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Discussion Starter #1
So the very last thing I have to fix is kicking my tail. After a long rebuild I've been test driving this weekend, knocking out minor problems. Here's the on big reoccurring one: 4150 double pumper floats sticking. At least i'm almost sure that's the problem. Fuel pressure is 6psi, motor ran and idled great for many weeks. Then the rear bowl started overflowing with fuel. Changed out the jets and power valve and it stopped, no issues. Starting yesterday the front bowl starting doing the same thing.

From what I've read it looks like either the floats are not floating or the needles are stuck. I plan on pulling it off the car and giving it a good cleaning tonight. My question is, where should I focus the cleaning? Is there a trick to testing needles for flow before I put it back on? This carb used to run like a champ but since the rebuild it's been problematic. It sounds like this is a common problem so hopefully I'll get some good feedback on the best cleaning methods. Thanks!
 

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In all my years of Holley carbs, I have rarely seen the needle itself leak unless it was really, really old. Usually the o-rings around the needle assembly are the culprit. They seem to dry out sooner thanks to the stuff they use in fuel nowadays (same with the accelerator pumps). I've had better luck using the ones listed for alcohol fuel, little more pricey but worth it IMO. Spray the assembly with some WD40 when screwing it into the float bowl, less chance of tearing the o-ring as it goes past the threads. Don't just go to the local hardware store for those o-rings, make sure you get some that are rated for use in fuel.
 

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Using Holley's for over 40 years without too many problems,
I have had a rash of float troubles lately.
What I have found is it depends on the float type you are using.
The older floats had a tang for the needle, The newer float style has a dimple.
If you mix the float and needle assy they seem to be more likely to cause problems. The adjustment window for fuel level is very small and too far down can cause flooding from the overflow.

I have found the simplest way to adjust them is with the bowl off and upside down. Moving the needle seat till the float is just slightly raised from level.
Checking the needle for sealing by placing a piece of tubing in the hole and blowing air into it. I can set the level to where I want it and it seems to stay.
 

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Thanks for the replies! I do have the old style metal floats and I DID recently replace the needles and seats so it's possible I have a mixed assembly. I'll try the tube test after I've pulled them and cleaned them out with carb cleaner. I really hope it's just junk clogging them up. Since it happened twice with two different bowls (and the car ran great all other times) I'm leaning that way.
 

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Discussion Starter #5
I managed to figure this out last night. The needles/seats were completely clean and moved easily. However the spring on the primary float was keeping the float from rising with the fuel level. I don't know if the spring was put on backwards or if it bound up, but it wasn't working correctly. The rear float has the spring set so that it assists the bowl rise instead of impeding it like the front does.

Anyway, after reading a bit it looks like you can run without the spring unless you're expecting off road type conditions. I drove around for about 15mins without it and everything went fine.

On to replacing the fuse box! Thanks again for the suggestions!
 
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