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Discussion Starter · #1 ·
Hello!

Have noticed that bubbles (of air?) rise up through the fuel in the fuel filter. It does this when the car is warm/hot and continues for a few minutes after the engine is turned off. Can't say that I notice any sort of symptom in the running of the car.

Have read in another thread (now closed) about this problem and the OP struck out for an answer even after 15 pages of posts.

(Stock 283 PP motor – everything is new.)

What's the deal?
 

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Your fuel is boiling. Not much you can do about it. If your not experiencing any problems with vapor lock, I wouldnt worry too much about it.
 

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Check the routing of the fuel line from the fuel pump to the carb. You might have to reposition the line if its too close to the exhaust manifold or cyl. head. Also inspect all connections of the line from tank to pump and to the carb for a seep and air going in thru a fitting.Might have to wrap a line also if you're having some vapor lock.Good luck,keep us updated. :anim_25:
Big Bob:flag4::bowtieb:
 

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Discussion Starter · #4 ·
On that basis, I would suspect it to be an issue of heat – since it keeps bubbling for a few minutes after I turn the engine off.

If it was any sort of leak, it would stop immediately, right?

Also, if it were a leak, could it only be at a point before the fuel filter? That is, nothing coming back from the carb? (The reason I ask this, is we were looking at it just this morning at the carb shop and the mechanic identified that even though mine is a re-built carb, the throttle rod is worn and loose, and probably creating unwanted vacuum. So that's being fixed next week.)
 

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Have to keep an eye on this John, I think many members have similar symptoms with no direct answer, may be caused by a variety of problems
 

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Mine does the same thing. I think it's heat. Mine will also go empty shortly after I shut it off, then about an hour later, it fills back up again...
 

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Discussion Starter · #7 · (Edited)
Have to keep an eye on this John, I think many members have similar symptoms with no direct answer, may be caused by a variety of problems
Will do, Ang.

I can't say that I know it is doing anything to engine function or performance – but it just does not seem right.

I'll wait until the carb is fixed and monitor from then. And will ask the mechanic when the car goes back to the shop.
 

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On that basis, I would suspect it to be an issue of heat – since it keeps bubbling for a few minutes after I turn the engine off.

If it was any sort of leak, it would stop immediately, right?

Also, if it were a leak, could it only be at a point before the fuel filter? That is, nothing coming back from the carb? (The reason I ask this, is we were looking at it just this morning at the carb shop and the mechanic identified that even though mine is a re-built carb, the throttle rod is worn and loose, and probably creating unwanted vacuum. So that's being fixed next week.)
Hi John ; You're seeing bubbles , but it doesn't sound like it's AIR bubbles . Gasoline is an "aromatic" , and vapourizes or turn into a "gas" at lower temps than most liquids . I think you're just seeing fuel vapour bubbling up through fuel liquid . If you can , just insulate the section of fuel line that's adjacent to any heat sources. One other thing ; if your carb throttle shaft is worn , it will LOSE vacuum , not create more vacuum . I wouldn't worry about the bubbles in the fuel either once the heat source is covered . Then you have to stop watching the bubbles , and just drive and enjoy . I don't want to knock your mechanic , BUT.... you may be spending more money than you need to . Be safe...Bob.
 

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It's probably normal. If they are mounted on an angle or horizontal the bubbles are more noticeable and it is normal to see bubbles. If it is mounted vertical it should keep bubbles out.
A metal filter is better than glass or plastic. And you won't see the bubbles either.
Fuel boiling is another problem though.


Don
 

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bubbles

I noticed mine would do the same thing until I quit using oxygenated gas. Running without the alcohol in the gas cured the bubbling and the car also gets better gas mileage. The only drawback is the higher price for non-oxy.
 

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Discussion Starter · #11 ·
With the carb fixed, and running may leaner, the running temperature of the motor is much lower and the bubbling has stopped. (The carb guy said this would happen.) And I could previously notice the radiant engine heat from outside the car when I got out after driving.

And I can see this reduction on my newly fixed temp gauge. Woo hoo! Before, when the gauge first started to display properly, the running temperature was indicated by about 80% on the scale, which was too high. Now it reads about 40% on the highway, 50% at (hot) idle.

Btw, am running 95 octane fuel.
 

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It's probably normal. If they are mounted on an angle or horizontal the bubbles are more noticeable and it is normal to see bubbles. If it is mounted vertical it should keep bubbles out.
A metal filter is better than glass or plastic. And you won't see the bubbles either.
The right answer.
 
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