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  #11  
Old 07-21-2013, 12:57 AM
philbird60 philbird60 is offline
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When I got it, it leaked some,stumbled, popped,and flooded from choke staying closed. It took a lot of messing with it. (New floats too).
I had a leak ,only when it was running, just drizzling out of the annular boosters, and you could see it happening.
The rebuild kit cured that.
Now, I never had a flooding issue, at least the way you describe it.
When I replaced my floats they were not identical to the originals. Yes, they fit, but the float height measurement procedure in the shop manual goes out the window.
SO, I actually set the floats with the entire carb top off, in a tupperware container, with a funnel and a gas can. I set them about 5/16" below the edge, allowing some leeway for slosh. Been good since.
I have to say, I don't think you could see fuel pooling on a piston, it might be a little bit of a trick of the eye. The plenum might look a little wet, but that is a little normal. If you aren't actually seeing fuel fall out of the carburetor into the manifold, then I have one other thing for you to check out.
The original fuel filter was a giant thing screwed right into the front bowl. It was unidirectional (a check valve of sorts) A lot of people swapped out with something else. Something generic. The routing of the fuel system in the 352 will act like a siphon when there's no check valve. Effectively, it will send all the gas that used to be in your bowls back to the tank. It doesn't take all that long, even less time if your float height is on the low side.
Then you'd be cranking and cranking and pumping and pumping, thinking you're trying to clear a flooded engine, but you're just waiting for the fuel pump to fill the bowls again.
Simple test for this... next time she doesn't want to start, drip a few oz. of gas right down it's gullet. If it catches, you found your problem!
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  #12  
Old 07-21-2013, 06:37 AM
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You must confirm fuel line pressure with the electric pump even if it was described as a low pressure model. If needed, install a pressure regulator to limit pressure to OEM specs (found in Shop Manual).

Fuel cannot leak past the needle and seat unless it is defective on the 4100 (or if the float is incorrectly adjusted). The line will remain pressurized for some time by the mech. fuel pump (check valve) (and this contained fuel will also expand with heat soak and cause the needle to raise off the seat). Any loss of bowl volume will be caused by an internal leak and/or heat soak (fuel volume expansion) after shutdown or evaporation.

As suggested, verify power valve integrity. When you remove the cover and see fuel, it is defective. Use only quality kits. Do not shop by price but quality.

Verify correct jet sizes.

Start with the basics.
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  #13  
Old 07-23-2013, 09:40 AM
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Quote:
Originally Posted by Tbird1044 View Post
Are you still using the Autolite 4100 carburetor? I am beginning to realize that these are notorious for leaking fuel into the intake manifold. Seems the fuel drains out of the primary float chamber and into the engine. I have had mine apart several times for this and so far have made a little progress, but still seems to be leaking fuel into the engine. I have found several here that have switched to an Edelbrock 1406 and they seem to be happy with that. I'm stubborn and am still trying to figure out why the primary float bowl drains into the intake manifold. I'm beginning to think that it may be porosity in the carburetor castings. If anyone has successfully solved this problem please post what you did.
Nyles
The rebuild kit that matchs the carb I have say's it is a Model F-4. Like you I am stubborn and want to determine what is causing the problem. Don't want to change if others are not having the problem. Thanks
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  #14  
Old 07-23-2013, 10:30 AM
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Quote:
Originally Posted by KULTULZ View Post
You must confirm fuel line pressure with the electric pump even if it was described as a low pressure model. If needed, install a pressure regulator to limit pressure to OEM specs (found in Shop Manual).

Fuel cannot leak past the needle and seat unless it is defective on the 4100 (or if the float is incorrectly adjusted). The line will remain pressurized for some time by the mech. fuel pump (check valve) (and this contained fuel will also expand with heat soak and cause the needle to raise off the seat). Any loss of bowl volume will be caused by an internal leak and/or heat soak (fuel volume expansion) after shutdown or evaporation.

As suggested, verify power valve integrity. When you remove the cover and see fuel, it is defective. Use only quality kits. Do not shop by price but quality.

Verify correct jet sizes.

Start with the basics.
The gasket was soaked as I lifted the carb off the manifold. The primary was mostly empty (Had sat for a couple days). The power valve seemed OK (no fuel) but I messed up the gasket so I will replace both. Small question on power valve. Say it was bad, does heat soak (which I may not entirely understand) pull fuel from bowl through power valve into the manifold through the vacuum hole? And since the hole is small it would take some time to dump that much fuel into the manifold, I would think.

I am going to get a fuel regulator to eliminate any fuel pressure issues. I don't understand yet, how and where that much fuel actually travels into the manifold if the fuel expands and lifts the needle off the seat and if it does it immediately after the engine is shut down.

Thanks for all the insights from the post. Will continue to learn and work through this problem.
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  #15  
Old 07-23-2013, 03:27 PM
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Gas and gasohol have a much lower boiling point than water. An engine oil temp at the pan is typically close to 300*F. In addition, there is an exhaust crossover in your intake manifold. So, after heating up the engine and you park the car, heat migrates straight up the carb. That heat boils your gas, causes the needle and seat to open, and the liquid goes down the intake.

