Checking Compression
Banned
Joined: Mar 2006
Posts: 8,603
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RE: Checking Compression
i do it cold but it really doesnt matter...cold will have lower #'s...it should read at least 150 cold or 165 hot...no more than 190 for easy cranking...both should be very close for optimum performance
Ultimate HDF Member
Joined: Feb 2006
Posts: 5,939
Likes: 3
From: TX
RE: Checking Compression
Steve ~ It was suggested to me, long ago, to unplug the input connector from the coil so as not to have it charging with no way to discharge. THat also eliminates the plug grounding part of the equasion.
Tourer
Joined: Oct 2006
Posts: 341
Likes: 0
From: Ponchatoula, Louisiana
RE: Checking Compression
Steve, holding the TB wide open allows air to fill the cylinders, If you leave the TB closed your numbers will be very low and misreading.
I also don't worry about grounding plugs
I also don't worry about grounding plugs
Intermediate
Joined: Nov 2005
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From:
RE: Checking Compression
Haven't seen anybody mention to hold the slide up on a carbed version along with the WFO throttle, holding the throttle open only opens the throttle plate and the slide is still mostly blocking the intake tract.
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Elite HDF Member
Joined: Mar 2006
Posts: 4,722
Likes: 5
From: Biddeford, Maine
RE: Checking Compression
OK, so I unplug the small plug on the coil............that will keep the plugs from firing.
Remove the fuel pump fuse...........that keeps the pump from running. What about disconnecting the fuel line at the tank, will that work the same?
Crank the motor over 5-6 times with the throttle wide open.
Sounds easy enough.
Steve
Remove the fuel pump fuse...........that keeps the pump from running. What about disconnecting the fuel line at the tank, will that work the same?
Crank the motor over 5-6 times with the throttle wide open.
Sounds easy enough.
Steve
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Elite HDF Member
Joined: Mar 2006
Posts: 4,722
Likes: 5
From: Biddeford, Maine
RE: Checking Compression
If I disconnect the fuel supply line at the quick disconnect at the tank, will that be the same as removing the fuel pump fuse?
I'm going to check it out tonight and see how it does.
Steve
I'm going to check it out tonight and see how it does.
Steve
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Banned
Joined: Nov 2005
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From:
RE: Checking Compression
ORIGINAL: maineultraclassic
If I disconnect the fuel supply line at the quick disconnect at the tank, will that be the same as removing the fuel pump fuse?
I'm going to check it out tonight and see how it does.
Steve
If I disconnect the fuel supply line at the quick disconnect at the tank, will that be the same as removing the fuel pump fuse?
I'm going to check it out tonight and see how it does.
Steve
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Elite HDF Member
Joined: Mar 2006
Posts: 4,722
Likes: 5
From: Biddeford, Maine
RE: Checking Compression
I just checked them out, and took the measurements.
Both cylinders measured 178..........exactly the same reading.
Motor was cold, throttle held wide open, fuel pump fuse pulled, and coil plug pulled......cranked the motor over 5-6 times until the reading didn't go higher.
Does that sound about right for this build -
1550 Flattops
Cometic .030 head gasket
Big Boyz Ported Heads
9.6-1 compression (assuming 0 deck height)
Andrews 26g Cams
Ness Big Sucker
Supertrapp 2-1
PCIIIusb
SE Quick-Install Pushrods
SE Clutch Spring
Steve
Both cylinders measured 178..........exactly the same reading.
Motor was cold, throttle held wide open, fuel pump fuse pulled, and coil plug pulled......cranked the motor over 5-6 times until the reading didn't go higher.
Does that sound about right for this build -
1550 Flattops
Cometic .030 head gasket
Big Boyz Ported Heads
9.6-1 compression (assuming 0 deck height)
Andrews 26g Cams
Ness Big Sucker
Supertrapp 2-1
PCIIIusb
SE Quick-Install Pushrods
SE Clutch Spring
Steve