Packard Forum Index » Pre-War (1899-1942)

Made some progress....

Flow from the fuel pump looked good. Filled a coffee can about ? way cranking for 30 seconds.

Vacuum test was good, held 20 in Hg steady at idle, cold and hot.

Back pressure test on the exhaust was good, showed 0.5 - 1.0 psi at all speeds, cold and hot.

Compression test hot was good, first column cold numbers.

90 105
95 105
95 105
100 110
90 110
95 105
100 110
100 110

In addition to the loss of performance I was having a hard time starting it. Would just crank and crank. When I checked the carburetor fuel level by removing the drain screw on the bottom of the DL carburetor the first time, to install a tool I made, there was no fuel in the carburetor.

I've been usually checking the engine running, but this time I shut it off to do the hot compression test. This is when I noticed fuel dripping from the main jet adjusting needle. It was only about a drop every four seconds. When the engine was running I didn't see a leak.

Tightening the packing nut around the needle valve didn't help so I pulled the assembly out. This carburetor was supposed to have been rebuilt by an expert. There was no sealant on the threads holding the assembly in the carburetor and there wasn't enough packing inside around the needle valve. Even though the packing nut was snug it never forced the packing against the needle valve to form a seal.

Put everything back together and started it up. It ran smoother and I was able to get better adjustment of the idle. Will road test it when I get time.

I believe the leak around the needle valve was allowing fuel to drain out of the carburetor when it sat, causing the hard starting problem. When the engine started there was enough vacuum to pull air thru the leak. The leak wasn't enough to be noticed at idle or low speeds, but it leaned the mixture out enough at higher speeds to cause a lack of performance.

Thanks again for the comments / suggestions.

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