Running a compression test for the first time on my carbureted '79. What are good ways to cut fuel for the test? Do I just unhook the throttle cable at the clip, or find which hose(s) are the fuel lines from the carburetor and clamp them with vice grips? Also is there anything electrical that needs to be removed? Do I unplug the "bobina" plug from the distributor? Do the spark plug wires just hang loose or do they need to be capped somehow?
Any other general tips? Should I block open the big semicircles on my ADHA with a screwdriver?
Setting up for compression test
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Topless
- Posts: 48
- Joined: Mon Apr 20, 2020 12:03 pm
- Your car is a: 1979 Fiat 124 Spider 2000
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18Fiatsandcounting
- Posts: 3798
- Joined: Fri Mar 15, 2019 11:23 pm
- Your car is a: 1969 and 1971 124 spiders
- Location: San Francisco Bay Area
Re: Setting up for compression test
No need to disconnect anything fuel related. I would disconnect the main lead from the ignition coil to the "bobina" post on the distributor cap. (Bobina is Italian for "coil")
Pull all 4 spark plugs. Since there is no main coil wire, there is no need to worry about the 4 spark plug wires.
Install your compression tester in the #1 cylinder. I have a fairly long hose on my compression tester, so I can lay it on the cowl and see the gauge while I'm cranking. Hold the gas pedal to the floor, and crank 6 to 8 times, or until the gauge stops rising. Repeat for the other cylinders.
Ideally all four cylinders are about the same. Plus or minus 5 or 10 psi is OK between cylinders. 130 psi and below would be low, 140 to 160 is good, and anything too much higher than that means that you have a high compression setup or different cams. Or your gauge is overly optimistic.
-Bryan
PS: The big semicircles in your carb are the throttle plates, or butterflies, or butterfly valves.
Pull all 4 spark plugs. Since there is no main coil wire, there is no need to worry about the 4 spark plug wires.
Install your compression tester in the #1 cylinder. I have a fairly long hose on my compression tester, so I can lay it on the cowl and see the gauge while I'm cranking. Hold the gas pedal to the floor, and crank 6 to 8 times, or until the gauge stops rising. Repeat for the other cylinders.
Ideally all four cylinders are about the same. Plus or minus 5 or 10 psi is OK between cylinders. 130 psi and below would be low, 140 to 160 is good, and anything too much higher than that means that you have a high compression setup or different cams. Or your gauge is overly optimistic.
-Bryan
PS: The big semicircles in your carb are the throttle plates, or butterflies, or butterfly valves.