If your fuel line pressure is too high, the needle isn't designed to stop it, so your bowl floods. If the gas keeps coming, it simply dumps down your intake. Normal fuel pressure and a good rebuild kit will remedy this problem. Keep your pressure under six psi. - Dave
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  #16  
Old 07-24-2013, 08:14 AM
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Quote:
Originally Posted by simplyconnected View Post
Gas and gasohol have a much lower boiling point than water. An engine oil temp at the pan is typically close to 300*F. In addition, there is an exhaust crossover in your intake manifold. So, after heating up the engine and you park the car, heat migrates straight up the carb. That heat boils your gas, causes the needle and seat to open, and the liquid goes down the intake.

If your fuel line pressure is too high, the needle isn't designed to stop it, so your bowl floods. If the gas keeps coming, it simply dumps down your intake. Normal fuel pressure and a good rebuild kit will remedy this problem. Keep your pressure under six psi. - Dave
OK ...I think I get it. The exhaust crossover in the intake manifold explains a lot. After doing some reading, apparently some are blocking that port to avoid the problem with the heat soak/boiling gas problem in there rods. Will be going to Helena NAPA today to get a pressure regulator and power valve. Thanks for the explanation.
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  #17  
Old 07-24-2013, 01:50 PM
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The exhaust crossover in your intake is run by your heat riser valve (in your RH exhaust manifold).

When the engine is cold, reach down to the end of the passenger's side exhaust manifold and see if the valve operates freely. When they freeze up, it's usually in the closed position. That sends most of the exhaust gasses over to the LH side through your intake manifold. This quickly warms your engine in cold winter weather. When the exhaust temp is hot, a bi-metal spring (it looks like a large clock spring) on the outside of that valve relaxes, which keeps the valve open. - Dave
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  #18  
Old 07-24-2013, 10:23 PM
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Today, I did a wet test on the float levels. BTW, the secondary float bowl was close to full and the Primary float bowl was empty when I pulled the top. It had been about 2 days since I ran the car. I Pulled the top and cranked the car over to fill float bowls. I checked the levels and they were pretty close to the dry preset. Then I started the car, ran it, and check again. The Primary was a bit high and the secondary was right on. Never ran the engine long enough to develope any heat for "heat soak" problems. Engine was basically cold. I set the top back over the carb and waited about an hour and again checked the float levels. The primary had dropped about 3/16" and the secondary was still right on spec.
Tomorrow, I'm going to buy another rebuild kit and put all new gaskets, power valve etc in it and see if it solves this problem. I'm not totally convinced this will solve the problem, but I'll try it one more time.
Nyles
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  #19  
Old 07-27-2013, 09:53 AM
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Quote:
Originally Posted by simplyconnected View Post
The exhaust crossover in your intake is run by your heat riser valve (in your RH exhaust manifold).

When the engine is cold, reach down to the end of the passenger's side exhaust manifold and see if the valve operates freely. When they freeze up, it's usually in the closed position. That sends most of the exhaust gasses over to the LH side through your intake manifold. This quickly warms your engine in cold winter weather. When the exhaust temp is hot, a bi-metal spring (it looks like a large clock spring) on the outside of that valve relaxes, which keeps the valve open. - Dave
REALLY appreciate this information. I actually removed the butterfly on this valve since it was hopelessly froze into position. Since I don't pull the car out of storage until June and back again in October it shouldn't be a problem. I would think however that the heat still concentrates through this bi pass when engine is shut down which adds to potential heat soak.
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  #20  
Old 07-28-2013, 12:26 AM
Tbird1044 Tbird1044 is offline
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Well, the saga continues. I rebuilt the carb, and put in all new gaskets, power valve, secondary diaphragm etc. etc. etc. I put the carb back on the car and did a wet float level check, with the car running, just to verify proper setting. All good. Car actually ran pretty good, but the idle needle valves are closed a lot more than specs. When the car is running in the garage, it does NOT get nearly as smelly as it used to. I did not put all the screws into the top of the carb so I could pull it and physically check the gas level in the primary float bowl. After about 24 hours, the fuel level dropped about 1/2". I pulled the carb back off of the car and again disassembled it to methodically look at everything and trace any carb ports to see where they all go. I put the carb back together and set it on the bench with fuel in the primary bowl. After about 16 hours, the fuel dropped about a 1/4". There was absolutely NO indication of leakage anywhere. Evaporation seems to be a bit excessive at that rate.
I put the carb back on the car today and ran it and all seemed good. I still do not have the top secured to the carb so I can check the fuel level vs. time and see what is going on. So far, it looks like the level is still dropping, but not near as fast as it was before I rebuilt it.
I hate to give up, but the Edelbrock is looking better all the time.
Nyles
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