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this is Gerrit from Germany once more. I have some trouble with the (center) Holley-Tripower on my '69 L68 Auto:
I found out, that engine doesn't stall, when the right idle-mixture-screw is fully in it's seat (on the left side, engine stalls). So there might be a leak inside the carb, where fuel passes by. That would declare as well, that engine oftens backfires, when ignition went to "off". I imagine, that there is still some fuel dropping from inside the carb to the manifold.
My question is, where I have to look for the leak. Might be the power-valve the reason? Do you have any experiences?
I had a similar problem with my carbs and adjusted the float valves to the correct setting . they should be adjusted with the car running and just to the bottom of the plug on the side of the carb .Messy job you will need a rag under the carb when adjusting .
I also used 3 holley carb rebuild kits 37-396 that come with all the gaskets and power valves you only need one for the middle carb so you will have a couple of spares plus 3 diaphragms for the accelerator pump and again you will have a couple of spares as you only need one for the centre carb .Make sure you match the metering gaskets to what is in there already because there is a few different ones .Hope this helps .
If the engine continues to run with the mixture screws fully seated, it's getting fuel from somewhere. So, in this regard, your reasoning is sound and the prime suspect is going to be in the power valve. Check the valve but also make sure you are using the correct gasket for the valve. There are two style valves; One with two opposing square holes. That one takes a round gasket. And one with holes around the valve discharge. That one takes a round gasket with three tabs on the inner circumference. If you use the wrong gasket, the valve will leak.
Before you dig into the carburetor, make sure you are not dripping fuel from the boosters with the engine running at idle speed. If you do see fuel dripping from the boosters, you'd be looking at a problem with the float or the needle and seat.
If it's not the power valve and the fuel level is correct and nothing is coming from the boosters, then you have a problem with the seal between the metering block and the main body. This could be due to the wrong gasket being used, a damaged gasket or non-flat mating surface in the block or the main body.
The fuel-level is adjusted correctly, so that no fuel leaks from sight-plug-hole while engine is idling.
As far as I can see, there is no fuel leaking from the venturis, as far as throttle-valves are completly dry while engine is idling.
So it looks, as if the power-valve or the seal between metering-block and main-body has the leak. That means completely disassembling of the carb-setup (without the rear secondary) .
My garage has disassbled the center-carb and found out, that the seal between metering-block and main body wasn't pressed properly, because of fail-alignment of the metering-block. The block was replaced so I hope, that will be the solution.
Sure. There are both fiber and nylon gaskets for the fuel bowl screws. Take your pick. You could also make your own gaskets with a fiber gasket sheet. A bit of a pain in the *** to do, but if you don't want to order the right gaskets or you don't have the time to wait for delivery, it's an option. Yes, I have done it using scissors and a razor blade.
the metering blocks get warped or bent from over tightening the bowl screws. you need a fixture to press them straight again so they seal to the gaskets. never use those never stick gaskets on old carbs as they are made for fresh new flat surfaces and don't conform to warped one
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Leaky Holley
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