Compression testing how to.
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Intermediate
Joined: Nov 2021
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From: Delaware
Compression testing how to.
I gotta be doing something wrong here because there's gotta be posts about how to do it here but my keyword search pulls nothing. So if anyone can answer my questions or point me to a thread that will I'd appreciate it greatly.
Novice home mechanic and I recently upgraded my cams on 2008 fatbob and even thought its running good, instructions say to perform a compression test. I've found a dozen different places with 100 different ways that all contradict eachother. Mainly with the electrical aspect. My bike is fuel injected, I installed woods 222 cams.
Do I unscrew plugs and leave them in the wires but lay them on the body/frame to ground them? Or do I just remove the plugs and let wires hang? Or do I just remove plugs and pull the fuse to the ignition?
also I'm assuming I want to pull fuse to the fuel pump?
Thanks in advance.
Novice home mechanic and I recently upgraded my cams on 2008 fatbob and even thought its running good, instructions say to perform a compression test. I've found a dozen different places with 100 different ways that all contradict eachother. Mainly with the electrical aspect. My bike is fuel injected, I installed woods 222 cams.
Do I unscrew plugs and leave them in the wires but lay them on the body/frame to ground them? Or do I just remove the plugs and let wires hang? Or do I just remove plugs and pull the fuse to the ignition?
also I'm assuming I want to pull fuse to the fuel pump?
Thanks in advance.
Stellar HDF Member
Joined: Aug 2020
Posts: 3,193
Likes: 2,237
From: College Station, TX
I just remove the plugs and let the wires hang out of the way.
Be sure you have a fully charged battery that will spin the engine fast and long enough to complete the test. You also need to prop the throttle wide open while doing the test so the cylinders can fill with air without the restriction. Crank the engine with the throttle fully open for about 5-6 seconds or until the pressure gauge stops increasing.
Some people suggest unplugging the fuel pump so no fuel is injected into the cylinders. I don't, but can see why some do. The cam you have added will likely lower the cranking compression a little because of valve timing differences from the stock cams. But that cam closes the intake valve early (34 deg) so you should still have good pressure.
Paul
Be sure you have a fully charged battery that will spin the engine fast and long enough to complete the test. You also need to prop the throttle wide open while doing the test so the cylinders can fill with air without the restriction. Crank the engine with the throttle fully open for about 5-6 seconds or until the pressure gauge stops increasing.
Some people suggest unplugging the fuel pump so no fuel is injected into the cylinders. I don't, but can see why some do. The cam you have added will likely lower the cranking compression a little because of valve timing differences from the stock cams. But that cam closes the intake valve early (34 deg) so you should still have good pressure.
Paul
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