Merc 5.7 Flooded when checking compression

[BuzzM]

I have a 1982 mercruiser 5.7 . I was checking the compression ( one at a time), but was flooding the carb badly in the process. I would remove the coil cable, remove old plug, checked the compression, gap and installed new plug, then reattached the coil - distributor cable. When attempted a restart after half the cylinders were done, I found the flooded condition. I removed the coil - distributor cable to disable the engine each time.
Is there a better ( correct ) way ?
Compression was 120 - 130 on each one, I guess o.k.?
thx.

 

[Don S]

Re: Merc 5.7 Flooded when checking compression

You need to have the choke and the throttle WIDE OPEN when you do the compression test.
Could also be your carb is flooding over. Needle valve stuck open????

 

[wire2]

Re: Merc 5.7 Flooded when checking compression

Pull all 8 plugs first, then check compression 1 cyl at a time.
That cuts intake vacuum to almost nil and is much easier on starter & battery.

 

[Bondo]

Re: Merc 5.7 Flooded when checking compression

Ayuh,......

And,.......
Ground Out the High Tension Lead from the Coil,.......

Just pulling it can cause a High Tension Arc that can ruin your day.........

Btw,........
120/ 130psi are Good cold test #s.......

 

[John_S]

Re: Merc 5.7 Flooded when checking compression

Don't be surprised to see your numbers rise after doing what Don and Wire said. Another thing to watch for with the flooding, is the fuel pump vent hose. Any gas in that line, and you have a ruptured fuel pump that needs replacing.

 

[Don S]

Re: Merc 5.7 Flooded when checking compression

Pull all 8 plugs first, then check compression 1 cyl at a time.

Good point, when I first read his original post, I thought he did have all of them out. After re-reading, he many have been doing only one at a time. Hard to tell.

Here is the Merc service bulletin on how to do a proper compression test.
http://www-alt.mercurymarine.com/mnetdata/Service/Cruiser/Bullet/97/mc9725r1.pdf

 

[BuzzM]

Re: Merc 5.7 Flooded when checking compression

Thanks guys, I WAS doing it incorrectly one at a time. I'll use the link for the instructions.