January 2011 Chevy High Performance Q&A - Performance Q&A

Tom Truty Dec 9, 2010 0 Comment(s)
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Now that you mention the geardrive scenario, this also goes for mechanical lifter camshafts, high-clearance forged pistons, and even sometimes roller rockers. The knock sensors are calibrated to a specific noise frequency that engine detonation puts off. These mechanical components will sometimes mimic that same frequency, which will also drive the knock sensors crazy.

This is something you must really keep in mind as many more builders are retrofitting their early cars with EFI systems. They may have a very nice small-block between the fenders of their rides. Dropping a knock sensor-equipped EFI system on a geardrive-equipped early small-block could drive a man to drink, chasing problems. Thanks for your help, Chris.

Carb Help
Q: We built a 383 engine for my '69 Camaro in 2004. We've had no problems with it, and it runs great. However, lately it has an issue when we drive it and let it sit for anything more than 10-15 minutes. It will start and run maybe 5 seconds, then die. I have to floor the pedal as if it was flooded to restart it. I've been told it may be boiling some of the gas out of the carburetor. I have checked the temperature on the carburetor immediately after shutting it off and it's between 118 and 146 on the bowl casing. The carburetor is a Holley 650 with manual choke, and I do run headers. There is a 1/2-inch spacer between the carb and the Edlebrock Torker intake. Is boiling the fuel out possible? What would cause this problem to start after six years? Thank you for your help.
Danny Meyers
Taylor, MO

A: Before we started chasing fuel percolation, we'd be looking to the power valve, located in the primary metering block. Holleys can blow the power valve diaphragm during a backfire situation. Especially after many years of service, these diaphragms dry up and can crack on their own. With the diaphragm damaged, the fuel will leak under high-vacuum conditions, like at idle, making it difficult to fuel the engine correctly at idle. Also, the fuel will seep through while sitting and drain the fuel bowl. You will notice it after the vehicle has sat for a couple of days and you must crank the engine to get fuel back into the bowl before the engine will run. In short periods of time, as you mentioned, it could cause a hot engine to act flooded.

While you're in there changing the power valve, we would replace the needle and seats for good measure. If the needle is worn and has a poor sealing surface, it could be allowing fuel to migrate into the bowl after the engine is turned off. If your fuel pump check valves are in good shape it will retain pressure on the seats for quite some time after the engine is shut down. If the needle and seats cannot control this pressure, as the engine heat soaks it will raise the fuel level in the bowl and drip over through the main boosters.

Either way it may be a good time to rebuild your carb, replace the internal components, and install new gaskets. This will take care of all the simple nagging troubles we've mentioned above. Get the Holley list number off of the choke housing on the primary side and order the appropriate carb rebuild kit from Holley. The original gaskets and components are the best. Don't use an auto parts store rebuild kit on a Holley. You're just asking for trouble.
Source: holley.com

Retro Roller Runner
Q: I am finishing a total resto of a '67 Camaro with the original 327 bored 0.030-inch with KB flat-tops, Edelbrock Performer heads (2.02/1.60-inch valves, 64cc), using an Isky RR-265/272HYD roller on 108 centers. The cam was installed using a Torrington bearing and a thrust button.


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