided to start it after a couple months sitting. Took full choke and some cracking to get her to fire. You shouldn’t have to manually feed the bowls. I would check the fuel lines clamps for air leaks.


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 A couple of questions. How does the engine run when it's warmed up? Have you done any work on the carbs such as tuning? Having to crank the engine a little longer could be considered normal if the car sat for a few weeks but having to prime the carbs is "abby normal". Fuel lines and or connections sucking air is a good possibility. Choke cables that aren't pulling the nozzles all the way down is another. A fuel pump pressure and volume check would eliminate the possibility of a weak (as in going bad) pump, which could give you the symptoms you've described.

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I had exactly the same problem with down draft Weber carbs and solved the problem by mounting an electric pump between the tank and hard line. Rather than powering the pump anytime the engine was running, I mounted a push button switch under the steering column cover. Pushing the button for 10-15 seconds until the bowls refilled and closed the float valves was all that was needed. You could hear the change in the pump pulsing once the valves closed.

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